Transforming Anodized WO<sub>3</sub> Films into Visible-Light-Active Bi<sub>2</sub>WO<sub>6</sub> Photoelectrodes by Hydrothermal Treatment

We directly transformed anodized tungsten oxide film (WO<sub>3</sub>·2H<sub>2</sub>O) into bismuth tungstate (Bi<sub>2</sub>WO<sub>6</sub>) by substituting the intercalated water molecules with [Bi<sub>2</sub>O<sub>2</sub>]<sup>2+</sup> in a hydrothermal treatment. The resultant Bi<sub>2</sub>WO<sub>6</sub> was readily used as an electrode to produce anodic photocurrent in H<sub>2</sub> evolution on the Pt counter electrode observed under visible light irradiation.