Tuning the defects of the triple conducting oxide BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_{3-: δ} perovskite toward enhanced cathode activity of protonic ceramic fuel cells

Protonic ceramic fuel cells (PCFCs) have interesting potential to efficiently produce electrical power from fuels in a low-temperature range (<650 °C). However, the sluggish activity of the oxygen reduction reaction is one of the greatest obstacles to the development of PCFCs. Single-phase triple-conducting (e^-/O^2-/H⁺) oxides are considered to be the most promising candidates for highly active PCFC cathodes because they can extend the electrochemically active sites to the entire cathode surface. Here, A-site deficiency of perovskite is introduced to tune the triple-conducting properties, which can stimulate the generation of oxygen vacancies and increase the oxygen-ion bulk diffusion and proton hydration kinetics. The so-obtained A-site-deficient perovskite oxides, Ba_xCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ (x = 1, 0.95, 0.9), exhibit area specific resistance values of 1.61, 0.94, and 0.52 Ω cm² for BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ, Ba_0.95Co_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ, and Ba_0.9Co_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ, respectively, at 500 °C in wet air (p_H2O = 0.1 atm). Peak power densities of 797.47, 668.64, 548.07, and 376.27 mW cm^-2 are obtained from the PCFC with the Ba_0.9Co_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ cathode at 650, 600, 550 and 500 °C, respectively. Such remarkable performance demonstrates that introducing A-site deficiency is an effective strategy to enhance the triple-conducting properties of perovskite oxides for the high-activity cathode of PCFCs.