This paper describes the structure and electrochemical properties of composite cathodes for solid oxide fuel cells fabricated by infiltration of aqueous solutions corresponding to SrFe0.75Mo0.25O3-delta (SFMO) into porous La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM) backbones. XRD measurement confirms the predominance of the perovskite SFMO oxides in the infiltrates together with some minor impurities of SrMoO4 after calcinations at 850-1100 degrees C. The cathode polarization resistance as obtained from impedance measurement on symmetric cathode fuel cells exhibits a pronounced increase as a function of calcinations temperature due to increased SFMO particle sizes, e.g., 0.04 Omega cm(2) for 70 nm-sized catalysts calcinated at 850 degrees C versus 0.11 Omega cm(2) for 400 nm-sized catalysts calcinated at 1100 degrees C. Oxygen partial pressure and temperature dependence of impedance data shows that oxygen reduction kinetics is largely determined by ionization of adsorbed oxygen atoms on the SFMO catalysts. (C) 2013 Elsevier B.V. All rights reserved.