Analysis of the Surface Oxidation Process on Pt Nanoparticles on a Glassy Carbon Electrode by Angle-Resolved, Grazing-Incidence X-ray Photoelectron Spectroscopy.

We have analyzed the surface oxidation process of Pt nanoparticles that were uniformly dispersed on a glassy carbon electrode (Pt/GC), which was adopted as a model of a practical Pt/C catalyst for fuel cells, in N-purged 0.1 M HF solution by using angle-resolved, grazing-incidence X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-ARGIXPS). Positive shifts in the binding energies of Pt 4f spectra were clearly observed for the surface oxidation of Pt nanoparticles at potentials E > 0.7 V vs RHE, followed by a bulk oxidation of Pt to form Pt(II) at E > 1.1 V. Three types of oxygen species (HO, OH, and O) were identified in the O 1s spectra. It was found for the first time that the surface oxidation process of the Pt/GC electrode at E < ca. 0.8 V (OH formation) is similar to that of a Pt(111) single-crystal electrode, whereas that in the high potential region (O formation) resembles that of a Pt(110) surface or polycrystalline Pt film.