In Situ Hard X-ray Photoelectron Study of O2 and H2O Adsorption on Pt Nanoparticles

To improve the efficiency of Pt-based cathode catalysts in polymer electrolyte fuel cells, understanding of the oxygen reduction process at surfaces and interfaces in the molecular level is essential. In this study, H2O and O-2 adsorption and dissociation as the first step of the reduction process were investigated by in situ hard X-ray photoelectron spectroscopy (HAXPES). Pt 5d valence band and Pt 3d, Pt 4f core HAXPES spectra of Pt nanoparticles upon H2O and O-2 adsorption revealed that H2O adsorption has a negligible effect on the electronic structure of Pt, while O-2 adsorption has a significant effect, reflecting the weak and strong chemisorption of H2O and O-2 on the. Pt nanoparticle, respectively. Combined with ab initio theoretical calculations, it is concluded that Pt 5d states responsible for Pt-V bonding reside within 2 eV from the Fermi level.