A route toward the synthesis of several Pt/Co-based catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells is described here. The composition of these catalysts has been determined by X-ray diffraction studies, while their electrochemical activity was established using slow sweep cyclic voltammetry in 0.5 M H2SO4 at room temperature. We have found that by mixing a Co oxide sol precursor with Pt supported on carbon (Pt/C), followed by heat-treatment at 700 or 900 degrees C, the active PtCo alloy catalyst is formed. In contrast, when exactly the same procedure is followed but a Co oxide sol-derived Co/N/C catalytic material is employed, Pt3Co alloy catalysts, which are somewhat less active toward the ORR, are formed. Catalysts formed by heating at 900 degrees C are more active than those formed at 700 degrees C, and all of our Pt/Co catalysts are more active toward the ORR than pure Pt on carbon. (c) 2005 The Electrochemical Society.