Electrochemical preparation of tungsten oxide hydrate films with controlled bandgap energy

Tungsten oxide hydrate films of WO3 ∙ H2O and WO3 ∙(H2O)0.33 were prepared on conductive glass substrates by anodic deposition in aqueous 0.01-0.5 mol/L WO42 − solutions. Structural and optical characterizations were carried out by X-ray photoelectron spectroscopy, X-ray diffraction, SEM observation, optical absorption measurements, and photoelectrochemical measurements. The films composed of large WO3 ∙ H2O grains with square shapes, which was obtained in the 0.01-0.09 mol/L WO42 − solutions, possessed a bandgap energy of approximately 2.5 eV, and the granular-WO3 ∙(H2O)0.33 films, which was obtained in the 0.05-0.5 mol/L WO42 − solutions, showed 3.3 eV in bandgap energy. The WO3 ∙ H2O-WO3 ∙(H2O)0.33 mixtured films prepared in the 0.01-0.09 mol/L WO42 − solutions showed a photoresponse for visible light at 380-600 nm, due to the presence of 2.5 eV-bandgap WO3 ∙ H2O.