Higher oxygen vacancy content and hydration capability enabled by magnesium doping for high-activity protonic ceramic fuel cell cathode

Abstract

Protonic ceramic fuel cells (PCFCs) are promising power generation equipment because of their high efficiency and low operating temperature. However, the sluggish oxidation-reduction reaction (ORR) kinetics of the cathode seriously limits their further development. Here, a low-valent alkaline-earth metal Mg-doped BaCo0.4Fe0.4Zr0.2O3-δ (BaCo0.4Fe0.4Zr0.1Mg0.1O3-δ = BCFZMg0.1) cathode is developed to increase oxygen vacancy concentration and hydration capability of mixed oxygen ion-electron conducting (MIEC) electrode materials. The phase composition, microstructure, and stability in wet air were examined, while the oxygen vacancy, hydration capability, conductivity, and surface species of the materials were investigated. Experimental results demonstrate that the oxygen vacancy concentration, hydration capability, and conductivity are all increased by Mg doping. Consequently, the ORR active sites were expanded to the whole electrode surface, and the electrochemical performance of PCFCs with BCFZMg0.1 cathode was greatly improved (peak power density: >40% increase; polarization resistance: 60–70% decrease). This work provides a new strategy to develop cathodes with high ORR activity for PCFCs by doping Mg into the MIEC perovskite B-site.