Wetting Induced Oxidation of Pt-based Nano Catalysts Revealed by In Situ High Energy Resolution X-ray Absorption Spectroscopy

In situ high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS) was used to systematically evaluate interactions of H(2)O and O(2) adsorbed on Pt and Pt(3)Co nanoparticle catalysts in different particle sizes. The systematic increase in oxidation due to adsorption of different species (H(2)O adsorption <O(2) adsorption <O(2) + H(2)O coadsorption) suggests that cooperative behavior between O(2) and H(2)O adsorptions is responsible for the overpotential induced by hydrated species in fuel cells. From the alloying and particle size effects, it is found that both strength of O(2)/H(2)O adsorption and their cooperative effect upon coadsorption are responsible for the specific activity of Pt catalysts.