Professor Guoxiu Wang

Biography

2011- ARC Future Fellowship Level 3 (FT3)

2011- Director, Centre for Clean Energy Technology

2010 - Professor, Department of Chemistry and Forensic, Faculty of Science, University of Technology Sydney, Australia

2008 - 2010, Associate Professor, School of MMM, UOW, Australia

2007 - 2011, ARC QEII Fellow, School of MMM, UOW, Australia

2006 - 2007, Senior Lecturer, School of MMM, UOW, Australia

2004 - 2006, Research Fellow, ISEM, UOW, Australia

2001 - 2004, ARC APDI Fellow, ISEM, UOW, Australia

1990 - 1997, Lecturer, Jiangsu University, P.R. China

Awards:

  • Oversea education award, 1997, Ministry of Education, P.R.C.
  • OPRS Scholarship Award, 1998
  • Best PhD thesis award, 2001, Faculty of Engineering, University of Wollongong.
  • ARC Queen Elizabeth II (QEII) Fellowship Award, 2007.
  • International Year of Chemistry 2011, IUPAC 7th International Conference on Novel Materials and Synthesis (NMS-VII) and 21st International Symposium on Fine Chemistry and Functional Polymers (FCFP-XXI) “Distinguished Award for Novel Materials and their Synthesis”
  • ARC Future Fellowship (FT3) awarded to Materials Engineering Professor
  • 2012 New South Wales Science and Engineering Awards
Category Winner for the Renewable Energy Innovation

Image of Guoxiu Wang
Professor, School of Chemistry and Forensic Science
Director, Research Centre for Clean Energy Technology
Core Member, Research Strength Materials and Technology for Energy Efficiency Member
Doctor of Philosophy
 
Phone
+61 2 9514 1741
Fax
+61 2 9514 1460
Room
CB04.04.37C

Research Interests

Dr. G.X. Wang has been working in the research area of Materials Chemistry, Electrochemistry, and Semiconductor Nanomaterials for over 10 years.

He has performed extensive research into electromaterials for applications in rechargeable Lithium-ion battery, lithium-air batteries, Na-ion batteries, lithium–sulfur batteries, supercapacitors and fuel-cells, controllable synthesis of one dimensional semiconductor nanostructures and their applications for chemical and biosensors, and semiconductor quantum dots, quantum wires and quantum tubes for nanoscale electronic and photonic devices. He has won a large number of external research grants, has published over 260 refereed journal papers, delivered 100 keynote/invited talks/seminars worldwide.

His entire publications have been cited for over 8100 times (without self-citations 7900 times, from Web of Science), cited 1800 times in year 2013, the H-index of his publications is 50. He has strong international collaborations.

Research areas:

  • Electrochemistry
  • Electromaterials for battery applications
  • Battery technology
  • Supercapacitors
  • Hydrogen storage and Fuel-cells
  • Materials Chemistry
  • Semiconductor quantum dots, quantum wires and quantum tubes
  • Molecular nanoelectronics and photonics
  • Molecular chemical and bio nanosensors

Academic Activities

Australian Research Council Aussie Reader. Editorial Board of Scientific Reports and some professional journals.
Dr. Wang is actively participating in the activities and services in scientific professional societies. He has served as chair and co-chair for national and international conferences organized symposia and chaired sessions in national and international conferences. 

International Scientific Committee: The International Conference on Electrochemical Energy Science and Technology (EEST2014) 31 Oct. - 4 Nov. Shanghai China http://www.iaoees.org/events/EEST2014/index.html

Conference Co-Chairs: 10th IUPAC International Conference on Novel materials and their Synthesis (NMS-X) China from 10-15 Oct. 2014. Organized by Zhengzhou University, Fudan University and The University of Technology Sydney http://www.nms-iupac.org/present/index.asp

Invited Speaker: International Forum on New Energy Material and Technology
August 2-6, 2014 Baotou, Inner Mongolia, China  http://cssi2014.imust.cn/12-1.html

Session Chair and Invited Speaker: The 5th Australia-China Conference on Science, Technology and Education and The 5th Australia-China Symposium for Materials Science 20-23 July 2014 Wollongong Australia http://isem.uow.edu.au/UOW166554.html

Invited Speaker: 1st Sino-German Symposium on All Solid State Battery 30thJune - 2nd July 2014 Shanghai Jiao Tong University, Shanghai, China.

Invited Speaker: 2nd International Conference on Clean Energy science (ICCES2) 13- 16 April 2014 Qingdao China http://www.icces.cn/

Invited Speaker: International Battery Association 2014 March 3-7th in Brisbane, Australia. http://iba2014brisbane.com/index.html

Invited Speaker: Asian Pacific Conference on Energy and Environmental Materials (APCEEM) Gold Coast City, Queensland 9th –11th February 2014 http://www.griffith.edu.au/conference/asia-pacific-conference-energy-environmental-materials

Invited Speaker: Asia-Pacific Conference on Electrochemical Energy Storage & Conversion (APEnergy 2014) 5–8 February 2014 Brisbane Convention & Exhibition Centre, Australia http://mesostructured.org/2013/05/energy-conference-apenergy2014-in-feb-2014-in-brisbane-australia/

Invited Lecture at Beijing Jiaotong University, China 28 Oct. 2013

Invited Seminar National Center for Nanoscience and Technology (NCNST) China 28 Oct. 2013

Keynote Speaker and Committee Chair: IEEE 2013 International Conference on Applied Superconductivity and Electromagnetic Devices(ASEMD2013) 25-27 October 2013, Beijing, China http://asemd.org/

Invited Speaker: 4th China-Australia Symposium for Materials Science 20-24 Oct. 2013, Zhuhai, Guangdong, China http://www.cza-online.org.cn/4th/index.php

Co-Chairs and Keynote Speaker: 9th IUPAC International Conference on Novel Materials and their Synthesis (NMS-VIII) & 23rd International Symposium on Fine Chemistry and Functional Polymers (FCFP-XXIII), Shanghai China from 17 to 22 October, 2013. Organized by: Fudan University, East China University of Science and Technology and the University of Technology Sydney
Symposium brochure http://www.nms-iupac.org/present/

Invited Speaker: China Australia Alliance for New Energy Vehicle Innovation 9-11 October 2013, Melbourne

Keynote Speaker: International Conference on Electrochemical Materials and Technologies for Clean Sustainable Energy 5 -9 July 2013 Guangzhou, China http://www.fuelcellscn.com/conference/Home.html

Invited Speaker: The 5th international symposium on functional materials 17-20 Dec 2012 Perth Western Australia

Keynote: Advances in functional nanomaterials for energy and environmental applications 15-16 Nov 2012 Sydney

Invited Speaker: Smart Battery/Cell Forum 2012 18-19 Oct 2012 Seoul Korea

Session Chair & Keynote Speaker: International union of materials research society- international conference in Asia IUMRS-ICA 2012 Busan Korea 26-31 Aug 2012

Invited Lecture: The NSW Branch of Materials Australia, Sydney, July 2012

Session Chair and Keynote: OzCarbon2012 1st July 2012 Adelaide Australia

Invited Lecture: Nanjing University of aeronautics and astronautics China 23 May 2012

Invited Lecture: Fudan University Shanghai China 21 May 2012

Invited Lecture: The University of New South Wales School of Chemistry 29th March 2012

Invited Speaker: The 3rd International Symposium on Environment and Renewable Energy (ISERE2011) 9 Dec 2011 Pusan National University. Korea.

Invited Speaker: Korean Battery Society 10th Anniversary Conference 1-3 Dec 2011 Jeju Island, Korea.

Invited Speaker: 3rd Australia-China Symposium for Materials Science 19 to 23 November 2011 Gold Coast, Australia

Co-Organizer, Technical Program Committee, Invited Speaker: International Conference on Advanced Electromaterials (ICAE 2011), Nov 7th-10th 2011 Jeju, Korea.

Invited Speaker: 2011 International conference on vehicle noise vibration and safety technology 23-25 October 2011 Chongqing China

Co-Chair and Keynote Speaker: The IUPAC 7th International Conference on Novel Materials and Their Synthesis (NMS-VII) & 21st International Symposium on Fine Chemistry and Functional Polymers (FCFP-XXI) on 16th~21st October, 2011 Shanghai China. Organized by: Fudan University, East China University of Science and Technology and the University of Technology Sydney

Symposium brochure (opens an external site)
Symposium website (opens an external site)

Invited Speaker: The Institute of Physic Chinese Academy of Sciences Beijing China 21 April 2011

Invited Lecture: The University of Sydney Australian Centre for Microscopy & Microanalysis 11 Nov 2010

Co-Chairs: International symposium on next generation battery, South Korea 2010

Co-Chairs: Symposium 5th IUPAC international symposium on novel materials and their synthesis & 19th international symposium on fine chemistry and functional polymers & 3rd symposium on power sources for energy storage and their key materials, October 2009 China

Chairs: International Symposium on Renewable Energy Storage and Conversion Technologies, Australia 2009
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Referee
He is a referee for prestigious journals, such as:
Science, Advanced Materials, Advanced Functional Materials, JACS, Angewandte Chemie, Journal of Power Sources, Electrochemistry Communications, Electrochim Acta, Journal of the Electrochemical Society, Carbon, APL, Journal of Physical Chemistry B, Journal of Alloy and Compounds, Chemistry of Materials, Journal of Nanoscience and Nanotechnology.

Can supervise: Yes

Chemistry

Nanomaterials

Book Chapters

Wang, B., Ranjbartoreh, A. & Wang, G. 2013, 'Controlled size and shape of grapheme and its application in Li-ion battery' in Ru-Shi Liu (ed), Controlled Nanofabrication: Advances and Applications, Pan Stanford Publishing, USA, pp. 623-656.
Graphene is one-atom-thick film of carbon atoms packed in honeycomb structure with exceptional electrical, thermal, optical, and mechanical properties, which opened up new horizons for next generation nanotechnology-based devices. Two University of Manchester scientists, Andre Geim and Konstantin Novoselov, were awarded the 2010 Nobel Prize in physics 'for groundbreaking experiments regarding the two-dimensional material graphene'. This chapter reviews the brief history and development of graphene, considers its properties, characterizations and the synthesis methods, and provides a few examples for its advanced application in lithium-ion battery.
Wang, G. 2007, 'Layer and spinel structure cathode materials' in Sheng Shui Zhang (ed), Advanced materials and methods for lithium ion batteries, Transworld Research Network, India, pp. 23-48.
Lithium ion batteries are widely used as the most admnced power sources Jar portable electronic devices. As one oj important technologies to combat globalwal7lling by reducing green-hollSe gas emission, large-scale lithium-ion batteries have great potentials to be used Jor distribllted power storage, electric vehicles rEVs), and hybrid electric vehicles (HEVs). Cathode materials playa pivotal role in litlzium-ion batteries. This chapter gives a brief review 011 the development oj layer and Splilel stmctllre cathode materials Jor lithium-ion batteries. The histDlY, the state-oflhe -art oj/hose materials technology and the related problems are described.
Wang, G. 2007, 'Layer and spinel structure cathode materials' in Sheng Shui Zhang (ed), Advanced Materials and Methods for Lithium-Ion Batteries, Transworld Research Network, India, pp. 23-48.

Conference Papers

Wang, G., Yao, J., Liu, H.K., Dou, S.X. & Ahn, J.h. 2003, 'Nanosized tin microencapsulated graphite as the anode in lithium ion cells', 9th International Symposium on Metastable, Mechanically Alloyed and Nanocrystalline Materials (ISMANAM-2002), Seoul, South Korea, September 2002 in METASTABLE, MECHANICALLY ALLOYED AND NANOCRYSTALLINE MATERIALS: 9th International Symposium on Metastable, Mechanically Alloyed and Nanocrystalline Materials (ISMANAM-2002), ed Ahn, JH; Hahn, YD, Trans Tech Publications Ltd, Switzerland, pp. 739-744.
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Microencapsulating nanosized Sn particles in graphite developed a series of new anode composite materials for lithium-ion batteries. The nanosized Sn particles are homogeneously dispersed in graphite matrix via in situ chemical reduction. The tin-graphite composite showed a great improvement in lithium storage capacity. Since Sn is an active element to lithium, Sn can react with lithium to form Li4.4Sn alloys, with an accompanying 400 % volume increase. The ductile graphite. matrix provides a perfect buffer layer to absorb such volume expansion. Therefore, the integrity of the composite electrode is preserved during lithium insertion and extraction. The reaction process of lithium insertion and extraction into the graphite structure, and lithium alloying with tin has been identified by cyclic voltammetry measurement. The new tin-graphite composites provide a new. type of anode materials for lithium-ion, batteries with increased capacity.

