Electrochemical performance of composite cathodes consisted of an electron-oxygen-ion mixed conductor, Sm0.5Sr0.5CoO3-delta (SSC), and a proton conductor, BaCe0.8Sm0.2O3-delta (BCS) was investigated for intermediate temperature solid oxide fuel cells with proton-conducing ceramics as the electrolytes. Interfacial polarization resistance of the composite decreased with SSC content to the minimum at 60 wt.% SSC and then increased. Firing temperature of the cathodes also affected the resistance, and high performance cathode could be obtained by firing at 1050 degrees C. The minimum interfacial polarization resistance was 0.21 Omega cm(2) at 700 degrees C, where powder density of 0.24 W/cm(2) was achieved with humidified hydrogen as the fuel and ambient air as the oxidant. The low interfacial polarization resistance suggests promise applications of SSC-BCS composites as the cathodes for SOFCs based on proton-conducting electrolytes. (C) 2007 Elsevier B.V. All rights reserved.