High-performance composite cathodes with tailored mixed conductivity for intermediate temperature solid oxide fuel cells using proton conducting electrolytes

A new composite cathode material made of La_0.6Sr _0.4Co_0.2Fe_0.8O_{3 - δ} (LSCF), a mixed oxygen-ion/electron conductor, and BaZr_0.5Pr _0.3Y_0.2O_{3 - δ} (BZPY30), a mixed proton/electron conductor, is here developed for application in intermediate temperature solid oxide fuel cells (IT-SOFCs) based on proton conducting electrolytes. The wet chemical synthesis route allows sub-micrometre particle powders to be obtained, resulting in a highly porous microstructure. The developed composite cathode shows improved performance compared to the reported cathodes working in protonic SOFCs, achieving a total area specific resistance (ASR) in wet O₂ of 0.011, 0.089, and 0.6 Ω cm² at 700, 600, and 500 °C, respectively. Electrochemical impedance spectroscopy measurements indicate that several processes contribute to the overall cathode resistance. Performing area specific resistance measurements at different pO₂ values allows the correlation of the various semicircles observed in the LSCF-BZPY30 impedance plots to different cathode reaction processes, i.e. water formation, oxygen surface dissociation, and diffusion. Fuel cell tests confirm the good performance of the LSCF-BZPY30 cathode for proton conducting oxide electrolytes.