Journal Articles

Chen, S., Bao, P., Huang, X., Sun, B. & Wang, G. 2014, 'Hierarchical 3D mesoporous silicon@graphene nanoarchitectures for lithium ion batteries with superior performance', Nano Research, vol. 7, no. 1, pp. 85-94.
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Silicon has been recognized as the most promising anode material for high capacity lithium ion batteries. However, large volume variations during charge and discharge result in pulverization of Si electrodes and fast capacity loss on cycling. This drawback of Si electrodes can be overcome by combination with well-organized graphene foam. In this work, hierarchical three-dimensional carbon-coated mesoporous Si nanospheres@graphene foam (C@Si@GF) nanoarchitectures were successfully synthesized by a thermal bubble ejection assisted chemical-vapor-deposition and magnesiothermic reduction method. The morphology and structure of the as-prepared nanocomposites were characterized by field emission scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. When employed as anode materials in lithium ion batteries, C@Si@GF nanocomposites exhibited superior electrochemical performance including a high specific capacity of 1,200 mAh/g at the current density of 1 A/g, excellent high rate capabilities and an outstanding cyclability. Post-mortem analyses identified that the morphology of 3D C@Si@GF electrodes after 200 cycles was well maintained. The synergistic effects arising from the combination of mesoporous Si nanospheres and graphene foam nanoarchitectures may address the intractable pulverization problem of Si electrode.
Huang, X., Sun, B., Chen, S. & Wang, G. 2014, 'Self-Assembling Synthesis of Free-standing Nanoporous Graphene-Transition-Metal Oxide Flexible Electrodes for High-Performance Lithium-Ion Batteries and Supercapacitors', Chemistry An Asian Journal, vol. 9, no. 1, pp. 206-211.
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The synthesis of nanoporous graphene by a convenient carbon nanofiber assisted self-assembly approach is reported. Porous structures with large pore volumes, high surface areas, and well-controlled pore sizes were achieved by employing spherical silica as hard templates with different diameters. Through a general wet-immersion method, transition-metal oxide (Fe3O4, Co3O4, NiO) nanocrystals can be easily loaded into nanoporous graphene papers to form three-dimensional flexible nanoarchitectures. When directly applied as electrodes in lithium-ion batteries and supercapacitors, the materials exhibited superior electrochemical performances, including an ultra-high specific capacity, an extended long cycle life, and a high rate capability. In particular, nanoporous Fe3O4-graphene composites can deliver a reversible specific capacity of 1427.5 mAh-g-1 at a high current density of 1000 mA-g-1 as anode materials in lithium-ion batteries. Furthermore, nanoporous Co3O4 graphene composites achieved a high supercapacitance of 424.2 F-g-1. This work demonstrated that the as-developed freestanding nanoporous graphene papers could have significant potential for energy storage and conversion applications.
Mondal, A.K., Wang, B., Su, D., Wang, Y., Chen, S., Zhang, X. & Wang, G. 2014, 'Graphene/MnO2 hybrid nanosheets as high performance electrode materials for supercapacitors', Materials Chemistry And Physics, vol. 143, no. 2, pp. 740-746.
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Graphene/MnO2 hybrid nanosheets were prepared by incorporating graphene and MnO2 nanosheets in ethylene glycol. Scanning electron microscopy and transmission electron microscopy analyses confirmed nanosheet morphology of the hybrid materials. Graphene/MnO2 hybrid nanosheets with different ratios were investigated as electrode materials for supercapacitors by cyclic voltammetry (CV) and galvanostatic charge+discharge in 1 M Na2SO4 electrolyte. We found that the graphene/MnO2 hybrid nanosheets with a weight ratio of 1:4 (graphene:MnO2) delivered the highest specific capacitance of 320 F g-1. Graphene/MnO2 hybrid nanosheets also exhibited good capacitance retention on 2000 cycles.
Mondal, A.K., Su, D., Wang, Y., Chen, S., Liu, Q. & Wang, G. 2014, 'Microwave hydrothermal synthesis of urchin-like NiO nanospheres as electrode materials for lithium-ion batteries and supercapacitors with enhanced electrochemical performances', Journal Of Alloys And Compounds, vol. 582, no. 1, pp. 522-527.
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Urchin-like NiO nanospheres were synthesised by a microwave hydrothermal method. The as-synthesised NiO nanospheres were characterised by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. It was found that NiO nanosphere consists of a nanoporous structure and nanosize crystals. When applied as anode materials in lithium-ion batteries, NiO nanospheres exhibited a high reversible specific capacity of 1027 mA h g-1, an excellent cycling performance and a good high rate capability. NiO nanospheres also showed a high specific capacitance as electrode materials for supercapacitors.
Zhang, Y., Zhang, Y., Qu, Q., Wang, G. & Wang, C. 2014, 'Determination of glyphosate and aminomethylphosphonic acid in soybean samples by high performance liquid chromatography using a novel fluorescent labeling reagent', Analytical Methods, vol. 5, pp. 6465-6472.
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A highly sensitive pre-column derivatization HPLC method for simultaneous determination of glyphosate (GLYP) and its major metabolite aminomethylphosphonic acid (AMPA) in soybean samples was developed. The analytes were labeled with a novel fluorescent labeling reagent 3,6-dimethoxy-9-phenyl-9H-carbazole-1-sulfonyl chloride (DPCS-Cl) at 70 C for 25 min. The optimized concentration of DPCS-Cl was 25 g mL-1 and the molar ratio of analytes to DPCS-Cl was 1:4.2. The derivatives were separated on a reversed-phase column by gradient elution and were monitored with fluorescence detection at 318 nm (excitation) and 440 nm (emission). The method linearity, calculated for GLYP and AMPA, had a correlation coefficient greater than 0.999. The detection limits for GLYP and AMPA were 0.02 ng mL-1 and 0.01 ng mL-1 (S/N = 3), respectively. In addition, a simple sample pretreatment for the soybean samples was developed to extract GLYP and AMPA. The recovery of extraction was more than 95%. Then, this method gave the detection limits of 0.002 mg kg-1 for GLYP and 0.001 mg kg-1 for AMPA in soybean samples. This HPLC method was applied to the determination of glyphosate and AMPA in soybean samples with its merits of simplicity in pretreatment, rapidity in derivatization, stability of the derivatives and high sensitivity.
Liu, L., Wang, C. & Wang, G. 2014, 'Novel cysteic acid/reduced graphene oxide composite film modified electrode for the selective detection of trace silver ions in natural waters', Analytical Methods, vol. 5, pp. 5812-5822.
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Novel cysteic acid/reduced graphene oxide composite film on a glassy carbon electrode has been prepared through the electrochemical oxidation of L-cysteine for silver sensing. Differential pulse anodic stripping voltammetry (DPASV) was employed for the detection of trace Ag(I) in aqueous solutions with the composite film modified electrode, which is referred to as an efficient method for the detection of trace heavy metals. We found the linear relationship between the peak current of the stripping voltammetry of Ag(I) and the concentration of Ag(I) in the range of 1.0 10-8 2.0 10-4 M with a correlation coefficient R2 = 0.996, and the detection limit can be down to 1.0 10-9 M (S/N = 3). The as-developed cysteic acid/reduced graphene oxide composite film modified electrode demonstrated ultrahigh sensitivity, reproducibility and recovery for the selective detection of trace Ag(I) without any interference from other metal ions.
Mondal, A.K., Chen, S., Su, D., Liu, H. & Wang, G. 2014, 'Fabrication and enhances electrochemical performances of Mo03/graphene composite as anode material for lithium-ion batteries', International Journal of Smart Grid and Clean Energy, vol. 3, no. 2, pp. 142-148.
Molybdenum trioxide (Mo0#)/graphene composite were prepared by integrating Mo03 and graphene in dimethylformamide (DMF). The morphology and structure of the materials were characterized by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. The electrochemical properties of Mo03/graphene composite with different ratios were studied as anode materials for lithium-ion batteries using galavanostatic charge-discharge and cyclic voltammetry. We observed that the Mo03/graphene anode with a weight ratio of 1:1 (Mo03 graphene) exhibits a high lithium storage capacity of 967 mA h g-1 at the current density of 500 mA g-1, satisfactory cycling stability and good rate capability.
Guan, J., Zhang, Y., Zhou, G., Qu, Q., Wang, C., Hu, X. & Wang, G. 2014, 'Determination Of Proline, Hydroxyproline And Nethylglycine In Urine By Using A New Hplc Labeling Reagent, And Its Application In Detection Of Tumor Markers', Journal of liquid Chromatography & Related Technologies, vol. 37, no. 12, pp. 1731-1749.
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According to previous reports, the concentration of urinary proline (Pro), hydroxyproline (Hyp) and N-ethylglycine (Neg) varies in association with various diseases, especially, Neg as a tumor marker is recently found in association with bone metastatsis cancers. We developed a low-cost, highly sensitive pre-column high-performance liquid chromatography (HPLC) method for simultaneous determination of Pro, Hyp and Neg in urine of patients with cancers, bone metastasis cancers, and bone metastasis cancers that have appeared after radiotherapy and chemotherapy treatment. The analytes in the urine were labeled with 4-methoxybenzenesulfonyl fluoride (MOBS-F) at 40 degrees celsius. The derivatives were separated on a reverse-phase column by gradient elution and monitored with ultraviolet (UV) detection at 232nm. The detection limits for Pro, Hyp and Neg were 6.0 pmol/injection, 4.0 pmol/injection, and 50 pmol/injection (S/N=3), respectively. To some extent, Neg levels in their urine show there were relevance to their health conditions or therapy progress. We believe that the developed method may be a promising measure for providing a useful reference to diagnose the illness and monitor the results for bone metastasis cancers after radiotherapy and chemotherapy treatment.
Liu, Q., Yang, Y., Sun, B., Su, D., li, z., Xia, Q. & Wang, G. 2014, 'Hydrothermal synthesis of FeP4 and Fe2P-loaded alpha-Fe2O3 hollow spheres and applications in gas sensors', Sensors and Actuators B: Chemical, vol. 194, pp. 27-32.
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FeP4 and Fe2P-loaded hematite (alpha-Fe2O3) (FFH) hollow spheres with a diameter of 130+410 nm were synthesized by a hydrothermal method. The structure and morphology of the FFH hollow spheres were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), field-emission scanning electron microscope (FESEM), and X-ray photoelectron spectroscopy (XPS). Nitrogen adsorption+desorption isothermal measurements revealed that the FFH hollow spheres have larger BET surface area and mesopores. The gas-sensing performance of the FFH hollow spheres was investigated towards a series of typical organic solvents and fuels. The FFH hollow spheres exhibited a superior sensitivity towards flammable and irritant gases. The possible sensing mechanism of the FFH hollow spheres sensor is also proposed.
Chen, Y., Zhang, H., Xue, H., Hu, X., Wang, G. & Wang, C. 2014, 'Construction of a non-enzymatic glucose sensor based on copolymer P4VP-co-PAN and Fe2O3 nanoparticles', Materials Science and Engineering C, vol. 35, pp. 420-425.
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An electrochemical sensor based on a copolymer poly(4-vinylpyridine)-co-poly(acrylonitrile), P4VP-co-PAN, and Fe2O3 nanoparticle film modified glassy carbon electrode was developed for the determination of glucose. We studied the response of glucosewith the proposed electrode, and determined the optimumconditions by changing the potential, pH and P4VP-co-PAN. The current responsemeasurementswere performed in PBS (c = 0.1 M) with a potential of 0.7 V. The current response of this glucose sensor showed a linear relationship with the concentration in the range of 2.5 M+0.58 mM (r = 0.997). The experimental results demonstrate that this method has suchmerits as simple operation, lowcost, high sensitivity, long termstability and good reproducibility, with satisfactory results.
Sun, B., Huang, X., Chen, S., Zhang, J. & Wang, G. 2014, 'An optimized LiNO3/DMSO electrolyte for high-performance rechargeable Li+O2 batteries', RSC Advances, vol. 4, pp. 11115-11120.
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Finding stable electrolytes is essential to address the poor cycling capability of current rechargeable non-aqueous Li+O2 batteries. An optimized dimethyl sulfoxide (DMSO) based electrolyte using lithium nitrate (LiNO3) as the lithium salt has been first investigated for rechargeable Li+O2 batteries. The charge over-potential of Li+O2 batteries with LiNO3/DMSO electrolyte is 0.42 V lower than that of batteries with LiClO4/DMSO electrolyte. The Li+O2 batteries with LiNO3/DMSO electrolyte also showed excellent high C-rate performance and good cycling stability.
Su, D., Xie, X. & Wang, G. 2014, 'Hierarchical Mesoporous SnO Microspheres as High Capacity Anode Materials for Sodium-Ion Batteries', Chemistry -A European Journal, vol. 20, pp. 3192-3197.
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Mesoporous SnO microspheres were synthesised by a hydrothermal method using NaSO4 as the morphology directing agent. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) analyses showed that SnO microspheres consist of nanosheets with a thickness of about 20 nm. Each nanosheet contains a mesoporous structure with a pore size of approximately 5 nm. When applied as anode materials in Na-ion batteries, SnO microspheres exhibited high reversible sodium storage capacity, good cyclability and a satisfactory high rate performance. Through ex situ XRD analysis, it was found that Na+ ions first insert themselves into SnO crystals, and then react with SnO to generate crystalline Sn, followed by Na+Sn alloying with the formation of crystalline NaSn2 phase. During the charge process, there are two slopes corresponding to the de-alloying of Na+Sn compounds and oxidisation of Sn, respectively. The high sodium storage capacity and good electrochemical performance could be ascribed to the unique hierarchical mesoporous architecture of SnO microspheres.
Su, D., Dou, S. & Wang, G. 2014, 'WS2@graphene nanocomposites as anode materials for Na-ion batteries with enhanced electrochemical performances', Chemical Communications, vol. 50, pp. 4192-4195.
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WS2@graphene nanocomposites were synthesized by a hydrothermal approach. When applied as anodes in Na-ion batteries, the WS2@graphene nanocomposite exhibited a high reversible sodium storage capacity of about 590 mA h g-1. It also demonstrated excellent high rate performance and cyclability.
Wei, Y., Chen, S., Su, D., Sun, B., Zhu, J. & Wang, G. 2014, '3D Mesoporous Hybrid NiCo2O4@graphene Nanoarchitectures as Electrode Materials for Supercapacitors with Enhanced Performances', Journal of Materials Chemistry A, vol. 2, pp. 8103-8109.
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3D mesoporous hybrid NiCo2O4@graphene nanoarchitectures were successfully synthesized by a combination of freeze drying and hydrothermal reaction. Field-emission scanning electron microscopy (FESEM) and TEM analyses revealed that NiCo2O4@graphene nanostructures consist of a hierarchical mesoporous sheet-on-sheet nanoarchitecture with a high specific surface area of 194 m2 g-1. Ultrathin NiCo2O4 nanosheets, with a thickness of a few nanometers and mesopores ranging from 2 to 5 nm, were wrapped in graphene nanosheets and formed hybrid nanoarchitectures. When applied as electrode materials in supercapacitors, hybrid NiCo2O4@graphene nanosheets exhibited a high capacitance of 778 F g-1 at the current density of 1 A g-1, and an excellent cycling performance extending to 10000 cycles at the high current density of 10 A g-1.
Mondal, A.K., Su, D., Chen, S., Sun, B., Li, K. & Wang, G. 2014, 'A simple approach to prepare nickel hydroxide nanosheets for enhanced pseudocapacitive performance', RSC Advances, vol. 4, pp. 19476-19481.
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Nickel hydroxide nanosheets were synthesized by a simple microwave assisted heating method and investigated as electrochemical pseudo-capacitive materials for supercapacitors. The crystalline structure and morphology of the as-obtained Ni(OH)2 nanosheets were characterized by X-ray di?raction, nitrogen adsorption+desorption isotherms, ?eld emission scanning electron microscopy and transmission electron microscopy. The electrochemical properties of the Ni(OH)2 nanosheets were evaluated by cyclic voltammetry and chronopotentiometry technology in 2 M KOH solution. The nickel hydroxide nanosheet electrode shows a maximum speci?c capacitance of 2570 F g-1 at a current density of 5 A g-1 and exhibits superior cycling stability. These results suggest its potential application as an electrode material for supercapacitors.
Huang, X., Sun, B., Su, D., Zhao, D. & Wang, G. 2014, 'Soft-template synthesis of 3D porous graphene foams with tunable architectures for lithium-O2 batteries and oil adsorption applications', Journal of Materials Chemistry A, vol. 2, pp. 7973-7979.
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We report a general emulsion soft-template method to synthesize porous graphene foams for multifunctional applications, including lithium+oxygen batteries and oil-adsorption. Multiple micro-emulsions and micelles were employed to produce three-dimensional porous graphene with well-tailored interarchitecture for the first time. Detailed mechanism study reveals that specific interfacial interactions, such as p+p interaction, hydrophobic affinity or electrostatic interaction, are vital for the formation of porous graphene materials. When applied as cathode materials in lithium+oxygen batteries, the porous graphene foams exhibited good catalytic activity. Besides, the porous graphene materials also demonstrated the capability for oil adsorption with a high efficiency.
Wang, B., Wen, Y., Ye, D., Yu, H., Sun, B., Wang, G., Hulicova-Jurcakova, D. & Wang, L. 2014, 'Dual Protection of Sulfur by Carbon Nanospheres and Graphene Sheets for Lithium+Sulfur Batteries', Chemistry -A European Journal, vol. 20, pp. 5224-5230.
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Well-confined elemental sulfur was implanted into a stacked block of carbon nanospheres and graphene sheets through a simple solution process to create a new type of composite cathode material for lithium+sulfur batteries. Transmission electron microscopy and elemental mapping analysis confirm that the as-prepared composite material consists of graphene-wrapped carbon nanospheres with sulfur uniformly distributed in between, where the carbon nanospheres act as the sulfur carriers. With this structural design, the graphene contributes to direct coverage of sulfur to inhibit the mobility of polysulfides, whereas the carbon nanospheres undertake the role of carrying the sulfur into the carbon network. This composite achieves a high loading of sulfur (64.2 wt%) and gives a stable electrochemical performance with a maximum discharge capacity of 1394 mAhg 1 at a current rate of 0.1 C as well as excellent rate capability at 1 C and 2 C. The improved electrochemical properties of this composite material are attributed to the dual functions of the carbon components, which effectively restrain the sulfur inside the carbon nano-network for use in lithium+sulfur rechargeable batteries.
Xie, X., Su, D., Chen, S., Zhang, J., Dou, S. & Wang, G. 2014, 'SnS2 Nanoplatelet@Graphene Nanocomposites as High-Capacity Anode Materials for Sodium-Ion Batteries', Chemistry An Asian Journal, vol. 9, pp. 1611-1617.
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Na-ion batteries have been attracting intensive investigations as a possible alternative to Li-ion batteries. Herein, we report the synthesis of SnS2 nanoplatelet@graphene nanocomposites by using a morphology-controlled hydrothermal method. The asprepared SnS2/graphene nanocomposites present a unique two-dimensional platelet-on-sheet nanoarchitecture, which has been identified by scanning and transmission electron microscopy. When applied as the anode material for Na-ion batteries, the SnS2/graphene nanosheets achieved a high reversible specific sodium-ion storage capacity of 725 mAhg 1, stable cyclability, and an enhanced high-rate capability. The improved electrochemical performance for reversible sodium-ion storage could be ascribed to the synergistic effects of the SnS2 nanoplatelet/graphene nanosheets as an integrated hybrid nanoarchitecture, in which the graphene nanosheets provide electronic conductivity and cushion for the active SnS2 nanoplatelets during Na-ion insertion and extraction processes.
Choi, M., Ham, G., Jin, B., Lee, S., Lee, Y.M., Wang, G. & Kim, H. 2014, 'Ultra-thin Al2O3 coating on the acid-treated 0.3Li2MnO30.7LiMn0.60Ni0.25Co0.15O2 electrode for Li-ion batteries', Journal Of Alloys And Compounds, vol. 608, pp. 110-117.
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The Li and Mn-rich layered composites represented by Li2MnO3+LiMO2 has been attracting great interests owing to its exceptional high capacity (P250 mA h g 1) and enhanced structural stability. In order to improve the initial coulombic efficiency and cyclability of the composites, the material has been activated by an acid-treatment and coated with an Al2O3 using an atomic layer deposition (ALD). The acid-treated electrode showed a higher discharge capacity than the as-prepared electrode. The alumina-coated electrode provided an improved specific capacity of the electrode but also cycling stability, when compared with the bare electrode. The electrode coated with the alumina could lead to a decrease in undesirable reactions, thereby acting as a stable protecting layer that could quickly transport Li+ ions during charge and discharge process.
Su, D., Dou, S. & Wang, G. 2014, 'Mesocrystal Co3O4 nanoplatelets as high capacity anode materials for Li-ion batteries', Nano Research, vol. 7, no. 5, pp. 794-803.
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Faceted crystals with exposed highly reactive planes have attracted intensive investigations for applications. Herein, we demonstrate a general synthetic method to prepare mesocrystal Co3O4 with predominantly exposed {111} reactive facets by the in situ thermal decomposition from Co(OH)2 nanoplatelets. The mesocrystal feature was identified by field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and N2 isotherm analyses. When applied as anode material in lithium-ion batteries, mesocrystal Co3O4 nanoplatelets delivered a high specific capacity and an outstanding high rate performance. The superior electrochemical performance should be ascribed to the predominantly exposed {111} active facets and highly accessible surfaces. This synthetic strategy could be extended to prepare other mesocrystal functional nanomaterials.
Liu, H. & Wang, G. 2014, 'An investigation of the morphology effect in Fe2O3 anodes for lithium ion batteries', Journal of Materials Chemistry A, vol. 2, pp. 9955-9959.
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Morphology control strategies have been widely used to boost the tolerance of anode materials against a dramatic volume change during charge/discharge processes. Herein, we found solid scientific evidence demonstrating that the electrochemical properties of cavity containing materials are superior to their solid counterparts.
Liu, J., Liu, H., Yang, T., Wang, G. & Tade, M.O. 2014, 'Mesoporous carbon with large pores as anode for Na-ion batteries', Chinese Science Bulletin, vol. 59, no. 18, pp. 2186-2190.
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Sodium ion (Na+) batteries have attracted increased attention for energy storage owing to the natural abundance and low cost of sodium. Herein, we report the synthesis of mesoporous carbon with large pores as anode for Na-ion batteries. The mesoporous carbon was obtained by carbonization and dense packing of 50 nm resorcinol and formaldehyde spheres synthesized through an extension Stber method. Our work demonstrates that replacement of lithium by sodium using large pore carbon as anode might offer an alternative route for rechargeable batteries.
Sun, B., Huang, X., Chen, S., Munroe, P. & Wang, G. 2014, 'Porous Graphene Nanoarchitectures: An Efficient Catalyst for Low Charge-Overpotential, Long Life, and High Capacity Lithium-Oxygen Batteries', Nano Letters, vol. 14, pp. 3145-3152.
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The electrochemical performance of lithium-oxygen (Li-O2) batteries awaits dramatic improvement in the design of porous cathode electrodes with sufficient spaces to accommodate the discharge products and discovery of effective cathode catalysts to promote both oxygen reduction reactions and oxygen evolution reactions. Herein, we report the synthesis of porous graphene with different pore size architectures as cathode catalysts for Li-O2 batteries. Porous graphene materials exhibited significantly higher discharge capacities than that of nonporous graphene. Furthermore, porous graphene with pore diameter around 250 nm showed the highest discharge capacity among the porous graphene with the small pores (about 60 nm) and large pores (about 400 nm). Moreover, we discovered that addition of ruthenium (Ru) nanocrystals to porous graphene promotes the oxygen evolution reaction. The Ru nanocrystal-decorated porous graphene exhibited an excellent catalytic activity as cathodes in Li-O2 batteries with a high reversible capacity of 17 700 mA h g-1, a low charge/discharge overpotential (about 0.355 V), and a long cycle life up to 200 cycles (under the curtaining capacity of 1000 mAh g-1). The novel porous graphene architecture inspires the development of high-performance Li-O2 batteries.
Sun, B., Huang, X., Chen, S., Zhao, Y., Zhang, J., Munroe, P. & Wang, G. 2014, 'Hierarchical macroporous/mesoporous NiCo2O4 nanosheets as cathode catalysts for rechargeable Li-O2 batteries', Journal of Materials Chemistry A, vol. 2, pp. 12053-12059.
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The key factor to improve the electrochemical performance of Li-O2 batteries is to find bi-functional cathode catalysts to promote the oxygen reduction and evolution reactions. Despite tremendous effects, developing cathode catalysts with high activity remains a great challenge. Herein, we report the synthesis of hierarchical macroporous/mesoporous NiCo2O4 nanosheets as an effective cathode catalyst for Li-O2 batteries. The hierarchical porous catalyst was synthesized by a hydrothermal method, followed by low temperature calcination. SEM and TEM observations clearly present that the as-prepared NiCo2O4 nanosheets showed a hierarchical porous structure with mesopores distributed through the surface of NiCo2O4 nanosheets and macropores formed between the crumpled nanosheets. When investigating as the cathode catalyst in Li-O2 batteries, the as-prepared NiCo2O4 nanosheets exhibited higher reversible capacity, lower charge/discharge overpotential, and better cycling stability than those of pristine carbon black. The enhanced electrochemical performance of NiCo2O4 nanosheets should be attributed not only to the high catalytic activity of NiCo2O4 towards oxygen reduction reaction and oxygen evolution reaction, but also to the novel hierarchical porous structure of NiCo2O4.
Su, D., Dou, S.X. & Wang, G. 2014, 'Hierarchical orthorhombic V2O5 hollow nanospheres as high performance cathode materials for sodium-ion batteries', Journal of Materials Chemistry A, vol. 2, pp. 11185-11194.
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Vanadyl ethylene glycolate hollow hierarchical nanospheres were synthesized via a template-free polyolinduced solvothermal process. After sintering, vanadium pentoxide (V2O5) with well-preserved spherical structures was obtained. Refined X-ray diffraction and transmission electron microscopy analyses identified that the V2O5 hollow nanospheres were constructed from hierarchical nanocrystals with predominantly exposed {110} crystal planes. When applied as cathode materials for sodium-ion batteries (Na-ion batteries), the V2O5 hollow nanospheres delivered a specific discharge capacity of ~150 mA h g-1, which is equal to one Na+ ion insertion per V2O5 formula unit. Theoretical modelling on the volume expansion and stress evolution on Na+ ion insertion revealed that the prolonged cycling stability could be ascribed to the porous hollow spherical architecture. Furthermore, the exposed {110} facets of V2O5 nanocrystals with two-dimensional diffusion paths for Na+ ion intercalation also contribute to high rate capacity and excellent cycling performance.
Su, D., Ahn, H. & Wang, G. 2013, 'One-dimensional magnetite Fe3O4 nanowires as electrode material for Li-ion batteries with improved electrochemical performance', Journal of Power Sources, vol. 244, no. 1, pp. 742-746.
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One-dimensional magnetite (Fe3O4) nanowires were synthesized by the low temperature hydrothermal method. The as-prepared Fe3O4 nanowires were systematically characterized by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. X-ray diffraction and transmission electron microscopy have confirmed the cubic structure of Fe3O4 nanowires with a space group of Fdm. Electrochemical properties of Fe3O4 nanowires were tested as anodes in lithium-ion cells by cyclic voltammetry and galvanostatic charge/discharge. Fe3O4 nanowires exhibited an excellent reversible lithium storage capacity and a satisfactory cycling performance.
Chen, Y., Liu, L., Wang, M., Wang, C., Hu, X. & Wang, G. 2013, 'Self-made non-enzymatic silver electrode from recordable CDs for fast detection of glucose in blood', Sensors and Actuators B: Chemical, vol. 177, pp. 555-561.
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An electrochemical sensor based on a self-made electrode from recordable CDs was developed for the non-enzymatic detection of glucose by chronoamperometry. We discussed the amperometric current response of glucose with the change of potential, pH and electrode area, and determined the optimum detection conditions. The current response measurements were performed in a phosphate buffered solution (pH 6.5) with a potential of ++0.50 V, and presented a linearity over the range of 0.5++13 mmol/L (r = 0.996). The experimental results of the designed sensor demonstrate that this method has merits such as simple operation, low cost and rapid responses. The results of detecting glucose in blood samples were satisfactory.
Wang, Y., Su, D., Wang, C. & Wang, G. 2013, 'SnO2@MWCNT nanocomposite as a high capacity anode material for sodium-ion batteries', Electrochemistry Communications, vol. 29, pp. 8-11.
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We report the synthesis and characterization of SnO2@multiwalled carbon nanotubes (MWCNTs) nanocomposite as a high capacity anode material for sodium-ion battery. SnO2@MWCNT nanocomposite was synthesized by a solvothermal method. SEM and TEM analyses show the uniform distribution of SnO2 nanoparticles on carbon nanotubes. When applied as anode materials in Na-ion batteries, SnO2@MWCNT nanocomposite exhibited a high sodium storage capacity of 839 mAh g++ 1 in the first cycle. SnO2@MWCNT nanocomposite also demonstrated much better cycling performance than that of bare SnO2 nanoparticles and bare MWCNTs. Furthermore, the nanocomposite electrode also showed a good cyclability and an enhanced Coulombic efficiency on cycling.
Ryu, H.S., Park, J.W., Park, J., Ahn, J., Kim, K., Ahn, J., Nam, T., Wang, G. & Ahn, H.j. 2013, 'High capacity cathode materials for Li-S batteries', Journal of Materials Chemistry A, vol. 1, pp. 1573-1578.
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To enhance the stability of sulfur cathode for a high energy lithium+sulfur battery, sulfur+activated carbon (S+AC) composite was prepared by encapsulating sulfur into micropores of activated carbon using a solution-based processing technique. In the analysis using the prepared specimen of S+AC composite by the focused ion beam (FIB) technique, the elemental sulfur exists in a highly dispersed state inside the micropores of activated carbon, which has a large surface area and a narrow pore distribution. The S+ AC composite was characterized through X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer+Emmett+Teller (BET) method, selected area electron diffraction (SAED), energy dispersive X-ray spectrometry (EDX), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis (TGA), and field emission scanning electron microscopy (FESEM). A lithium+ sulfur cell using the S+AC composite has a high first discharge capacity over 800 mA h g 1 S even at a high current density such as 2C (3200 mA g 1 S) and has good cycleability around 500 mA h g 1 S discharge capacity at the 50th cycle at the same current density.
Wang, Y., Sharma, N., Su, D., Bishop, D.P., Ahn, H.j. & Wang, G. 2013, 'High capacity spherical Li[Li0.24Mn0.55Co0.14Ni0.07]O2 cathode material for lithium ion batteries', Solid State Ionics, vol. 233, no. NA, pp. 12-19.
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Li[Li0.24Mn0.55Co0.14Ni0.07]O2 cathode materials with controlled spherical morphology and particle size in the range of 5++10 ++m were synthesized by a modified co-precipitation method. The crystal structure of Li[Li0.24Mn0.55Co0.14Ni0.07]O2 was investigated by Rietveld analysis of structural models using X-ray and neutron powder diffraction data, indicating the presence of Li2MnO3 in the final product. Li[Li0.24Mn0.55Co0.14Ni0.07]O2 shows low initial irreversible capacity loss (47.2 mAh/g), high reversible capacity (264.6 mAh/g), good capacity retention (90.4% over 50 cycles) and satisfactory rate capability when used as the cathode material in lithium ion batteries. X-ray photoelectron spectroscopy analysis of the pristine, charged and discharged electrodes of Li[Li0.24Mn0.55Co0.14Ni0.07]O2 reveals that the Mn4 +/Mn3 + redox couple participates in the delithiation/lithiation process. Overall, the improved electrochemical performance of the Li[Li0.24Mn0.55Co0.14Ni0.07]O2 electrode can be ascribed to the controlled and specially designed morphology and the composition of the sample that is produced by the co-precipitation method.
Zhang, Y., Wang, C., Yao, F., Zhu, X., Qu, Q., Hu, X. & Wang, G. 2013, 'Determination of alkylamine carbonate nonionic-anion oil displacement agent in oil-field water using HPLC after derivatization with 4-methoxybenzenesulfonyl fluoride', Analytical Methods, vol. 5, no. 3, pp. 729-734.
