In this work, the replacement of platinum by palladium in carbon-supported catalysts as anodes for hydrogen oxidation reaction (HOR), in proton exchange membrane fuel cells (PEMFCs), has been studied. Anodes with carbon-supported Pt, Pd, and equiatomic Pt:Pd, with various Nafion (R) contents, were prepared and tested in H(2)vertical bar O(2) (air) PEmFCs fed with pure or CO-contaminated hydrogen. An electrochemical study of the prepared anodes has been carried out in situ, in membrane electrode assemblies, by cyclic voltammetry and CO electrooxidation voltammetry. The analyses of the corresponding voltammograms indicate that the anode composition influences the cell performance. Single cell experiments have shown that platinum could be replaced, at least partially, saving cost with still good performance, by palladium in the hydrogen diffusion anodes of PEMFCs. The performance of the PtPd catalyst fed with CO-contaminated H(2) used in this work is comparable to Pt, thus justifying further work varying the CO concentration in the H(2) fuel to assert its CO tolerance and to study the effect of the Pt:Pd atomic ratio. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.