A comparative study of SrCo_0.8Nb_0.2O_3-δ and SrCo_0.8Ta_0.2O_3-δ as low-temperature solid oxide fuel cell cathodes: Effect of non-geometry factors on the oxygen reduction reaction

The oxygen reduction reaction (ORR) activity of cathodes has to be improved to realize the low-temperature operation of solid-oxide fuel cells (SOFCs). Whilst geometric factors are conventionally accepted to influence the ORR activity of perovskite cathodes, other factors may also contribute and therefore need to be explored. Here, we substituted 20% niobium and tantalum which have similar ionic radii into strontium cobaltites to obtain the two perovskite oxides SrCo_0.8Nb_0.2O_3-δ (SCN20) and SrCo_0.8Ta_0.2O_3-δ (SCT20), respectively. Our study of the isostructural SCN20 and SCT20 allows geometric effects to be separated from other factors, and we observe better cathode performance of SCT20 cathode, which may be related to the lower electronegativity of Ta⁵⁺, thus resulting in higher oxygen surface exchange kinetics and diffusivity as compared with Nb⁵⁺.