The influence of the Nafion content in polymer electrolyte fuel cell (PEFC) gas diffusion electrodes with intermixed ionomer in the catalyst was evaluated. Electrochemical studies were carried out in a 50 cm(2) single cell in H-2/air operation at 70 degreesC. Low platinum loading (0.1 mg cm(2)) electrodes with a Nafion content ranging from 14 to 66 wt% were studied. The performance of PEFC electrodes is affected by the Nafion content and an optimal content of about 33 wt% of ionomer was found. Hg intrusion porosimetry and cyclic voltammetry were carried out to evaluate the pore size distribution and the electrochemical surface area respectively. These data were correlated with single-cell performance. The electrochemical experimental data were analysed using a theoretical equation and the kinetics parameters obtained were related to the catalytic layer structure. (C) 2001 Elsevier Science Ltd. All rights reserved.