Catalytic Properties of the Perovskite Oxide La0.75Sr0.25Cr0.5Fe0.5O3- in Relation to Its Potential as a Solid Oxide Fuel Cell Anode Material

Natural gas is an extremely attractive fuel for use in fuel cells. Steam-reforming and oxidation of methane are particularly important for the direct methane fuel cell. A perovskite-related material, La0.75Sr0.25Cr0.5Fe0.5O3- (LSCrF), has been synthesized, and its catalytic properties as a potential anode material for solid oxide fuel cells (SOFCs) have been examined. The material exhibits an overall orthorhombic structure with a = 5.4926(5) A, b = 5.5339(4) A, c = 7.7646(8) A, and V = 236.01(5) A3 according to the X-ray data. It is at its limit of stability under reducing SOFC anode conditions. An 11% conversion for methane steam-reforming was observed at 900 C when the steam-to-methane ratio was 1/1. A conversion of 68% for methane oxidation with a CO2 selectivity of 99% was achieved at 900 C when an equimolar mixture of CH4 and O2 was introduced into the reactor. The partial or complete oxidation depends on both temperature and the pO2/pCH4 ratio. Therefore, LSCrF is a good catalyst for methane-reforming and oxidation. LSCrF is a methane complete oxidation catalyst when close to oxygen stoichiometric and a methane partial oxidation catalyst when the oxygen vacancy content increases. The anode polarization resistances in wet 5% H2/Ar and wet H2 are about 1.79 and 1.15 (omega)cm2, respectively, at 850 C. This was improved to 0.98 (omega)cm2 in wet H2 when the operation temperature was increased to 900 C, but this is still too high for a viable SOFC electrode system.