Sr-doped LaCrO3 anode for solid oxide fuel cells

A number of doped lanthanum chromite perovskites are considered as anode ma terials for solid oxide fuel cells with an yttria-stabilized zirconia (YSZ) electrolyte operating in hydrogen at 850 degreesC. The polarization resist ance is measured by impedance spectroscopy, and shown to depend significant ly on the type and amount of doping. In particular, the composition La0.8Sr 0.2Cr0.97V0.03O3 (LSCV) is examined in detail. Reactivity studies indicate the presence of secondary phases in LSCV. These phases are reactive toward YSZ, resulting in the formation of SrZrO3. The secondary phases may be read sorbed during prolonged calcination under reducing conditions. The polariza tion resistance is shown to increase severely over a few days, and to he re coverable by temporary oxidation. The time constant of the degradation is s hown not to match that of the changes in stoichiometry and conductivity dur ing reduction of the perovskite. Two rate limiting processes are generally observed. The low frequency process is suggested to relate to adsorption of hydrogen on the LSCV surface or a chemical reaction step. The high frequen cy process is suggested to relate to the LSCV/YSZ contact interface. LSCV d oes not exhibit significant catalytic activity toward steam reforming of me thane, and shows no sign of direct methane oxidation. (C) 2000 The Electroc hemical Society. S0013-4651(00)07-036-1. All rights reserved.