Proton uptake into the protonic cathode material BaCo0.4Fe0.4Zr0.2O3-δ and comparison to protonic electrolyte materials

Proton uptake in mixed-conducting cathode materials is of particular interest as it allows the oxygen reduction reaction to proceed via the bulk path in proton conducting ceramic fuel cells (PCFC). This work investigates the proton concentration of BaCo0.4Fe0.4Zr0.2O3−δ (BCFZr) and the predominant proton uptake reactions using thermogravimetry. Based on the obtained proton concentrations increasing from 0.5 mol% at 400 °C to 1.5 mol% at 200 °C, the bulk path is expected to be active for BCFZr. The variation of proton concentrations with the concentration of electronic defects indicates nonideal behavior with detrimental interactions between protons and (trapped) holes. The comparison of BCFZr with other materials emphasizes that several factors determine the proton concentration such as oxide ion basicity, B-site cations and their oxidation state and B-O covalency.