Catalytic properties of the perovskite oxide La0.75Sr0.25Cr0.5Fe0.5O3-δ 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-delta (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) Angstrom, b = 5.5339(4) Angstrom, c = 7.7646(8) Angstrom, and V = 236.01(5) Angstrom(3) 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 degreesC 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 degreesC when an equimolar mixture of CH4 and O-2 was introduced into the reactor. The partial or complete oxidation depends on both temperature and the pO(2)/pCH(4) 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% H-2/Ar and wet H-2 are about 1.79 and 1.15 Omega cm(2), respectively, at 850 degreesC. This was improved to 0.98 Omega cm(2) in wet H-2 when the operation temperature was increased to 900 degreesC, but this is still too high for a viable SOFC electrode system.