Electrostatic spray deposition of transparent tungsten oxide thin-film photoanodes for solar water splitting

Photocatalytic water splitting has been explored extensively as a promising way to capture and store solar energy. In this study, stable WO₃ thin-film photoelectrodes for water splitting applications were prepared with the simple, inexpensive, and scalable technique of electrostatic spray deposition. The physicochemical, structural, optical, and morphological properties of the WO₃ films were studied with X-ray diffraction, Raman spectroscopy, UV-visible spectroscopy, and scanning electron microscopy. The thickness of the films prepared was varied from 50 to 400 nm in order to establish a relationship between film thickness and water splitting performance. The photocurrent of the WO₃ thin films, measured in a 0.5 M Na₂SO₄ electrolyte solution against a standard Ag/AgCl reference electrode, increased with increasing film thickness. The film electrosprayed for 10 min exhibited a photocurrent density of 0.04 mA/cm². The photocurrent density was increased by 10-fold to 0.40 mA/cm² when the electrospraying time was increased to 60 min. Of all the films tested in this study, the film electrosprayed for 60 min, which had a thickness of 400 nm, showed the best photoelectrochemical cell activity.