Aiyu Yan

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.

Low-Temperature Solid Oxide Fuel Cell with a La0.8Sr0.2MnO3-Modified Cathode/Electrolyte Interface

A low-temperature solid oxide fuel cell with a La0.8Sr0.2MnO3 (LSM) modified interface between the Ce0.9Gd0.1O1.95 (GDC) electrolyte and the Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF)-GDC composite cathode was fabricated and showed lower ohmic resistance, lower polarization resistance, and higher exchange current densities than the unmodified cell. The higher power densities on the LSM-modified cell than the unmodified BSCF cell, especially at lower temperatures, are attributed to an improved electrode/electrolyte contact through high-temperature sintering and an enhancement of catalytic activity through the mutual diffusion of elements between LSM and BSCF during firing of the BSCF cathode. (c) 2008 The Electrochemical Society.

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.