Chusheng Chen

Enhancing the Oxygen Permeation Rate of Zr0.84Y0.16O1.92 - La0.8Sr0.2Cr0.5Fe0.5O3-δ Dual-Phase Hollow Fiber Membrane by Coating with Ce0.8Sm0.2O1.9 Nanoparticles

Zr0.84Y0.16O1.92-La0.8Sr0.2Cr0.5Fe0.5O3-δ (YSZ-LSCrF) dual-phase composite hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The shell surface of the hollow fiber membrane was modified with Ce0.8Sm0.2O1.9 (SDC) via a drop-coating method. As the rate of oxygen permeation of the unmodified membrane is partly controlled by the surface exchange kinetics, coating of a porous layer of SDC on the shell side (oxygen reduction side) of the hollow fiber membrane was found to improve its oxygen permeability. Rate enhancements up to 113 and 48% were observed, yielding a maximum oxygen flux of 0.32 and 4.53 mL min(-1) cm(-2) under air/helium and air/CO gradients at 950 °C, respectively. Excess coating of SDC was found to induce significant gas phase transport limitations and hence lower the rate of oxygen permeation. A model was proposed to calculate the length of triple phase boundaries (TPBs) for the coated dual-phase composite membrane and to explain the effect of coating on the oxygen permeability.

Phase composition, oxidation state and electrical conductivity of SrFe1.5−xCoxOy

Mixed ionic and electronic conducting oxides SrFe 1.5-x Co x O y (x=0-0.6) were investigated. In the layered Sr 4 (Fe,Co) 6 O 13-δ phase dominant region (x<0.375), the average valence of the transition metals (Fe,Co) determined by iodometric titration decreases monotonically with increasing cobalt content and varies slightly with temperature. In the multiphase region (x≥0.375), the valence changes significantly with temperature. The electrical conductivity increases with increasing cobalt content. Unusual changes in electrical conductivity were observed at ∼900 °C in the multiphase region, which may be associated with the conversion of the contained perovskite phase into the layered phase.

Highly Porous Spongelike Ceramic Films with Bimodal Pore Structure Prepared by Electrostatic Spray Deposition Technique

With a high feeding rate of the precursor solution, highly porous spongelike lithium–cobalt–oxide films with bimodal pore structure and porosity over 90% were fabricated at 235°C by the electrostatic spray deposition (ESD) technique. The metal acetates were used as the precursors dissolved in a mixed solvent of ethanol and butyl carbitol. Scanning electron microscopy (SEM) and X–ray diffraction were used to analyze the structure of the as–deposited films. The growth rate was found to be 7.8 μm/h and 0.24 mg/(cm2 h). At a relatively long deposition time, this bimodal porous structure may evolve into a porous columnar structure. Other morphologies such as flattened reticular structure and rather dense structure can be obtained at deposition temperatures between 270 and 320°C.

Spinel MgAl2O4 modification on LiCoO2 cathode materials with the combined advantages of MgO and Al2O3 modifications for high-voltage lithium-ion batteries

In order to improve the electrochemical performance of LiCoO2 cathode in a high-voltage range of 3.0–4.5 V, spinel MgAl2O4 has been modified on the surface of LiCoO2 particle by a facile high-temperature solid state reaction. The structure and morphology of the MgAl2O4-modified LiCoO2 are investigated in comparison with the pristine, Al2O3-modified and MgO-modified LiCoO2. The MgAl2O4 modification is highly conformal and uniform just similar as the Al2O3 modification, while the MgO modification is not uniform. In terms of electrochemical performance as a high-voltage cathode material, the MgAl2O4-modified LiCoO2 delivers an initial discharge capacity of 184 mA h g−1 between 3.0 V and 4.5 V at 0.1C (1C-rate = 160 mA g−1) and a capacity retention of 96.8% after 70 cycles at 1C rate. There is a significant improvement on high-voltage cycling stability for the MgAl2O4-modified LiCoO2 since the capacity retention of the pristine LiCoO2 is only 38.7% after 70 cycles. Moreover, the MgAl2O4-modified LiCoO2 exhibits an enhanced rate capability. Compared with the Al2O3 modification and the MgO modification, spinel MgAl2O4 modification has the combined advantages of Al2O3 and MgO modifications on improving the electrochemical performance of the LiCoO2 cathode for high-voltage applications. The modified spinel MgAl2O4 layer can effectively protect the charged Li1−xCoO2 cathode from structural collapse and impede the oxidation decomposition of the electrolyte for the high-voltage application of LiCoO2.

Shape‐Dependent Activity of Ceria for Hydrogen Electro‐Oxidation in Reduced‐Temperature Solid Oxide Fuel Cells

Single crystalline ceria nanooctahedra, nanocubes, and nanorods are hydrothermally synthesized, colloidally impregnated into the porous La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) scaffolds, and electrochemically evaluated as the anode catalysts for reduced temperature solid oxide fuel cells (SOFCs). Well-defined surface terminations are confirmed by the high-resolution transmission electron microscopy--(111) for nanooctahedra, (100) for nanocubes, and both (110) and (100) for nanorods. Temperature-programmed reduction in H2 shows the highest reducibility for nanorods, followed sequentially by nanocubes and nanooctahedra. Measurements of the anode polarization resistances and the fuel cell power densities reveal different orders of activity of ceria nanocrystals at high and low temperatures for hydrogen electro-oxidation, i.e., nanorods > nanocubes > nanooctahedra at T ≤ 450 °C and nanooctahedra > nanorods > nanocubes at T ≥ 500 °C. Such shape-dependent activities of these ceria nanocrystals have been correlated to their difference in the local structure distortions and thus in the reducibility. These findings will open up a new strategy for design of advanced catalysts for reduced-temperature SOFCs by elaborately engineering the shape of nanocrystals and thus selectively exposing the crystal facets.