Surface and structure of carbon-supported Pd3Pt1 (Pd3Pt1/C) bimetallic nanoparticles of small particle size can be tuned during synthesis through the use or nonuse of trisodium citrate (TC) as the complexing agent. The addition of TC during the synthesis results in Pd enrichment on the surface layers of the Pd3Pt1/C catalysts and to an abnormal lattice expansion as compared to that of pure Pd/C and Pt/C. However, without the addition of TC, a normal lattice constant and Pt enrichment on the surface layers of the catalysts are obtained. Among the prepared catalysts, the maximum activity for the oxygen reduction reaction (ORR) occurs for Pd3Pt1/C Catalyst With Pt surface enrichment. Importantly, the Pd3Pt1/C catalysts with Pd surface enrichment exhibited substantially higher methanol tolerance during the ORR than both the Pd3Pt1/C catalyst with Pt surface enrichment and the Pt/C catalyst. Thus, Pd3Pt1/C catalysts may represent a methanol-tolerant ORR cathode catalyst. (C) 2009 Elsevier Inc. All rights reserved.