Sr-doped LaCrO3 anode for solid oxide fuel cells

A number of doped lanthanum chromite perovskites are considered as anode materials for solid oxide fuel cells with an yttria-stabilized zirconia (YSZ) electrolyte operating in hydrogen at 850 degreesC. The polarization resistance is measured by impedance spectroscopy, and shown to depend significantly on the type and amount of doping. In particular, the composition La0.8Sr0.2Cr0.97V0.03O3 (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 readsorbed during prolonged calcination under reducing conditions. The polarization resistance is shown to increase severely over a few days, and to he recoverable by temporary oxidation. The time constant of the degradation is shown not to match that of the changes in stoichiometry and conductivity during 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 frequency process is suggested to relate to the LSCV/YSZ contact interface. LSCV does not exhibit significant catalytic activity toward steam reforming of methane, and shows no sign of direct methane oxidation. (C) 2000 The Electrochemical Society. S0013-4651(00)07-036-1. All rights reserved.