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In order to enhance the electrochemical performance of cobalt-free Bi 0.7 Sr 0.3 FeO 3-δ (BSFO) cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs), a composite cathode consisting of BSFO and La 0.8 Sr 0.2 MnO 3-δ (LSM) is developed. The optimized polarization resistance of the composite cathode (0.11 Ω cm2 at 800 °C) is found to be only 61 % that of pure BSFO (0.18 Ω cm2 at 800 °C), indicating a significant improvement in performance. The first-principles calculation indicates that the enhanced electrochemical performance is mainly due to the domain of low oxygen vacancy formation energies of BSFO-LSM-L interfaces (E vac , −3.63 eV) and LSM (E vac , −3.11 eV). The anode-supported single cell of NiO-SDC/SDC/BSFO－LSM shows a peak power density of 825.83 mW cm−2 at 800 °C using wet H 2 (∼3 vol% H 2 O) as fuels and ambient air as oxidants. In addition, the single cell exhibits a good stability at the electric current density 400 mA cm−2 for 50 h measured at 650 °C. • BSFO-LSM composite cathode is developed for IT-SOFCs application. • The polarization resistance of BSFO dramatically decreases by introducing LSM. • The electrochemical property is explained by the first-principles calculation. • The single cell shows a peak power density of 825.83 mW cm−2 at 800 °C. [ABSTRACT FROM AUTHOR]