Nano-sized Sm0.5Sr0.5SCoO3-delta (SSC) was fabricated onto the inner face of porous BaCe0.8Sm0.2O2.9 (BCS) backbone by ion impregnation technique to form a composite cathode for solid oxide fuel cells (SOFCs) with BCS, a proton conductor, as electrolyte. The electro-performance of the composite cathodes was investigated as function of fabricating conditions, and the lowest polarization resistance, about 0.21 Omega cm(2) at 600 degrees C, was achieved with BCS backbone sintered at 1100 degrees C. SSC layer fired at 800 degrees C, and SSC loading of 55 wt.%. Impedance spectra of the composite cathodes consisted of two depressed arcs with peak frequency of 1 kHz and 30 Hz, respectively, which might correspond to the migration of proton and the dissociative adsorption and diffusion of oxygen, respectively. There was an additional arc peaking at 1 Hz in the Nyquist plots of a single cell, which should correspond to the anode reactions. With electrolyte about 70 mu m in thickness, the simulated anode, cathode and bulk resistances of cells were 0.021, 0.055 and 0.68 Omega cm(2) at 700 degrees C, relatively, and the maximum power density was 307 mW cm(-2) at 700 degrees C. (C) 2009 Elsevier Ltd. All rights reserved.