Enhanced oxygen reduction reaction through Ca and Co Co-doped YFeO₃ as cathode for protonic ceramic fuel cells

Protonic ceramic fuel cells offer the potential for environmentally sustainable and cost-effective electric power generation. However, the power outputs of protonic ceramic fuel cells are far from the requirements due to the lack of active cathodes. In this work, porous thin sheets Ca_xY_1-xFe_0.5Co_0.5O_3-δ (x = 0.1, 0.3 and 0.5) are synthesized by a modified pechini method and investigated as cathode materials for protonic ceramic fuel cells. Ca_xY_1-xFe_0.5Co_0.5O_3-δ show high electrical conductivities and excellent chemical compatibility with Ba(Zr_0.1Ce_0.7Y_0.2)O₃ electrolyte. The maximum electrical conductivity of Ca_0.3Y_0.7Fe_0.5Co_0.5O_3-δ reaches 202 S cm⁻¹ in air at 750 °C. The detailed mechanism for oxygen reduction reaction reveals that the rate-limiting step of oxygen reduction reaction is transformed from charge transfer to O₂ adsorption-dissociation with temperature rising or Ca doping. The composite cathode Ca_0.3Y_0.7Fe_0.5Co_0.5O_3-δ-Ba(Zr_0.1Ce_0.7Y_0.2)O₃ presents a relatively low polarization resistance of 0.07 Ω cm² at 750 °C in air. The power density of the anode-supported cell of NiO– Ba(Zr_0.1Ce_0.7Y_0.2)O₃∣Ba(Zr_0.1Ce_0.7Y_0.2)O₃∣Ca_0.3Y_0.7Fe_0.5Co_0.5O_3-δ-Ba(Zr_0.1Ce_0.7Y_0.2)O₃ is 798 mW cm⁻² as the electrolyte thickness is about 150 μm. The prepared Ca_xY_1-xFe_0.5Co_0.5O_3-δ oxides are promising candidates as high-performance cathodes for protonic ceramic fuel cells.