The citric acid treated carbon supported Ru85Se15 catalysts are synthesized by microwave assisted polyol method at the optimal solution pH = 7. The catalyst coated membrane method with ultrasonic-spray technique is employed to prepare electrodes without hot press step. The cell performances with different Nation contents and Ru loads in the cathode catalyst layer are systematically examined in both H-2/air and H-2/O-2 fuel cells at 65 degrees C under ambient pressure. The surface morphologies of membrane electrode assemblies and the interfacial characteristics of single cells are studied using scanning electron microscopy and electrochemical impedance spectroscopy, respectively. The Nation content is optimized to be 33% when the catalyst loadings are lower than 0.8 and 0.6 mg Ru cm(-2) in the H-2/air and H-2/O-2 fuel cells, respectively, but reduced to 20% at the higher Ru loads. The maximum peak power densities of 190 mW cm(-2) at 620 mA cm(-2) and 400 mW cm(-2) at 1430 mA cm(-2) are achieved in the H-2/air and H-2/O-2 fuel cells, respectively, with 0.27 mg Ru cm(-2) and 33% Nafion. The best catalyst utilizations are obtained at 0.14 mg Ru cm(-2) with 33% Nation, resulting in the maximum peak power densities per unit mass Ru of 917 and 2460 mW mg(-1) in the H-2/air and H-2/O-2 fuel cells, respectively. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.