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In this study, a method for the determination of alkylamine carbonate (AAC) nonionic++anion oil displacement agent in oil-field water was developed for the first time, involving pre-column derivatization using a novel labeling agent and HPLC with diode-array detection. The derivatization and chromatographic separation conditions were investigated thoroughly. The analyte was labeled with 4-methoxybenzenesulfonyl fluoride at 50 -C for 20 min. When the method was applied in the determination of C18A5C (an AAC oil displacement agent containing eighteen alkyl and five amino groups) a linear calibration curve was obtained from 1.0 to 100.0 ++g mL++1 with a correlation coefficient of more than 0.999 and a detection limit of 0.05 ++g mL++1. In the determination of real oil-field water samples, the recovery range of C18A5C was 91.8% to 96.2%, and the intra-day and inter-day relative standard deviations were 2.9++3.5% and 3.8++4.3%, respectively. The experimental results demonstrate that this method, with its merits of simplicity in pretreatment, rapidity in derivatization, and stability of the derivatives, can be employed in the analysis of C18A5C and has potential application in the detection of other oil displacement surfactants containing amino groups. It is of great significance to develop a fast, easy-to-operate, sensitive and reliable method for environmental impact assessment.
Wang, M., Zhang, H., Wang, C., Hu, X. & Wang, G. 2013, 'Direct electrosynthesis of poly-o-phenylenediamine bulk materials for supercapacitor application', Electrochimica Acta, vol. 91, no. 28, pp. 144-151.
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For the first time, poly-o-phenylenediamine (PoPD) bulk material was electrochemically synthesized using an electrochemical method. Sodium dodecyl sulfate (SDS) was added to o-phenylenediamine (oPD) solution and PoPD with different morphologies were obtained. The as-prepared materials were applied as the electrode materials in supercapacitors. The specific capacitance (SC) of the resultant PoPD was determined to be 106.4 F g++1 in 1 mol L++1 KNO3 electrolyte from CV test. The electrochemical stability of PoPD electrode was investigated by charging and discharging the electrode for 1000 times in the potential range of ++0.2 to 0.6 V versus SCE at the current density of 500 mA g++1. The electrode exhibits a good cycling stability, retaining up to 82% of its initial specific capacitance at 1000th cycle. This novel technique enables PoPD non-film material for supercapacitor application.
Park, J., Kim, J., Park, J.W., Nam, T., Kim, K., Ahn, J., Wang, G. & Ahn, H.j. 2013, 'Discharge mechanism of MoS2 for sodium ion battery: Electrochemical measurements and characterization', Electrochimica Acta, vol. 92, pp. 427-432.
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New emerging large scale battery market has demanded low cost and high power or energy density materials. Sodium (Na) is a promising candidate for an anode material because of its low cost and natural abundance. Also molybdenum disulfide (MoS2) is an attractive cathode material with layered structure. In this study a Na/MoS2 cell was assembled so as to evaluate its electrochemical properties as a rechargeable battery. In the first discharge Na/MoS2 cell showed two characteristic plateaus at 0.93 V and 0.8 V. Galvanostatic charge/discharge cycle was carried out in different voltage ranges according to the discharge depths (0.85 V and 0.4 V). The electrochemical behaviors of Na/MoS2 cells at each discharge depth were analyzed through characterization of the crystallographic changes by employing ex situ X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Finally, Na/MoS2 reaction mechanism was suggested.
Ryu, H.S., Kim, J., Park, J., Park, J.W., Kim, K., Ahn, J.H., Nam, T., Wang, G. & Ahn, H.j. 2013, 'Electrochemical properties and discharge mechanism of Na/TiS2 cells with liquid electrolyte at room temperature', Journal of Electrochemical Society, vol. 160, no. 2, pp. A338-A343.
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The electrochemical properties of Na/TiS2 cells fabricated from Na anodes and TiS2 cathodes and 1M sodium trifluoromethanesulfonate in tetraethyleneglycol dimethylether liquid electrolyte have been investigated. The discharge curve has two plateau regions of 2.1 V and 1.6 V. The loss of discharge capacity appeared mainly in the upper plateau (UP) region (2.0-2.6 V) and the discharge capacity in the low plateau (LP) region (0.8-2.0 V) does not decrease and is consistent during 40 cycles. The discharge process between Na and TiS2 has a complex reaction mechanism, the intercalation at the upper plateau region and the conversion at the low plateau region. Because, a distorted TiS2 phase appeared in the upper plateau, a new phase of NaxTiS2 was observed in the lower plateau, and the NaxTiS2 phase was disappeared after full discharge from the XRD and TEM results. The decrease of discharge capacity during cycling is occurred from the formation of NaxTiS2 phase in the cathode after full charging and is accumulated over cycling (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.084302jes] All rights reserved.
Wang, B., Wang, Y., Sun, B., Munroe, P. & Wang, G. 2013, 'Coral-like V2O5 nanowhiskers as high-capacity cathode materials for lithium-ion batteries', RSC Advances, vol. 3, pp. 5069-5075.
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Coral-like V2O5 nanowhiskers were prepared by a direct electrolytic synthesis method. The as-prepared V2O5 nanowhiskers are approximately 1 ++m in length and 50++60 nm in width, which was confirmed by scanning electron microscopy and transmission electron microscopy analysis. When applied as cathode materials in lithium-ion batteries and combined with an ionic liquid electrolyte, the V2O5 nanowhiskers exhibited an initial capacity of 461 mAh g++1, which is a significant enhancement compared to commercial V2O5 powders. The high rate performance of the V2O5 nanowhiskers was further improved at an elevated working temperature of 50 -C. The V2O5 nanowhiskers demonstrated a high specific capacity and an excellent high-rate performance at elevated temperatures.
Chen, S., Bao, P. & Wang, G. 2013, 'Synthesis of Fe2O3-CNT-graphene hybrid materials with an open three-dimensional nanostructure for high capacity lithium storage', Nano Energy, vol. 2, no. 3, pp. 425-434.
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Fe2O3-CNT-graphene nanosheet (Fe2O3-CNT-GNS) hybrid materials were synthesized using a chemical vapor deposition method. The as-prepared materials consist of Fe2O3 nanorings, bamboo-like carbon nanotubes and graphene nanosheets, which form an open threedimensional architecture. For the first time, we observed the growth of bamboo-like carbon nanotubes with open tips, which were catalyzed by iron nanorings. When applied as anode materials in lithium ion batteries, the Fe2O3+CNT+GNS hybrid materials exhibited a high specific capacity of 984 mAh g!1 with a superior cycling stability and high rate capability. This could be ascribed to short Li+ diffusion path of bamboo-like CNTs, more active reaction sites provided by graphene layers inside CNTs, flexible and highly conductive graphene nanosheets, and an open three-dimensional structure.
Ryu, H.S., Kim, J., Park, J., Park, J., Cho, G., Liu, X., Ahn, I., Kim, K., Ahn, J.H., Ahn, J., Martin, S.W., Wang, G. & Ahn, H. 2013, 'Degradation mechanism of room temperature Na/Ni3S2 cells using Ni3S2 electrodes prepared by mechanical alloying', Journal of Power Sources, vol. 244, pp. 764-770.
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Ni3S2 powder has been fabricated by mechanical alloying Ni and S powders and the electrochemical properties of Na/Ni3S2 cells fabricated from Na anodes and Ni3S2 cathodes and 1 M sodium trifluoromethanesulfonate in tetraethyleneglycol dimethylether liquid electrolyte have been investigated. Upon discharging, the Ni3S2 cathode transformed to amorphous Na2S, Ni and residual unconverted Ni3S2. On charging, the pristine structure of Ni3S2 is fully recovered. The reversibility of this anode/cathode pair has been demonstrated and the discharge capacity loss of Na/Ni3S2 cells has been investigated over 100 cycles. From TEM, EDS, XRD, and EIS results, the degradation mechanism appears to be the formation of nano-particles of Ni3S2 and Na2S which become detached from the bulk cathode material causing the continuous increase in the interfacial resistance. Furthermore, many small cracks in Ni3S2 cathode material are caused during repeated cycling and this is an additional phenomenon that leads to further degradation of the discharge capacity during cycling.
Kim, I., Park, J., Nam, T., Kim, K., Ahn, J.H., Park, D., Ahn, C., Wang, G. & Ahn, H. 2013, 'Electrochemical properties of an as-deposited LiFePO4 thin film electrode prepared by aerosol deposition', Journal of Power Sources, vol. 244, no. 1, pp. 646-651.
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Prepared by the deposition of a solid electrode and electrolyte, all-solid-state batteries are a promising next generation battery system. Aerosol deposition (AD) offers many advantages compared to the conventional thin film deposition methods, including the deposition of a crystallized thin film with no heat treatment and a fast deposition rate. In this study, a LiFePO4/C composite thin film is directly fabricated using a LiFePO4/C composite raw powder. SEM and EDS results show the successful deposition of a LiFePO4/C composite thin film on a stainless steel substrate and X-ray diffraction patterns reveal that the as-deposited thin film has a crystalline structure, corresponding to the olivine phase, without any heat treatment. In a CV test, oxidation and reduction peaks appear at 3.51 and 3.36 V, corresponding closely to the peaks of bulk olivine LiFePO4. Furthermore, the profiles of the charge and discharge curves are similar to those of the bulk electrode and the discharge capacity is 31.1 ++Ah cm++2 ++m++1 in the first cycle. After 20 cycles of 10.65 and 106.5 ++A cm++2 ++m++1, the capacity is recovered to 30.7 ++Ah cm++2 ++m++1. Aerosol deposition can potentially be used in the fabrication of all-solid-state batteries.
Sun, B., Wang, Y., Wang, B., Kim, H., Kim, W. & Wang, G. 2013, 'Porous LiFePO4/C microspheres as high-power cathode materials for lithium ion batteries', Journal of Nanoscience and Nanotechnology, vol. 13, no. 5, pp. 3655-3659.
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Porous LiFePO4/C microspheres were synthesized by a novel hydrothermal reaction combined with high-temperature calcinations. The morphology of the prepared material was investigated by fieldemission scanning electron microscopy. Porous microspheres with diameters around 1++3 m were obtained, which consisting of primary LiFePO4 nanoparticles. The electrochemical performances of the as-prepared LiFePO4 microspheres were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge++discharge cycling. The carbon coated LiFePO4 microspheres showed lower polarization, higher rate capability, and better cycling stability than that of pristine LiFePO4 microspheres, indicating the potential application as the cathode material for high-power lithium ion batteries.
Wang, C., Liu, L., Xue, H., Hu, X. & Wang, G. 2013, 'Fabrication of nanoelectrode ensembles formed via PAN-co-PAA self-assembly and selective voltammetric detection of uric acid in biologic samples', Sensors and Actuators B: Chemical, vol. 181, pp. 194-201.
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In this work, we have developed a novel approach that fabricating carbon nanoelectrode ensembles (carbon NEEs) with the pores of 50+120 nm in radii by self-assembling a copolymer [poly(acrylonitrile-coacrylic acid)]. Only conventional, inexpensive electrochemical instrument is required for this procedure, which is simple and fast. The electrochemical behavior of AA and UA at this carbon NEEs has been studied by CV and differential pulse voltammetry (DPV). The carbon NEEs can suppress the response of ascorbic acid (AA) drastically and resolve the overlapping voltammetric response of uric acid (UA) and AA into two well-defined peaks with a large anodic peak difference (!Epa) of about 330 mV. Meanwhile, the carbonbased electrodes have the weak absorption and fast electron transfer. The reaction of UA and AA take place in the different micro-environment in the presence of the carboxylic functional groups in the nanopores. The sensor offers the peak current that was linearly dependent on the UA concentration in the range from 5.0 10-7 mol/L to 5.0 10-5 mol/L at neutral pH (PBS, pH 6.86) with a correlation coefficient of 0.998, and the detection limit was 1.0 10-7 mol/L (S/N = 3). The carbon NEEs shows excellent sensitivity and selectivity and has been used for the determination of UA in real serum and urine samples with satisfied results.
Liu, Q., Yu, L., Wang, Y., Ji, Y., Horvat, J., Cheng, M., Jia, X. & Wang, G. 2013, 'Manganese-based layered coordination polymer: Synthesis, structural characterization, magnetic property, and electrochemical performance in lithium-ion batteries', Inorganic Chemistry, vol. 52, pp. 2817-2882.
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Manganese-based layered coordination polymer ([Mn- (tfbdc)(4,4!-bpy)(H2O)2], Mn-LCP) with microporous structure was synthesized by reaction of 2,3,5,6-tetrafluoroterephthalatic acid(H2tfbdc) and 4,4!-bipyridine(4,4!-bpy) with manganese(II) acetate tetrahydrate in water solution. Mn-LCP was characterized by elemental analysis, IR spectra, thermogravimetric analysis, X-ray single-crystal structure analysis, and powder X-ray diffraction. Magnetic susceptibility data from 300 to 1.8K show that there is a weak antiferromagnetic exchange between Mn(II) ions in Mn-LCP. As anode material, the Mn-LCP electrode exhibits an irreversible high capacity in the first discharge process and a reversible lithium storage capacity of up to about 390 mA h/g from the fourth cycle. It might provide a new method for finding new electrode materials in lithium-ion batteries
Su, D., Ahn, H. & Wang, G. 2013, 'SnO2@graphene nanocomposites as anode materials for Na-ion batteries with superior electrochemical performance', Chemical Communications, vol. 49, pp. 3131-3133.
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An in situ hydrothermal synthesis approach has been developed to prepare SnO2@graphene nanocomposites. The nanocomposites exhibited a high reversible sodium storage capacity of above 700 mA h g++1 and excellent cyclability for Na-ion batteries. In particular, they also demonstrated a good high rate capability for reversible sodium storage.
Su, D., Ahn, H. & Wang, G. 2013, 'Hydrothermal synthesis of +-MnO2 and +-MnO2 nanorods as high capacity cathode materials for sodium ion batteries', Journal of Materials Chemistry A, vol. 1, pp. 4845-4850.
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Two types of MnO2 polymorphs, +-MnO2 and +-MnO2 nanorods, have been synthesized by a hydrothermal method. Their crystallographic phases, morphologies, and crystal structures were characterized by XRD, FESEM and TEM analysis. Different exposed crystal planes have been identified by TEM. The electrochemical properties of +-MnO2 and +-MnO2 nanorods as cathode materials in Na-ion batteries were evaluated by galvanostatic charge/discharge testing. Both +-MnO2 and +-MnO2 nanorods achieved high initial sodium ion storage capacities of 278 mA h g++1 and 298 mA h g++1, respectively. +-MnO2 nanorods exhibited a better electrochemical performance such as good rate capability and cyclability than that of +-MnO2 nanorods, which could be ascribed to a more compact tunnel structure of +-MnO2 nanorods. Furthermore, the one-dimensional architecture of nanorods could also contribute to facile sodium ion diffusion in the charge and discharge process.
Sun, B., Zhang, J., Munroe, P., Ahn, H.j. & Wang, G. 2013, 'Hierarchical NiCo2O4 nanorods as an efficient cathode catalyst for rechargeable non-aqueous Li-O2 batteries', Electrochemistry Communications, vol. 31, pp. 88-91.
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NiCo2O4 nanorods were synthesized by a hydrothermal method followed by low temperature calcination. FESEM and TEM analyses confirmed that the as-prepared materials consist of a hierarchical nanorod structure. When applied as cathode catalysts in rechargeable Li+O2 batteries, NiCo2O4 nanorods exhibited a superior catalytic activity, including low charge over-potential, high discharge capacity and high-rate capability.
Zhang, J., Sun, B., Ahn, H., Wang, C. & Wang, G. 2013, 'Conducting polymer-doped polyprrrole as an effective cathode catalyst for Li-O2 batteries', Materials Research Bulletin, vol. 48, no. 12, pp. 4979-4983.
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Polypyrrole conducting polymers with different dopants have been synthesized and applied as the cathode catalyst in Li-O2 batteries. Polypyrrole polymers exhibited an effective catalytic activity towards oxygen reduction in lithium oxygen batteries. It was discovered that dopant significantly influenced the electrochemical performance of polypyrrole. The polypyrrole doped with Cl- demonstrated higher capacity and more stable cyclability than that doped with ClO4-. Polypyrrole conducting polymers also exhibited higher capacity and better cycling performance than that of carbon black catalysts.
Yang, D., Wei, K., Liu, Q., Yang, Y., Guo, X., Rong, H., Cheng, M. & Wang, G. 2013, 'Folic acid-functionalized magnetic ZnFe2O4 hollow microsphere core/mesoporous silica shell composite particles: Synthesis and application in drug release', Materials Science and Engineering: C, vol. 33, no. 5, pp. 2879-2884.
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A drug delivery system was designed by deliberately combining the useful functions into one entity, which was composed of magnetic ZnFe2O4 hollow microsphere as the core, and mesoporous silica with folic acid molecules as the outer shell. Amine groups coated magnetic ZnFe2O4 hollow microsphere core/mesoporous silica shell (MZHM-MSS-NH2) composite particles were first synthesized by a one-pot direct co-condensation method. Subsequently a novel kind of folic acid-functionalized magnetic ZnFe2O4 hollow microsphere core/mesoporous silica shell (MZHM-MSS-NHFA) composite particles were synthesized by conjugating folic acid as targeted molecule to MZHM-MSS-NH2. Ibuprofen, a well-known antiphlogistic drug, was used as a model drug to assess the loading and releasing behavior of the composite microspheres. The results show that the MZHM-MSS-NHFA system has the higher capacity of drug storage and good sustained drug-release property.
Wang, Y., Su, D. & Wang, G. 2013, 'The Effect Of Carbon Coating On The Electrochemical Performance Of Nanosized Li2FeSiO4 Cathode Materials', Acta Physica Polonica A, vol. 123, no. 2, pp. 279-282.
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Carbon-coated Li2FeSiO4/C cathode materials have been synthesized through a modified ball-milling process. The physical characterizations of Li2FeSiO4 were conducted by using X-ray powder diffraction, field-emission scanning electron microscopy and transmission electron microscopy techniques. Field-emission scanning electron microscopy and transmission electron microscopy images revealed that Li2FeSiO4/C consists of nanosized particles coated with an amorphous carbon layer. The electrochemical performances of Li2FeSiO4/C cathode materials were evaluated through fully assembled lithium batteries via cyclic voltammetry, charge/discharge test and electrochemical impedance spectroscopy. The Li2FeSiO4/C cathode materials showed a much improved electrochemical performance in terms of higher specific capacity, better cycling performance and less charge transfer resistance than that of the pristine Li2FeSiO4.
Su, D., Wang, C., Ahn, H. & Wang, G. 2013, 'Octahedral tin dioxide nanocrystals as high capacity anode materials for Na-ion batteries', Physical Chemistry Chemical Physics, vol. 15, pp. 12543-12550.
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Single crystalline SnO2 nanocrystals (60 nm in size) with a uniform octahedral shape were synthesised using a hydrothermal method. Their phase and morphology were characterized by XRD and FESEM observation. TEM and HRTEM analyses identified that SnO2 octahedral nanocrystals grow along the [001] direction, consisting of dominantly exposed {221} high energy facets. When applied as anode materials for Na-ion batteries, SnO2 nanocrystals exhibited high reversible sodium storage capacity and excellent cyclability (432 mA h g-1 after 100 cycles). In particular, SnO2 nanocrystals also demonstrated a good high rate performance. Ex situ TEM analysis revealed the reaction mechanism of SnO2 nanocrystals for reversible Na ion storage. It was found that Na ions first insert into SnO2 crystals at the high voltage plateau (from 3 V to 0.8 V), and that the exposed (1 1) tunnel-structure could facilitate the initial insertion of Na ions. Subsequently, Na ions react with SnO2 to form NaxSn alloys and Na2O in the low voltage range (from 0.8 V to 0.01 V). The superior cyclability of SnO2 nanocrystals could be mainly ascribed to the reversible Na+Sn alloying and de-alloying reactions. Furthermore, the reduced Na2O +matrix+ may help retard the aggregation of tin nanocrystals, leading to an enhanced electrochemical performance.
Su, D., Fu, H., Jiang, X. & Wang, G. 2013, 'ZnO nanocrystals with a high percentage of exposed {4 2 2 3} reactive facets for enhanced gas sensing performance', Sensors and Actuators B: Chemical, vol. 186, pp. 286-292.
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Zinc oxide single crystals with a high percentage of exposed {4?2?2?3} reactive facet were prepared by a facile hydrothermal route. X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission microscopy confirmed the faceted single crystal structure. Through the density functional theory (DFT) calculations, it is validated that the {4?2?2?3} surface of ZnO crystals has high surface energy. When used as a sensing material in gas sensors, ZnO crystals with dominating exposed {4?2?2?3} planes exhibited a superior sensitivity toward toxic and flammable gases.
Su, D., Wang, C., Ahn, H. & Wang, G. 2013, 'Single Crystalline Na0.7MnO2 Nanoplates as Cathode Materials for Sodium-Ion Batteries with Enhanced Performance', Chemistry: A European Journal, vol. 19, no. 33, pp. 10884-10889.
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Single crystalline rhombus-shaped Na0.7MnO2 nanoplates have been synthesized by a hydrothermal method. TEM and HRTEM analyses revealed that the Na0.7MnO2 single crystals predominantly exposed their (100) crystal plane, which is active for Na+-ion insertion and extraction. When applied as cathode materials for sodium-ion batteries, Na0.7MnO2 nanoplates exhibited a high reversible capacity of 163 mA?h?g-1, a satisfactory cyclability, and a high rate performance. The enhanced electrochemical performance could be ascribed to the predominantly exposed active (100) facet, which could facilitate fast Na+-ion insertion/extraction during the discharge and charge process.
Du, X., Zhou, C., Liu, H., Mai, Y. & Wang, G. 2013, 'Facile chemical synthesis of nitrogen-doped graphene sheets and their electrochemical capacitance', Journal of Power Sources, vol. 241, no. NA, pp. 460-466.
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To improve the electrochemical performance of graphene materials, nitrogen-doped graphene sheets (NGS) were simultaneously reduced and functionalized with nitrogen (N) doping from graphene oxide (GO) by a simple process using 1 wt.% ammonia water solution as the reducing agent, nitrogen precursor and solvent. The NGS were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy+energy dispersive spectroscopy microanalysis, and differential scanning calorimetry. The thermal stability of NGS was much higher than that of GO. The N content in NGS was 4.4 at.% and a maximum specific capacitance up to 233.3 F g-1 was obtained at 0.5 A g-1. At 0.02 V s-1, the NGS exhibited a specific capacitance of 140.3 F g-1, which was over 8 times that of GO and nearly 2 times that of graphene without N-doping. These results revealed that N-doping of functional graphene provide remarkable improvements on the electrochemical capacitive performance of graphene materials. The NGS also showed high cycle stability of capacitive performance.
Sun, B., Munroe, P. & Wang, G. 2013, 'Ruthenium nanocrystals as cathode catalysts for lithium-oxygen batteries with a superior performance', Scientific Reports, vol. 3, no. 1, pp. 2247-1-2247-7.
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The key factor to improve the electrochemical performance of Li-O-2 batteries is to find effective cathode catalysts to promote the oxygen reduction and oxygen evolution reactions. Herein, we report the synthesis of an effective cathode catalyst of ruthenium nanocrystals supported on carbon black substrate by a surfactant assisting method. The as-prepared ruthenium nanocrystals exhibited an excellent catalytic activity as cathodes in Li-O-2 batteries with a high reversible capacity of about 9,800 mAh g(-1), a low charge-discharge over-potential (about 0.37 V), and an outstanding cycle performance up to 150 cycles (with a curtaining capacity of 1,000 mAh g(-1)). The electrochemical testing shows that ruthenium nanocrystals can significantly reduce the charge potential comparing to carbon black catalysts, which demonstrated that ruthenium based nanomaterials could be effective cathode catalysts for high performance lithium- O-2 batteries.
Su, D., Liu, H., Ahn, H.j. & Wang, G. 2013, 'Synthesis of Highly Ordered Mesoporous Co3O4 for Gas Sensing', Journal of Nanoscience & Nanotechnology, vol. 13, no. 5, pp. 3354-3359.
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Highly ordered mesoporous Co3O4 nanostructures were prepared using SBA-15 silica as hard templates. The mesoporous structures were characterized by X-ray diffraction, high resolution transmission electron microscopy, and N-2 adsorption/desorption isotherm analysis. The results demonstrated that the as-prepared mesoporous Co3O4 has an ordered P6mm symmetric mesoporous structure. The optical absorption properties of the mesoporous Co3O4 were investigated by UV-Vis spectroscopy and the results indicate that the mesoporous Co3O4 materials are semiconducting with direct band gaps of 2, 1.385 and 0.38 eV. The gas-sensing performance of the mesoporous Co3O4 was tested towards a series of typical solvents. They demonstrated a good sensing performance towards these vapour with rapid response and high sensitivity at low operating temperature.
Su, D., Kim, H., Kim, W. & Wang, G. 2013, 'A study of PtxCoy alloy nanoparticles as cathode catalysts for lithium-air batteries with improved catalytic activity', Journal of Power Sources, vol. 244, pp. 488-493.
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A series of PtxCoy (x:y + 4, 2, 1, and 0.5) alloy nanoparticles deposited on Vulcan XC-72 carbon was prepared through a chemical reduction method. The structures and morphologies of the as-prepared nanoparticles were characterized by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy, which revealed the formation of PteCo alloys during the co-reduction process. PtxCoy alloy nanoparticles were applied as catalysts in lithium-air batteries. Through electrochemical testing, we found that the Pt based alloy nanocatalysts significantly increased the specific capacity of lithium-air batteries and the increase of Co content in PtxCoy alloy nanoparticles further enhanced the catalytic activity. This result illustrated that PtxCoy alloy nanoparticles could be used as an efficient catalyst material for lithium-air batteries with the feature of much reduced cost, but drastically increased catalytic activity.
Chen, S., Bao, P., Xiao, L.H. & Wang, G. 2013, 'Large-scale and low cost synthesis of graphene as high capacity anode materials for lithium-ion batteries', Carbon, vol. 64, no. 1, pp. 158-169.
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Graphene has emerged as an intriguing and attractive functional material for a wide range of applications, owing to its unique physical, chemical and mechanical properties. Herein, we report large-scale production of high quality single crystalline graphene sheets based on the ambient pressure chemical vapor deposition (APCVD) method using acetylene (C2H2) as the carbon source and coral-like iron with body-centered-cubic structure as the catalyst. The process can be scaled up for large quantity production at a low cost. The optimum APCVD temperature has been identified to be 850 C, which is much lower than that catalyzed by other metals. Transmission electron microscopy (TEM), atomic force microscopy, Raman spectroscopy and X-ray photoemission spectroscopy characterizations show the single crystalline and high quality nature of the as-prepared graphene produced by the bottom-up APCVD approach. A new horizontal +dissolution+deposition+growth+ mechanism is proposed and verified by high resolution TEM. When applied as anode materials in lithium ion batteries, graphene sheets exhibited a high lithium storage capacity and an excellent cyclability. The capability of preparing crystalline graphene on a large scale with low cost opens an avenue for technological applications of graphene in many fields.
Huang, X., Sun, B., Li, K., Chen, S. & Wang, G. 2013, 'Mesoporous graphene paper immobilised sulfur as a flexible electrode for lithium-sulfur batteries', Journal of Materials Chemistry A, vol. 1, no. 43, pp. 13484-13489.
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Free-standing flexible mesoporous graphene-sulfur nanocomposite electrodes have been prepared by a sulfur vapor treatment approach. Amorphous sulfur homogeneously was distributed in the mesoporous architectures of porous graphene paper, in which sulfur was immobilized. The as-prepared mesoporous graphene+sulfur papers can be directly applied as electrodes in lithium+sulfur batteries without using a binder, conductive additives or an extra current collector. The conductive flexible porous graphene networks can effectively facilitate electron transfer and electrolyte diffusion. The free-standing sulfur+graphene nanocomposite electrodes achieved a high discharge capacity of 1393 mA h g-1 with an enhanced cycling stability and good rate performance.
Su, D., Ahn, H. & Wang, G. 2013, '-MnO2 nanorods with exposed tunnel structures as high-performance cathode materials for sodium-ion batteries', NPG Asia Materials, vol. 5, no. e70, p. 1.
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Sodium-ion batteries are being considered as a promising system for stationary energy storage and conversion, owing to the natural abundance of sodium. It is important to develop new cathode and anode materials with high capacities for sodium-ion batteries. Herein, we report the synthesis of -MnO2 nanorods with exposed tunnel structures by a hydrothermal method. The as-prepared -MnO2 nanorods have exposed {111} crystal planes with a high density of (1 1) tunnels, which leads to facile sodium ion (Na-ion) insertion and extraction. When applied as cathode materials in sodium-ion batteries, -MnO2 nanorods exhibited good electrochemical performance with a high initial Na-ion storage capacity of 350?mAh ?g-1. -MnO2 nanorods also demonstrated a satisfactory high-rate capability as cathode materials for sodium-ion batteries.
Su, D. & Wang, G. 2013, 'Single-Crystalline Bilayered V2O5 Nanobelts for High-Capacity Sodium-Ion Batteries', ACS Nano, vol. 7, no. 12, pp. 11218-11226.
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Single-crystalline bilayered vanadium oxide nanobelts were synthesized by a simple solvothermal method. FESEM and AFM analyses identified the nanobelt morphology of the as-prepared vanadium oxide with a rectangular cross-section and a thickness of approximately 50 nm. XRD and TEM characterizations revealed the presence of a large (001) interlayer spacing (11.53 +), which can accommodate Na-ion insertion and extraction. When applied as cathode materials in Na-ion batteries, vanadium oxide nanobelts exhibited a high capacity of 231.4 mA h g+1 at a current density of 80 mA g+1. This corresponds to the theoretical capacity to form Na2V2O5 on Na-ion insertion. Vanadium oxide nanobelts also demonstrated an excellent high-rate performance and a satisfactory cyclability. These superior electrochemical performances could be ascribed to the unique bilayered vanadium oxide nanobelts with dominantly exposed {100} crystal planes, which provide large interlayer spacing for facile Na-ion insertion/extraction. Single-crystalline bilayered vanadium oxide nanobelts could be promising cathode materials for high-performance Na-ion batteries.
Wang, Y. & Wang, G. 2013, 'Facile Synthesis of Ge@C Core-Shell Nanocomposites for High-Performance', Chemistry An Asian Journal, vol. 8, no. 12, pp. 3142-3146.
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Herein, we report a facile and 'green' synthetic route for the preparation of Ge@C core-shell nanocomposites by using a low-cost Ge precursor. Field-emission scanning electron microscopy and transmission electron microscopy analyses confirmed the core+shell nanoarchitecture of the Ge@C nanocomposites, with particle sizes ranging from 60 to 100 nm. Individual Ge nanocrystals were coated by a continuous carbon layer, which had an average thickness of 2 nm. When applied as an anode materials for lithium-ion batteries, the Ge@C nanocomposites exhibited a high initial discharge capacity of 1670 mAhg-1 and superior rate capability. In particular, Ge@C nanocomposite electrodes maintained a reversible capacity of 734 mAhg-1 after repeated cycling at a current density of 800 mAg-1 over 100 cycles.
Mondal, A.K., Su, D., Wang, Y., Chen, S. & Wang, G. 2013, 'Hydrothermal Synthesis of Nickel Oxide Nanosheets for Lithium-Ion Batteries and Supercapacitors with Excellent Performance', Chemistry An Asian Journal, vol. 8, no. 11, pp. 2828-2831.
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Nickel oxide nanosheets have been successfully synthesized by a facile ethylene glycol mediated hydrothermal method. The morphology and crystal structure of the nickel oxide nanosheets were characterized by X-ray diffraction, field-emission SEM, and TEM. When applied as electrode materials for lithium-ion batteries and supercapacitors, nickel oxide nanosheets exhibited a high, reversible lithium storage capacity of 1193 mAhg-1 at a current density of 500 mAg-1, an enhanced rate capability, and good cycling stability. Nickel oxide nanosheets also demonstrated a superior specific capacitance of 999 Fg-1 at a current density of 20 Ag-1 in supercapacitors.
Liu, H., Chen, S., Wang, G. & Qiao, S.Z. 2013, 'Ordered Mesoporous Core/Shell SnO2/C Nanocomposite as High capacity Anode Material for Lithium Ion Battery', Chemistry -A European Journal, vol. 19, no. 50, pp. 16897-16901.
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An ordered mesoporous core/shell structured SnO2/C nanocomposite was obtained from a facile vacuum-assisted impregnation route by using SBA-15 as a hard template. The nanocomposoite exhibits high specific capacity and excellent high-rate performance as an anode material for lithium-ion battery (see graph).
Wang, M., Zhang, H., Wang, C. & Wang, G. 2013, 'Synthesis of MnO2/poly-o-phenylenediamine composite and its application in supercapacitors', Electrochimica Acta, vol. 106, no. 1, pp. 301-306.
