The influence of the electrocatalyst loading (2.0-40.7 wt.%) on a carbon support on its suitability as a cathode for proton-exchange membrane (PEM) fuel cells was evaluated at a constant membrane electrocatalyst loading of 0.15 mg/cm(2). The results clearly demonstrate that different electrocatalyst loadings on a carbon support in the investigated range significantly affect not only the electrocatalyst activity but also the performance in H-2/O-2 fuel cells. Increasing the electrocatalyst loading on a carbon support led to an increase in the particle size of electrocatalyst and the pore size of the membrane electrode assembly (MEA) but a decrease in the particle size distribution and MEA thickness. The maximum oxygen-reduction reaction (ORR) activity and cell performance (745 mA/cm(2) and 520 mW/cm(2) at 0.6 V) were obtained at an electrocatalyst loading of 24.1 wt.% on a carbon support. (C) 2010 Elsevier Ltd. All rights reserved.