Electrodeposited WO3 Film on Various Metal Substrates and Its Morphological Effect for Photoelectrochemical Water Splitting

Metal oxides such as TiO₂, WO₃, ZnO, SnO₂ etc. have widely investigated because of low cost, environmental friendliness, and the application to various energy related devices. In particular, WO₃ having the energetic band gap of about 2.8 eV has the absorption of more visible light, the suitable position of conduction band to transfer the photogenerated electrons to the substrate, and the stable photoresponse in the strong acidic condition. Herein, we prepared the WO₃ film by electrodeposition that provides the clean and reproducible technique. That is, a compact structured WO₃ film with a thickness of 780 nm was prepared by facile electrodeposition at a constant potential of -0.47 V versus saturated Ag/AgCl electrode. For a nanoporous structured WO₃ film, polystyrene (PS) beads with a size of 320 nm were used as the template, and the electrodeposition was performed under the same experimental conditions by varying the reaction time from 1 to 3 min to adjust the thickness of the depositing layer. The PS beads were completely removed from the template by the calcination at 450 °C for 3 h under air, affording inverse opal WO₃ films with a pore size of 300 nm. For the inverse opal WO₃ film with a thickness of 790 nm prepared by electrodeposition for 1 min, the highest photocurrent density (1.75 mA/cm² at 1.5 V versus sat. Ag/AgCl) was achieved, followed by compact WO₃, inverse opal WO₃ (2 min), and inverse opal WO₃ (3 min) films with photocurrent densities of 1.2, 0.74, and 0.35 mA/cm², respectively. The further discussion on the morphological and crystalline properties of the prepared WO₃ film was confirmed by a field emission scanning electron microscope and X-ray diffraction.