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A composite of MnO2 and poly-o-phenylenediamine (PoPD) was one-step synthesized by co-precipitation with the reaction of KMnO4 and o-phenylenediamine in acidic solution at room temperature. The influence of the addition of cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) on the morphology and electrochemical performance was investigated. FT-IR, XRD and SEM were adopted to examine the obtained materials, and the electrochemical properties of the products were characterized by cyclic voltammetry and galvanostatic charge+discharge. The material synthesized in the presence of 2.5 g L-1 had a specific capacitance of 262.2 F g-1 determined with cyclic voltammetry in a potential window of 0+0.9 V vs. saturated calomel electrode in 1.0 mol L-1 KNO3 solution.
Zhang, Y., Zhang, Y., Qu, Q., Wang, G. & Wang, C. 2013, 'Determination of glyphosate and aminomethylphosphonic acid in soybean samples by high performance liquid chromatography using a novel fluorescent labeling reagent', Analytical Methods, vol. 5, no. 22, pp. 6465-6472.
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A highly sensitive pre-column derivatization HPLC method for simultaneous determination of glyphosate (GLYP) and its major metabolite aminomethylphosphonic acid (AMPA) in soybean samples was developed. The analytes were labeled with a novel fluorescent l
Liu, L., Wang, C. & Wang, G. 2013, 'Novel cysteic acid/reduced graphene oxide composite film modified electrode for the selective detection of trace silver ions in natural waters', Analytical Methods, vol. 5, no. 20, pp. 5812-5822.
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Novel cysteic acid/reduced graphene oxide composite film on a glassy carbon electrode has been prepared through the electrochemical oxidation of L-cysteine for silver sensing. Differential pulse anodic stripping voltammetry (DPASV) was employed for the d
Su, D., Kim, H.S., Kim, W.S. & Wang, G. 2012, 'Synthesis of tuneable porous hematites (alpha-Fe2O3) for gas sensing and lithium storage in lithium ion batteries', Microporous and Mesoporous Materials, vol. 149, no. 1, pp. 36-45.
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Tuneable porous +-Fe2O3 materials were prepared by using a selective etching method. The structure and morphology of the as-prepared porous hematites have been systematically characterised by X-ray diffraction, field emission scanning electron microscope, and transmission electron microscope. We found that the pore size and pore volume can be controlled by adjusting the etching time during the synthesis process. The porous hematites have been applied for gas sensing and lithium storage in lithium ion cells. The porous +-Fe2O3 materials demonstrated a reversible lithium storage capacity of 1269 mAh/g. When used as a sensing material in gas sensors, porous +-Fe2O3 exhibited a superior sensitivity towards toxic and flammable gases.
Sun, B., Wang, B., Su, D., Xiao, L.H., Ahn, H. & Wang, G. 2012, 'Graphene nanosheets as cathode catalysts for lithium-air batteries with an enhanced electrochemical performance', Carbon, vol. 50, no. 2, pp. 727-733.
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Graphene nanosheets have been investigated as cathode catalysts for lithium-air batteries with alkyl carbonate electrolyte. Field emission scanning electron microscopy, transmission electron microscope and Raman spectroscopy have confirmed the high quality of the as-prepared graphene nanosheets and the surface analysis has identified the mesoporous characteristic of graphene nanosheets. The electrochemical properties of graphene nanosheets as cathode catalysts in lithium-air batteries were evaluated by a galvanostatic charge/discharge testing. The reaction products on the graphene nanosheets cathode were analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. The graphene nanosheet electrodes exhibited a much better cycling stability and lower overpotential than that of the Vulcan XC-72 carbon. This work demonstrated that graphene nanosheets could be an efficient catalyst for lithium-air batteries.
Su, D., Josip, H., Paul, M., Ahn, H., Ranjbartoreh, A. & Wang, G. 2012, 'Polyhedral magnetite nanocrystals with multiple facets: Facile synthesis, structural modelling, magnetic properties and application for high capacity lithium storage', Chemistry: A European Journal, vol. 18, no. 2, pp. 488-497.
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Polyhedral magnetite nanocrystals with multiple facets were synthesised by a low temperature hydrothermal method. Atomistic simulation and calculations on surface attachment energy successfully predicted the polyhedral structure of magnetite nanocrystals with multiple facets. X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission microscopy confirmed the crystal structure of magnetite, which is consistent with the theoretical modelling. The magnetic property measurements show the superspin glass state of the polyhedral nanocrystals, which could originate from the nanometer size of individual single crystals. When applied as an anode material in lithium ion cells, magnetite nanocrystals demonstrated an outstanding electrochemical performance with a high lithium storage capacity, a satisfactory cyclability, and an excellent high rate capacity.
Liu, H., Du, X., Xing, X., Wang, G. & Qiao, S.z. 2012, 'Highly ordered mesoporous Cr2O3 materials with enhanced performance for gas sensors and lithium ion batteries', Chemical Communications, vol. 48, no. 6, pp. 865-867.
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Highly ordered mesoporous Cr2O3 materials with high specific surface area and narrow pore size distribution were successfully prepared by a vacuum assisted impregnation method. Both 2-dimensional hexagonal and 3-dimensional cubic Cr2O3 mesoporous replicas from SBA-15 and KIT-6 templates exhibit enhanced performance for gas sensors and lithium ion batteries, compared to the bulk Cr2O3 counterpart.
Wang, Y., Su, D., Ung, A.T., Ahn, J. & Wang, G. 2012, 'Hollow CoFe(2)O(4) nanospheres as a high capacity anode material for lithium ion batteries', Nanotechnology, vol. 23, no. 5, pp. 1-6.
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Hollow structured CoFe(2)O(4) nanospheres were synthesized by a hydrothermal method. The uniform hollow nanosphere architecture of the as-prepared CoFe(2)O(4) has been confirmed by field emission scanning electron microscopy and transmission electron microscopy analysis, which give an outer diameter of 200-300 nm and a wall thickness of about 100 nm. CoFe(2)O(4) nanospheres exhibited a high reversible capacity of 1266 mA h g(-1) with an excellent capacity retention of 93.6% over 50 cycles and an improved rate capability. CoFe(2)O(4) could be a promising high capacity anode material for lithium ion batteries.
Li, K., Wang, B., Su, D., Park, J., Ahn, H. & Wang, G. 2012, 'Enhance electrochemical performance of lithium sulfur battery through a solution-based processing technique', Journal of Power Sources, vol. 202, pp. 389-393.
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Sulfur/carbon nanocomposites have been successfully prepared by a solution-based processing technique using dimethyl sulfoxide as the solvent. The as-prepared nanocomposites were characterized by X-ray diffraction and field emission scanning electron microscopy. The electrochemical performance of sulfur/carbon nanocomposites were tested by cyclic voltammetry and galvanostatic charge/discharge cycling. When applied as the cathode material in lithium sulfur batteries, the as-prepared sulfur/carbon nanocomposites exhibited a high reversible capacity of 1220 mAh g(-1) in the first cycle and maintained a satisfactory cyclability. This drastic improvement of specific capacity and cycling performance could be attributed to the reduced particle size of sulfur and the homogeneous distribution of sulfur nanoparticles on a carbon matrix, resulting from this novel solution-based processing technique.
Kim, I., Nam, T., Kim, K., Ahn, J., Park, D., Ahn, C., Chun, B.S., Wang, G. & Ahn, H. 2012, 'LiNi0.4Co0.3Mn0.3O2 thin film electrode by aerosol deposition', Nanoscale Research Letters, vol. 7, p. art64.
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LiNi0.4Co0.3Mn0.3O2 thin film electrodes are fabricated from LiNi0.4Co0.3Mn0.3O2 raw powder at room temperature without pretreatments using aerosol deposition that is much faster and easier than conventional methods such as vaporization, pulsed laser deposition, and sputtering. The LiNi0.4Co0.3Mn0.3O2 thin film is composed of fine grains maintaining the crystal structure of the LiNi0.4Co0.3Mn0.3O2 raw powder. In the cyclic voltammogram, the LiNi0.4Co0.3Mn0.3O2 thin film electrode shows a 3.9-V anodic peak and a 3.6-V cathodic peak. The initial discharge capacity is 44.6 mu Ah/cm(2), and reversible behavior is observed in charge-discharge profiles. Based on the results, the aerosol deposition method is believed to be a potential candidate for the fabrication of thin film electrodes.
Wu, H., Wexler, D., Wang, G. & liu, H. 2012, 'Co-core-Pt-shell nanoparticles as cathode catalyst for PEM fuel cells', Journal of Solid State Electrochemistry, vol. 16, no. 3, pp. 1105-1110.
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Nanoscale Co-core-Pt-shell particles were successfully synthesized based on a successive reduction strategy. The as-prepared core-shell nanoparticles were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscope, and electrochemical methods. It was found that the catalytic reactivity of Co-core-Pt-shell/C catalysts toward oxygen reduction was enhanced. It is believed that the prepared Co-core-Pt-shell/C nanoparticles could be promising for cathode catalysis in proton exchange membrane fuel cells with much reduced Pt content, but significantly increased catalytic activity.
Ranjbartoreh, A. & Wang, G. 2012, 'Practical molecular dynamic simulation of monolayer graphene with consideration of structural defects', Journal of Nanoscience and Nanotechnology, vol. 12, no. 2, pp. 1398-1401.
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Molecular dynamic simulation method has been employed to consider the mechanical properties of pristine and defected armchair and zigzag monolayer graphene sheets under tension and compression. Effects of Stone Wales (SW), Cell deformed (CD) and cell vacancy (CV) defects on ultimate stress and strain of graphene sheets have been considered. Obtained results indicate that zigzag graphene sheet has higher elastic modulus and stiffness than armchair type. Three SW defects have the highest destructive effect on ultimate stress and strain of zigzag graphene sheet while CV defect reveals the highest reducing effect on those of armchair type
Wang, B., Su, D., Park, J., Ahn, H. & Wang, G. 2012, 'Graphene-supported SnO2 nanoparticles prepared by a solvothermal approach', Nanoscale Research Letters, vol. 7, no. 2012, pp. 1-10.
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SnO2 nanoparticles were dispersed on graphene nanosheets through a solvothermal approach using ethylene glycol as the solvent. The uniform distribution of SnO2 nanoparticles on graphene nanosheets has been confirmed by scanning electron microscopy and transmission electron microscopy. The particle size of SnO2 was determined to be around 5 nm. The assynthesized SnO2/graphene nanocomposite exhibited an enhanced electrochemical performance in lithium-ion batteries, compared with bare graphene nanosheets and bare SnO2 nanoparticles. The SnO2/graphene nanocomposite electrode delivered a reversible lithium storage capacity of 830 mAh g++1 and a stable cyclability up to 100 cycles. The excellent electrochemical properties of this graphene-supported nanocomposite could be attributed to the insertion of nanoparticles between graphene nanolayers and the optimized nanoparticles distribution on graphene nanosheets.
Wang, B., Li, K., Su, D., Ahn, H. & Wang, G. 2012, 'Superior electrochemical performance of sulfur/graphene nanocomposite material for high-capacity lithium-sulfur batteries', Chemistry - An Asian Journal, vol. 7, no. 7, pp. 1637-1643.
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Abstract Sulfur/graphene nanocomposite material has been prepared by incorporating sulfur into the graphene frameworks through a melting process. Field-emission scanning electron microscope analysis shows a homogeneous distribution of sulfur in the graphene nanosheet matrix. The sulfur/graphene nanocomposite exhibits a super-high lithium-storage capacity of 1580++mAh++g++1 and a satisfactory cycling performance in lithium++sulfur cells. The enhancement of the reversible capacity and cycle life could be attributed to the flexible graphene nanosheet matrix, which acts as a conducting medium and a physical buffer to cushion the volume change of sulfur during the lithiation and delithiation process. Graphene-based nanocomposites can significantly improve the electrochemical performance of lithium++sulfur batteries.
Wang, Y., Park, J., Sun, B., Ahn, H. & Wang, G. 2012, 'Wintersweet-flower-like CoFe2O4/MWCNTs hybrid material for high-capacity reversible lithium storage', Chemistry - An Asian Journal, vol. 7, no. 8, pp. 1940-1946.
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Abstract CoFe2O4/multiwalled carbon nanotubes (MWCNTs) hybrid materials were synthesized by a hydrothermal method. Field emission scanning electron microscopy and transmission electron microscopy analysis confirmed the morphology of the as-prepared hybrid material resembling wintersweet flower ++buds on branches+ , in which CoFe2O4 nanoclusters, consisting of nanocrystals with a size of 5++10++nm, are anchored along carbon nanotubes. When applied as an anode material in lithium ion batteries, the CoFe2O4/MWCNTs hybrid material exhibited a high performance for reversible lithium storage. In particular, the hybrid anode material delivered reversible lithium storage capacities of 809, 765, 539, and 359++mA++h++g++1 at current densities of 180, 450, 900, and 1800++mA++g++1, respectively. The superior performance of CoFe2O4/MWCNTs hybrid materials could be ascribed to the synergistic pinning effect of the wintersweet-flower-like nanoarchitecture. This strategy could also be applied to synthesize other metal oxide/CNTs hybrid materials as high-capacity anode materials for lithium ion batteries.
Su, D., Kim, H., Kim, W. & Wang, G. 2012, 'Mesoporous nickel oxide nanowires: hydrothermal synthesis, characterisation and applications for lithium-ion batteries and supercapacitors with superior performance.', Chemistry -A European Journal, vol. 18, no. 26, pp. 8224-8229.
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Mesoporous nickel oxide nanowires were synthesized by a hydrothermal reaction and subsequent annealing at 400?degrees C. The porous one-dimensional nanostructures were analysed by field-emission SEM, high-resolution TEM and N2 adsorption/desorption isotherm measurements. When applied as the anode material in lithium-ion batteries, the as-prepared mesoporous nickel oxide nanowires demonstrated outstanding electrochemical performance with high lithium storage capacity, satisfactory cyclability and an excellent rate capacity. They also exhibited a high specific capacitance of 348 F?g-1 as electrodes in supercapacitors.
Liu, H., Su, D., Zhou, R., Sun, B., Wang, G. & Qiao, S.Z. 2012, 'Highly ordered mesoporous MoS2 with expanded spacing of the (002) crystal plane for ultrafast lithium ion storage', Advanced Energy Materials, vol. 2, no. 8, pp. 970-975.
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Many alternative energy technologies have been developed in an attempt to alleviate the critical problems of an escalating energy crisis and greenhouse gas pollution, derived from the consumption of fossil fuels. Rechargeable lithium ion batteries have attracted great attention at fundamental application levels because of their high energy density and design fl exibility. As such, they are considered as the most promising next generation power sources for electric vehicles. The development of electric vehicles and hybrid electric vehicles demands high power energy sources which can operate under much higher current condition (tens of Amperes) than the operating current of mobilephones ( ~ 100 milli-Amperes).
Chen, S., Wang, Y., Ahn, H. & Wang, G. 2012, 'Microwave hydrothermal synthesis of high performance tin-graphene nanocomposites for lithium ion batteries', Journal of Power Sources, vol. 216, no. October2012, pp. 22-27.
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Tin-graphene nanocomposites are prepared by a combination of microwave hydrothermal synthesis and a one-step hydrogen gas reduction. Altering the weight ratio between tin and graphene nanosheets has critical influences on their morphologies and electrochemical performances. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) analysis confirm the homogeneous distribution of tin nanoparticles on the surface of graphene nanosheets. When applied as an anode material in lithium ion batteries, tin-graphene nanocomposite exhibits a high lithium storage capacity of 1407 mAh g -1. The as-prepared tin-graphene nanocomposite also demonstrates an excellent high rate capacity and a stable cycle performance. The superior electrochemical performance could be attributed to the synergistic effect of the three-dimensional nanoarchitecture, in which tin nanoparticles are sandwiched between highly conductive and flexible graphene nanosheets
Fu, H., Jiang, X., Yang, X., Yu, A., Su, D. & Wang, G. 2012, 'Glycothermal synthesis of assembled vanadium oxide', Journal of nanoparticle Research, vol. 14, no. 6, pp. 1-14.
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This study demonstrates a facile but effective glycothermal method to synthesize vanadium oxide nanostructures for gas sensing detection. In this method, sodium orthovanadate was first dispersed and heated in ethylene glycol at 120-180 degrees C for a few hours, and then the precipitates were collected, rinsed, and sintered at high temperatures (e.g., 600 degrees C) for V2O5 in air and V2O3 in nitrogen, respectively. The as-prepared vanadium oxide particles are nanorods (200 nm x 1 mu m) and can assemble into microspheres or urchin-like structures with a diameter of similar to 3 mu m. The experimental parameters (temperature, time, and surfactants) and the formation mechanisms were investigated by various advanced techniques, such as transmission electron microscope, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and thermo-gravimetric analysis. Finally, the V2O5 nanoparticles were tested for sensing detection of gas species of acetone, isopropanol, and ammonia. The microurchin structures show higher sensing performance than the nanorods.
Chen, S., Yeoh, W., Liu, Q. & Wang, G. 2012, 'Chemical-free synthesis of graphene-carbon nanotube hybrid materials for reversible lithium storage in lithium-ion batteries', Carbon, vol. 50, no. 12, pp. 4557-4565.
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Graphene-carbon nanotube hybrid materials were successfully prepared through the p-p interaction without using any chemical reagent. We found that the ratio between carbon nanotube and graphene had critical influences on the state in aqueous solution and morphology of hybrid materials. Field emission scanning electron microscope and transmission electron microscope analysis confirmed that graphene nanosheets wrap around individual carbon nanotubes and form a homogeneous three-dimensional hybrid nanostructure. When applied as an anode material in lithium ion batteries, graphene-carbon nanotube hybrid materials demonstrated a high reversible lithium storage capacity, a high Coulombic efficiency and an excellent cyclability.
Ranjbartoreh, A. & Wang, G. 2012, 'Consideration of bending and buckling behaviors of monolayer and multilayer graphene sheets', Journal of Nanoscience & Nanotechnology, vol. 12, no. 2, pp. 1395-1397.
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Abstract: Graphene is a two-dimensional carbon based material. Remarkable mechanical, thermal and electrical properties of graphene make it as promising material for advanced applications; nevertheless, majority of its mechanical properties are still unknown. This research investigates buckling and bending behaviors of monolayer and multilayer armchair and zigzag graphene sheets. Bending stiffness, critical buckling force per unit length and critical strain of graphene sheets have been measured by molecular dynamic simulation method. Zigzag graphene sheet shows higher bending stiffness than armchair sheet. Van der Waals interaction between graphene sheets has an improving effect on the stability of middle layers. Cross-linkages reduce the buckling force per unit length and the buckling strain of multi layer graphene sheets.
Wang, B., Park, J., Su, D., Wang, C., Ahn, H. & Wang, G. 2012, 'Solvothermal synthesis of CoS2 graphene nanocomposite material for high-performance supercapacitors', Journal of Materials Chemistry, vol. 22, no. 31, pp. 15750-15756.
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A CoS2-graphene nanocomposite was prepared by a facile solvothermal method. FESEM and TEM analyses have confirmed that CoS2 nanoparticles with sizes of 5-15 nm are densely anchored on graphene nanosheets. The as-prepared nanocomposite was electrochemically tested as an electrode material for supercapacitors. The CoS2-graphene nanocomposite exhibited specific capacitances of 314 F g(-1) in the aqueous electrolyte and 141 F g(-1) in the organic electrolyte at a current rate of 0.5 A g(-1) with excellent cycling stability. The electrochemical performance of the nanocomposite has been significantly improved, compared to bare graphene nanosheets and CoS2 nanoparticles. This could be credited to the 3D nanoarchitecture, in which CoS2 nanoparticles were sandwiched between graphene nanosheets, and the additional electrochemical contribution of the decorated CoS2 nanoparticles.
Liu, H., Su, D., Wang, G. & Qiao, S.Z. 2012, 'An ordered mesoporous WS2 anode material with superior electrochemical performance for lithium ion batteries', Journal of Materials Chemistry, vol. 22, no. 34, pp. 17437-17440.
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Ordered mesoporous tungsten sulfide (WS2) with high surface area and narrow pore size distribution was synthesized by a vacuum assisted impregnation route. The as-prepared mesoporous WS2 exhibited a high lithium storage capacity of 805 mA h g(-1) at a current of 0.1 A g(-1) and an excellent high rate capability.
Sun, B., Liu, H., Munroe, P., Ahn, H. & Wang, G. 2012, 'Nanocomposites of CoO and a mesoporous carbon (CMK-3) as a high performance cathode catalyst for lithium-oxygen batteries', Nano Research, vol. 5, no. 7, pp. 460-469.
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A nanocomposite of CoO and a mesoporous carbon (CMK-3) has been studied as a cathode catalyst for lithium-oxygen batteries in alkyl carbonate electrolytes. The morphology and structure of the as-prepared nanocomposite were characterized by field emission scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy. The electrochemical properties of the mesoporous CoO/CMK-3 nanocomposite as a cathode catalyst in lithium-oxygen batteries were studied using galvanostatic charge-discharge methods. The reaction products on the cathode were analyzed by Fourier transform infrared spectroscopy. The CoO/CMK-3 nanocomposite exhibited better capacity retention than bare mesoporous CMK-3 carbon, Super-P carbon or CoO/Super-P nanocomposite. The synergistic effects arising from the combination of CoO nanoparticles and the mesoporous carbon nanoarchitecture may be responsible for the optimum catalytic performance in lithium-oxygen batteries.
Bai, S., Chen, S., Shen, X., Zhu, G. & Wang, G. 2012, 'Nanocomposites of hematite (+-Fe2O3) nanospindles with crumpled reduced graphene oxide nanosheets as high-performance anode material for lithium-ion batteries', RSC Advances, vol. 2, pp. 10977-10984.
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Nanocomposites of Fe2O3 nanospindles with crumpled reduced graphene oxide (RGO) nanosheets were prepared using a facile solvothermal synthesis method. The RGO-Fe2O3 nanocomposite with about 24.4 wt% RGO demonstrated an excellent electrochemical performance as a promising anode material for lithium-ion batteries (LIBs), which achieved a high reversible capacity of 969 mA h g++1 after 100 cycles at a current density of 100 mA g++1 (0.1 C). Furthermore, it also exhibited a large capacity of 336 mA h g++1 after 100 cycles at the high rate of 5 C. The cycling performance and reversible capacities of the RGO-Fe2O3 composites were much better than those of bare Fe2O3 nanospindles and pure RGO nanosheets, as well as previously reported RGO-Fe2O3 nanocomposites. The enhanced performance towards lithium storage can be ascribed to the crumpled RGO nanosheets, which may act as efficient volume buffer and electron conductor in the composites. The strategy proposed here could be extended to produce other nanocomposites based on crumpled graphene nanosheets for various applications.
Yu, J., Park, J., Wang, Q., Ryu, H., Kim, K., Ahn, J., Kang, Y., Wang, G. & Ahn, H. 2012, 'Electrochemical properties of all solid state Li/S battery', Materials Research Bulletin, vol. 47, pp. 2827-2829.
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All-solid-state lithium/sulfur (Li/S) battery is prepared using siloxane cross-linked network solid electrolyte at room temperature. The solid electrolytes show high ionic conductivity and good electrochemical stability with lithium and sulfur. In the first discharge curve, all-solid-state Li/S battery shows three plateau potential regions of 2.4 V, 2.12 V and 2.00 V, respectively. The battery shows the first discharge capacity of 1044 mAh g++1-sulfur at room temperature. This first discharge capacity rapidly decreases in 4th cycle and remains at 512 mAh g++1-sulfur after 10 cycles.
Hung, T., Wang, B., Tsai, C., Tu, M., Wang, G., Liu, R., Tsai, D.P., Lo, M., Shy, D. & Xing, X. 2012, 'Sulfonation of graphene nanosheet-supported platinum via a simple thermal-treatment toward its oxygen reduction activity in acid medium', International Journal Of Hydrogen Energy, vol. 37, no. 19, pp. 14205-14210.
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The sulfonated graphene nanosheet-supported platinum (s-Pt/GNS) catalyst synthesized via a simple thermal-treatment in the presence of concentrated sulfuric acid was reported in this study. Influence of sulfonation on its structural, surface, morphological and catalytic characteristics of as-prepared s-Pt/GNS was explored using X-ray diffractometer, Raman spectrometry, zeta potential analyzer, scanning and transmission electron microscopes, and cyclic voltammetry. For the oxygen reduction reaction, the current density generated from the s-Pt/GNS at 0.6 V was approximately 32.5 A g++1 Pt, which was about 193% higher than that of original Pt/GNS. --------------------------------------------------------------------------------
Mondal, A.K., Wang, B., Su, D., Wang, Y., Zhang, X. & Wang, G. 2012, 'Preparation and enhanced electrochemical performance of MnO2 nanosheets for supercapacitors', Journal of the Chinese Chemical Society, vol. 59, pp. 1275-1279.
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MnO2 nanosheets have been synthesized by using a redox reaction of manganese nitrate tetrahydrate and potassium permanganate without any surfactants. The morphology and microstructure of the as-prepared material were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction (XRD). Electrochemical performances as electrode materials for supercapacitor were evaluated using cyclic voltammetry and galvanostatic charge-discharge in 1 M Na2SO4 aqueous electrolyte. It was found that MnO2 nanosheets showed an excellent capacitive behaviour with good cycling stability. The specific capacitance of the MnO2 nanosheet electrode can reach up to 332.8 Fg++1 at a current density of 500 mA/g and a stable cycling performance.
Su, D., Ford, M.J. & Wang, G. 2012, 'Mesoporous NiO crystals with dominantly exposed {110} reactive facets for ultrafast lithium storage', Scientific Report, vol. 2, p. 924.
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Faceted crystals with exposed highly reactive planes have attracted intensive investigations for applications such as hydrogen production, enhanced catalytic activity, and electrochemical energy storage and conversion. Herein, we report the synthesis of mesoporous NiO crystals with dominantly exposed {110} reactive facets by the thermal conversion of hexagonal Ni(OH)2 nanoplatelets. When applied as anode materials in lithium-ion batteries, mesoporous NiO crystals exhibit a high reversible lithium storage capacity of 700++mAh g++1 at 1 C rate in 100++cycles and an excellent cyclability. In particular, the dominantly exposed {110} reactive facets and mesoporous nanostructure of NiO crystals lead to ultrafast lithium storage, which mimics the high power delivery of supercapacitors.
Zhang, L., Wang, M., Wang, C., Hu, X. & Wang, G. 2012, 'Label-free impedimetric immunosensor for sensitive detection of 2,4-dichlorophenoxybutyric acid (2,4-DB) in soybean', Talanta, vol. 101, pp. 226-232.
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Electrochemical impedance immunosensor, with its high sensitivity from electrochemical impedance analysis and ideal specificity from the immunoassay, is increasingly used in the detection of a kind of phenoxy acid herbicides which is 2,4-Dichlorophenoxybutyric acid (2,4-DB). In this experiment, synthetic 2,4-DB antibodies were immobilized on the electrode by the crosslinking of l-Cysteine/glutaraldehyde, and 2,4-DB were measured by the increase of electron-transfer resistance when the immune reaction occurred, with Fe(CN)63++/Fe(CN)64++ as the probe. Under optimal conditions, the change of resistance is in a linear relationship with the logarithm of the concentration in the range of 1.0++10++7++1.0++10++3 g/L (R=0.994) with the detection limit of 1.0++10++7 g/L (0.1 ppb). This method bears such merits as simplicity in operation, high sensitivity, wide linear range, specificity, reproducibility and good stability. The actual soybean samples were analyzed with the recovery of 82.8%++102.3%.
Wang, Q., Yu, J., Kim, J., Kim, K., Wang, G., Ahn, J., Kang, Y. & Ahn, H.j. 2012, 'Electrochemical properties of all solid Li/Ni3S2 cells using polymer electrolyte based on star-shaped siloxane acrylate cross-linker', Journal of Ceramic Processing Research, vol. 13, no. S2, pp. S398-S402.
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All solid Li/Ni3S2 cells were assembled with a novel solid polymer electrolyte cured via in-situ chemical cross-linking with siloxane acrylate. Several ether plasticizers with various chain lengths were used to optimize the cycling property of Li/ Ni3S2 cell. The Li/ Ni3S2 cell containing the Triethylene glycol dimethyl ether as plasticizer show optimum first charging-discharge and cycling performance, that capacity still maintain 413.32 mAh/g after 20 cycles.
Park, J., Kim, D.J., Park, J.W., Ryu, H.S., Kim, K.W., Wang, G. & Ahn, H.j. 2012, 'Evaluation of sulfur and multi-walled carbon nanotube composite synthesized by dissolution and precipitation for Li/S batteries', Journal of Nanoscience and Nanotechnology, vol. 12, no. 7, pp. 5794-5798.
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An elemental sulfur and multi-walled carbon nanotube (S-MWNT) composite was synthesized by dissolving sulfur in ammonium sulfides and then precipitating on MWNT. Morphology observation by scanning electron microscopy (SEM) confirmed that S-MWNT product was successfully prepared by incorporating sulfur into MWNT network. Without additional conducting material, the S-MWNT composite cathodes were prepared for electrochemical tests. The properties measured in discharge-charge cycling test showed that the composite had the initial discharge capacity of 1024 mAh g-1, which is about 61% sulfur utilization. However, in the subsequent cycling, the capacities faded. To determine the reason of rapid capacity drop, S-MWNT composite cathodes were compared in the cycling tests with varying three kinds of electrolytes and the cathode was subjected to physical force by rolling. The changes in the cycle performances proved that the deterioration of S-MWNT composite cathodes was not related to the electrolytes but to physical bonding that may not maintain the conducting path between sulfur and MWNT.
Ranjbartoreh, A., Su, D. & Wang, G. 2012, 'Consideration of critical axial properties of pristine and defected carbon nanotubes under compression', Journal of Nanoscience & Nanotechnology, vol. 12, no. 6, pp. 5025-5029.
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Carbon nanotubes are hexagonally configured carbon atoms in cylindrical structures. Exceptionally high mechanical strength, electrical conductivity, surface area, thermal stability and optical transparency of carbon nanotubes outperformed other known mat
Wang, Y., Sun, B., Park, J., Kim, W., Kim, H. & Wang, G. 2011, 'Morphology control and electrochemical properties of nanosize LiFePO4 cathode material synthesized by co-precipitation combined with in situ polymerization', Journal Of Alloys And Compounds, vol. 509, no. 3, pp. 1040-1044.
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Nanosize carbon coated LiFePO4 cathode material was synthesized by in situ polymerization. The as-prepared LiFePO4 cathode material was systematically characterized by X-ray diffraction, thermogravimetric-differential scanning calorimetry, X-ray photo-electron spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy techniques. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images revealed that the morphology of the LiFePO4 consists of primary particles (40-50 nm) and agglomerated secondary particles (100-110 nm). Each particle is evenly coated with an amorphous carbon layer, which has a thickness around 3-5 nm. The electrochemical properties were examined by cyclic voltammetry and charge-discharge testing. The as-prepared LiFePO4 can deliver an initial discharge capacity of 145 mAh/g, 150 mAh/g, and 134 mAh/g at 0.2 C, 1 C, and 2 C rates, respectively, and exhibits excellent cycling stability. At a higher C-rate (5 C) a slight capacity loss could be found. However after being charge-discharge at lower C-rates, LiFePO4 can be regenerated and deliver the discharge capacity of 145 mAh/g at 0.2 C. (C) 2010 Elsevier B.V. All rights reserved.
Ranjbartoreh, A., Wang, B., Shen, X. & Wang, G. 2011, 'Advanced mechanical properties of graphene paper', Journal of Applied Physics, vol. 109, pp. 014306-014313.
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Graphene paper (GP) has been prepared by flow-directed assembly of graphene nanosheets. The mechanical properties of as-prepared GPs were investigated by tensile, indentation, and bending tests. Heat treated GPs demonstrate superior hardness, ten times that of synthetic graphite, and two times that of carbon steel; besides, their yielding strength is significantly higher than that of carbon steel. GPs show extremely high modulus of elasticity during bending test; in the range of a few terapascal. The high strength and stiffness of GP is ascribed to the interlocking-tile microstructure of individual graphene nanosheets in the paper. These outstanding mechanical properties of GPs could lead to a wide range of engineering applications.
