Shuqin Song

Novel Hierarchically Porous Carbon Materials Obtained from Natural Biopolymer as Host Matrixes for Lithium-Sulfur Battery Applications

Novel hierarchically porous carbon materials with very high surface areas, large pore volumes and high electron conductivities were prepared from silk cocoon by carbonization with KOH activation. The prepared novel porous carbon-encapsulated sulfur composites were fabricated by a simple melting process and used as cathodes for lithium sulfur batteries. Because of the large surface area and hierarchically porous structure of the carbon material, soluble polysulfide intermediates can be trapped within the cathode and the volume expansion can be alleviated effectively. Moreover, the electron transport properties of the carbon materials can provide an electron conductive network and promote the utilization rate of sulfur in cathode. The prepared carbon-sulfur composite exhibited a high specific capacity and excellent cycle stability. The results show a high initial discharge capacity of 1443 mAh g(-1) and retain 804 mAh g(-1) after 80 discharge/charge cycles at a rate of 0.5 C. A Coulombic efficiency retained up to 92% after 80 cycles. The prepared hierarchically porous carbon materials were proven to be an effective host matrix for sulfur encapsulation to improve the sulfur utilization rate and restrain the dissolution of polysulfides into lithium-sulfur battery electrolytes.

Sulfur-rich polymeric materials with semi-interpenetrating network structure as a novel lithium–sulfur cathode

Novel polymeric materials with a very high content of sulfur were successfully synthesized via a facile copolymerization of elemental sulfur with 1,3-diethynylbenzene (DEB). For the as-prepared sulfur-rich polymeric materials (C–S copolymer), diynes or polydiynes are chemically cross-linked with a large amount of polymeric sulfur to form a cage-like semi-interpenetrating network (semi-IPN) structure. Due to the strong chemical interaction of sulfur with the carbon framework and the unique cage-like structure in C–S copolymers, the dissolution and diffusion of polysulfides out of the cathode is effectively suppressed through chemical and physical means. As a result, the sulfur-rich C–S polymeric materials with semi-IPN structure exhibit excellent cycling stability and high coulombic efficiency. The initial discharge capacity is 1143 mA h g−1 at a 0.1 C rate. The capacity still remains at 70% even after about 500 cycles at a high current density of 1 C. In addition, a high coulombic efficiency of over 99% is obtained during the entire range of cycling.

Nanochain-structured mesoporous tungsten carbide and its superior electrocatalysis

A unique nanochain-structured mesoporous tungsten carbide (m-NCTC) was synthesized through a simple combined hydrothermal reaction–post heat-treatment approach. When loaded with Pt, the nanostructure (Pt/m-NCTC), as a catalyst, demonstrates high unit mass electroactivity (323 A (g Pt)−1) and high resistance to CO poisoning for methanol oxidation, and is much superior to Pt/C, one of the known excellent electrocatalysts. Its high reaction activity and strong poison-resistivity is very likely due to the unique mesoporous nanochain structure and high specific surface area (113 m2 g−1). This work provides a universal and economic method to synthesize novel mesoporous structured materials and provides scientific insight of mesoporous structured electrocatalysis, thus leading to various important applications as a catalyst in fuel cells, solar cells, sensors and in organic synthesis reactions.

Thermodynamic and Kinetic Considerations for Ethanol Electrooxidation in Direct Ethanol Fuel Cells

Abstract Thermodynamic and kinetic considerations for the ethanol electrooxidation in a proton exchange membrane fuel cell (PEMFC) were discussed. Theoretical calculations show that direct ethanol fuel cells (DEFCs) exhibit better exergic efficiency than ethanol reforming PEMFC. The thermodynamic analysis show that when temperature is lower than 100°C, the conversion of ethanol steam reforming is less than 14% for ethanol complete oxidation. The kinetic study shows that PtSn/C anodes have a relatively high ac-tivity for ethanol electrooxidation, but such activity is not high enough for ethanol complete electrooxidation. The thermodynamic and kinetic analyses suggest that the cell temperature is one of the key factors for the DEFC development.

Nanopores array of ordered mesoporous carbons determine Pt's activity towards alcohol electrooxidation

A nanopores array in ordered mesoporous materials matters significantly to the reactant molecules arriving at the active catalytic sites in the interior of the nanostructure. However, how this effect works in the case of electrocatalysis needs investigating. We present that the nanopores array of carbon supports plays a significant role in determining Pts accessibility and electroactivity. The ordered mesoporous carbons with interconnected pore channels (CMK-3) provide Pt nanoparticles with more than one order of magnitude superior Pt utilization efficiency and alcohol electrooxidation activity to those with isolated pore channels by carbon wall (FDU-15). This becomes more prominent in the case of the electrooxidation of isopropanol with a bigger molecular size and lower polarization. These findings indicate the significant role of nanoarchitectures in Pts accessibility and electroactivity. It is possible to extend this concept to the other fine chemistry typical of surface activity and facile mass transport of molecules.

