When a Metastable Oxide Stabilizes at the Nanoscale: Wurtzite CoO Formation upon Dealloying of PtCo Nanoparticles

Abstract

Ambient pressure photoelectron and absorption spectroscopies were applied under 0.2 mbar of O₂ and H₂ to establish an unequivocal correlation between the surface oxidation state of extended and nanosized PtCo alloys and the gas-phase environment. Fundamental differences in the electronic structure and reactivity of segregated cobalt oxides were associated with surface stabilization of metastable wurtzite-CoO. In addition, the promotion effect of Pt in the reduction of cobalt oxides was pronounced at the nanosized particles but not at the extended foil