Wang, C., Wang, D., Hu, X. & Wang, G. 2011, 'Interface interaction within nanopores in thin films of an amphiphilic block copolymer and CTAB', Journal of Colloid and Intrface Science, vol. 354, no. 1, pp. 219-225.
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With water droplets as sacrificed templates at a particular humidity, micro-porous solid thin films were successfully fabricated by self-assembly using an amphiphilic block polymer, polystyrene-b-polyacrylic acid (PS-b-PAA). Interface interactions between the micro-porous thin film and a cationic surfactant, cetyltrimethylammonium bromide (CTAB), are investigated by in-situ AFM in aqueous solutions. An interesting phenomenon was observed in water and CTAB solution, which the dimensions of the micropores are remarkably larger than the dimensions of those in air. The solid thin films exhibit different surface morphologies in response to stimulus by different concentrations of CTAB. These observations were explained by positing that the PAA chains in the micropores stretch and contract with interface interactions between PAA and CTAB. A promising electrochemical application of this film is suggested. This study is aimed at strategies for the functionalization of stimulus-responsive micro-porous solid thin films with tunable surface morphologies, and exploring new smart materials.
Liu, H., Wang, G., Liu, J., Qiao, S. & Ahn, H. 2011, 'Highly ordered mesoporous NiO anode material for lithium ion batteries with an excellent electrochemical performance', Journal of Materials Chemistry, vol. 21, no. 9, pp. 3046-3052.
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In this work, we have synthesized highly ordered mesoporous NiO materials by a nanocasting method using mesoporous silica KIT-6 as the hard templates. Mesoporous NiO particles were characterized by small angle X-ray diffraction (XRD), nitrogen adsorption/desorption, and transmission electron microscopy (TEM). The results demonstrated that the as-prepared mesoporous NiO had an ordered Ia3d symmetric mesostructure, with a high surface area of 96 m(2)/g. Mesoporous NiO materials were tested as an anode material for lithium ion batteries, exhibiting much lower activation energy (20.75 kJ mol(-1)) compared to the bulk NiO (45.02 kJ mol(-1)). We found that the mesoporous NiO electrode has higher lithium intercalation kinetics than its bulk counterpart. The specific capacity of mesoporous NiO after 50 cycles was maintained 680 mAh/g at 0.1 C, which was much higher than that of the commercial bulk NiO (188 mAh/g). Furthermore, at a high rate of 2C, the discharge capacity of mesoporous NiO was as high as 515 mAh/g, demonstrating the potential to be used for high power lithium ion batteries.
Sun, B., Chen, Z., Kim, H.S., Ahn, H. & Wang, G. 2011, 'MnO/C core-shell nanorods as high capacity anode materials for lithium-ion batteries', Journal of Power Sources, vol. 196, no. 6, pp. 3346-3349.
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MnO/C core-shell nanorods were synthesized by an in situ reduction method using MnO2 nanowires as precursor and block copolymer F127 as carbon source. Field emission scanning electron microscopy and transmission electron microscopy analysis indicated that a thin carbon layer was coated on the surfaces of the individual MnO nanorods. The electrochemical properties were evaluated by cyclic voltammetry and galvanostatic charge-discharge techniques. The as-prepared MnO/C core-shell nanorods exhibit a higher specific capacity than MnO microparticles as anode material for lithium ion batteries.
Wu, H., Wexler, D., Wang, G. & Liu, H. 2011, 'Pt/C catalysts using different carbon supports for the cathode of PEM fuel cells', Advanced Science Letters, vol. 4, no. 1, pp. 115-120.
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20 wt% Pt/C catalysts were prepared using a chemical reduction method, with pristine double-walled carbon nanotubes (DWCNTs) and activated double-walled carbon nanotubes, respectively, used as the carbon source, and compared to commercial BASF 20 wt% Pt/C (using Vulcan XC-72 carbon as support). The materials were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and Brunauer-Emmett-Teller (BET) surface area measurements. The electrochemical performance of the Pt/C catalysts was evaluated by cyclic voltammetry, steady-state measurements, and chronoamperometric testing. Electrochemical measurements indicate that the Pt nanocatalysts exhibited enhanced electrochemically active surface areas and improved activity in the oxygen reduction reaction (ORR) on the chemically activated double-walled carbon nanotubes compared to the pristine double-walled carbon nanotubes or the Vulcan XC-72 carbon. It is suggested that activated double-walled carbon nanotubes would provide better catalyst support than Vulcan XC-72 carbon.
Wang, B., Wang, Y., Park, J., Ahn, H. & Wang, G. 2011, 'In situ synthesis of Co(3)O(4)/graphene nanocomposite material for lithium-ion batteries and supercapacitors with high capacity and supercapacitance', Journal Of Alloys And Compounds, vol. 509, no. 29, pp. 7778-7783.
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Abstract: Co(3)O(4)/graphene nanocomposite material was prepared by an in situ solution-based method under reflux conditions. In this reaction progress, Co(2+) salts were converted to Co(3)O(4) nanoparticles which were simultaneously inserted into the graphene layers, upon the reduction of graphite oxide to graphene. The prepared material consists of uniform Co(3)O(4) nanoparticles (15-25 nm), which are well dispersed on the surfaces of graphene nanosheets. This has been confirmed through observations by field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The prepared composite material exhibits an initial reversible lithium storage capacity of 722 mAh g(-1) in lithium-ion cells and a specific supercapacitance of 478 F g(-1) in 2 M KOH electrolyte for supercapacitors, which were higher than that of the previously reported pure graphene nanosheets and Co(3)O(4) nanoparticles. Co(3)O(4)/graphene nanocomposite material demonstrated an excellent electrochemical performance as an anode material for reversible lithium storage in lithium ion cells and as an electrode material in supercapacitors. (C) 2011 Elsevier B.V. All rights reserved.
Jeong, J.H., Jin, B.S., Kim, W.S., Wang, G. & Kim, H.S. 2011, 'The influence of compositional change of 0.3Li(2)MnO(3).0.7LiMn(1-x)Ni(y)Co(0.1)O(2) (0.2 <= x <= 0.5, y = x-0.1) cathode materials prepared by co-precipitation', Journal of Power Sources, vol. 196, no. 7, pp. 3439-3442.
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Cathode materials prepared by a co-precipitation are 0.3Li(2)MnO(3).0.7LiMn(1-x)Ni(y)Co(0.1)O(2) (0.2 <= x <= 0.4) cathode materials with a layered-spinet structure. In the voltage range of 2.0-4.6 V, the cathodes show more than one redox reaction peak during its cyclic voltammogram. The Li/0.3Li(2)MnO(3).0.7LiMn(1-x)Ni(y)Co(0.1)O(2) (x=0.3, y=0.2) cell shows the initial discharge capacity of about 200 mAh g(-1). However, when x=0.2 and y=0.1, the cell exhibits a rapid decrease in discharge capacity and poor cycle life. (C) 2011 Elsevier B.V. All rights reserved.
Wu, H., David, W., Wang, G. & Liu, H. 2011, 'Acid treatment of carbon supports for proton exchange membrane fuel cell electrocatalyst', Advanced Science Letters, vol. 4, no. 2, pp. 492-495.
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Pt/carbon and Pt/activated carbon catalysts were prepared using a simple chemical reduction method with a view to application in proton exchange membrane (PEM) fuel cells. The catalysts were characterized by X-ray diffraction, energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy, and Brunauer-Emmett-Teller (BET) surface area measurements. The electrochemical performance of the Pt/carbon and Pt/activated carbon catalysts were evaluated by cyclic voltammetry, and linear scan voltammetry testing. Electrochemical measurements indicate that the Pt nanocatalysts exhibited enhanced electrochemically active surface areas and improved activity in the oxygen reduction reaction (ORR) on the activated carbon compared to the pristine carbon. It is suggested that acid activated carbon would provide better catalyst support than pristine carbon in proton exchange membrane fuel cells.
Ryu, J.H., Kim, T., Kim, K., Ahn, J., Nam, T., Wang, G. & Ahn, H. 2011, 'Discharge Reaction Mechanism Of Room-Temperature Sodium-Sulfur Battery With Tetra Ethylene Glycol Dimethyl Ether Liquid Electrolyte', Journal Of Power Sources, vol. 196, no. 11 Special Issue, pp. 5186-5190.
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The first discharge curve of a sodium-sulfur cell using a tetra ethylene glycol dimethyl ether liquid electrolyte at room temperature shows two different regions: a sloping region and a plateau region of 1.66V. The first discharge capacity is 538 mAhg(-1) sulfur and then decreases with repeated charge-discharge cycling to give 240 mAh g(-1) after ten cycles. Elemental sulfur of the cathode changes to sodium polysul-fides Na(2)S(2) and Na(2)S(3),during full discharge. The sodium polysulfides, however, do not reduce completely to elemental sulfur after full charging. In summary, the mechanism of the battery with liquid electrolyte is 2Na + nS -> Na(2)S(n)(4 > n >= 2) on discharge and Na(2)S(n)(4 > n >= 2) -> x(2Na + nS)+ (1 -x)Na(2)S(n)(5 > n > 2) on charge.
Su, D., Ahn, H. & Wang, G. 2011, 'Ab initio calculations on Li-ion migration in Li2FeSiO4 cathode material with a P21 symmetry structure', Applied Physics Letters, vol. 99, no. 14, pp. 1-3.
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We have systematically investigated the diffusion mechanism of Li ions in Li2FeSiO4 and its delithiated product LiFeSiO4 based on the P21 symmetry using the first principle method. Calculations on the energy barriers for possible spatial hopping pathways predicted that the activation barriers along the [101] direction and Li ion layer in the ac plane are relatively low, which can ensure the facile lithium diffusion along those directions. The results indicate that Li2FeSiO4 with the P21 symmetry is an ionic conductor for Li ions with two-dimensional diffusion.
Kim, J.S., Yu, J.H., Ryu, H.S., Kim, K., Nam, T., Ahn, J.H., Wang, G. & Ahn, H. 2011, 'The electrochemical properties of sodium/iron sulfide battery using iron sulfide powder coated with nickel', Reviews on Advanced Materials Science, vol. 28, no. 1, pp. 107-110.
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To develop the battery with low cost and high energy density, Na/TEGDME/FeS cell was prepared using Ni-plated FeS powder. Electrochemical properties of Na/FeS cells were investigated by cyclic voltammogram measurement and charge-discharge tests. The Na/FeS cell showed a high initial discharge capacity of 525 mAh/g-FeS in the current density of 0.1C-rate. The FeS electrode showed two reduction peak potentials at 0.87 and 1.39 V and broad one oxidation peak between 1.23 V and 2.3 V. The discharge products might be sodium sulfide of Na2Sx (x = 1 to 5). The discharge capacity of 195 mAh/g-FeS was maintained after 150th cycle.
Kim, J., Lee, S., Liu, X., Cho, G., Kim, K., Ahn, I., Ahn, J.h., Wang, G. & Ahn, H. 2011, 'Electrochemical properties of Na/Ni3S2 cells with liquid electrolytes using various sodium salts', Current Applied Physics, vol. 11, no. 4, pp. S11-S14.
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For a Na/Ni3S2 cell operating at room temperature, three kinds of tetra (ethylene glycol) dimethyl ether (TEGDME) electrolytes, containing sodium trifluoromethane sulfonate (NaCF3SO3), sodium hexafluorophosphate (NaPF6), and sodium perchlorate (NaClO4) salts, respectively, were prepared. Na/Ni3S2 cells with 1 M NaCF3SO3 in TEGDME showed a discharge plateau potential of 0.85 V and a first discharge capacity of 448 mAh/g. The discharge capacity decreased to 250 mAh/g after 40 cycles, which represented the best cycling performance among the three electrolytes.
Kim, J., Cho, G., Kim, K., Ahn, J., Wang, G. & Ahn, H. 2011, 'The addition of iron to Ni3S2 electrode for sodium secondary battery', Current Applied Physics, vol. 11, no. 1, pp. S215-S218.
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In order to investigate the role of iron additive in the Ni3S2 electrode, the Ni3S2 electrode was prepared by addition of iron. The discharge properties of Na/Ni3S2 cells using 1 M NaCF3SO3 in tetra(ethylene glycol)dimethyl ether liquid electrolyte were investigated at room temperature. The Na/Ni3S2 cell had an initial discharge capacity of 400 mAh g++1 with a plateau potential at 0.84 V versus Na/Na+. The discharge capacity decreased to 255 mAh g++1 after 15 cycles. Iron additive in Ni3S2 electrode played a role as a conductive agent and did not form iron sulfide during charging.
Kim, H., Jin, K.M., Jin, B.S., Kim, W., Koo, H. & Wang, G. 2011, 'Synthesis and electrochemical performance of LiMnxFex-1PO4/C cathode material for lithium secondary batteries', Metals and Materials International, vol. 17, no. 5, pp. 817-821.
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Carbon-coated LiMn0.8Fe0.2PO4/C (C = 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.%) cathode material is synthesized using a solid-state method. No impurity is found within the synthesized active material, which is confirmed to have an olivine structure with particle sizes in the range of 100 nm to 200 nm. The LiMn0.8Fe0.2PO4/C (C = 10 wt.%) active material shows an outstanding discharge capacity of 121.7 mAh.g(-1), along with a high capacity maintenance rate of 87.9 % at 2 C against the 0.2 C rate. In addition, this sample shows the most outstanding discharge capacity and coulombic efficiency in the cycling performance tests.
Ranjbartoreh, A. & Wang, G. 2010, 'Consideration of mechanical properties of single-walled carbon nanotubes under various loading conditions', Journal of nanoparticle Research, vol. 12, no. 2, pp. 537-543.
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In this article, mechanical properties of single-walled carbon nanotubes (SWCNTs) with various radiuses under tensile, compressive and lateral loads are considered. Stress+strain curve, elastic modulus, tensile, compressive and rotational stiffness, buckling behaviour, and critical axial compressive load and pressure of eight different zigzag and armchair SWCNTs are investigated to figure out the effect of radius and chirality on mechanical properties of nanotubes. Using molecular dynamic simulation (MDS) method, it can be explained that SWCNTs have higher Young+s modulus and tensile stiffness than compressive elastic modulus and compressive stiffness. Critical axial force of zigzag SWCNT is independent from the radius, but that of armchair type rises by increasing of radius, also these two types show different buckling modes.
Ranjbartoreh, A. & Wang, G. 2010, 'Molecular dynamic investigation of mechanical properties of armchair and zigzag double-walled carbon nanotubes under various loading conditions', Physics Letters A, vol. 374, no. 7, pp. 969-974.
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Using molecular dynamic simulation (MDS), effects of chirality and Van der Waals interaction on Young's modulus, elastic compressive modulus, bending, tensile, and compressive stiffness, and critical axial force of double-walled carbon nanotube (DWCNT) and its inner and outer tubes are considered. Achieving the highest safety factor, mechanical properties have been investigated under applied load on both inner and outer tubes simultaneously and on each one of them separately. Results indicate that as a compressive element, DWCNT is more beneficial than single-walled carbon nanotube (SWCNT) since it carries two times higher compression before buckling. Except critical axial pressure and tensile stiffness, in other parameters zigzag DWCNT shows higher amounts than armchair type. Outer tube has lower strength than inner tube; therefore, most reliable design of nanostructures can be attained if the mechanical properties of outer tube taken as the properties of DWCNT.
Wang, C., Sun, Y., Wen, Q., Wang, G., Wang, X., Qu, Q., Yang, G. & Hu, X. 2010, 'Novel reagents for quantitative analysis of valiolamine in biological samples by high-performance liquid chromatography with pre-column UV derivatization', Talanta, vol. 81, no. 4-5, pp. 1613-1618.
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A rapid, lowcost, high sensitive and quantitative method to detect valiolamine in a medium for microbial culture, involving derivatization with a new labeling reagent, 4methoxybenzenesulfonyl fluoride (MOBSF), followed by reversephase highperformance liquid chromatography with ultraviolet (UV) detection with simple operation procedure. 4Methoxybenzenesulfonyl chloride (MOBSCl) and 2nitrobenzenesulfonyl chloride (NBSCl) were compared with MOBSF as novel reagents in this paper, and the MOBSF was chosen as the most suitable derivatization reagent. The column was thermostatic at 35 C, the mobile phase flowrate was 1.0 mL/min and the detection wavelength was 240 nm. For a biological sample, the separation of the derivatives was achieved using a gradient mobile system. The elution program is 88% phosphate buffer (50mM; pH= 3.0) and 12% methanol for 23 min, then 70% of phosphate buffer and 30% methanol for another 15 min and finally 88% of phosphate buffer and 12% of methanol for 5 min to reequilibrate the column. The optimized conditions of the derivatization were as follows: derivatization reaction temperature 30 C; derivatization reaction pH value 11.0, reaction time 10 min and MOBSF concentration higher than 1.5mg/mL for standard solutions and higher than 5.0mg/mL for the biological sample. Calibration curves were linear in the range of 0.050+25mg/mL for the standard solutions and 1.0+75mg/mL for the biological sample. The sensitive analytical method is helpful to control the biotechnological process of voglibose production and product quality control.
Sun, J., Shen, X., Guo, L., Wang, G., Park, J. & Wang, K. 2010, 'Solvothermal synthesis of ternary sulfides of Sb2-x BixS3 (x = 0.4, 1) with 3D flower-like architectures', Nanoscale Research Letters, vol. 5, no. 2, pp. 364-369.
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Flower-like nanostructures of Sb2 - x Bi x S3 (x = 0.4, 1.0) were successfully prepared using both antimony diethyldithiocarbamate [Sb(DDTC)3] and bismuth diethyldithiocarbamate [Bi(DDTC)3] as precursors under solvothermal conditions at 180 C. The prepared Sb2 - x Bi x S3 with flower-like 3D architectures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). The flower-like architectures, with an average diameter of ~4 ?m, were composed of single-crystalline nanorods with orthorhombic structures. The optical absorption properties of the Sb2 - x Bi x S3 nanostructures were investigated by UV+Visible spectroscopy, and the results indicate that the Sb2 - x Bi x S3 compounds are semiconducting with direct band gaps of 1.32 and 1.30 eV for x = 0.4 and 1.0, respectively. On the basis of the experimental results, a possible growth mechanism for the flower-like Sb2 - x Bi x S3 nanostructures is suggested.
Liu, H., Park, J. & Wang, G. 2010, 'Nanosize SnO2 for highly responsive gas sensor applications', Sensor Letters, vol. 8, no. 2, pp. 243-246.
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Novel nanosize SnO2 particles were synthesized by a hard template method. The crystal structure and morphologies were characterized by X-ray diffraction and transmission electron microscopy. The particle size is around 4 nm, which is less than two times the depth (L) of the of the surface depletion layer. The sensing properties towards a series of gases, including ethanol, isopropanol, 1-butanol, formaldehyde, acetic acid, acetone, and 92# gasoline, were tested at different gas concentrations. The results reveal that the SnO2 nanoparticles have high responsivity towards forementioned toxic and flammable gases.
Wu, H.M., Wexler, D., Ranjbartoreh, A., Liu, H. & Wang, G. 2010, 'Chemical processing of double-walled carbon nanotubes for enhanced hydrogen storage', International Journal Of Hydrogen Energy, vol. 35, no. 12, pp. 6345-6349.
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Double-walled carbon nanotubes (DWCNTs) were modified for enhanced hydrogen storage by employing a combination of two techniques: KOH activation for the formation of defects on DWCNT surfaces and loading of the DWCNTs with nanocrystalline Pd. The physical properties of the pristine DWCNTs and chemically modified DWCNTs were systematically characterised by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and Brunauer-Emmett-Teller (BET) surface area measurements. The amounts of hydrogen storage capacity were measured at ambient temperature and found to be 1.7, 2.0, 3.7, and 2.8 wt% for pristine DWCNTS, 2 wt% Pd DWCNTs, activated DWCNTs, and 2 wt% Pd activated DWCNTs, respectively. Hydrogen molecules could be adsorbed on defect sites created by chemical activation in DWCNTs through van der Waals forces. For Pd nanoparticle loaded DWCNTs, H-2 molecules could be dissociated into atomic hydrogen and adsorbed on defect sites. We found that the hydrogen storage capacity of DWCNTs can be significantly enhanced by chemical activation or loading with Pd nanoparticles. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Shen, X., Sun, J., Wang, G., Park, J. & Chen, K. 2010, 'A facile single-source approach to urchin-like NiS nanostructures', Materials Research Bulletin, vol. 45, no. 7, pp. 766-771.
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Highly regular urchin-like NiS architectures were synthesized on a large scale by solvothermal treatment of a single-source molecular precursor of nickel diethyldithiocarbamate [Ni(DDTC)(2)] at 180 degrees C. The urchin-like architectures, with an average diameter of similar to 16 mu m, were composed of single-crystalline NiS nanoneedles with a diameter of similar to 100 nm and a length of up to 8 mu m. It was revealed that the solvent medium can strongly affect the composition and crystal phases of the products, and a surfactant is crucial to form urchin-like patterns. Based on the experimental observations, a probable three-step growth mechanism is proposed to explain the formation of the urchin-like nanostructures. The optical properties were investigated by ultraviolet-visible (UV-vis) absorption spectroscopy. This simple and mild single-source solvothermal route may be expected to extend to fabricating other inorganic nano-/micro-superstructures with novel morphologies and complex architectures.
Sun, B., Horvat, J., Kim, H., Kim, W., Ahn, J.h. & Wang, G. 2010, 'Synthesis Of Mesoporous Alpha-Fe2O3 Nanostructures For Highly Sensitive Gas Sensors And High Capacity Anode Materials In Lithium Ion Batteries', Journal Of Physical Chemistry C, vol. 114, no. 44, pp. 18753-18761.
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Mesoporous alpha-Fe2O3 materials were prepared in large quantity by the soft template synthesis method using the triblock copolymer surfactant F127 as the template. Nitrogen adsorption desorption isothermal measurements and transmission electron microsco
Ahn, J.h., Kim, Y. & Wang, G. 2010, 'Hydrothermally Processed Oxide Nanostructures And Their Lithium-Ion Storage Properties', Nanoscale Research Letters, vol. 5, no. 11, pp. 1841-1845.
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Y- and Si-based oxide nanopowders were synthesized by a hydrothermal reaction of Y or Si powders with NaOH or LiOH aqueous solution. Nanoparticles with different morphology such as elongated nanospheres, flower-like nanoparticles and nanowires were produ
Wang, G., Liu, H., Horvat, J., Wang, B., Qiao, S., Park, J. & Ahn, H. 2010, 'Highly Ordered Mesoporous Cobalt Oxide Nanostructures: Synthesis, Characterisation, Magnetic Properties, And Applications For Electrochemical Energy Devices', Chemistry: A European Journal, vol. 16, no. 36, pp. 11020-11027.
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Highly ordered mesoporous Co3O4 nanostructures were prepared using KIT-6 and SBA-15 silica as hard templates. The structures were confirmed by small angle X-ray diffraction, high resolution transmission electron microscopy, and N-2 adsorption-desorption
Wu, H., Wexler, D., Liu, H., Savadogo, O., Ahn, J.h. & Wang, G. 2010, 'Pt1-XCox Nanoparticles As Cathode Catalyst For Proton Exchange Membrane Fuel Cells With Enhanced Catalytic Activity', Materials Chemistry And Physics, vol. 124, no. 1, pp. 841-844.
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Nanosize carbon-supported Pt1-xCox (x = 0.2, 0.3, and 0.45) electrocatalysts were prepared by a chemical reduction method using sodium borohydride (NaBH4) as the reduction agent. Transmission electron microscopy examination showed uniform dispersion of P
Sun, Y., Wang, C., Wen, Q., Wang, G., Wang, H., Qu, Q. & Hu, X. 2010, 'Determination Of Glyphosate And Aminomethylphosphonic Acid In Water By Lc Using A New Labeling Reagent, 4-Methoxybenzenesulfonyl Fluoride', Chromatographia, vol. 72, no. 7-8, pp. 679-686.
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A rapid, low-cost, and highly sensitive analytical method to detect glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA), in water samples has been developed, involving a derivatization with a new labeling reagent, 4-methoxybenzenesulfo
Wang, B., Park, J., Wang, C., Ahn, H. & Wang, G. 2010, 'Mn3O4 Nanoparticles Embedded Into Graphene Nanosheets: Preparation, Characterization, And Electrochemical Properties For Supercapacitors', Electrochimica Acta, vol. 55, no. 22, pp. 6812-6817.
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Mn3O4/graphene nanocomposites were synthesized by mixing graphene suspension in ethylene glycol with MnO2 organosol, followed by subsequent ultrasonication processing and heat treatment. The as-prepared product consists of nanosized Mn3O4 particles homog
Wang, G., Wu, H., Wexler, D., Liu, H. & Savadogo, O. 2010, 'Ni@Pt Core-Shell Nanoparticles With Enhanced Catalytic Activity For Oxygen Reduction Reaction', Journal Of Alloys And Compounds, vol. 503, no. 1, pp. L1-L4.
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Ni@Pt core-shell nanoparticles were synthesized by chemical reduction and sequential chemical deposition. The as-prepared nanoparticles were characterized by X-ray diffraction and high resolution transmission electron microscopy. Cyclic voltammetry and s
Wang, G., Liu, H., Liu, J., Qiao, S., Lu, G.M., Munroe, P. & Ahn, H. 2010, 'Mesoporous LiFePO4/C Nanocomposite Cathode Materials for High Power Lithium Ion Batteries with Superior Performance', Advanced Materials, vol. 22, no. 44, pp. 4944-4948.
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Abstract: Hexagonally ordered mesoporous LiFePO4/C nanocomposites can be synthesized with LiFePO4 nanoparticles embedded in an interconnected carbon framework. Mesoporous LiFePO4/C nanocomposites exhibit superior electrochemical performance and ultra-high specific power density, which makes this architecture suitable for high power applications such as hybrid electric vehicles (HEVs) and stationary energy storage for smart grids.
Kwon, J.h., Ahn, H., Jeon, M.S., Kim, K.W., Ahn, I.S., Ahn, J.h., Wang, G. & Rye, H.S. 2010, 'The electrochemical properties of Li/TEGDME/MoS2 cells using multi-wall carbon nanotubes as a conducting agent', RESEARCH ON CHEMICAL INTERMEDIATES, vol. 36, no. 6-7, pp. 749-759.
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We investigated the first charge-discharge behavior and cycling property of Li batteries using MoS2 electrodes with multi-wall carbon nanotubes (MWNT) as a conducting agent. The MoS2 electrode was prepared using MWNT as the conducting agent. The battery gave a high first discharge capacity of 440 mAhg(-1) with a plateau potential region at 1.1 V. The Li/MoS2 battery using MWNT showed a higher discharge capacity compared to acetylene black. After ten cycles of the battery using MWNT, the discharge capacity decreased to 120 mAhg(-1), which corresponded to 30% of the first discharge capacity. Adding a carbon nanotube into the MoS2 electrode improved the first discharge behavior, but did not affect the cycling property of the Li/MoS2 cell.
Ahn, J.h., Wang, G., Kim, Y.J., Lee, H.M. & Shin, H.S. 2010, 'Synthesis and properties of Ti-O based nanowires', Journal Of Alloys And Compounds, vol. 504, no. S1, pp. S361-S363.
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Ti6Na2O13 center dot nH(2)O and Ti6Na2O13 nanowires were synthesized by a hydrothermal method. The synthesized Ti6Na2O13 nanowires were used as anode materials for Li-ion cells to examine Li-storage property. The preliminary result shows that this material exhibited a discharge capacity of 1635 mAh/g at first cycle and >1050 mAh/g after second cycle. The Ti6Na2O13 nanowire electrode also showed good property retention upon cycling. (C) 2010 Elsevier B.V. All rights reserved.
Ranjbartoreh, A. & Wang, G. 2010, 'Molecular dynamic investigation of length dependency of single-walled carbon nanotube', Physica E: Low-dimensional Systems and Nanostructures, vol. 43, no. 1, pp. 202-206.
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This paper investigates the effects of length's variations on Young's modulus, compressive elastic modulus, tensile, compressive, and lateral stiffness, critical buckling strain, critical axial force and pressure of armchair and zigzag single-walled carbon nanotubes (SWCNTs). Molecular dynamic simulation (MDS) method employed to analyse the mechanical properties of SWCNTs under tensile, compressive, and lateral loads. Both armchair and zigzag SWCNTs demonstrate higher tensile properties than compressive properties. Buckling modes of SWCNTs change with the length. Critical buckling strain of armchair nanotube is higher than that of zigzag type. Stiffness of SWCNTs is independent of length and chirality whereas elastic modulus increases with increase in nanotube++s length.
Wang, C., Wang, D.Y., Wang, G. & Hu, X. 2010, 'Determination of Lysozyme Using Microcantilever Sensor Based on Atomic Force Microscopy', CHINESE JOURNAL OF ANALYTICAL CHEMISTRY, vol. 38, no. 12, pp. 1771-1775.
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A novel sensor based on an atomic force microscopy (AFM) microcantilever was developed to detect lysozome in a pharmaceutical formulation sample. By measuring the cantilever bending, using the optical reflection technique, the lysozyme adsorption by a dodecanethiol-modified cantilever surface was detected in real time. Under optimal conditions, a linear relationship was established between the deflection of the cantilever and the logarithm of the concentration of lysozome in the concentration range of 0.01 - 100 mu g/L with a correlation coefficient of 0.998; the limit of detection(S/N = 3) was 5.0 ng/L. The method described has been applied to determine lysozyme in pharmaceutical formulation sample with satisfactory results.
Yang, J., Zang, C., Wang, G., Xu, G. & Cheng, X. 2010, 'Synthesis of CdSe microspheres via solvothermal process in a mixed solution', Journal Of Alloys And Compounds, vol. 495, no. 1, pp. 158-161.
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CdSe particles with wurtzite structure have been synthesized via solvothermal method using a mixed solution of triethylenetetramine (TETA) and de-ionized water (DIW). It was found that ball-like CdSe precursor with zinc-blende phase could be transformed to wurtzite structure after heat-treating at 580 degrees C in Ar atmosphere and the obtained microspheres were made up of many nanometer sized CdSe particles. The experimental results were compared with CdSe obtained via hydrothermal method using N2H4 center dot H2O as the reducing agent and it was found that CdSe nanorods with wurtzite structure were obtained. It was speculated that TETA in the mixed solution played the role of reducing agent and surfactant. Both the as-prepared products and the annealed powders were systematically characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). Fourier transform infrared absorbance spectroscopy (FTIR) and thermogravimetric analysis (TGA). (C) 2010 Elsevier B.V. All rights reserved.
Wu, Y. & Wang, G. 2010, 'Preface', Pure and Applied Chemistry, vol. 82, no. 11, p. iv.
The main objectives of the symposium were to present state-of-the-art preparation of novel materials, and to discuss their performance and application potentials. The wide scope of the symposium provided a multidisciplinary high-level academic exchange chance on new ideas and latest findings for the scientific community. At the same time, the forum gave young scientists the opportunity to know some international authorities in their specialized areas and to develop professionally as quickly as possible. The symposium also opened other doors for the participants to learn more about Fudan University, Shanghai, and China.
Ranjbartoreh, A. & Wang, G. 2009, 'Bending stability of inner and outer tubes of double-walled carbon nanotube', International Journal of Nanoscience, vol. 8, no. 1-2, pp. 9-13.
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This paper considers the effects of bending moment on the structure of double-walled carbon nanotube (DWCNT). Two types of DWCNTs with almost the same aspect ratio (length/radius) are selected; also continuum modeling is utilized to study the bending stability of inner and outer tubes. As a result of the van der Waals interaction between adjacent tubes the critical bending moment of inner tube is higher than this moment of outer tube which is indicated from the obtained results of this research; thus, achieving higher reliability in nanostructures, the critical bending moment of outer tube should be taken into account.
Yang, J., Wang, G., Liu, H., Park, J. & Cheng, X. 2009, 'Controlled synthesis and characterization of ZnSe nanostructures via a solvothermal approach in a mixed solution', Materials Chemistry And Physics, vol. 115, no. 1, pp. 204-208.
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In the present study, ZnSe nanostructures with complex morphologies and different phase structures were synthesized via a solvothermal approach using a mixed solution of triethylenetetramine (TETA) and de-ionized water (DIW). It was found that the phase and morphology of the as-prepared products could be controlled by changing the volume ratio of TETA to DIW. Metastable ZnSe nanoflowers with layered structure could be obtained from pure TETA, which can be transformed to the wurtzite structure after heat-treating at 500 C in Ar atmosphere. With the addition of DIW, the morphology changed from flowers to spheres, and when the volume ratio of TETA to DIW was 1:1, loose spheres composed of nanoparticles were obtained. Variation of the TETA content in the mixed solvent also allows controlling of the crystallographic phase of ZnSe (wurtzite or zinc blende). Both the as-prepared products and the annealed powders were systematically characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared absorbance spectroscopy (FTIR), thermogravimetric analysis (TGA), and ultraviolet+visible (UV+vis) spectroscopy methods.
