The preparation of a Pt-Co/C electrocatalyst for the oxygen reduction reaction in PEM fuel cells was achieved via a combined process of impregnation and seeding. The effects of initial pH of the precursor solution and Pt loading were all found to have a significant effect on both the electrocatalyst morphology and the cell performance when tested in a single PEM fuel cell. The optimum condition found for preparing the Pt-Co/C electrocatalyst was from an initial precursor solution pH of 2 at the metal loading of 23.6-30.3% (w/w). The Pt-Co/C electrocatalysts, formed under these optimal conditions, tested in a single PEM fuel cell with the carbon sub-layer, gave a cell performance of 772 mA/cm(2) or 460 mW/cm(2) at 0.6 V in a H(2)/O(2) system. An electron pathway of oxygen reduction on the prepared Pt-Co/C electrocatalyst was also determined using a rotating disk electrode. (C) 2010 Elsevier Ltd. All rights reserved.