BaZr0.1Ce0.7Y0.2O3−δ (BZCY)-based proton-conducting solid oxide fuel cells (H-SOFC) with a cobalt-free proton-blocking La0.7Sr0.3FeO3−δ–Ce0.8Sm0.2O2-δ (LSF–SDC) composite cathode were fabricated and evaluated. The effect of firing temperature of the cathode layer on the chemical compatibility, microstructure of the cathode and cathode–electrolyte interface, as well as electrochemical performance of single cells was investigated in detail. The results indicated that the cell exhibited the most desirable performance when the cathode was fired at 1000 °C; moreover, at the same firing temperature, the power performance had the least temperature dependence. With humidified hydrogen (∼2% H2O) as the fuel and ambient air as the oxidant, the polarization resistance of the cell with LSF–SDC cathode fired at 1000 °C for 3 h was as low as 0.074 Ω cm2 at 650 °C after optimizing microstructures of the anode and anode-electrolyte interface, and correspondingly the maximum power density achieved as high as 542 mW cm−2, which was the highest power output ever reported for BZCY-based H-SOFC with a cobalt-free cathode at 650 °C.Highlights► Proton-blocking La0.7Sr0.3FeO3−δ–Ce0.8Sm0.2O2−δ (LSF–SDC) was employed as cathode for proton-conducting SOFC. ► The effect of firing temperature of LSF–SDC on cell performances was investigated. ► The cell exhibited the best performance when LSF–SDC was fired at 1000 °C for 3 h ► The cell performance was significantly improved after optimizing the anode microstructure.