Liu, H., Wang, G., Park, J., Wang, J., Liu, H. & Zhang, C. 2009, 'Electrochemical performance of alpha-Fe2O3 nanorods as anode material for lithium-ion cells', Electrochimica Acta, vol. 54, no. 6, pp. 1733-1736.
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Alpha-Fe2O3 nanorods were synthesized by a facile hydrothermal method. The as-prepared alpha-Fe2O3 nanorods have a high quality crystalline nanostructure with diameters in the range of 60+80 nm and lengths extending from 300 to 500 nm. The crystal structure of the alpha-Fe2O3 nanorods was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The alpha-Fe2O3 nanorod anodes exhibit a stable specific capacity of 800 mAh/g. This indicates significantly improved electrochemical performance in lithium-ion cells, compared to that of commercial microcrystalline alpha-Fe2O3 powders.
Ahn, J.h., Kim, Y.J. & Wang, G. 2009, 'Electrochemical properties of SnO2 nanowires prepared by a simple heat treatment of Sn-Ag alloys', Journal Of Alloys And Compounds, vol. 483, no. 1-2, pp. 422-424.
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One-dimensional (1D) SnO2 nanowires were synthesized by a simple heat treatment of Sn+Ag alloys. The presence of Ag in the alloy and a small amount of impurity oxygen in an inert gas played an important role in the growth of SnO2 nanowires. The oxygen content higher than 1 vol.% in the gas resulted in the formation of fine spherical powders. The Li storage property of nano-sized SnO2 for the spherical and 1D SnO2 was evaluated from the lithium intercalation process in a Li-ion cell. The SnO2 nanowires exhibited a better electrochemical performance as an anode than the spherical powders.
Ahn, J.h., Wang, G. & Kim, Y.J. 2009, 'Facile synthesis of tin oxide nanofibres', Current Applied Physics, vol. 9, no. 2, pp. e176-e179.
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In this paper, we present a facile method to synthesize SnO2 nanofibres. Unlike the conventional CVD process for synthesizing nanofibres, the present synthesis method needs neither specific source gas nor substrates. Sn+Ag alloys or powder mixtures were heat-treated at temperatures above their melting point in a vertical or horizontal alumina tube furnace. During the heat treatment, a small amount of oxygen in an atmospheric gas reacted with tin in the alloys to form SnO2 nanofibres. Silver in the tin alloys acts as a catalytic material to facilitate the formation of nanofibres. An excess amount of oxygen in the gas resulted in the formation of SnO2 nanoparticles instead of nanofibres. The synthesized nanofibres have straight form with high purity.
Wang, X., Zeng, Z., Ahn, H. & Wang, G. 2009, 'First-principles study on the enhancement of lithium storage capacity in boron doped graphene', Applied Physics Letters, vol. 95, no. 18, pp. 183103-1-183103-3.
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The adsorption of Li ions on boron doped graphene was investigated using a first-principles method. Our results show that, as boron doping turns graphene into an electron-deficient system, more Li ions can be captured around boron doped centers than in pristine graphene. One boron atom doped into graphene (6C ring unit) can adsorb six Li ions, which indicates that boron doped graphene is an efficient Li-ion storage material for lithium batteries. Further investigations show that, under limited conditions, boron doped graphene (BC5) can form Li6BC5 compound after Li-ion adsorption, corresponding to a lithium storage capacity of 2271 mAh/g which is six times that of graphite
Wang, G., Shen, X., Yao, J. & Park, J. 2009, 'Graphene nanosheets for enhanced lithium storage in lithium ion batteries', Carbon, vol. 47, no. 8, pp. 2049-2053.
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Graphene nanosheets were synthesized in large quantities using a chemical approach. Field emission electron microscope observation revealed that loose graphene nanosheets agglomerated and crumpled naturally into shapes resembling flower-petals. High resolution transmission electron microscope analysis, Raman spectroscopy and ultraviolet+visible spectroscopy measurements confirmed the graphitic crystalline structure of the graphene nanosheets. The nanosheets exhibited an enhanced lithium storage capacity as anodes in lithium-ion cells and good cyclic performance.
Wang, G., Wang, B., Park, J., Wang, Y., Sun, B. & Yao, J. 2009, 'Highly efficient and large-scale synthesis of graphene by electrolytic exfoliation', Carbon, vol. 47, no. 14, pp. 3242-3246.
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Highly efficient and large-scale synthesis of graphene from graphite was produced by electrolytic exfoliation using poly(sodium-4-styrenesulfonate) as an effective electrolyte. Scanning and transmission electron microscopy, and atomic force microscopy confirmed the existence of monolayer graphene sheets and stacks containing a few graphene sheets. Raman spectroscopy demonstrated that the as-prepared graphene sheets have low defect content. Based on the measurement of FTIR spectra, the edge-to-face interaction (?+? interaction) between the graphene surface and aromatic rings of poly(sodium-4-styrenesulfonate) could be primarily responsible for producing exfoliation of the graphite electrode to graphene during electrolysis. In contrast to micromechanical exfoliation, electrolytic exfoliation can be scaled up for large-scale and continuous graphene production.
Wang, J., Chou, S.L., Liu, H., Wang, G., Zhang, C., Chew, S.Y. & Liu, H. 2009, 'Highly flexible and bendable free-standing thin film polymer for battery application', Materials Letters, vol. 63, no. 27, pp. 2352-2354.
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Highly flexible and bendable free-standing polypyrrole (PPy) films were prepared using the electrochemical polymerization method. The paper-like films are soft, lightweight, mechanically robust, and highly electrically conductive. The morphologies and electrochemical behaviour of the free-standing pure PPy films were affected by the electrochemical polymerization conditions. The free-standing films show promise as cathodes for flexible and bendable batteries
Wang, G., Shen, X., Horvat, J., Wang, B., Liu, H., Wexler, D. & Yao, J. 2009, 'Hydrothermal synthesis and optical, magnetic, and supercapacitance properties of nanoporous cobalt oxide nanorods', Journal of Physical Chemistry C, vol. 113, no. 11, pp. 4357-4361.
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Nanoporous cobalt oxide nanorods were synthesized by a hydrothermal method. Transmission electron microscopy analysis showed that the individual Co3O4 nanorods have a nanoporous structure, consisting of the textured aggregations of nanocrystals. Optical properties of Co3O4 nanorods were characterized by Raman and UV-vis spectroscopy. Magnetic property measurement shows that Co3O4 nanorods have a low Nel transition temperature of 35 K. We observed quite significant exchange bias for nanoporous Co3O4 nanorods, indicating the existence of magnetic coupling between the nanocrystals in Co3O4 nanorods. When applied as electrode materials in supercapacitors, Co3O4 demonstrated a high capacitance of 280 F/g.
Wang, G., Shen, X., Yao, J., Wexler, D. & Ahn, J.h. 2009, 'Hydrothermal synthesis of carbon nanotube/cobalt oxide core-shell one-dimensional nanocomposite and application as an anode material for lithium-ion batteries', Electrochemistry Communications, vol. 11, no. 3, pp. 546-549.
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Carbon nanotube/cobalt oxide core-shell one-dimensional nanostructures were prepared via a hydrothermal synthesis method, in which nanosize cobalt oxide crystals were homogeneously coated on the surface of carbon nanotubes. The morphologies and crystal structures of the as-prepared core-shell nanocomposites were analysed by X-ray diffraction, field emission gun scanning electron microscopy, and transmission electron microscopy. When applied as anodes in lithium-ion cells, carbon nanotube/cobalt oxide core-shell nanostructures exhibited an initial lithium storage capacity of 1250 mAh/g and a stable capacity of 530 mAh/g over 100 cycles. The good electrochemical performance could be attributed to the nanocrystalline cobalt oxide and the unique core-shell one-dimensional nanostructures.
Yao, J., Shen, X., Wang, B., Liu, H. & Wang, G. 2009, 'In situ chemical synthesis of SnO(2)-graphene nanocomposite as anode materials for lithium-ion batteries', Electrochemistry Communications, vol. 11, pp. 1849-1852.
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An in situ chemical synthesis approach has been developed to prepare SnO2+graphene nanocomposite. Field emission scanning electron microscopy and transmission electron microscopy observation revealed the homogeneous distribution of SnO2 nanoparticles (4+6 nm in size) on graphene matrix. The electrochemical reactivities of the SnO2+graphene nanocomposite as anode material were measured by cyclic voltammetry and galvanostatic charge/discharge cycling. The as-synthesized SnO2+graphene nanocomposite exhibited a reversible lithium storage capacity of 765 mAh/g in the first cycle and an enhanced cyclability, which can be ascribed to 3D architecture of the SnO2+graphene nanocomposite.
Shen, X., Wang, G. & Wexler, D. 2009, 'Large-scale synthesis and gas sensing application of vertically aligned and double-sided tungsten oxide nanorod arrays', Sensors and Actuators B: Chemical, vol. 143, no. 1, pp. 325-332.
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Large-scale vertically aligned and double-sided Co-doped hexagonal tungsten oxide nanorod arrays have been successfully synthesized by a facile hydrothermal method without using any template, catalyst, or substrate. Scanning electron microscopy and transmission electron microscopy analyses reveal an interesting three-order hierarchical nanostructure from small, single-crystalline nanorods via nanorod bundles to double-sided nanorod arrays. The optical absorption properties of the Co-doped WO3 samples were investigated by ultraviolet+visible spectroscopy, and the results indicate that the Co-doped WO3 nanostructures are semiconducting with direct band gaps of 2.26 eV and 2.77 eV. The gas sensing performance of the as-prepared Co-doped WO3 double-sided nanorod arrays was tested towards a series of typical organic solvents and fuels. The sample shows excellent gas sensing performance towards 1-butanol vapor, with rapid response and high sensitivity. We propose that the double-sided nanorod arrays are formed from urchin-like microspheres via a self-assembly and fusion process. This new synthesis strategy could be extended to prepare other well-aligned nanorod arrays for many functional applications.
Wang, G., Shen, X. & Yao, J. 2009, 'One-dimensional nanostructures as electrode materials for lithium-ion batteries with improved electrochemical performance', Journal of Power Sources, vol. 189, no. 1, pp. 543-546.
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One-dimensional (1D) nanosize electrode materials of lithium iron phosphate (LiFePO4) nanowires and Co3O4+carbon nanotube composites were synthesized by the hydrothermal method. The as-prepared 1D nanostructures were structurally characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. We tested the electrochemical properties of LiFePO4 nanowires as cathode and Co3O4+carbon nanotubes as anode in lithium-ion cells, via cyclic voltammetry and galvanostatic charge/discharge cycling. LiFePO4 nanorod cathode demonstrated a stable performance over 70 cycles, with a remained specific capacity of 140 mAh g-1. Nanocrystalline Co3O4+carbon nanotube composite anode exhibited a reversible lithium storage capacity of 510 mAh g-1 over 50 cycles. 1D nanostructured electrode materials showed strong potential for lithium-ion batteries due to their good electrochemical performance.
Liu, H., Wexler, D. & Wang, G. 2009, 'One-pot facile synthesis of iron oxide nanowires as high capacity anode materials for lithium ion batteries', Journal Of Alloys And Compounds, vol. 487, no. 1-2, pp. L24-L27.
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Alpha-Fe2O3 nanowires were synthesized by a facile hydrothermal method. The crystalline structure and morphology of the synthesized materials have been characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results revealed that the prepared Alpha-Fe2O3 product was uniform nanowires with the length/diameter ratio as high as 500. The electrochemical properties of Alpha-Fe2O3 nanowires were evaluated by cyclic voltammetry (CV) and charge/discharge measurements. The initial charge/discharge capacities can reach 947/1303 mAh/g at the rate of 0.1 C. The lithium storage capacity maintained 456 mAh/g after 100 cycles. This good electrochemical performance may be attributed to the large surface area and short pathways in nanowires for lithium ion migration.
Wu, H., Wexler, D. & Wang, G. 2009, 'PtxNi alloy nanoparticles as cathode catalyst for PEM fuel cells with enhanced catalytic activity', Journal Of Alloys And Compounds, vol. 488, no. 1, pp. 195-198.
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A series of PtxNi/C (x = 1+3) nanoparticle catalysts were prepared using a chemical reduction method, where the aim was to reduce the Pt loading and maintain high catalytic reactivity towards the oxygen reduction reaction. The catalysts were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical performance of the PtxNi/C alloy catalysts was evaluated by cyclic voltammetry, steady-state measurements, and chronoamperometric testing. We found that the catalytic reactivity of Pt catalysts towards oxygen reduction can be maintained or even enhanced by partially replacing platinum with nickel.
Gou, X., Li, R., Wang, G., Chen, Z.x. & Wexler, D. 2009, 'Room-temperature solution synthesis of Bi2O3 nanowires for gas sensing application', Nanotechnology, vol. 20, no. 49, pp. 495501-1-495501-5.
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A simple room-temperature solution chemical route for bulk synthesis of high quality ?- Bi2O3 nanowires has been demonstrated. The nanowires have a diameter of about 50 nm and a length in the range of several to tens of micrometers. It was found that oleic acid played an important role in directing the growth of ?- Bi2O3 nanowires along the [10\bar {2}] direction, and the diameter of the nanowires increased with an increase of the reaction temperature. Furthermore, the Bi2O3 nanowire sensors are highly sensitive to ppm-levels of NO2 in ambient air with fast response, good selectivity and stability, indicating their potential applications for environmental monitoring and pollution control.
Park, J., Shen, X. & Wang, G. 2009, 'Solvothermal synthesis and gas-sensing performance of Co3O4 hollow nanospheres', Sensors and Actuators B: Chemical, vol. 136, no. 2, pp. 494-498.
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Co3O4 hollow nanospheres with a diameter of 200+300 nm were synthesized by a surfactant-assisted solvothermal method. X-ray diffraction and Raman spectrum measurements demonstrate that the products are pure face-centered cubic Co3O4. Transmission electron microscopy and selected area electron diffraction analyses reveal that the walls of Co3O4 hollow nanospheres have a uniform thickness of not, vert, similar40 nm and are constructed by an oriented aggregation of Co3O4 nanocrystals. The optical absorption properties of the Co3O4 hollow nanospheres were investigated by UV+vis spectroscopy and the results indicate that the Co3O4 hollow nanospheres are semiconducting with direct band gaps of 2.23, 1.25 and 1.00 eV. The gas-sensing performance of the as-prepared Co3O4 hollow nanospheres was investigated towards a series of typical organic solvents and fuels. The Co3O4 hollow nanospheres show good sensing performances towards toluene and acetone vapors with rapid response and high sensitivity at low operating temperature.
Wang, G., Shen, X., Wang, B., Yao, J. & Park, J. 2009, 'Synthesis and characterisation of hydrophilic and organophilic graphene nanosheets', Carbon, vol. 47, no. 5, pp. 1359-1364.
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Hydrophilic graphene nanosheets were rapidly synthesized by reacting graphene oxide nanosheets with poly(sodium 4-styrene sulfonate) and simultaneously reducing by hydrazine hydrate under hydrothermal conditions. Organophilic graphene nanosheets were prepared by reacting with octadecylamine and reduction by hydroquinone through a reflux process. Ultraviolet+visible spectroscopy and Fourier transform infrared spectroscopy measurements confirmed the attachment of organic molecules to the graphene nanosheets to achieve hydrophilic and organophilic affinity. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy analysis indicated that the crystal structure of the graphene nanosheets was maintained intact after chemical functionalisation.
Wang, G., Wang, B., Park, J., Yang, J., Shen, X. & Yao, J. 2009, 'Synthesis of enhanced hydrophilic and hydrophobic graphene oxide nanosheets by a solvothermal method', Carbon, vol. 47, no. 1, pp. 68-72.
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We report that the hydrophilic affinity of graphene oxide nanosheets can be significantly increased by reacting with allylamine. High resolution transmission electron microscopy and electron diffraction analysis confirmed that the graphene oxide nanosheets were amorphous in structure. Hydrophobic graphene oxide nanosheets were also prepared via functionalising with phenylisocynate (C6H5NCO) through a solvothermal synthesis process. Hydrophobic graphene oxide nanosheets can be used as additives in polymer-based composites and other functional applications.
Wang, B., Konstantinov, K., Wexler, D., Liu, H. & Wang, G. 2009, 'Synthesis of nanosized vanadium pentoxide/carbon composites by spray pyrolysis for electrochemical capacitor application', Electrochimica Acta, vol. 54, no. 5, pp. 1420-1425.
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Nanostructured vanadium pentoxide/carbon (V2O5/carbon) composite powders with enhanced specific capacitance were synthesized by the spray pyrolysis technique. Electrochemical properties were examined by the cyclic voltammetry technique. Following analysis of powders sprayed at different temperatures, composite powders obtained at an optimum temperature of 450 C yielded a maximum specific capacitance of 295 F g-1 in 2 M KCl electrolyte at a 5-mV s-1 scan rate. The weight percentage of carbon-related species was 2.7 wt% in this V2O5/carbon composite, as detected by thermogravimetric analysis (TGA) and confirmed by transmission electron microscope energy dispersive spectroscopy (TEM-EDS) analysis. Following initial X-ray diffraction (XRD) characterization, scanning electron microscope (SEM), TEM and high-resolution TEM (HRTEM) imaging revealed a specific morphology of spherical shell agglomerates of V2O5 nanorods and nanoribbons, with each shell comprising a network of these one- and two-dimensional nanoparticles in an amorphous carbon matrix. The V2O5 network was not fully dense, and the majority of the nanorod sizes were in the range of 50+150 nm, with additional long nanoribbons extending from the outsides of the spherical shells. The specific surface area was 18 m2 g-1 for the composite powders, and the pore size distribution revealed that the majority of pores had diameters in the range of 40+50 +, which was relatively larger than the pore diameters obtained at 500 C and would be beneficial for electrochemical performance. The enhancement of the specific capacitance in V2O5/carbon composites was attributed to the distribution of amorphous carbon throughout the V2O5 and the particular open nanostructure.
Wright, A.R., Wang, G., Xu, W., Zeng, Z. & Zhang, C. 2009, 'The spin-orbit interaction enhanced terahertz absorption in graphene around the K point', Microelectronics Journal, vol. 40, no. 4-5, pp. 857-859.
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We present a quantitative analysis on the effect of the spin+orbit interaction in the optical absorption of ?-electrons in graphene. It has been shown that the optical absorption amplitude of graphene around the K point in the Brillouin zone has a node in the two-dimensional Brillouin zone of honeycomb lattice. We calculated the k-dependent absorption matrix by taking into account the finite spin+orbit interaction in graphene. It was found that the spin+orbit interaction lifts the nodes in the absorption matrix. Furthermore, in the terahertz frequency regime, the spin+orbit interaction can significantly enhance the optical absorption in graphene, by up to 100%.
Kim, H.S., Kim, W.S., Gu, H.B. & Wang, G. 2009, 'Electrochemical performance of SnPO4-coated LiNi1/3Mn1/3Co1/3O2 cathode materials', Journal of New Materials for Electrochemical Systems, vol. 12, no. 4, pp. 207-212.
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A Sn phosphate was successfully coated to the surface of LiNi1/3Co1/3Mn1/3O2 particles using a new method we developed. The elements Sn and P were observed to be uniformly distributed on the surface of the LiNi1/3Co1/3Mn1/3O2. After the Sn phosphate coating, the onset temperature shifted up to about 250 oC, and the exothermic value also decreased to 116.3 J/g, i.e. the thermal stability of the material was enhanced. The rate capability of the 1 wt% Sn phosphate-coated LiNi1/3Co1/3Mn1/3O2 materials was enhanced at room temperature and 60 oC. However, a 3 wt% Sn phosphate coating degraded the electrochemical performance. The 1 wt% Sn phosphate-coated material showed improved cycle performance compared to that of the bare material at room temperature and 60 oC. It is believed that the oxide coating layer prevented direct contact with the organic electrolyte.
Wang, G., Wang, B., Wang, X., Park, J., Dou, S.X., Ahn, H.j. & Kim, K. 2009, 'Sn/graphene nanocomposite with 3D architecture for enhanced reversible lithium storage in lithium ion batteries', Journal of Materials Chemistry, vol. 19, no. 44, pp. 8378-8384.
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A general strategy has been demonstrated to achieve optimum electrochemical performance by constructing 3D nanocomposite architecture with the combination of nanosize Sn particles and graphene nanosheets. In the first step, the lithium storage properties of graphene have been investigated by first principles calculations. The results show that lithium can be stably stored on both sides of graphene sheets (LiC3), inducing in a theoretical capacity of 744 mAh/g. In the second step, a synthetic approach has been designed to prepare Sn/graphene nanocomposite with 3D architecture, in which Sn nanoparticles act as a spacer to effectively separate graphene nanosheets. FESEM and TEM analysis revealed the homogeneous distribution of Sn nanoparticles (2+5 nm) in graphene nanosheet matrix. Cyclic voltammetry measurement has proved the highly reversible nature of the reaction between Li+ and Sn/graphene nanocomposite. The 3D nanoarchitecture gives the Sn/graphene nanocomposite electrode an enhanced electrochemical performance. This strategy can be extended to prepare other anode and cathode materials for advanced energy storage and conversion devices such as lithium ion batteries, supercapacitors, and fuel cells.
Konstantinov, K., Wang, G., Lao, Z.J. & Liu, H.K. 2009, 'Nanostructured metal oxides as electrode materials for electrochemical capacitors', Journal of Nanoscience & Nanotechnology, vol. 9, no. 2, pp. 1263-1267.
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In this study, nanostructured transition metal oxides, such as Co3O4, NiO and MnO2 were comprehensively studied and reported as promising electrode materials for electrochemical capacitors. The materials have been obtained by solution or spray solution techniques, which are cost-effective and promising for industry application. All materials feature a large specific surface area, which can reach up to 270 m2/g. The high surface area is a compulsory condition for high capacitance. The best MnO2 materials yielded up to 406 F/g.
Yao, J., Park, J.S., Konstantinov, K., Wang, G., Ahn, J.h. & Liu, H.K. 2009, 'Electrochemical performance of nanocrystalline SnO2-carbon nanotube composites as anode in lithium-ion cells', Journal of Nanoscience & Nanotechnology, vol. 9, no. 2, pp. 1474-1478.
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SnO2-carbon nanotube composites were prepared by chemical treatment of tin chloride salt mixed with carbon nanotubes, followed by heat-treatment at high temperature. Nanosize SnO2 particles were formed and embedded in a carbon nanotube matrix. TEM and HRTEM observation confirmed the homogeneous distribution of SnO2 nanoparticles. SnO2-carbon nanotube anodes demonstrated high lithium storage capacity and stable cyclability, which could be attributed to the nanosize SnO2 crystals and the formation of carbon nanotube networks in the electrode.
Wang, G., Park, J.S. & Park, M.S. 2009, 'Growth, characterisation and technological applications of semiconductor SnO(2) nanotubes and In(2)O(3) nanowires', Journal of Nanoscience & Nanotechnology, vol. 9, no. 2, pp. 1144-1147.
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Tin dioxide nanotubes (200 nm in diameter) were synthesised by the sol-gel template method. The gas sensitivity of SnO2 nanotubes has been investigated. Due to the small grain size and large amount of grain boundary, SnO2 nanotubes demonstrated good sensitivity in sensing ethanol gas and had an ability to detect ammonia gas without any doping or surface modification. In2O3 semiconductor nanowires were synthesized efficiently by the chemical vapor deposition method through carbon thermal reduction. The diameter, length and morphologies of In2O3 nanowires can be varied by controlling the synthetic conditions. The In2O3 nanowires were characterised by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM). The application of In2O3 nanowires for gas sensors was tested.
Ranjbartoreh, A., Wang, G., Arani, A.G. & Loghman, A. 2008, 'Comparative consideration of axial stability of single- and double- walled carbon nanotube and its inner and outer tubes', Physica E: Low-dimensional Systems and Nanostru..., vol. 41, no. 2, pp. 202-208.
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he variations of critical axial forces for the inner and outer tubes of the double-walled carbon nanotube (DWCNT) in different buckling modes are studied in this paper. The effects of growth in the radius, length, and aspect ratio (length/radius) on the stability of a DWCNT and its inner and outer tubes are also considered, while the effects of the surrounding elastic medium on the outer tube and the van der Waals forces between two adjacent tubes are taken into account. Comparison between the DWCNT as a whole, its outer tube, inner tube, and single-walled carbon nanotube (SWCNT) indicates that the critical axial force of the inner tube of a DWCNT is almost two times more than the critical axial force of a SWCNT, showing the positive effect of the van der Waals interaction on the inner tube, DWCNT surrounded by an elastic medium has greater axial stability than DWCNT, without the surrounding elastic medium. This study demonstrates that the critical axial force of DWCNT is larger than for SWCNT, and it rises as the radius and aspect ratio increase.
Park, M.S., Kang, Y.M., Kim, J.H., Wang, G., Dou, S.X. & Liu, H. 2008, 'Effects of low-temperature carbon encapsulation on the electrochemical performance of SnO2 nanopowders', Carbon, vol. 46, no. 1, pp. 35-40.
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arbon encapsulated SnO2 composites were prepared by a thermal evaporation and decomposition of malic acid (C4H6O5) at low temperature to demonstrate their potential use for application in lithium ion batteries. The solution-based chemical approach was effective for coating amorphous C layers on the surface of SnO2 nanopowders without significant oxygen reduction. The desirable crystalline structure and oxygen stoichiometry of SnO2 were maintained, while amorphous C homogeneously encapsulated SnO2 nanopowders. The strong enhancement on the anodic reversible capacity and cyclic performance was discussed for the C-encapsulated SnO2 composites. It is expected that the low-temperature processing can be a new general route for preparing composites with C from economic point of view.
Liu, H., Wang, G., Wexler, D., Wang, J.Z. & Liu, H. 2008, 'Electrochemical performance of LiFePO4 cathode material coated with ZrO2 nanolayer', Electrochemistry Communications, vol. 10, no. 1, pp. 165-169.
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ZrO2 nanolayer coated LiFePO4 particles were successfully prepared by a chemical precipitation method. Nanolayer structured ZrO2 was found on the surface of LiFePO4 particles by high resolution transmission electron microscopy (HRTEM). The coating does not affect the crystal structure of the LiFePO4 core, as determined by X-ray diffraction (XRD) and selected area electron diffraction (SAED) on individual particles. The ZrO2 coating can remarkably improve the electrochemical performance at high charge/discharge rate. This improvement may be due to the amelioration of the electrochemical dynamics on the LiFePO4 electrode/electrolyte interface resulting from the effects of the ZrO2 nanolayer coating.
Shanmukaraj, D., Wang, G., Murugan, R. & Liu, H. 2008, 'Electrochemical studies on LiFe1-xCoxPO4/carbon composite cathode materials synthesized by citrate gel technique for lithium-ion batteries', Materials Science and Engineering B: Solid State M..., vol. 149, no. 1, pp. 93-98.
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LiFePO4/carbon and LiFe1-xCoxPO4/carbon (x = 0.02, 0.04, 0.08 and 0.1) composite cathode materials were synthesized by citrate gel technique. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the phase and morphology of un-doped and Co doped lithium iron phosphate/carbon composites. The SEM images revealed that the particles were agglomerated and the particle sizes were almost homogeneously distributed. The particle size was found to be between 200 and 300 nm from transmission electron microscopy. Cyclic voltammetric studies were taken to investigate the electrochemical performance of the prepared composite materials. The high intensity of the anodic and cathodic peaks indicates that Li-ions and electrons were participating actively in redox reactions due to the carbon coating. Charge/discharge studies carried out on a CR2032 coin cell revealed that the carbon coated LiFePO4/carbon composite exhibited an improved discharge capacity of 157 mAh/g at low rates. We found that cobalt doping does not have a favourable effect on the electrochemical performance of lithium iron phosphate cathode materials.
Wang, G., Park, J., Kong, X.y., Wilson, P.R., Chen, Z. & Ahn, J.h. 2008, 'Facile Synthesis and Characterization of Gallium Oxide (-Ga2O3) 1D Nanostructures: Nanowires, Nanoribbons, and Nanosheets', Crystal Growth and Design, vol. 8, no. 6, pp. 1940-1944.
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?-Ga 2O 3 one-dimensional (1D) nanostructures including nanowires, nanoribbons and nanosheets were synthesized via a combined carbon thermal reduction and chemical vapor deposition (CVD) approach. All of these nanostructures consist of single-crystalline monoclinic structure, which has been confirmed via high-resolution TEM and electron diffraction analysis. We obtained ?-Ga 2O 3 nanowires at high temperature zone, nanosheets, and nanoribbons at medium temperature zone at low-pressure environments. We found that ?-Ga 2O 3 nanowires and nanoribbons have diversified different growth directions. The optical properties of ?-Ga 2O 3 nanowires and nanoribbons from UV-vis spectra show that the bandgaps are red-shifted by 0.13 eV
Wang, G., Yang, J., Park, J., Gou, X., Wang, B., Liu, H. & Yao, J. 2008, 'Facile synthesis and characterization of Graphene nanosheets', Journal of Physical Chemistry C, vol. 112, no. 22, pp. 8192-8195.
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Graphene nanosheets were produced in large quantity via a soft chemistry synthetic route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. X-ray diffraction and transmission electron microscopy (TEM) observations show that graphene nanosheets were produced with sizes in the range of tens to hundreds of square nanometers and ripple-like corrugations. High resolution TEM (HRTEM) and selected area electron diffraction (SAED) analysis confirmed the ordered graphite crystal structure of graphene nanosheets. The optical properties of graphene nanosheets were characterized by Raman spectroscopy
Wang, G., Gou, X.l., Horvat, J. & Park, J. 2008, 'Facile synthesis and characterization of iron oxide semiconductor nanowires for gas sensing application', Journal of Physical Chemistry C, vol. 112, no. 39, pp. 15220-15225.
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We report a facile and efficient synthesis technique for the preparation of iron oxide semiconductor nanowires in large quantity by using nitrilotriacetic acid (NTA) as a chelating agent to form polymeric chains, followed by heat treatment. This technique can also be applied for preparing other transition metal oxide nanowires such as MnO2 nanowires and NiO nanowires. The as-prepared ?-Fe2O3 nanowires have exhibited a blue shift of bandgap, peculiar magnetic properties, and high sensitivities toward ethanol and acetic acid gases.
Shanmukaraj, D., Wang, G., Murugan, R. & Liu, H. 2008, 'Ionic conductivity and electrochemical stability of poly(methylmethacrylate)-poly(ethylene oxide) blend-ceramic fillers composites', Journal Of Physics And Chemistry Of Solids, vol. 69, no. 1, pp. 243-248.
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The role of inorganic ceramic fillers namely nanosized Al2O3 (15+25 nm) and TiO2 (10+14 nm) and ferroelectric filler SrBi4Ti4O15 (SBT CIT) (0.5 ?m) synthesized by citrate gel technique (CIT) on the ionic conductivity and electrochemical properties of polymer blend 15 wt% PMMA+PEO8:LiClO4+2 wt% EC/PC electrolytes were investigated. Enhancement in conductivity was obtained with a maximum of 0.7210-5 S cm-1 at 21 C for 2 wt% of SrBi4Ti4O15 (SBT CIT) composite polymer electrolyte. The lithium-ion transport number and the electrochemical stability of the composite polymer electrolytes at ambient temperature were analyzed. An enhancement in electrochemical stability was observed for polymer composites containing 2 wt% of SrBi4Ti4O15 (SBT CIT) as fillers.
Liu, H., Wang, G., Wang, J. & Wexler, D. 2008, 'Magnetite/carbon core-shell nanorods as anode materials for lithium-ion batteries', Electrochemistry Communications, vol. 10, no. 12, pp. 1879-1882.
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Carbon coated magnetite (Fe3O4) core-shell nanorods were synthesized by a hydrothermal method using Fe2O3 nanorods as the precursor. Transmission electron spectroscopy (TEM) and high resolution TEM (HRTEM) analysis indicated that a carbon layer was coated on the surfaces of the individual Fe3O4 nanorods. The electrochemical properties of Fe3O4/carbon nanorods as anodes in lithium-ion cells were evaluated by cyclic voltammetry, ac impedance spectroscopy, and galvanostatic charge/discharge techniques. The as-prepared Fe3O4/C core-shell nanorods show an initial lithium storage capacity of 1120 mAh/g and a reversible capacity of 394 mAh/g after 100 cycles, demonstrating better performance than that of the commercial graphite anode material.
