The effect of perfluorosulfonic acid ionomer loadings on electrochemical surface area, gas transfer resistance and output voltage performance was systematically studied by both electrochemical and fuel cell experiments. Differently from the previous reports, a high Pt loading catalyst (60 wt.% Pt/C) was used to evaluate the effect in this work. The optimum loading of perfluorosulfonic acid ionomers in catalyst layers was determined. It was found that the ionomer anode content slightly influenced single ell performance and the optimum ionomer anode loading was 30 wt.%. Based on reasonable gas transfer resistance and fuel cell performance, the optimum ionomer cathode loading was 25-30 wt.%. Significantly, the optimum loading of the ionomer showed a nondependence relationship with Pt loadings in catalyst layers. (C) 2011 Elsevier Ltd. All rights reserved.