Two composite electrode structures for proton exchange membrane fuel cells, comprising an outer and an inner catalyst layer, are proposed to improve the CO tolerance and utilization efficiency of the catalyst. These two composite anodes have structures I and II, and are prepared by a combination of direct printing and magnetron sputtering deposition. The only difference between them is the third layer of the outer catalyst layer, which is a layer of deposited Pt-29-Ru-71 alloy nanoparticles in structure II and a screen-printed Pt-50-Ru-50 layer in structure I. The loadings of each layer at the anode for these two membrane electrode assemblies (MEAs) are identical. The electrode performance and CO tolerance of the proposed catalyst layer structure are compared to those of the conventional structure. The roles of the outer and inner catalyst layers in improving the CO tolerance and utilization efficiency of the catalyst are studied. The results indicate that the structure II anode catalyst layer outperforms the conventional structure, with a higher utilization efficiency of the catalyst and a similar CO tolerance. The structure I anode catalyst layer has a greater CO tolerance and outperforms the conventional and Huag's structures in 50ppm CO-containing hydrogen fuels and pure hydrogen fuel. The filtering effect of the outer catalyst layer improves the CO tolerance. The electron probe micro-analysis result reveals that the composite anode has an effective catalyst distribution. This proposed composite MEA is expected to have the advantage of ease of process and is suited for mass production. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.