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H G (h + g)

Distribution by Scientific Domains
Polymers and Materials Science100%

Kinds of H G

  • ma h g
    		•

    Selected Abstracts

    Titanium Containing ,-MnO2 (TM) Hollow Spheres: One-Step Synthesis and Catalytic Activities in Li/Air Batteries and Oxidative Chemical Reactions

    ADVANCED FUNCTIONAL MATERIALS, Issue 19 2010
    Lei Jin
    Abstract Titanium containing ,-MnO2 octahedral molecular sieves having hollow sphere structures are successfully prepared for the first time using a one-step synthesis method. Titanium cations are used as structure-directing agents in the synthesis process. The assembly of the hollow spheres is carried out at the beginning of the process. Various techniques including XRD, N2 adsorption, SEM, EDX, RAMAN, TEM, XPS, and TGA are employed for the materials characterization. Ti is incorporated into the MnO2 framework in isolated sites, and TiO2 phases (anatase and rutile) are not observed. When introduced in medium-sized lithium-air batteries, the materials give very high specific capacity (up to 2.3 A h g,1). These materials are also catalytically tested in the oxidation of toluene with molecular oxygen at atmospheric pressure, showing significant oxidative catalytic activities in this difficult chemical reaction. [source]

    Topotactic Conversion Route to Mesoporous Quasi-Single-Crystalline Co3O4 Nanobelts with Optimizable Electrochemical Performance

    ADVANCED FUNCTIONAL MATERIALS, Issue 4 2010
    Li Tian
    Abstract The growth of mesoporous quasi-single-crystalline Co3O4 nanobelts by topotactic chemical transformation from , -Co(OH)2 nanobelts is realized. During the topotactic transformation process, the primary , -Co(OH)2 nanobelt frameworks can be preserved. The phases, crystal structures, morphologies, and growth behavior of both the precursory and resultant products are characterized by powder X-ray diffraction (XRD), electron microscopy,scanning electron (SEM) and transmission electron (TEM) microscopy, and selected area electron diffraction (SAED). Detailed investigation of the formation mechanism of the porous Co3O4 nanobelts indicates topotactic nucleation and oriented growth of textured spinel Co3O4 nanowalls (nanoparticles) inside the nanobelts. Co3O4 nanocrystals prefer [0001] epitaxial growth direction of hexagonal , -Co(OH)2 nanobelts due to the structural matching of [0001] , -Co(OH)2//[111] Co3O4. The surface-areas and pore sizes of the spinel Co3O4 products can be tuned through heat treatment of , -Co(OH)2 precursors at different temperatures. The galvanostatic cycling measurement of the Co3O4 products indicates that their charge,discharge performance can be optimized. In the voltage range of 0.0,3.0,V versus Li+/Li at 40,mA g,1, reversible capacities of a sample consisting of mesoporous quasi-single-crystalline Co3O4 nanobelts can reach up to 1400,mA h g,1, much larger than the theoretical capacity of bulk Co3O4 (892,mA h g,1). [source]

    A Novel Cathode Material with a Concentration-Gradient for High-Energy and Safe Lithium-Ion Batteries

    ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
    Yang-Kook Sun
    Abstract A high-energy functional cathode material with an average composition of Li[Ni0.72Co0.18Mn0.10]O2, mainly comprising a core material Li[Ni0.8Co0.2]O2 encapsulated completely within a stable manganese-rich concentration-gradient shell is successfully synthesized by a co-precipitation process. The Li[Ni0.72Co0.18Mn0.10]O2 with a concentration-gradient shell has a shell thickness of about 1,µm and an outer shell composition rich in manganese, Li[Ni0.55Co0.15Mn0.30]O2. The core material can deliver a very high capacity of over 200,mA h g,1, while the manganese-rich concentration-gradient shell improves the cycling and thermal stability of the material. These improvements are caused by a gradual and continuous increase of the stable tetravalent Mn in the concentration-gradient shell layer. The electrochemical and thermal properties of this cathode material are found to be far superior to those of the core Li[Ni0.8Co0.2]O2 material alone. Electron microscopy also reveals that the original crystal structure of this material remains intact after cycling. [source]

