Evaluation and optimization of Bi_1-xSr_xFeO _3-δ perovskites as cathodes of solid oxide fuel cells

Lattice expansion behaviour, oxygen nonstoichiometry, mean iron oxidation state, electrical conductivity and interfacial polarization resistance of Bi_1-xSr_xFeO_3-δ were reported as a function of Sr-doping content for x = 0.3, 0.5 and 0.8. Among the series, Bi_0.5Sr_0.5FeO_3-δ (BSF5) demonstrates the optimum performance in terms of the lowest interfacial polarization resistance and the largest oxygen nonstoichiometry. It is demonstrated that the best microstructure and the lowest interfacial resistance can be obtained by firing BSF5 onto dense Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte at 1000°C. BSF5 exhibits good chemical compatibility with SDC; however, firing temperature above 1000 °C results in the formation of bismuth-deficient perovskite with inferior activity for oxygen reduction reaction. We also show that single-phase BSF5 cathode provides better electrode performance than its composite with SDC. This is due to the increased charge-transfer resistance upon adding SDC which have negligible electronic conductivity.