Tuning the visible light activity of tungsten oxide layers by changing the anodization conditions

Abstract

Photoelectrochemical water splitting under solar radiation is one of the most studied methods of solar-to-fuel energy conversion. The search for effective photoelectrode materials operating under solar radiation is still ongoing, and in this paper, it is shown how to control the optical and photoelectrochemical properties of anodic tungsten oxide layers by changing the anodizing potential. Anodic tungsten oxide layers were obtained in an aqueous electrolyte with 1 M ammonium sulfate and 75 mM ammonium fluoride at a constant voltage of 20–70 V and annealed at 500 °C in air. Comprehensive characterization of materials was performed using SEM, XRD, UV–Vis DRS, Mott-Schottky analyses, and photoelectrochemical water splitting tests. It was found that with increasing the anodizing potential the band gap narrows from 3.09 eV to 2.75 eV, donor density increases, and the IPCE spectrum shifts towards the visible light range.