Pt/C/MnO 2 hybrid electrocatalysts for degradation mitigation in polymer electrolyte fuel cells

Abstract

Pt/C/MnO 2 hybrid catalysts were prepared by a wet chemical method. Pt/C electrocatalysts were treated with manganese sulfate monohydrate (MnSO 4·H 2O) and sodium persulfate (Na 2S 2O 8) to produce MnO 2. The presence of MnO 2 was confirmed by FTIR spectroscopy. Rotating ring–disk electrode (RRDE) experiments were performed on electrodes prepared using the hybrid electrocatalysts to estimate the amount of hydrogen peroxide (H 2O 2) formed during the oxygen reduction reaction (ORR) as a function of MnO 2 content. Pt/C/MnO 2 (5% by weight of MnO 2) 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 °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/MnO 2 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 MnO 2 introduction. The activity of the hybrid catalyst was improved by switching to a water-based synthesis.