    Hard Macrocellular Silica Si(HIPE) Foams Templating Micro/Macroporous Carbonaceous Monoliths: Applications as Lithium Ion Battery Negative Electrodes and Electrochemical Capacitors

    ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
    Nicolas Brun
    Abstract By using Si(HIPEs) as hard, exotemplating matrices, interconnected macro-/microporous carbon monolith-type materials with a surface area of around 600,m2 g,1 are synthesized and shaped. The carbonaceous foams exhibit a conductivity of 20,S cm,1, addressed with excellent mechanical properties (Young's modulus of 0.2,GPa and toughness of 13,J g,1, when the carbon core is optimized). The above-mentioned specificities, combined with the fact that the external shape and size can be easily designed on demand, are of primary importance for applications. The functionality of these carbonaceous monoliths is tested as both an electrochemical capacitor and a lithium ion negative electrode. The electrochemical capacitors' voltage,current profiles exhibit a non-ideal rectangular response, confirming the double-layer behavior of the carbon studied, while the charge-discharge current profile of the electric double-layer capacitor is directly proportional to the scan where the current response during charge and discharge exhibits high reversibility. When acting as a lithium ion negative electrode, after initial irreversibility, a good cyclability is obtained, associated with a stable capacity of 200,mA h g,1 during the first 50 cycles at a reasonable current density (C/10). [source]

    Reduced Surfactant Uptake in Three Dimensional Assemblies of VOx Nanotubes Improves Reversible Li+ Intercalation and Charge Capacity

    ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009
    Colm O'Dwyer
    Abstract The relationship between the nanoscale structure of vanadium pentoxide nanotubes and their ability to accommodate Li+ during intercalation/deintercalation is explored. The nanotubes are synthesized using two different precursors through a surfactant-assisted templating method, resulting in standalone VOx (vanadium oxide) nanotubes and also "nano-urchin". Under highly reducing conditions, where the interlaminar uptake of primary alkylamines is maximized, standalone nanotubes exhibit near-perfect scrolled layers and long-range structural order even at the molecular level. Under less reducing conditions, the degree of amine uptake is reduced due to a lower density of V4+ sites and less V2O5 is functionalized with adsorbed alkylammonium cations. This is typical of the nano-urchin structure. High-resolution TEM studies revealed the unique observation of nanometer-scale nanocrystals of pristine unreacted V2O5 throughout the length of the nanotubes in the nano-urchin. Electrochemical intercalation studies revealed that the very well ordered xerogel-based nanotubes exhibit similar specific capacities (235,mA h g,1) to Na+ -exchange nanorolls of VOx (200,mA h g,1). By comparison, the theoretical maximum value is reported to be 240,mA h g,1. The VOTPP-based nanotubes of the nano-urchin 3D assemblies, however, exhibit useful charge capacities exceeding 437,mA h g,1, which is a considerable advance for VOx based nanomaterials and one of the highest known capacities for Li+ intercalated laminar vanadates. [source]

    Cross-Stacked Carbon Nanotube Sheets Uniformly Loaded with SnO2 Nanoparticles: A Novel Binder-Free and High-Capacity Anode Material for Lithium-Ion Batteries

    ADVANCED MATERIALS, Issue 22 2009
    Hao-Xu Zhang
    SnO2,carbon nanotube (CNT) composite sheets are synthesized using poly(vinylpyrrolidone) to uniformly load a monolayer of SnO2 nanoparticles onto the surfaces of CNTs and CNT bundles within cross-stacked CNT sheets. When they are used as high-capacity (over 850,mA h g,1) and binder-free anodes in rechargeable lithium-ion batteries, they exhibit good cycle performance, as shown in the lower portion of the figure. [source]