Tailoring the Oxygen Vacancy to Achieve Fast Intrinsic Proton Transport in a Perovskite Cathode for Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) are receiving increasing attention because of their high energy conversion efficiency. However, traditional mixed oxygen-ionic and electronic conductors (MOECs) show sluggish oxygen reduction kinetics when used in PCFCs because of their intrinsic low protonic conductivity. Herein, it is reported that cooperatively regulating the concentration and basicity of oxygen vacancies can result in fast proton transport in MOECs, which is demonstrated in a Zr4+-doped Sr2Fe1.5Mo0.5O6-δ (SFMZ) perovskite. The so-obtained SFMZ perovskite renders plentiful oxygen vacancies and strong hydration ability, which can boost the formation of protonic defects. Furthermore, the chemical diffusion coefficient of protons (DH,chem) is established first to determine the proton mobility of the cathode. The results indicate that SFMZ exhibits improved proton diffusion kinetics with a DH,chem value of 8.71 × 10-7 cm2 s-1 at 700 °C, comparable to the diffusion coefficient of the commonly used protonic electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3-δ of 1.84 × 10-6 cm2 s-1. A low polarization resistance of 0.169 ω cm2 and a peak power density as high as 0.79 W cm-2 were achieved at 700 °C with the SFMZ cathode. Such excellent performance suggests that rationally tailoring the oxygen vacancy is a feasible strategy to promote proton diffusion in perovskite-structured electrode materials as efficient PCFC cathodes.