Here we report the fabrication of composite cathodes for reduced-temperature solid oxide fuel cells by impregnating aqueous solutions corresponding to SmBa0.5Sr0.5Co2O5 (SBSCO) into the porous La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM) backbones. Examination of X-Ray diffraction patterns indicates that phase-pure SBSCO layered perovskite oxides can be only achieved at calcination temperatures >= 900 degrees C. Based upon impedance measurement of symmetric cells, the SBSCO-LSGM composites calcinated at 850 degrees C show a trade-off between the SBSCO phase purity and catalyst size, and thereby exhibit minimal cathode polarization resistances with respect to the infiltrate calcination temperature, e.g., 0.035 Omega cm(2) at 550 degrees C and 0.12 Omega cm(2) at 500 degrees C at the loadings of 21 wt%. Analysis of impedance spectra under varied oxygen partial pressures suggests that oxygen reduction reactions on the nano-scale SBSCO-LSGM composite are largely dominated by ionization of adsorbed oxygen atoms on the SBSCO surfaces. Thin LSGM electrolyte fuel cells with impregnated Ni anodes and SBSCO cathodes show high power densities of 1.5 W cm(-2) at 600 degrees C and 0.70 W cm(-2) at 500 degrees C. (C) 2013 Published by Elsevier B.V.