Hydrothermal Surface Engineering of Anodic WO₃ Photoelectrode by Simultaneous Iron Doping and Fe₃O₄/FeWO₄ Formation

This study reports a hydrothermal surface modification approach to porous anodized WO₃ to enhance its photoelectrochemical water oxidation performance. This results in the Fe doping of monoclinic WO₃ and the simultaneous formation of Fe-containing phases, such as FeWO₄ and Fe₃O₄. The photocurrent generated at the surface-engineered electrodes was double that of pure WO₃ with long-term stability. The enhancement is attributable to the creation of oxygen vacancies due to Fe doping and the formation of the heterojunction between WO₃ and FeWO₄, a p-type semiconductor, which likely improved the charge carrier lifetime and charge transfer properties. Incident photon to current efficiency (IPCE) measurements revealed enhanced visible light performance, supported by the observed red shift in the light absorption edge. This work is one of the few explorations of WO₃ photoanodes with an opaque metal substrate that involves fabrication of a light-facing overlayer at the surface. Characterization of the fabricated electrodes was carried out using X-ray diffraction (XRD), scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and diffuse reflectance spectroscopy (UV-Vis DRS). Photoelectrochemical studies were conducted using linear voltammetry, amperometry, and electrochemical impedance spectroscopy (Nyquist, Bode, and Mott-Schottky plots).