We report oil surface CO diffusion processes in relation to properties of nanoparticle Pt and Pt/Ru fuel cell catalysts. The COad diffusion was Studied by the use of C-13 electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy. Measurements were carried out in the temperature range 253-293 K, where the Solution side of the nanoparticle-electrolyte interface is liquid. in contrast to previous measurements. ill ice. We Offer concerted view of the effect of particle size and surface coverage on COad diffusion, and find that both are important. We also found that the diffusion parameters were influenced by the variations in the distribution of chemisorption energies on particles of different sizes, and by the CO-CO lateral interactions. Oil all Pt nanoparticle surfaces investigated, we conclude that CO surface diffusion is too fast to be considered as the rate-limiting factor in methanol reactivity. The addition of Ru to Ill increases the surface diffusion rates of CO. and there is a direct correlation between the Fermi level local density of states (E-f-LDOS) of the 2 pi* molecular orbital of adsorbed CO and the activation energy for surface diffusion. These results are of interest since they improve our knowledge of surface dynamics of molecules at electrochemical interfaces, and may help to formulate better models for the electrooxidation of adsorbed CO oil nanoparticle Surfaces. (c) 2008 Elsevier Ltd. All rights reserved.