Chemical reactivity of perovskite oxide SOFC cathodes and yttria stabilized zirconia

Abstract

The chemical reactivity of perovskite oxide SOFC cathodes and yttria stabilized zirconia (YSZ) solid electrolyte was studied. The perovskite oxides that were examined were La 1− x Sr x Co 0.2Mn 0.8O 3− d , La 1− x Sr x Co 0.2Fe 0.8O 3− d and La 1− x Ca x Co 0.2Fe 0.8O 3− d (0≤ x≤0.5), as well as, the A-site deficient oxides La 0.6− z Sr 0.4Co 0.2Fe 0.8O 3− d , La 0.6Sr 0.4− z Co 0.2Fe 0.8O 3− d and (La 0.6Sr 0.4) 1− z Co 0.2Fe 0.8O 3− d (0≤ z≤0.2). Equimolar perovskite/YSZ powder mixtures were prepared and annealed at 1100°C for 120 h. X-ray diffraction analysis was conducted to identify any reaction products. Si-standard was used as an internal standard for d-value calibration, during the determination of the lattice parameter of cubic YSZ. The main reaction products were La 2Zr 2O 7 for the undoped and lightly doped Fe-containing compositions and (Sr/Ca)ZrO 3 for the Sr/Ca doped compositions. Also, CoFe 2O 4 was formed in the case of the Fe-containing compositions and monoclinic zirconia for La 1− x Ca x Co 0.2Fe 0.8O 3− d with x=0.4, 0.5. A-site deficiency in La 0.6Sr 0.4Co 0.2Fe 0.8O 3− d -based perovskites reduced the amount of SrZrO 3 formed, only in the case of La 0.6Sr 0.4− z Co 0.2Fe 0.8O 3− d with 0≤ z≤0.2 and (La 0.6Sr 0.4) 1− z Co 0.2Fe 0.8O 3− d with z=0.2. The lattice parameter of YSZ exhibited a shift, corresponding to a lattice contraction, due to the diffusion of the transition metal cations from the perovskite into YSZ.