Reactivity of atomically dispersed Pt2+ species towards H2: model Pt–CeO2 fuel cell catalyst

Abstract

The reactivity of atomically dispersed Pt²⁺ species on the surface of nanostructured CeO₂ films and the mechanism of H₂ activation on these sites have been investigated by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy in combination with density functional calculations. Isolated Pt²⁺ sites are found to be inactive towards H₂ dissociation due to high activation energy required for H–H bond scission. Trace amounts of metallic Pt are necessary to initiate H₂ dissociation on Pt–CeO₂ films. H₂ dissociation triggers the reduction of Ce⁴⁺ cations which, in turn, is coupled with the reduction of Pt²⁺ species. The mechanism of Pt²⁺ reduction involves reverse oxygen spillover and formation of oxygen vacancies on Pt–CeO₂ films. Our calculations suggest the existence of a threshold concentration of oxygen vacancies associated with the onset of Pt²⁺ reduction.