A-Site Nonstoichiometric Ba_xCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ Cathode for Protonic Ceramics Fuel Cells

Highly active triple (proton, oxygen-ion, and electron) conducting materials Ba_xCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ (BxCFZY, x = 0.9-1.1) were prepared and characterized as potential cathodes for protonic ceramic fuel cells (PCFCs) in this work. The crystal structure, oxygen vacancy concentration, electrical conductivity, oxygen ion transfer properties, and electrochemical performance of BxCFZY oxides were systematically evaluated. The electrical conductivity of BxCFZY decreases but oxygen vacancies increase with increasing Ba content, indicating that the charge compensation was mainly achieved by the production of oxygen vacancy rather than the increase in the valence of transition metal cations. The power density of 1170 mW cm^-2 and the polarization resistance of 0.05 Ω cm² were achieved at 700 °C for the anode-supported single cells with B1.1CFZY cathode, suggesting that the excess A site on the BxCFZY had a positive effect on the catalytic activity for the oxygen reduction reaction. Furthermore, the distribution of relaxation time (DRT) analysis method was adopted to determine the electrochemical processes of the cells with BxCFZY cathodes. The calculated results confirmed that the cell with B1.1CFZY cathode exhibited the optimum performance due to the best oxygen ion transfer properties in BxCFZY cathodes.