Surface CO diffusion processes were considered with regard to the properties of nanoparticle Pt and Pt/Ru fuel cell catalysts. The COad diffusion was studied by the use of 13C electrochemical nuclear magnetic resonance spectroscopy. Measurements were carried out at 253 to 293K, where the solution side of the nanoparticle–electrolyte interface was liquid, in contrast to previous measurements, in ice. A concerted view of the effect of particle size and surface coverage on COad diffusion was offered, and it was found that both were important. It was 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. On all Pt nanoparticle surfaces investigated, it was concluded that CO surface diffusion was too fast to be considered to be the rate-limiting factor in methanol reactivity. The addition of Ru to Pt increased the surface diffusion rates of CO, and there was a direct correlation between the Fermi level local density of states (Ef-LDOS) of the 2π* molecular orbital of adsorbed CO and the activation energy for surface diffusion. These results were of interest since they improve the knowledge of surface dynamics of molecules at electrochemical interfaces, and could help to formulate better models for the electro-oxidation of adsorbed CO on nanoparticle surfaces.

CO Surface Diffusion on Platinum Fuel Cell Catalysts by Electrochemical NMR. P.K.Babu, J.H.Chung, E.Oldfield, A.Wieckowski: Electrochimica Acta, 2008, 53[23], 6672-9