A Temperature-Programmed-Reduction Study on La1−xSrxCrO3 and Surface-Ruthenium-Modified La1−xSrxCrO3

A series of La1-xSrxCrO3 (0 <= x <= 0.3) composite oxides were prepared by a modified citric method. These perovskite oxides were further modified with Ru through impregnation. X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and temperature-programmed-reduction (TPR) techniques were adopted to investigate the properties of both the as-prepared perovskite oxides and the surface-Ru-modified La1-xSrxCrO3 samples. XPS results indicated the existence of Cr6+ ions in the fresh samples and transformed to Cr3+, after reduction. The hydrogen consumed by these perovskite oxides during TPR increased with the Sr doping, which was more than twice of the theoretical value according to Kroger-Vink notation. The reduction temperature of Cr ions of Ru/La1-xSrxCrO3 significantly decreased with an increase of the Ru loading. A small reduction peak at similar to 540 degrees C, which was not shifted by increasing Ru loadings, was observed and could be ascribed to the reduction of trace chromate phases. Oil all TPR profiles of the three doped perovskites with unity of the A-site and B-site ratio, the reduction of Ru species could not be observed at low Ru loadings (0.05% and 0.1%). A reduction peak from RuO2 Particles appeared at temperatures prior to the perovskite reduction on the TPR plots of modified La0.9Sr0.1CrO3 and La0.8Sr0.2CrO3 with high Ru loading (0.5% and 1%, respectively), but it did not occur with the Ru modified La0.7Sr0.3CrO3 in the investigated Ru loading range. The TPR results of the Ru modified La0.8Sr0.2Cr0.95O3 depicted that some Ru ions might be stabilized due to the incorporation into the oxide.

A novel lithium–sulfur battery cathode from butadiene rubber-caged sulfur-rich polymeric composites

Novel sulfur-rich polymeric materials were readily prepared via facile solution vulcanization of the commercial butadiene rubber (BR) and sulfur element, and were investigated as cathode materials for lithium–sulfur batteries. During the solution vulcanization procedure, the double bonds (CC) in butadiene rubber are chemically cross-linked with sulfur. Moreover, the sulfur canalso self-polymerize into polymeric sulfur with long molecular chain. The polymeric sulfur chains penetrate into the cross-linked BR network to form a unique semi-internal penetration network (semi-IPN) confinement structure, which can effectively alleviate the dissolution and diffusion of intermediate polysulfide into electrolytes. Meanwhile, the obtained sulfur-rich polymeric composites have high sulfur contents even over 90%. As a result, the as-prepared sulfur-rich polymeric composites (BR-SPC) with network confine caged structure exhibit excellent cycling stability and high coulombic efficiency. An initial discharge specific capacity of 811 mA h g−1 is reached, and retains 671 mA h g−1 after 50 cycles at 0.1 C. The capacity retention rate and coulombic efficiency are 83%, 100%, respectively. Additionally, Super P (carbon black) was added in situ before vulcanization to increase the conductivity of BR-SPC composites. The BR-SPC composite containing Super P (BR-SPC-SP) reveals higher capacity retention of 85% over 50 cycles at 0.5 C than the BR-SPC composite without Super P.

Investigation of the Reaction of Ethanol-Steam Mixtures in a YSZ Electrochemical Reactor Operated in a Fuel Cell Mode

In the present investigation ethanol-water mixtures were directly fed to a yttria stabilized zirconia (YSZ) electrochemical reactor operated in a fuel cell mode and the preliminary results are presented and discussed. Poly crystalline films of platinum (Pt) and silver (Ag) were, respectively, tested as anode catalysts in a wide range of experimental conditions while the cathode was exposed to the atmospheric air. The single direct ethanol solid oxide fuel cell (DE-SOFC) tests were performed in order to investigate separately Pt and Ags activities towards ethanol steam reaction and fuel cell performance (Pt-DESOFC and Ag-DESOFC). In both cases the products were on-line analyzed by a mass spectrograph, a gas chromatograph and a series of gas analysers under fuel cell mode of operation. The results showed that even at high temperature values (>750°C) the main products were CH 3 CHO, CH 4 , CO, H 2 , and CO 2 . Furthermore, as expected the single DESOFC performance was improved as the temperature increased. However, a relatively poor fuel cell performance has been obtained in both cases, which could be attributed to the following reasons: the relatively low (for YSZ electrolyte) operation temperature, the presence of homogeneous reactions, and the cell configuration.