Pt/C/MnO2 hybrid catalysts were prepared by a wet chemical method. Pt/C electrocatalysts were treated with manganese sulfate monohydrate (MnSO4 H2O) and sodium persulfate (Na2S2O8) to produce MnO2. The presence of MnO2 was confirmed by FTIR spectroscopy. Rotating ring-disk electrode (RRDE) experiments were performed on electrodes prepared using the hybrid clectrocatalysts to estimate the amount of hydrogen peroxide (H2O2) formed during the oxygen reduction reaction (ORR) as a function of MnO2 content. Pt/C/MnO2 (5% by weight of MnO2) hybrid electrocatalysts produced 50% less hydrogen peroxide than the baseline Pt/C electrocatalyst. The hybrid electrocatalysts were used to prepare membrane electrode assemblies that were tested at 90 degrees C and 50% RH at open circuit with pure hydrogen as fuel and air as the oxidant. The fluoride ion concentration was measured using an ion selective electrode. The concentration of F- in the anode condensate over 24 h was found to be reduced by a factor of 3-4 when Pt/C/MnO2 replaced Pt/C as the catalyst. Through cyclic voltammetry and RRDE kinetic studies, the lower ORR activity of the acid treated hybrid electrocatalysts was attributed to catalyst treatment with acid during MnO2 introduction. The activity of the hybrid catalyst was improved by switching to a water-based synthesis. (c) 2007 Elsevier B.V. All rights reserved.