Utilization of an Isovalent Doping Strategy in Cobalt-Free Ferrites for Highly Active and Stable Solid Oxide Fuel Cell Cathodes

Cobalt-free ferrites are attracting tremendous spotlight as prospective solid oxide fuel cell cathode material nowadays owing to their good structural stability and great thermo-mechanical compatibility with electrolytes. Nevertheless, the oxygen reduction reaction (ORR) activity for cobalt-free ferrites is comparatively lower than that for cobalt-based cathodes. Hence, an isovalent doping strategy is an attractive option to significantly promote the ORR activity of cobalt-free ferrites. Herein, we systematically investigate the optimal Sr2+ concentration in cobalt-free Pr0.5Ba0.5–ySryFeO3−δ (PBSF series). The replacement of Ba2+ by Sr2+ is beneficial to decrease the thermal expansion coefficient. Moreover, the Pr0.5Ba0.2Sr0.3FeO3−δ material demonstrates the highest electrical conductivity and the lowest area-specific resistance (Rp, 0.027 Ω cm2, 700 °C) among the PBSF series. To elucidate the close relationship between the Rp value and the electrical conductivity in the PBSF series, distribution of relaxation time analysis and density functional theory calculations are utilized. Furthermore, outstanding cell operational durability is exhibited for 200 h.