Photoelectrochemical Property of Tungsten Oxide Films of Vertically Aligned Flakes for Visible-Light-Induced Water Oxidation

A vertically arrayed flake film, "flake-wall film," of monoclinic tungsten oxide was prepared on a transparent conductive glass by controlling anisotropic crystal growth and self-arrayed growth of hydrate with a layered crystal structure. The flake-wall film exhibited superior performance for photoelectrochemical water oxidation under visible-light irradiation compared to that of a film consisting of horizontally laminated flakes. The small differences between photocurrents under front-side irradiation and back-side irradiation and between photocurrents in the absence and the presence of methanol indicate the excellent electron transport property and long photogenerated carrier lifetime in the flake-wall film.