Electrochemical performance of Sn-doped Bi0.5Sr0.5FeO3- perovskite as cathode electrocatalyst for solid oxide fuel cells

Abstract

Abstract The Sn-doped Bi0.5Sr0.5FeO3-δ (BSF)-based perovskite oxide is evaluated as novel cathode electrocatalyst for intermediate-temperature solid oxide fuel cells (IT-SOFCs). In particular, the effects of 10 mol% Sn substitution on phase evolution, thermal expansion behavior and electrochemical performance of Bi0.5Sr0.5Fe0.9Sn0.1O3-δ (BSFSn) material are systematically investigated. BSFSn crystallizes in cubic perovskite structure with space group Pm-3m. Sn doping is found to decrease the average thermal expansion coefficient (TEC) from 14.7 × 10−6 K−1 (BSF) to 12.9 × 10−6 K−1 (BSFSn) within a temperature range of 50–800 °C, due to the enlarged metal-oxygen (Sn-O) bond energy in BSFSn. The X-ray photoelectron spectroscopy (XPS) result proves that Sn doping promotes the oxygen adsorption ability on BSFSn surface. Consequently, the ORR activity of BSFSn is improved as expected. The polarization resistance (Rp) value of BSFSn cathode is 0.09 Ω cm2 at 700 °C in air, which is lower than BSF. The cathode overpotential is 35.6 mV at a current density of 140.8 mA cm−2 at 700 °C in air. The peak power density of the anode-supported cell reaches 960 mW cm−2 at 700 °C. Furthermore, the relationship between oxygen partial pressure and Rp demonstrates that oxygen surface adsorption-desorption is a major rate-limiting step for oxygen reduction reaction (ORR) process on BSFSn cathode. These attractive electrochemical properties suggest that BSFSn oxide is a promising potential cathode electrocatalyst for SOFCs.