Photo-stimulated proton-coupled electron transfer in quasi-amorphous WO₃ and MoO₃ thin films

Abstract

WO₃ and MoO₃ are important hydrogen storage and transport materials capable of accommodating large quantities of hydrogen. Upon insertion of hydrogen, their properties change dramatically, giving rise to electrochromic and photochromic transformations that have been intensively investigated. The materials are also effective catalysts for hydrogen production via photochemical surface reactions. The kinetics was investigated of the photo-injection of hydrogen into highly disordered WO₃ and MoO₃ thin films over a wide temperature range. A low-temperature non-zero reaction rate limit was discovered for photo-stimulated hydrogen atom transfer between adsorbed molecules and the oxide surface, which provides unambiguous evidence for a quantum mechanism reaction. The reaction model exhibits a similarity to proton-coupled electron transfer, which is a basic mechanism of bioenergetics conversion. A detailed description of the experiments is provided, together with a comprehensive discussion.