Gou, X., Wang, G., Park, J., Liu, H. & Yang, J. 2008, 'Monodisperse hematite porous nanospheres: synthesis, characterization, and applications for gas sensors', Nanotechnology, vol. 19, no. 12, pp. 125606-1-125606-7.
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Monodisperse -Fe2O3 porous nanospheres with uniform shape and size have been synthesized via a facile template-free route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Raman spectroscopy were employed to characterize the product, showing the high quality of the as-prepared -Fe2O3 porous nanospheres. Furthermore, the -Fe2O3 porous nanospheres can selectively detect ethanol, formaldehyde and acetic acid, with a rapid response and high sensitivity, from a series of flammable and toxic/corrosive gases, indicating their potential applications for high sensitivity gas sensors.
Wang, J., Chou, S.L., Chen, J., Chew, S.Y., Wang, G., Konstantinov, K., Wu, J., Dou, S.X. & Liu, H. 2008, 'Paper-like free-standing polypyrrole and polypyrrole-LiFePO4 composite films for flexible and bendable rechargeable battery', Electrochemistry Communications, vol. 10, no. 11, pp. 1781-1784.
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y flexible, paper-like, free-standing polypyrrole and polypyrrole+LiFePO4 composite films were prepared using the electropolymerization method. The films are soft, lightweight, mechanically robust and highly electrically conductivity. The electrochemical behavior of the free-standing films was examined against lithium counter electrode. The electrochemical performance of the free-standing pure PPy electrode was improved by incorporating the most promising cathode material, LiFePO4, into the PPy films. The cell with PPy+LiFePO4 composite film had a higher discharge capacity beyond 50 cycles (80 mA h/g) than that of the cell with pure PPy (60 mA h/g). The free-standing films can be used as electrode materials to satisfy the new market demand for flexible and bendable batteries that are suitable for the various types of design and power needs of soft portable electronic
Zhang, D.Y., Ma, Z.F., Wang, G., Chen, J., Wallace, G.C. & Liu, H. 2008, 'Preparation of low loading Pt/C catalyst by carbon xerogel method for ethanol electrooxidation', Catalysis Letters, vol. 122, no. 1-2, pp. 111-114.
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Low platium loading Pt/C catalyst was prepared by direct Pt-embedded carbon xerogel method. The Pt content of the as-prepared Pt/C is about 4.32 wt% and has a typical polycrystalline phase. Textural and structural characteristics of the catalysts were characterized by XRD, EDS and BET. Pt-embedded in carbon xerogel increases the specific surface area and pore volume of the X-Pt/C during carbon gelation and the carbonization process. Electrochemical characteristics of the catalysts for ethanol electrooxidation were measured. The results indicated that the as-prepared 4.32 wt% Pt/C has higher mass current density in ethanol electrooxidation as compared to the 20 wt% Pt/C. This may be due to the high roughness of the Pt surface that is formed during the carbon gelation and carbonization process.
Yang, J., Wang, G., Liu, H., Park, J., Gou, X. & Cheng, X.n. 2008, 'Solvothermal synthesis and characterization of ZnSe nanoplates', Journal of Crystal Growth, vol. 310, no. 15, pp. 3645-3648.
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ZnSe nanoplates were synthesized by a solvothermal method using ethylenediamine (EN) as the liganding solvent. The crystal structures, morphologies and optical properties of the precursor and ZnSe products were systematically characterized. Results reveal that precursor ZnSe(en)1/2 with a layered structure was initially obtained through solvothermal synthesis, which can be converted into hexagonal wurtzite structured ZnSe by heat-treatment in Ar atmosphere. The as-prepared ZnSe was composed of stacked nanoplates. The field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) results reveal that every nanoplate was made up of plenty of tiny single crystals. The room temperature ultraviolet+visible (UV/vis) measurements indicate that the bandgap of the obtained ZnSe is 2.7 eV and a large blue shift about 1.3 eV was observed in precursor ZnSe(en)1/2.
Gao, F., Wang, G. & Zhang, C. 2008, 'Strong photon-mixing of terahertz waves in semiconductor quantum wells induced by Rashba spin-orbit coupling', Nanotechnology, vol. 19, no. 46, pp. 465401-1-465401-3.
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We demonstrate that due to the Rashba spin+orbit coupling in semiconductor quantum wells, there is strong photo-mixing by mobile carriers in the terahertz frequency regime. The third order nonlinear current is of the same order of magnitude as the linear order current for an electric field intensity of 104 V cm-1 at frequency around 1 THz, a situation easily achievable in a laboratory system. Unlike other nonlinear effects, the nonlinear current density due to the spin+orbit coupling is inversely proportional to the concentration of mobile carriers.
Shanmukaraj, D., Wang, G., Liu, H.K. & Murugan, R. 2008, 'Synthesis and characterization of SrBi4Ti4O15 ferroelectric filler based composite polymer electrolytes for lithium ion batteries', Polymer Bulletin, vol. 60, pp. 351-361.
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Composite polymer electrolytes (CPEs) based on poly (ethylene oxide) (PEO) (Mol.Wt ~ 6 x 105) complexed with LiN(CF3SO2)2 lithium salt and SrBi4Ti4O15 ferroelectric ceramic filler have been prepared as films. Citrate gel technique and conventional solid state technique were employed for the synthesis of the ferroelectric fillers in order to study the effect of particle size of the filler on ionic conductivity of the polymer electrolyte. Characterization techniques such as X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and temperature dependant DC conductivity studies were taken for the prepared polymer composite electrolytes. The broadening of DTA endotherms on addition of ceramic fillers to the polymer salt complex indicated the reduction in crystallinity. An enhancement in conductivity was observed with the addition of SrBi4Ti4O15 as filler to the (PEO)8-LiN(CF3SO2)2 polymer salt complexes. Among the investigated samples (PEO)8-LiN(CF3SO2)2 +10 wt% SrBi4Ti4O15 (citrate gel) polymer composite exhibits a maximum conductivity.
Wang, G., Park, J.S., Park, M.S. & Gou, X. 2008, 'Synthesis and high gas sensitivity of tin oxide nanotubes', Sensors and Actuators B: Chemical, vol. 131, no. 1, pp. 313-317.
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Semiconductor tin oxide (SnO2) nanotubes have been synthesised in bulk quantities using a sol+gel template (AAO membrane) synthetic technique. The morphology and crystal structure of SnO2 nanotubes were characterised by a field emission scanning electron microscope (FESEM) and a transmission electron microscope (TEM). The as-prepared SnO2 nanotubes are polycrystalline with an outer diameter of 200 nm, an inner diameter of about 150 nm and a length extending to tens of micrometers. SnO2 nanotube sensors exhibited high sensitivity towards ethanol gas.
Park, M.S., Kang, Y.M., Wang, G., Dou, S.X. & Liu, H. 2008, 'The effect of morphological modification on the electrochemical properties of SnO2 nanomaterials', Advanced Functional Materials, vol. 18, no. 3, pp. 455-461.
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The electrochemical performances of 1D SnO2 nanomaterials, nanotubes, nanowires, and nanopowders, are compared to define the most favorable morphology when SnO2 nanomaterials are adopted as the electrode material for lithium-ion batteries. Changes in the morphology of SnO2 are closely related with its electrochemical performance. Some SnO2 nanomaterials feature not only an increased energy density but also enhanced Li+ transfer. The correlation between the morphological characteristics and the electrochemical properties of SnO2 nanomaterials is discussed. The interesting electrochemical results obtained here on SnO2 nanomaterials indicate the possibility of designing and fabricating attractive nanostructured materials for lithium-ion batteries.
Gou, X., Wang, G., Kong, X., Wexler, D., Horvat, J., Yang, J. & Park, J. 2008, 'Flutelike Porous Hematite Nanorods and Branched Nanostructures: Synthesis, Characterisation and Application for Gas-Sensing', Chemistry: A European Journal, vol. 14, no. 19, pp. 5996-6002.
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Flute-like porous ?-Fe2O3 nanorods and branched nanostructures such as pentapods and hexapods were prepared through dehydration and recrystallisation of hydrothermally synthesised ?-FeOOH precursor. Transmission electron microscopy (TEM), high-resolution TEM and selected area electron diffraction analyses reveal that the nanorods, which grow along the [110] direction, have nearly hollow cavities and porous walls with a pore size of 20+50 nm. The hexapods have six symmetric arms with a diameter of 60+80 nm and length of 400+900 nm. The growth direction of the arms in the hexapod-like nanostructure is also along the [110] direction, and there is a dihedral angle of 69.5o between adjacent arms. These unique iron oxide nanostructures offer the first opportunity to investigate their magnetic and gas sensing properties. The nanostructures exhibited unusual magnetic behaviour, with two different Morin temperatures under field-cooled and zero-field-cooled conditions, owing to their shape anisotropy and magnetocrystalline anisotropy. Furthermore, the ?-Fe2O3 nanostructures show much better sensing performance towards ethanol than that of the previously reported polycrystalline nanotubes. In addition, the ?-Fe2O3 nanostructure based sensor can selectively detect formaldehyde and acetic acid among other toxic, corrosive and irritant vapours at a low working temperature with rapid response, high sensitivity and good stability.
Gou, X., Wang, G., Yang, J., Park, J. & Wexler, D. 2008, 'Chemical synthesis, characterisation and gas sensing performance of copper oxide nanoribbons', Journal of Materials Chemistry, vol. 18, no. 9, pp. 965-969.
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Single crystalline copper oxide nanoribbons were synthesized via a surfactant-assisted hydrothermal route. The resulting CuO nanoribbons contain substantial amounts of nanorings and nanoloops. High resolution TEM analysis identified CuO nanoribbons growing along the [010] direction. CuO nanoribbons exhibited excellent sensing performance towards formaldehyde and ethanol vapours with rapid response and high sensitivity at low operating temperatures. We found that the loading of a small amount of Au or Pt nanoparticles on the surface of CuO nanoribbons can effectively enhance and functionalize the gas sensing performance of CuO nanoribbons.
Yao, J., Konstantinov, K., Wang, G. & Liu, H. 2007, 'Electrochemical and magnetic characterization of LiFePO4 and Li0.95Mg0.05FePO4 cathode materials', Journal of Solid State Electrochemistry, vol. 11, no. 2, pp. 177-185.
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A series of lithium iron phosphates was synthesized via the sol+gel route. Iron phosphides, which are electronic conductors, were formed when sintered at 850C. Magnetic susceptibility measurements on the samples show antiferromagnetic behaviour with T N=502 K for LiFePO4 and Li0.95Mg0.05PO4 sintered at temperatures below 850C. The LiFePO4 and Li0.95Mg0.05FePO4 cathodes show a stable electrochemical capacity in the range of 150+160 mA h/g on cycling. The cyclability deteriorates with increasing sample sintering temperature due to the increased crystal size and impurities.
Park, M.S., Wang, G., Kang, Y.M., Kim, S.Y., Liu, H. & Dou, S.X. 2007, 'Mesoporous organo-silica nanoarray for energy storage media', Electrochemistry Communications, vol. 9, no. 1, pp. 71-75.
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A SnO2+mesoporous organo-silica nanoarray (MOSN) composite was prepared by surfactant mediated synthesis combined with a sol+gel vacuum suction method in which SnO2 has been successfully incorporated inside the periodic nanoholes in the MOSN or coated on its surface. The MOSN with a high aspect ratio of length to width could not only maintain its structure but also effectively accommodate the volume expansion of the SnO2 during electrochemical reactions with Li+. The SnO2+MOSN composite showed a higher reversible capacity of 420 mA h g-1 with greatly improved capacity retention and lower initial irreversible capacity compared to SnO2 powder. This interesting anodic performance of SnO2+MOSN composite supports the potential use of MOSN for lithium ion batteries.
Wang, J., Chew, S.Y., Wexler, D., Wang, G., Ng, S.H., Zhong, S. & Liu, H.K. 2007, 'Nanostructured nickel sulfide synthesized via a polyol route as a cathode material for the rechargeable lithium battery', Electrochemistry Communications, vol. 9, no. 8, pp. 1877-1880.
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Nanostructured nickel sulfide (NiS) was synthesized via a simple polyol route. The NiS powders were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electrochemical testing. The results revealed that the cycle life of the annealed NiS sample was improved over that of the as-prepared sample. The electrochemical performance was also tested using 1 M lithium trifluoromethanesulfonimide (LiTFSI) in a solvent of poly(ethylene glycol) dimethyl ether (PEGDME) in order to compare with a sample tested in the conventional electrolyte of 1 M LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The results showed that the electrochemical properties were improved by using the 1 M LiTFSI/PEGDME electrolyte.
Park, M.S., Needham, S.A., Wang, G., Kang, Y.M., Park, J.S., Dou, S.X. & Liu, H. 2007, 'Nanostructured SnSb/carbon nanotube composites synthesized by reductive precipitation for lithium-ion batteries', Chemistry of Materials, vol. 19, no. 10, pp. 2406-2410.
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Nanosized particles of SnSb alloy were coated on the surface of multiwalled carbon nanotubes (CNTs) by reductive precipitation of metal chloride salts within a CNT suspension. The SnSb-CNT nanocomposite showed a high reversible capacity of 480 mAh g-1 and stable cyclic retention until the 50th cycle. The improvement of reversible capacity and cyclic performance of the SnSb-CNT composite is attributed to the nanoscale dimension of the SnSb alloy particles (<50 nm) and the structural advantages of CNTs as a framework material. The CNTs could be pinning the SnSb alloy particles on their surfaces so as to hinder the agglomeration of SnSb particles, while maintaining electronic conduction as well as accommodating drastic volume variation during electrochemical reactions
Park, M.S., Wang, G., Kang, Y.M., Wexler, D., Dou, S.X. & Liu, H. 2007, 'Preparation and electrochemical properties of SnO2 nanowires for application in lithium-ion batteries', Angewandte Chemie-international Edition, vol. 46, no. 5, pp. 750-753.
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SnO2 nanowires with tetragonal structure were successfully synthesized by a thermal evaporation method without any conventional metal catalysts. The enhanced electrochemical performance of SnO2 nanowires is believed to result from the combination of unique nanostructures with a high length/diameter ratio and the absence of traditional metal catalysts.
Needham, S.A., Wang, G., Liu, H.K., Drozd, V.A. & Liu, R.S. 2007, 'Synthesis and electrochemical performance of doped LiCoO2 materials', Journal of Power Sources, vol. 174, no. 2, pp. 828-831.
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Layered intercalation compounds LiM0.02Co0.98O2 (M = Mo6+, V5+, Zr4+) have been prepared using a simple solid-state method. Morphological and structural characterization of the synthesized powders is reported along with their electrochemical performance when used as the active material in a lithium half-cell. Synchrotron X-ray diffraction patterns suggest a single phase HT-LiCoO2 that is isostructural to ?-NaFeO2 cannot be formed by aliovalent doping with Mo, V, and Zr. Scanning electron images show that particles are well-crystallized with a size distribution in the range of 1+5 ?m. Charge+discharge cycling of the cells indicated first cycle irreversible capacity loss in order of increasing magnitude was Zr (15 mAh g-1), Mo (22 mAh g-1), and V (45 mAh g-1). Prolonged cycling the Mo-doped cell produced the best performance of all dopants with a stable reversible capacity of 120 mAh g-1 after 30 cycles, but was inferior to that of pure LiCoO2.
Wang, G., Park, J., Wexler, D., Park, M.S. & Ahn, J.h. 2007, 'Synthesis, characterization, and optical properties of In2O3 semiconductor nanowires', Inorganic Chemistry, vol. 46, no. 12, pp. 4778-4780.
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In2O3 semiconductor nanowires were synthesized by the chemical vapor deposition method through carbon thermal reduction at 900 C with 95% Ar and 5% O2 gas flow. The In2O3 nanowires were characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence spectroscopy (PL). For the first time, we observed the formation of corundum-type h-In2O3 nanowires and branched In2O3 nanowires. The PL spectra of In2O3 nanowires show strong visible red emission at 1.85 eV (670 nm) at low temperature, possibly caused by a small amount of oxygen vacancies in the nanowire crystal structure.
Liu, H.K., Wang, G., Guo, Z.P., Wang, J.Z. & Konstantinov, K. 2007, 'The impact of nanomaterials on Li-ion rechargeable batteries', Journal of New Materials for Electrochemical Systems, vol. 10, no. 2, pp. 101-104.
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In this paper we report on the impact of nanomaterials on lithium rechargeable battery performances. Nanotubes (single wall carbon nanotube and multi wall carbon nanotube, NiO and WS2), nano-intermetallic alloys (Cu6Sn5, Sn/SnSb and Sn/SnNi), nano-oxides (NiO, CoO, SnO2 and Co3O4), nano-composites (C-LiFePO4, Si-C, Si-MCMB (mesocarbon microbeads), Si-TiC, Si-PPY (polypyrrole) and MWNT(multiwalled nanotubes)/Sn/SnNi), as well as other nanoparticles (TiO2, SiO2 and Al2O3) have been used in lithium rechargeable batteries in our studies. +Free-standing+ single wall carbon nanotube (SWNT) papers produced without any binder and metal substrate shows a capacity slightly lower than that of the conventional electrode. Carbon-coated Si nanocomposites produced by a spray-pyrolysis technique can reversibly store lithium with a high capacity of 1489 mAh/g and a high coulumbic efficiency above 99.5%, even after 20 cycles. Nanosize 10 wt% TiO2 increased the ionic conductivity of PEO-LiClO4 polymer electrolyte by a factor of 2 at room temperature and at elevated temperature.
Wang, J.Z., Ng, S.H., Chew, S.Y., Wexler, D., Wang, G. & Liu, H.K. 2007, 'Characterization of nanosize molybdenum trisulfide for lithium batteries and MoS3 structure confirmation via electrochemistry', Electrochemistry and Solid-State Letters, vol. 10, no. 9, pp. A204-A207.
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Nanosize molybdenum trisulfide, MoS3, was synthesized in a polyoxyethylene (2) nonylphenyl ether/ cyclohexane/ water micro-emulsion by acidifying ammonium tetrathiomolybdate solubilized in the water cores of inverse micelles. MoS3 was also prepared by thermal decomposition for comparison. X- ray diffraction, TEM, and electrochemical testing characterized the molybdenum trisulfide. By comparing the cyclic voltammetry results on MoS3 and S electrodes in lithium cells, the conclusions about the structure of MoS3 from previous research work have been confirmed. That is, the molybdenum trisulfide molecules were not a mixture of MoS2 and elemental S. Molybdenum trisulfide exists as Mo3S9 clusters, which are, in turn, linked by bridging S - S bonds
Needham, S.A., Calka, A., Wang, G., Mosbah, A. & Liu, H.K. 2006, 'A new rapid synthesis technique for electrochemically active materials used in energy storage applications', Electrochemistry Communications, vol. 8, no. 3, pp. 434-438.
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LiFePO4 is a promising environmentally friendly and low cost alternative cathode material for use in lithium-ion batteries. The most common materials production process used to manufacture LiFePO4 is solid-state synthesis which entails several grinding and recalcination steps, occurring over many hours. We report on the synthesis of crystalline LiFePO4 in only 10 min via a versatile process of Electric discharge assisted mechanical milling (EDAMM). Preliminary electrochemical testing of the synthesized powder demonstrates good capacity and excellent cyclability. The EDAMM technique offers an exciting opportunity to synthesize a range of new and existing materials to be used in a variety of energy storage applications that include rechargeable lithium batteries, hydrogen fuel cells, and supercapacitors.
Wang, G., Needham, S.A., Yao, J., Wang, J.Z., Liu, R.S. & Liu, H.K. 2006, 'A study on LiFePO4 and its doped derivatives as cathode materials for lithium-ion batteries', Journal of Power Sources, vol. 159, no. 1, pp. 282-286.
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LiFePO4, doped LiMxFe1-xPO4, and Li1-xMxFePO4 compounds have been prepared via a sol+gel synthesis method. The physical properties of the as-prepared lithium iron phosphates were characterised by X-ray diffraction, X-ray absorption near-edge spectroscopy (XANES), and magnetic susceptibility. The electrochemical properties lithium iron phosphates were tested by a variety of electrochemical techniques. Lithium iron phosphate electrodes demonstrated a stable discharge capacity of 160+165 mAh g-1, almost approaching the theoretical capacity. The good electronic conductivity and nanocrystalline could contribute to the unique performance of lithium iron phosphate electrodes. Lithium iron phosphates have a significant potential to be used as a new cathode materials in Li-ion batteries.
Wang, J., Wang, G., Yang, L., Ng, S.H. & Liu, H. 2006, 'An investigation on electrochemical behavior of nanosize zinc sulfide electrode in lithium-ion cells', Journal of Solid State Electrochemistry, vol. 10, no. 4, pp. 250-254.
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Nanosize zinc sulfides were synthesized through the chemical reaction method. The as-prepared zinc sulfide nanopowders were characterized by X-ray diffraction, transmission electron microscopy and electrochemical testing. The results revealed that zinc sulfide electrodes exhibited a reversible lithium storage capacity of about 400 mAh/g with stable cyclability. Zinc sulfide nanopowders show promise as anode materials for lithium-ion batteries.
Yao, J., Bewlay, S., Konstantinov, K., Drozd, V.A., Liu, R.S., Wang, X.L., Liu, H.K. & Wang, G. 2006, 'Characterisation of olivine-type LiMnxFe1-xPO4 cathode materials', Journal Of Alloys And Compounds, vol. 425, pp. 362-366.
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A series of LiMnxFe1-xPO4 (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) compounds were synthesised by a sol+gel preparation route. X-ray diffraction and Rietveld structure refinement revealed that the lattice parameters (a, b and c) of orthorhombic LiMnxFe1-xPO4 increase with increasing Mn content. Magnetic susceptibility measurements show antiferromagnetic behaviour for LiMnxFe1-xPO4 samples. The electrochemical properties of LiMnxFe1-xPO4 as cathodes in lithium-ion cells were tested via cyclic voltammetry and galvanostatic charge/discharge measurements. The electrochemical performance of LiMnxFe1-xPO4 degrades with increasing Mn content.
Park, M.S., Wang, G., Liu, H. & Dou, S.X. 2006, 'Electrochemical properties of Si thin film prepared by pulsed laser deposition for lithium ion micro-batteries', Electrochimica Acta, vol. 51, no. 25, pp. 5246-5249.
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Si thin films were deposited directly on stainless steel substrates that act as current collectors using the pulsed laser deposition (PLD) technique. Amorphous Si films of different thicknesses were obtained at the Ar gas pressure of 5 10-5 Torr and a temperature of 500 C but different deposition times. The microstructure and morphology of the films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The anodic electrochemical performance of the films was examined in the range of 0.005+1.5 V, which revealed excellent cyclic stability without any large capacity fade up to the 70th cycle. The PLD process was suitable for improving the density and adhesion behavior of the films.
Hannoyer, B., Prince, A.A., Jean, M., Liu, R.S. & Wang, G. 2006, 'Mossbauer study on LiFePO4 cathode material for lithium ion batteries', Hyperfine Interactions, vol. 167, no. 1-3, pp. 767-772.
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Crystalline LiFePO4 has been synthesized using solid-state, spray pyrolysis, and wet chemical methods. The crystal parameters were obtained from Rietveld+s refinement methods of the X-ray diffraction patterns. A detailed investigation of the Fe valency carried out using Mssbauer spectroscopy at room temperature indicates that Fe is predominantly present in its bivalent state.
Konstantinov, K., Ng, S.H., Wang, J.Z., Wang, G., Wexler, D. & Liu, H.K. 2006, 'Nanostructured PbO materials obtained in situ by spray solution technique for Li-ion batteries', Journal of Power Sources, vol. 159, no. 1, pp. 241-244.
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This paper describes a systematic study of the effect of various spray pyrolysis parameters, such as temperature, solution concentration and solution flow rate on the morphology, crystallization process, crystal size, specific surface area and electrochemical performance of in situ prepared ?-PbO spherically agglomerated nano-structured powders. Different analytical methods such as XRD, SEM, TEM, BET gas sorption specific surface area measurements and electrochemical tests were performed. Crystallites in the range of 20+120 nm and easily dispersed powders were reproducibly prepared by optimization of the spray conditions. An increase of the temperature from 600 to 800 C was found to lead to a three times increase in the average crystal size, from 31 to 102 nm. An increase of concentration from 0.15 to 0.5 M dramatically suppresses the crystal size from 127 to 25 nm. The BET surface area of sprayed PbO powders is increased up to 6.6 m2 g-1. For such PbO powders applied as anode materials in Li-ion batteries, we have managed to retain a reversible capacity above 60 mAh g-1 beyond 50 cycles.
Wang, J., Chen, J., Konstantinov, K., Zhao, L., Ng, S.H., Wang, G., Guo, Z.P. & Liu, H.K. 2006, 'Sulphur-polypyrrole composite positive electrode materials for rechargeable lithium batteries', Electrochimica Acta, vol. 51, no. 22, pp. 4634-4638.
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A novel conducting sulphur-polypyrrole composite material was prepared by the chemical polymerization method with sodium p-toluenesulphonate as the dopant, 4-styrenesulphonic sodium salts as the surfactant, and FeCl3 as the oxidant. The new material was characterized by Raman spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Nanosize polypyrrole particles were uniformly coated onto the surface of the sulphur powder, which significantly improved the electrical conductivity, the capacity and the cycle durability in a lithium cell compared with the bare sulphur electrode
Wang, J., Ng, S.H., Wang, G., Chen, J., Zhao, L., Chen, Y. & Liu, H.K. 2006, 'Synthesis and characterization of nanosize cobalt sulfide for rechargeable lithium batteries', Journal of Power Sources, vol. 159, no. 1, pp. 287-290.
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Nanosize cobalt sulfides were synthesized through a one step chemical reaction method at room temperature. The cobalt sulfide nanopowders were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy and electrochemical testing. The results revealed that the cobalt sulfide is a semiconductor; the reversible capacity is increased with increasing content of electronic conductors in the active material of electrodes. The as prepared sample with 10 wt.% carbon black and 10 wt.% polypyrrole (PPy) powder as electronic conductors shows the best electrochemical properties, with a reversible capacity of over 300 mAh g-1 based on the total mass of the electrode. Cobalt sulfide nanopowders show promise as cathode active materials for lithium-rechargeable batteries.
Needham, S.A., Wang, G. & Liu, H.K. 2006, 'Synthesis of NiO nanotubes for use as negative electrodes in lithium ion batteries', Journal of Power Sources, vol. 159, no. 1, pp. 254-257.
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Nickel oxide (NiO) nanotubes have been produced for the first time via a template processing method. The synthesis involved a two step chemical reaction in which nickel hydroxide (Ni(OH)2) nanotubes were firstly formed within the walls of an anodic aluminium oxide (AAO) template. The template was then dissolved away using concentrated NaOH, and the freed nanotubes were converted to NiO by heat treatment in air at 350 C. Individual nanotubes measured 60 ?m in length with a 200 nm outer diameter and a wall thickness of 20+30 nm. The NiO nanotube powder was used in Li-ion cells for assessment of the lithium storage ability. Preliminary testing indicates that the cells demonstrate controlled and sustainable lithium diffusion after the formation of an SEI. Reversible capacities in the 300 mAh g-1 range were typical.
Lao, Z.J., Konstantinov, K., Tournaire, Y., Ng, S.H., Wang, G. & Liu, H.K. 2006, 'Synthesis of vanadium pentoxide powders with enhanced surface-area for electrochemical capacitors', Journal of Power Sources, vol. 162, no. 2, pp. 1451-1454.
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Single-phase, chemically pure vanadium pentoxide (V2O5) powders are prepared by co-precipitation and further calcination at 300 C. The materials obtained are agglomerated in sub-micron particles, and BET analysis shows that the as-prepared V2O5 powders have a high specific surface-area of 41 m2 g-1. V2O5 shows the highest capacitance in 2 M KCl electrolyte when compared with other electrolytes such as 2 M NaCl and 2 M LiCl. It yields a maximum specific capacitance of 262 F g-1. The higher specific surface-area may be the reason for the high capacitance compared with previously published results.
Zhang, D.Y., Ma, Z.F., Wang, G., Konstantinov, K., Yuan, X.X. & Liu, H.K. 2006, 'Electro-oxidation of ethanol on Pt-WO3/C electrocatalyst', Electrochemistry and Solid-State Letters, vol. 9, no. 9, pp. A423-A426.
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Pt-x-WO3/C electrocatalysts were prepared by microwave colloid-reduction method. Transmission electron microscopy examination showed uniform dispersion of platinum with particle sizes less than 5 nm. Structures of the Pt-x-WO3/C electrocatalysts were characterized by X- ray diffraction and energy dispersive spectroscopy, the electrochemical characteristics and electro-oxidation of electro-oxidation of ethanol on the Pt-x-WO3/C electrocatalysts were also studied by cyclic voltammetry, linear sweep, and chronoamperometry. The results show that the Pt-x-WO3/C electrocatalysts have higher catalytic activity to ethanol electro-oxidation than the commercial Pt/C catalysts; perhaps caused by the "hydrogen spill-over effect." The reaction mechanisms of the ethanol electro-oxidation on the Pt-x-WO3/C were inferred according to the electrochemical characteristics and the data in the reported literature.
Wang, G., Yao, J., Liu, H.K., Dou, S.X. & Ahn, J.h. 2006, 'Growth and lithium storage properties of vertically aligned carbon nanotubes', Metals and Materials International, vol. 12, no. 5, pp. 413-416.
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High-purity vertically aligned carbon nanotubes (CNTs) were prepared on a quartz substrate by thermal chemical vapour deposition (CVD). The as-prepared carbon nanotubes have an outer diameter of 40+60 nm and a length of 70+80 ?m. HRTEM observation revealed that there were compartment structures in the carbon nanotubes. The vertically aligned CNTs exhibit a high reversible lithium storage capacity of 950 mAh/g in lithium-ion cells.
Ahn, J.h., Kim, Y.J. & Wang, G. 2006, 'Electrochemical properties of carbon nanotube-dispersed PEO-LiX electrolytes', Metals and Materials International, vol. 12, no. 1, pp. 69-73.
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Multi-wall nanotubes (MWCNTs) were added to PEO-LiClO4 solid electrolytes in order to assess their enhancement of ionic conductivity. PEO-LiClO4-SiO2 composite electrolytes were also manufactured for comparison. In spite of the electrical conductivity of MWCNTs, PEO-LiClO4-MWCNT composites can be sucessfully used as solid electrolytes, provided that additive carbon nanotubes have discontinous forms and are homogeneously distributed within the PEO-LiClO4 matrix. Shortening and uniform dispersion of MWCNT were identified as crucial factors for the performance of PEO-LiClO4-MWCNT composite electrolytes. Compared with the PEO-LiClO4-SiO2 composite, the addition of MWCNT to PEO-LiClO4 resulted in greater enhancement in ionic conductivity. This might be attributable to enhanced amorphization by local modification of PEO chains from crystalline to disordered arrangements.
Wang, G., Park, M.S., Wexler, D., Chen, J. & Liu, H.K. 2006, 'Synthesis and characterization of one-dimensional CdSe nanostructures', Applied Physics Letters, vol. 88, no. 19, pp. 193115-1-193115-1.
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One-dimensional (1D) CdSe nanostructures, including nanowires, nanotubes, nanorods, nanobelts, and even nanostructures resembling saws and tree branches, have been synthesized by sublimation of CdSe powders under various experimental conditions. These 1D CdSe nanostructures were characterized by scanning electron microscopy, high resolution transmission electron microscopy observations, and Raman spectroscopy. Energy dispersive x-ray spectroscopy analysis confirmed the chemical stoichiometry of the CdSe nanostructures. It was found that the geometrical morphologies of the CdSe 1D nanostructures were significantly influenced by the synthetic parameters. Raman spectra of CdSe nanowires show an upward shift of the 2LO phonon peak.
Needham, S.A., Wang, G., Konstantinov, K., Tournayre, Y., Lao, Z. & Liu, H.K. 2006, 'Electrochemical performance of Co3O4-C composite anode materials', Electrochemical and Solid-State Letters, vol. 9, no. 7, pp. A315-A319.
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Co3O4+C composite powder has been synthesized via spray pyrolysis of cobalt nitrate-sugar solution at 600C and assessed for application as anode materials in Li-ion batteries. Microstructural characterization by scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy confirm an even distribution of carbon throughout particles, as well as the presence of a carbon-based surface sheath surrounding Co3O4+C particle agglomerates. Charge-discharge cycling of half-cells indicates a stable reversible discharge capacity above 800 mAh g-1. Equivalent circuit modeling of Nyquist plots show the Co3O4+C electrode has significant kinetic advantages over non-composite transition metal oxide electrodes.
