Crystal facet-dependent photocatalytic oxidation and reduction reactivity of monoclinic WO3 for solar energy conversion

Abstract

The reactivity of a photocatalyst is basically influenced by its surface atomic and linked electronic structure. Tuning different crystal facets is becoming an important strategy to optimize the reactivity of a photocatalyst for targeted reactions. Here we report a facile and new route of synthesizing a quasi-cubic-like WO₃ crystal with a nearly equal percentage of {002}, {200} and {020} facets, and a rectangular sheet-like WO₃ crystal with predominant {002} facet by controlling acidic hydrolysis of crystalline WB. As a result of electronic structure effects induced by crystal facet, the quasi-cubic-like WO₃ crystal with a deeper valence band maximum shows a much higher O₂ evolution rate in photocatalytic water oxidation than the rectangular sheet-like WO₃ crystal. The latter, with an elevated conduction band minimum of 0.3 eV, is able to photoreduce CO₂ to generate CH₄ in the presence of H₂O vapor.