Tuning oxygen vacancy of the Ba0·95La0·05FeO3−δ perovskite toward enhanced cathode activity for protonic ceramic fuel cells

Innovation of highly active cathode is of great significance to the development of protonic ceramic fuel cells (PCFCs). Herein, tailoring oxygen vacancies in Zn-doped Ba0·95La0·05FeO3−δ (BLFZ) perovskite is proved to be beneficial for promoting the formation of proton defects. Hydration ability of the triple conducting BLFZ perovskites is confirmed by electrical conductivity relaxation (ECR). The results demonstrate that BLFZ exhibits a proton surface exchange coefficient of 1.34 × 10−3 cm s−1 at 600 °C, which greatly extends active sites from the electrolyte/cathode interface to the entire electrode. Mechanism and process elementary steps of the oxygen reduction reaction (ORR) of BLFZ-BaCe0.7Zr0·1Y0.1Yb0.1O3−δ (BCZYYb) are detailedly studied. It is found that the rate-determining step of ORR is surface dissociative adsorption of oxygen on BLFZ-BCZYYb cathode. A maximum power density of 673 mW cm−2 at 700 °C is achieved and BLFZ-BCZYYb based single-cell shows no obvious degradation at 600 °C for 200 h. The good performance is ascribed to the rapid proton diffusion of BLFZ-BCZYYb composite electrode by regulating the oxygen vacancies.