Needham, S.A., Calka, A., Wang, G., Peleckis, G. & Liu, H.K. 2006, 'Synthesis of functional oxides by a novel mechanical milling-electric discharge method', Journal of Materials Chemistry, vol. 16, pp. 4488-4493.
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Functional metal oxide powders (LiCoO2, LiFePO4, SrTi1-xCoxO3) have been synthesized by a novel Electric Discharge Assisted Mechanical Milling (EDAMM) processing technique. Characterisation of the as-synthesized powders by XRD, SEM, and TEM confirm near pure phases with a highly controllable morphology can be produced in only minutes. The electrochemical (LiCoO2, LiFePO4) and magnetic (SrTi1-xCoxO3) behaviour of the powders indicates functionality that at least matches that of powders synthesized by traditional solid-state approaches. The EDAMM technique provides significant commercial opportunities as the method has proven to be scalable and powder morphologies can be made to order.
Liu, H., Wang, G., Guo, Z.P., Wang, J.Z. & Konstantinov, K. 2006, 'Nanomaterials for lithium-ion rechargeable batteries', Journal of Nanoscience & Nanotechnology, vol. 6, pp. 1-15.
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In lithium-ion batteries, nanocrystalline intermetallic alloys, nanosized composite materials, carbon nanotubes, and nanosized transition-metal oxides are all promising new anode materials, while nanosized LiCoO2, LiFePO4, LiMn2 O4, and LiMn2O4 show higher capacity and better cycle life as cathode materials than their usual larger-particle equivalents. The addition of nanosized metal-oxide powders to polymer electrolyte improves the performance of the polymer electrolyte for all solid-state lithium rechargeable batteries. To meet the challenge of global warming, a new generation of lithium rechargeable batteries with excellent safety, reliability, and cycling life is needed, i.e., not only for applications in consumer electronics, but especially for clean energy storage and for use in hybrid electric vehicles and aerospace. Nanomaterials and nanotechnologies can lead to a new generation of lithium secondary batteries. The aim of this paper is to review the recent developments on nanomaterials and nanotechniques used for anode, cathode, and electrolyte materials, the impact of nanomaterials on the performance of lithium batteries, and the modes of action of the nanomaterials in lithium rechargeable batteries.
Wang, G., Bewlay, S., Needham, S.A., Liu, H.K., Liu, R.S., Drozd, V.A., Lee, J.F. & Chen, J.M. 2006, 'Synthesis and characterization of LiFePO4 and LiTi0.01Fe0.99PO4 cathode materials', Journal of Electrochemical Society, vol. 153, pp. A25-A31.
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Nanocrystalline LiFePO4 and doped LiTi0.01Fe0.99PO4 powders were synthesized via a sol-gel preparation route. High-resolution tunneling electron microscopy observation and energy dispersive spectroscopy, mapping show the homogeneous distribution of dopant Ti cations in the crystals. Fe and O K-edge X-ray absorption near-edge structure (XANES) measurements show that Ti4+ doping induces an increased unoccupied d-state in LiFePO4, resulting in an enhanced p-type semiconductivity. In situ Fe K-edge XANES measurements of Ti-doped and undoped LiFePO4 electrodes have been performed to determine the change of Fe valence during the lithium intercalation and de-intercalation processes. Both LiFePO4 and doped LiTi0.01Fe0.99PO4 cathodes demonstrate good electrochemical performance.
Wang, G., Yang, L., Chen, Y., Wang, J.Z., Bewlay, S. & Liu, H.K. 2005, 'An investigation of polypyrrole-LiFePO4 composite cathode materials for lithium-ion batteries', Electrochimica Acta, vol. 50, no. 24, pp. 4649-4654.
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A series of polypyrrole-LiFePO4 (PPy-LiFePO4) composites were synthesised by polymerising pyrrole monomers on the surface of LiFePO4 particles. AC impedance measurements show that the coating of polypyrrole significantly decreases the charge-transfer resistance of LiFePO4 electrodes. The electrochemical reactivity of polypyrrole and PPy-LiFePO4 composites for lithium insertion and extraction was examined by charge/discharge testing. The PPy-LiFePO4 composite electrodes demonstrated an increased reversible capacity and better cyclability, compared to the bare LiFePO4 electrode.
Needham, S.A., Wang, G. & Liu, H. 2005, 'Electrochemical performance of SnSb and Sn/SnSb nanosize powders as anode materials in Li-ion cells', Journal Of Alloys And Compounds, vol. 400, pp. 234-238.
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nosized pure SnSb and SnSb with excess ductile Sn (referred to as Sn/SnSb) powders have been synthesised by careful reductive co-precipitation in NaBH4. Crystallite sizes for both powders measure in the 50+100 nm range with particles agglomerating up to a few micrometers in pure SnSb powder and several tens of micrometers in the Sn/SnSb composite. Pristine powders were mixed separately with carbon black in order to improve dispersion and electronic conduction. Electrodes were constructed using the powders and tested as Li-ion half cell in order to measure the electrochemical performance. The energy storage capacity of electrodes improved in excess of 50% by increasing quantity of carbon black from 20 wt.% to 50 wt.%. Capacity fade over repeated charge and discharge cycles still remains a challenge to practical application of SnSb and Sn/SnSb alloy electrodes.
Wang, G., Yang, L., Bewlay, S.L., Chen, Y., Liu, H. & Ahn, J.h. 2005, 'Electrochemical properties of carbon coated LiFePO4 cathode materials', Journal of Power Sources, vol. 146, no. 1-2, pp. 521-524.
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Carbon coated lithium iron phosphates were prepared by a carbon aerogel synthesis process, through which LiFePO4 particles were embedded in amorphous carbon. The carbon coating effect can significantly enhance the electronic conductivity of LiFePO4. The electrochemical properties of the as-prepared LiFePO4 cathode materials were systematically characterised. The carbon coated LiFePO4 cathode demonstrated a high capacity and stable cyclability.
Yuan, L., Konstantinov, K., Wang, G., Liu, H.K. & Dou, S.X. 2005, 'Nano-structured SnO2-carbon composites obtained by in situ spray pyrolysis method as anodes in lithium batteries', Journal of Power Sources, vol. 146, no. 1-2, pp. 180-184.
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In this paper, we report on a series of SnO2-carbon nano-composites synthesized by in situ spray pyrolysis of a solution of SnCl22H2O and sucrose at 700 C. The process results in super fine nanocrystalline SnO2, which is homogeneously distributed inside the amorphous carbon matrix. The SnO2 was revealed as a structure of broken hollow spheres with porosity on both the inside and outside particle surfaces. This structure promises a highly developed specific surface area. X-ray diffraction (XRD) patterns and transmission electron microscope (TEM) images revealed the SnO2 crystal size is about 5+15 nm. These composites show a reversible lithium storage capacity of about 590 mAh g-1 in the first cycle. The discharge curve of the composite indicates that lithium is stored in crystalline tin, but not in amorphous carbon. However, the conductive carbon matrix with high surface area provides a buffer layer to cushion the large volume change in the tin regions, which contributes to the reduced capacity fade compared to nonacrystalline SnO2 without carbon
Ng, S.H., Wang, J., Guo, Z.P., Chen, J., Wang, G. & Liu, H.K. 2005, 'Single wall carbon nanotube paper as anode for lithium-ion battery', Electrochimica Acta, vol. 51, no. 1, pp. 23-28.
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+Free-standing+ single wall carbon nanotube (SWNT) papers have been synthesised by simple filtration method via positive pressure. A conventional SWNT slurry coated electrode was fabricated to compare with the SWNT papers. The results show that the capacity of the +Free-standing+ electrode was slightly lower than that of the conventional electrode, but the +Free-standing+ electrode was produced without any binder, and metal substrate, so that the weight of electrode was reduced significantly. On the other hand, the procedures for SWNT electrode preparation were simplified, so the cost of the manufacturing could be reduced.
Wang, G., Chen, Y., Yang, L., Yao, J., Needham, S.A., Liu, H. & Ahn, J.h. 2005, 'Synthesis of nanocrystalline transition metal and oxides for lithium storage', Journal of Power Sources, vol. 146, no. 1-2, pp. 487-491.
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Nanosize silver and tin dioxide powders were synthesised by a novel reverse micelle technique. The reverse micelles were formed from a microemulsion of organic solvents, water based salts and surfactants. The spherical nanosize Ag powders were formed via in situ reduction. The tin hydroxide precipitates were formed in reverse micelles and converted to tin dioxide nanopowders after heat treatment. The Ag and SnO2 powders have a particle size in the range of 20+50 nm. The as-prepared nanosize Ag and SnO2 nanopowders were used in lithium-ion cells for lithium storage.
Wang, G., Bewlay, S., Yang, L., Wang, J.Z., Chen, Y., Liu, H.K. & Dou, S.X. 2005, 'Nanostructured electrode materials for rechargeable lithium-ion battery applications', Journals of Materials Science & Technology, vol. 21, no. S1, pp. 17-19.
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Nanocrystafline LiFeP04 and Si-C powders were prepared as electrode materials for lithium-ion batteries. Near full capacity (170 mAh/g) was achieved at the C/8 rate at room temperature for LiFeP04 electrodes. Nanosize Si-C composite anode materials demonstrated a reversible lithium storage capacity of 1450 mAh/g with good cyclability when used as anodes in lithium-ion cells. Nanostructured electrode materials have an important role to play in developing a new generation of lithium-ion batteries that will offer a dramatic improvement in power delivery.
Wang, G., Yang, L., Wang, J.Z., Liu, H.K. & Dou, S.X. 2005, 'Enhancement of ionic conductivity of PEO based polymer electrolyte by the addition of nanosize ceramic powders', Journal of Nanoscience & Nanotechnology, vol. 5, pp. 1135-1140.
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The ionic conductivity of polyethylene oxide (PEO) based solid polymer electrolytes (SPEs) has been improved by the addition of nanosize ceramic powders (TiO2 and Al2O3). The PEO based solid polymer electrolytes were prepared by the solution-casting method. Electrochemical measurement shows that the 10 wt% TiO2 PEO-LiClO4 polymer electrolyte has the best ionic conductivity (about 10(-4) S cm(-1) at 40-60 degrees C). The lithium transference number of the 10 wt% TiO2 PEO-LiClO4 polymer electrolyte was measured to be 0.47, which is much higher than that of bare PEO polymer electrolyte. Ac impedance testing shows that the interface resistance of ceramic-added PEO polymer electrolyte is stable. Linear sweep voltammetry measurement shows that the PEO polymer electrolytes are electrochemically stable in the voltage range of 2.0-5.0 V versus a Li/Li+ reference electrode.
Ahn, J.h., Kim, Y.J., Wang, G. & Liu, H.K. 2005, 'Li storage properties of Ag and SnO2 nanopowders synthesised from reverse micelles', Journal of Metastable and Nanocrystalline Materials, vol. 26, no. 1, pp. 1-7.
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Ag and SnO2 nanopowders were synthesized by reverse-micelle method. The reverse micelles were prepared to form tiny aqueous droplets dispersed in oil-based solvents. Two reverse micelles containing metallic salts and reductive agents were rigorously mixed to form nanoparticles inside aqueous droplets by a reductive reaction. The spherical powders of 20~50 nm were formed during the process. The resulting Ag and SnO2 nanopowders were examined as the anode electrode for lithium-ion cells. The reversible discharge capacity of the Ag and SnO2 nanopowders after 25 cycles were 315 and 380 mAh/g, respectively.
Wang, J., Wang, G., Chen, Y., Wang, C.Y. & Liu, H.K. 2004, 'Novel cureless pure lead oxide plate for valve-regulated lead-acid batteries', Journal of Applied Electrochemistry, vol. 343, pp. 1127-1133.
Bewlay, S.L., Konstantinov, K., Wang, G., Dou, S.X. & Liu, H.K. 2004, 'Conductivity improvements to spray-produced LiFePO4 by addition of a carbon source', Materials Letters, vol. 58, pp. 1788-1791.
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Wang, G., Guo, Z.P., Yang, X.Q., McBreen, J., Liu, H. & Dou, S.X. 2004, 'Electrochemical and in situ synchrotron X-ray diffraction studies of Li[Li0.3Cr0.1Mn0.6]O2 cathode materials', Solid State Ionics, vol. 167, pp. 183-189.
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Wang, G., Yao, J., Liu, H., Dou, S.X. & Ahn, J.h. 2004, 'Electrochemical characteristics of tin-coated MCMB graphite as anode in Lithium-ion cells', Electrochimica Acta, vol. 50, pp. 517-522.
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Wang, G., Yao, J., Ahn, J.h., Liu, H. & Dou, S.X. 2004, 'Electrochemical properties of nanosize Sn-coated graphite anodes in lithium-ion cells', Journal of Applied Electrochemistry, vol. 34, pp. 187-190.
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Prince, A.A., Mylswamy, S., Chan, T.S., Liu, R.S., Hannoyer, B., Jean, M., Shen, C.H., Huang, S.M., Lee, J.F. & Wang, G. 2004, 'Investigation of Fe valence in LiFePO4 by Mossbauer and XANES spectroscopic techniques', Solid State Communications, vol. 132, pp. 455-458.
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Wang, G., Ahn, J.h., Yao, J., Bewlay, S. & Liu, H.K. 2004, 'Nanostructured Si-C composite anodes for lithium-ion batteries', Electrochemistry Communications, vol. 6, pp. 689-692.
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Konstantinov, K., Bewlay, S., Wang, G., Lindsay, M., Wang, J.Z., Liu, H.K., Dou, S.X. & Ahn, J.h. 2004, 'New approach for synthesis of carbon-mixed LiFePO4 cathode materials', Electrochimica Acta, vol. 50, pp. 421-426.
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Wang, G., Bewlay, S.L., Konstantinov, K., Liu, H.K., Dou, S.X. & Ahn, J.h. 2004, 'Physical and electrochemical properties of doped lithium iron phosphate electrodes', Electrochimica Acta, vol. 50, pp. 443-447.
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Chen, Y., Wang, G., Tian, J.P., Konstantinov, K. & Liu, H.K. 2004, 'Preparation and properties of spherical LiNi0.75Co0.25O2 as a cathode for lithium-ion batteries', Electrochimica Acta, vol. 50, pp. 435-441.
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Wang, G., Bewlay, S., Yao, J., Liu, H. & Dou, S. 2004, 'Tungsten disulfide nanotubes for lithium storage', Electrochemistry and Solid-State Letters, vol. 7, no. 10, pp. 321-323.
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WS2 nanotubes were synthesized by sintering amorphous WS3 at high temperature under flowing hydrogen. High-resolution transmission electron microscopy observation revealed that the as-prepared WS2 nanotubes have an open end with an inner hollow core of about 4.6 nm. We studied the lithium intercalation behavior of WS2 nanotubes. The WS2 nanotubes demonstrated a stable cyclability in a wide voltage range (0.1-3.1 V vs. Li/Li+). The nanotubes could provide a new class of electrode materials for lithium-ion batteries.
Wang, G., Bewlay, S., Yao, J., Ahn, J.h., Dou, S.X. & Liu, H. 2004, 'Characterisation of LiMxFe1-xPO4 (M=Mg, Zr, Ti) cathode materials prepared by the sol-gel method', Electrochemistry and Solid-State Letters, vol. 7, no. 12, pp. 503-506.
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A series of LiMxFe1-xPO4 (M = Mg,Zr,Ti) phosphates were synthesized via a sol-gel method. Transmission electron microscopy observations show that LiMxFe1-xPO4 particles consist of nanosize crystals, ranging from 40 to 150 nm. High-resolution TEM analysis reveals that a layer of amorphous carbon was coated on the surface of the LiMxFe1-xPO4 particles, which substantially increases the electronic conductivity of LiMxFe1-xPO4 electrodes. The doped LiMxFe1-xPO4 powders are phase pure. Near full capacity (170 mAh/g) was achieved at the C/8 rate at room temperature for LiMxFe1-xPO4 electrodes. The doped LiMxFe1-xPO4 electrodes demonstrated better electrochemical performance than that of undoped LiFePO4 at high rate.
Wang, G., Yao, J. & Liu, H. 2004, 'Characterisation of nanocrystalline Si-MCMB composite anode materials', Electrochemistry and Solid-State Letters, vol. 7, no. 8, pp. 250-253.
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Nanocrystalline Si-mesocarbon microbeads (MCMB) composite anode materials were prepared by ballmilling. Scanning electron microscopic observation showed that the spherical shape of MCMB particles can be retained via moderate ballmilling. Ballmilling conditions have an impact on the capacity and cyclability of nanocrystalline Si-MCMB composites. The optimized Si-MCMB composite anode demonstrated a reversible capacity of 1066 mAh/g with good cyclability. A reaction model has been proposed to explain the reaction mechanisms of lithium insertion and extraction in the Si-MCMB electrode.
Wang, G., Bewlay, S., Lindsay, M., Konstantinov, K., Guo, Z.P., Yao, J., Liu, H.K. & Dou, S.X. 2004, 'Energy storage materials for lithium-ion batteries', Materials forum, vol. 27, pp. 33-44.
Lindsay, M.J., Wang, G. & Liu, H.K. 2003, 'Al-based anode materials for Li-ion batteries', Journal of Power Sources, vol. 119-121, pp. 84-87.
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Yao, J., Wang, G., Ahn, J.h., Liu, H. & Dou, S.X. 2003, 'Electrochemical studies of graphitized mesocarbon microbeads as an anode in lithium-ion cells', Journal of Power Sources, vol. 114, pp. 292-297.
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Wang, G., Bradhurst, D.H., Dou, S.X. & Liu, R.S. 2003, 'LiTi2(PO4)3 with NASICON-type structure as lithium-storage materials', Journal of Power Sources, vol. 124, pp. 231-236.
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Wang, G., Bewlay, S., Yao, J., Chen, Y., Guo, Z.P., Liu, H.K. & Dou, S.X. 2003, 'Multiple-ion-doped lithium nickel oxides as cathode materials for lithium-ion batteries', Journal of Power Sources, vol. 119-121, pp. 189-194.
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Ahn, J.h., Wang, G., Liu, H.K. & Dou, S.X. 2003, 'Nanoparticle-dispersed PEO polymer electrolytes for Li batteries', Journal of Power Sources, vol. 119-121, pp. 422-426.
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Wang, G., Ahn, J.h., Yao, J., Lindsay, M., Liu, H.K. & Dou, S.X. 2003, 'Preparation and characterization of carbon nanotubes for energy storage', Journal of Power Sources, vol. 119-121, pp. 16-23.
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Guo, Z.P., Konstantinov, K., Wang, G., Liu, H.K. & Dou, S.X. 2003, 'Preparation of orthorhombic LiMnO2 material via the sol++gel process', Journal of Power Sources, vol. 119-121, pp. 221-225.
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Guo, Z.P., Zhong, S., Wang, G., Liu, H.K. & Dou, S.X. 2003, 'Structure and electrochemical characteristics of LiMn0.7M0.3O2 (M=Ti, V, Zn, Mo, Co, Mg, Cr)', Journal Of Alloys And Compounds, vol. 348, pp. 231-235.
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Konstantinov, K., Wang, G., Yao, J., Liu, H.K. & Dou, S.X. 2003, 'Stoichiometry-controlled high-performance LiCoO2 electrode materials prepared by a spray solution technique', Journal of Power Sources, vol. 119-121, pp. 195-200.
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Chen, Y., Wang, G., Konstantinov, K., Liu, H.K. & Dou, S.X. 2003, 'Synthesis and characterization of LiCoxMnyNi1-x-yO2 as a cathode material for secondary lithium batteries', Journal of Power Sources, vol. 119-121, pp. 184-188.
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Ahn, J.h., Wang, G., Yao, J., Liu, H.K. & Dou, S.X. 2003, 'Tin-based composite materials as anode materials for Li-ion batteries', Journal of Power Sources, vol. 119-121, pp. 45-49.
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Konstantinov, K., Wang, J., Bewlay, S., Wang, G., Liu, H.K., Dou, S.X. & Ahn, J.h. 2003, 'Spray pyrolysis technique for fabrication of nano-sized spherical agglomerated oxide powders for batteries', Journal of Metastable and Nanocrystalline Materials, vol. 15-16, pp. 325-330.
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Application of the spray pyrolysis technique to in-situ fabrication ofnano-featured spherical oxide matcrials has been explored in this paper. Two different nano-featured single-phase materials for battery use, namely LiCOOl and PbO, were successfully prepared in spherical form. The diameters of the spheres are in the range of a few microns, generally 1-10 microns, and there is a narrow Gaussian particle size distribution. The diameter size can be controlled by the size of the spray nozzle and the concentration of the solution. The spherical agglomerates appear to consist of nano-particles, each one with dimensions of 20-50 run. The specific surface areas of these materials are several times higher than for the corresponding commercially available powders. The stoichiometry of the LiCoO, powders thus obtained was controlled by the ICP tcchnique in order to achieve the dcsired Li:Co = 1:1 ratio in the sintered materials. The materials prepared by the spray pyrolysis technique appear to be promising for battery use.
Chen, Y., Wang, G., Konstantinov, K., Ahn, J.h., Liu, H.K. & Dou, S.X. 2003, 'Studies of the electrochemical properties of nanosize Co3O4 oxide as an anode material for lithium-ion batteries', Journal of Metastable and Nanocrystalline Materials, vol. 15-16, pp. 625-628.
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Nanosize cobalt oxides (CoJ0 4) were synthesized by chemical decomposition of cobalt octacarbonyl (Co,(CO)g) in toluene at the low temperature of 130C. The crystallinity and microstructure were characterized using X-ray diffraction and scanning electron microscopy. The electrochemical properties of electrodes made of nanosized COJ04 particles were tested in Li-ion cells. The nanosized COJ04 electrode material demonstrates a stable reversible lithium storage capacity of about 460 mAhlg over 30 cycles.
Zhong, S., Howes, A., Wang, G., Bradhurst, D.H., Wang, C., Dou, S.X. & Liu, H.K. 2002, 'A new process for fabrication of metal-hydride electrodes for nickel-metal hydride batteries', Journal Of Alloys And Compounds, vol. 330-332, pp. 760-765.
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Guo, Z.P., Wang, G., Konstantinov, K., Liu, H.K. & Dou, S.X. 2002, 'Electrochemical properties of orthorhombic LiMnO prepared by one-step 2 middle-temperature solid-state reaction', Journal Of Alloys And Compounds, vol. 346, pp. 255-259.
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Wang, G., Chen, Y., Konstantinov, K., Lindsay, M., Liu, H. & Dou, S.X. 2002, 'Investigation of cobalt oxides as anode materials for Li-ion batteries', Journal of Power Sources, vol. 109, pp. 142-147.
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Wang, G., Chen, Y., Konstantinov, K., Yao, J., Ahn, J.h., Liu, H.K. & Dou, S.X. 2002, 'Nanosize cobalt oxides as anode materials for lithium-ion batteries', Journal Of Alloys And Compounds, vol. 340, pp. L5-L10.
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Guo, Z.P., Wang, G., Liu, H.K. & Dou, S.X. 2002, 'Structure and electrochemistry of LiCrxMn1-xO2 cathode for lithium-ion batteries', Solid State Ionics, vol. 148, pp. 359-366.
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Guo, Z.P., Zhong, S., Wang, G., Walter, G., Liu, H. & Dou, S.X. 2002, 'Synthesis of layered-structure LiMn1-xCrxO2 by the Pechini method and characterization as a cathode for rechargeable Li/LiMnO2 cells', Journal of Electrochemical Society, vol. 149, no. 6, pp. 792-795.
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LiMn1-xCrxO2 compounds with an alpha-NaFeO2 layer-type crystal structure have been prepared by the Pechini method. The effects of ethylene glycol (EG) content and calcination temperature on powder characteristics and electrochemical performance are evaluated. It is found that the homogeneity of the powder is increased by increasing the molar ratio of EG to citric acid, and a trace of MnO can be detected in the powder calcined below 800degreesC for 4 h. Compared with the ss-LiMn1-xCrxO2 powder (made by the solid-state reaction), the p-LiMn1-xCrxO2 compound (made by the Pechini method) yielded higher specific capacity for both charge and discharge, and the rate capability has been improved due to the smaller particle size and good homogeneity. The evolution of discharge curves with cycling shows that less additional spinel-type tetrahedral sites for Li formed during cycling of the p-LiMn1-xCrxO2 compound.
Ahn, J.h., Kim, Y.J., Wang, G., Lindsay, M., Liu, H. & Dou, S.X. 2002, 'Lithium storage properties of ball milled Ni-57 mass% Sn alloy', Materials Transactions, vol. 43, no. 1, pp. 63-66.
Ni-57 mass%Sn alloy has been examined as a new anode material for Li-ion batteries. Li ions can reversibly intercalate and de-intercalate in this alloy. Ball milled nanocrystalline and subsequently annealed microcrystalline Ni-57 mass%Sn alloy showed very high initial discharge capacity. The cell capacity decayed rapidly after the first discharge. The capacity of the ball milled Ni-57 mass%Sn alloy faded continuously on cycling, while the annealed alloy exhibited good cyclic properties. Therefore, Ni-57 mass%Sn alloy is an attractive intercalation host for Li.
Wang, G., Yao, J., Lindsay, M., Chen, Y., Liu, H.K., Ryu, S.H. & Ahn, J.h. 2002, 'Li storage properties of carbon nanotubes prepared by chemical vapour deposition', Journal of Metastable and Nanocrystalline Materials, vol. 12, p. 18.
Wang, J., Zhong, S., Wang, G., Bradhurst, D.H., Ionescu, M., Liu, H. & Dou, S.X. 2001, 'Electrochemical performance of nanocrystalline lead oxide in VRLA batteries', Journal Of Alloys And Compounds, vol. 327, pp. 141-145.
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Wang, G., Ahn, J.h., Lindsay, M.J., Sun, L., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 2001, 'Graphite-tin composites as anode materials for lithium-ion batteries', Journal of Power Sources, vol. 97-98, pp. 211-215.
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Wang, G., Lindsay, M.J., Ionescu, M., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 2001, 'Physical and electrochemical characterization of LiNi0.8Co0.2O2 thin-film electrodes deposited by laser ablation', Journal of Power Sources, vol. 97-98, pp. 298-302.
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Ahn, J.h., Wang, G., Lindsay, M., Dou, S.X. & Liu, H.K. 2001, 'Mechanically milled nanocrystalline Ni3Sn4 and FeSi2 alloys as an anode material for Li-ion batteries', Journal of Metastable and Nanocrystalline Materials, vol. 10, pp. 595-602.
Wang, G., Sun, L., Bradhurst, D.H., Zhong, S., Dou, S.X. & Liu, H. 2000, 'Innovative nanosize lithium storage alloys with silica as active centre', Journal of Power Sources, vol. 88, pp. 278-281.
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Wang, G., Sun, L., Bradhurst, D.H., Dou, S.X. & Liu, R.S. 2000, 'Lithium storage properties of nanocrystalline eta-Cu6 Sn5 alloys prepared by ball-milling', Journal Of Alloys And Compounds, vol. 299, pp. L12-L15.
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Wang, G., Sun, L., Bradhurst, D.H., Zhong, S., Dou, S.X. & Liu, H.K. 2000, 'Nanocrystalline NiSi alloy as an anode material for lithium-ion batteries', Journal Of Alloys And Compounds, vol. 306, pp. 249-252.
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Wang, G., Horvat, J., Bradhurst, D.H., Liu, H.K. & Dou, S.X. 2000, 'Structural, physical and electrochemical characterisation of LiNixCo1-xO2 solid solutions', Journal of Power Sources, vol. 85, pp. 279-283.
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Wang, G., Yao, P., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 2000, 'Structure characteristics and lithium ionic conductivity of La(0.57++2x/3)SrxLi0.3TiO3 perovskites', Journal of Materials Science, vol. 35, pp. 4289-4291.
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Sun, L., Wang, G., Liu, H., Bradhurst, D.H. & Dou, S.X. 2000, 'Synthesis of nonstoichiometric amorphous Mg-based alloy electrodes by mechanical milling', Electrochemistry and Solid-State Letters, vol. 3, no. 3, pp. 121-124.
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Nonstoichiometric amorphous Mg-Ni and Mg-Ni-V alloys were synthesized by mechanical milling the crystalline Mg2Ni alloy with Ni and/or V powders. All the nonstoichiometric amorphous Mg-based alloys result in Mg-based alloy electrodes with very high discharge capacities by comparison with crystalline Mg2Ni alloys. The results indicate that nonstoichiometric amorphous Mg-based alloys can be obtained either by increasing the Ni content, adding a range of other elements, or both, using a mechanical milling method. The nonstoichiometric Mg-based alloy electrodes studied have shown improved initial discharge capacities compared with the stoichiometric amorphous MgNi alloy. These results describe a method of achieving better Mg-based alloy electrodes with high discharge capacities and improved cycle life. The method enables a larger composition range to be achieved with a range of vanadium additions.
Zhong, S., Wang, G., Wang, J., Bradhurst, D.H., Ionescu, M., Dou, S.X. & Liu, H.K. 2000, 'An anode material with Perovskite structure for rechargeable Li-ion batteries', Journal of New Materials for Electrochemical Systems, vol. 3, no. 1, pp. 9-12.
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A conductive ceramic, barium metaplumbate (BaPbO3), has been synthesized by solid-state reactions for use as an anode in lithium-ion batteries. The electrochemical characteristics of the electrode were tested in ethylene and diethyl carbonate (EC-DEC) solutions of LiPF6 versus Li metal in rest cells. During cycling, the material showed voltage plateaus between 0.2 V and 0.6 V versus Li, demonstrated a gravimetric discharge capacity of about 110 mAh g(-1) and a volumetric capacity of 960 mAh cm(-3). Two phases, BaPbO3 and PbO, were found in compositions containing excess PbO. The free PbO in the fired bodies was found in the experiment to react with the lithium and form a new compound probably a Pb-Li alloy, which was unstable and brought an intensive capacity fading. A single phase, BaPbO3, which was obtained by increasing the calcining temperature and the partial pressure of O-2 in the ambient air presented an improved capacity and a stable pervoskite structure. The results from cyclic voltammograms suggest that the insertion and de-insertion of Li ions proceed in the voltage range from 0.01 to 1.2 V versus Li/ Li+.
Wang, G., Yao, J., Zhong, S., Bradhurst, D.H., Dou, S.X. & Liu, H. 1999, 'Electrochemical study on orthorhombic LiMnO2 as cathode in rechargeable lithium batteries', Journal of Applied Electrochemistry, vol. 29, pp. 1423-1426.
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Wang, G., Bradhurst, D.H., Liu, H. & Dou, S.X. 1999, 'Improvement of electrochemical properties of the spinel LiMn O 2 4 using a Cr dopant effect', Solid State Ionics, vol. 120, pp. 95-101.
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Wang, G., Zhong, S., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 1999, 'LiAl Ni O solid solutions as cathodic materials for rechargeable d 12d 2 lithium batteries', Solid State Ionics, vol. 116, pp. 271-277.
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Wang, G., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 1999, 'Spinel Li[Li1/3Ti5/3)O4 as an anode material for lithium ion batteries', Journal of Power Sources, vol. 83, pp. 156-161.
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Wang, G., Yao, P., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 1999, 'Structure characterisation and lithium insertion in La0.33NbO3 perovskite', Solid State Ionics, vol. 124, pp. 37-43.
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Sun, L., Wang, G., Liu, H., Bradhurst, D.H. & Dou, S.X. 1999, 'The effect of Co addition on Mg2Ni alloy hydride electrodes prepared by sintering and followed by ball milling', Journal of New Materials for Electrochemical Systems, vol. 2, no. 4, pp. 211-214.
In this paper, we have investigated the effect of Co addition on Mg2Ni alloy hydride electrodes prepared in two different ways: 1) by ball milling (BM) the Mg2Ni alloy prepared by sintering a mixture of Mg and Ni powders with Ni or Co powders; and 2) by ball milling Mg2Ni0.6Co0.4 alloy prepared by sintering a mixture of Mg, Ni and Co powders with Ni powders. The results show that the sintered Mg2Ni alloy ball-milled with Ni or Co powders can achieve an amorphous structure. The Mg2Ni0.6Co0.4 alloy ball-milled with Ni powders for 60 hours can also obtain an amorphous structure. The formation of an amorphous alloy structure is a key factor in order to obtain high initial discharge capacities. The addition of Co to amorphous Mg2Ni alloys can increase their crystallisation temperatures and alter the initial discharge capacity buy the Co addition has no effect on their cycle life. Increasing the ball milling time is an effective method of obtaining further improvements in the initial discharge capacity of Mg-based alloys.
Wang, G., Sun, L., Zhong, S., Yao, P., Bradhurst, D.H., Dou, S.X. & Liu, H. 1999, 'Electrochemical performance of orthorhombic LiMnO2 as cathode in lithium ion batteries', Journal of New Materials for Electrochemical Systems, vol. 2, no. 4, pp. 215-219.
Two types of orthorhombic LiMnO2 of different stoichiometry were synthesised using a solid-state reaction at high temperature. Their electrochemical performance is dependent on the synthesis conditions. It was found that a few charge/discharge cycles were necessary to activate the electrochemical reactivity of o-LiMnO2, which is related to the transformation from the orthorhombic phase to a spinel-like phase. AC impedance spectroscopy confirmed this phenomenon, which showed that initially the charge-transfer resistance (R-CT) for the o-LiMnO2 electrode is much larger than that for the electrode in the charged state. A maximum discharge capacity of 180-190 mAh/g was achieved for the o-LiMnO2 electrode.
Wang, G., Zhong, S., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 1999, 'Rare earth element (La) doped LiNiVO4 as a cathode material for secondary Lithium ion cells', Materials Science Forum, vol. 315-317, pp. 105-112.
Wang, G., Zhong, S., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 1998, 'Secondary aqueous lithium-ion batteries with spinel anodes and cathodes', Journal of Power Sources, vol. 74, pp. 198-201.
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Wang, G., Zhong, S., Bradhurst, D.H., Dou, S.X. & Liu, H.K. 1998, 'Synthesis and characterization of LiNiO2 compounds as cathodes for rechargeable lithium batteries', Journal of Power Sources, vol. 76, pp. 141-146.
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