An active anode electrocatalyst, consisting of 1/8 of a monolayer of Pt on a surface of carbon-supported Ru nanoparticles, has been shown to exhibit excellent long-term performance stability in an operating fuel cell. The electrocatalyst has the reduced susceptibility to poisoning by CO, which, in addition to the strong segregation of the Pt atoms on the Ru substrate, determines this characteristic. Kinetic parameters were determined by electrochemical techniques using thin-film rotating disk electrodes. X-ray absorption spectroscopy near edge structure was used to determine the d-band vacancies of a Pt submonolayer on a surface of carbon-supported Ru nanoparticles, and to relate it to the bonding strength of CO. The data point the way to ultimately reduce Pt content in anode electrocatalysts while maintaining their high activity and thereby alleviating the problem of high Pt loading in existing fuel cell technology. (C) 2004 Elsevier Ltd. All rights reserved.