The UV-vis diffuse reflectance spectra of the BiVO4, WO3, BiVO4/WO3, Au/BiVO4/WO3 photoanodes and the FTO substrate are shown in Figure . It is observed that the FTO thin film with a thickness of 550 nm has no significant light absorption in the spectral range of 400-800 nm where it could potentially overlap with the absorption of the produced visible light active materials.