A comparative study of oxygen reduction reaction on Bi-and La-doped SrFeO_3-δ perovskite cathodes

In this work the oxygen reduction reaction on Bi_0.5 Sr _0.5 FeO_3-δ (BSF) and La_0.5 Sr _0.5 Fe O_3-δ (LSF) as cathodes for intermediate temperature solid oxide fuel cells (600-750°C) is compared in detail. Partial substitution of Sr in SrFe O3-δ with 50 mole % of Bi or La results in the distinct structural features which strongly impact its electrochemical characteristics due to the presence of a lone electron pair in Bi³⁺, which is not available in La³⁺. Cubic structure for BSF favours higher ionic conductivity and enhanced formation of oxygen vacancies relative to rhombohedral structure for LSF. Large oxygen nonstoichiometry for BSF, nevertheless, leads to the dominance of Fe³⁺ and subsequent low electronic conductivity relative to LSF. It was found that upon cathodic polarization, the oxygen vacancies are created on LSF which helps reducing its interfacial resistance afterward, which is not the case for BSF. Overall, BSF demonstrates good electrochemical performance which can be further optimized by enhancing its electronic conductivity.