Effect of calcium doping on the electrocatalytic activity of the Bi_{1- x} Ca _x FeO_{3- δ} oxygen electrode for solid oxide fuel cells

For solid oxide fuel cell (SOFC) applications, there remains a growing interest in developing efficient cathode catalysts. Herein, iron-based Ca-doped Bi_1-x Ca _x FeO_3-δ (BCFx, x = 0.1, 0.2, and 0.3) oxides are evaluated as potential cathode materials for SOFCs. The phase structure, thermal expansion behavior, electrical conductivity, and electrocatalytic properties for the oxygen reduction reaction (ORR) of the BCFx cathodes are systematically characterized. Among all compositions, the Bi_0.8Ca_0.2FeO_3-δ (BCF0.2) cathode exhibits the highest oxygen vacancy concentration and considerable electrocatalytic activity, demonstrating the lowest polarization resistance (0.11 Ω cm²) and largest exchange current density of 41.91 mA cm^-2 at 700 °C. The BCF0.2 cathode-based single cell delivers excellent output performance, yielding a maximum power density of 760 mW cm^-2 700 °C along with exceptional stability over a period of 60 h. This work highlights the Ca-doping strategy for enhancing electrocatalytic activity of the cathode electrocatalysts in SOFCs.