K-doped BaCo_0.4Fe_0.4Zr_0.2O_3−δ as a promising cathode material for protonic ceramic fuel cells

Slow oxygen reduction reaction (ORR) involving proton transport remains the limiting factor for electrochemical performance of proton-conducting cathodes. To further reduce the operating temperature of protonic ceramic fuel cells (PCFCs), developing triple-conducting cathodes with excellent electrochemical performance is required. In this study, K-doped BaCo_0.4Fe_0.4Zr_0.2O_3−δ (BCFZ442) series were developed and used as the cathodes of the PCFCs, and their crystal structure, conductivity, hydration capability, and electrochemical performance were characterized in detail. Among them, Ba_0.9K_0.1Co_0.4Fe_0.4Zr_0.2O_3−δ (K10) cathode has the best electrochemical performance, which can be attributed to its high electron (e⁻)/oxygen ion (O²⁻)/H⁺ conductivity and proton uptake capacity. At 750 ℃, the polarization resistance of the K10 cathode is only 0.009 Ω·cm², the peak power density (PPD) of the single cell with the K10 cathode is close to 1 W·cm⁻², and there is no significant degradation within 150 h. Excellent electrochemical performance and durability make K10 a promising cathode material for the PCFCs. This work can provide a guidance for further improving the proton transport capability of the triple-conducting oxides, which is of great significance for developing the PCFC cathodes with excellent electrochemical performance.