Energy-efficient rapid thermal processing for enhanced photoelectrochemical performance of WO3 photoanodes

Abstract

Rapid thermal processing (RTP) has emerged as an effective strategy to tailor defect chemistry in metal oxide photoelectrodes while minimising thermal budget and substrate degradation. Here, we investigate the influence of RTP on the structural and photoelectrochemical properties of mesoporous WO3 photoelectrodes for water oxidation. WO3 photoelectrodes deposited by spray coating onto FTO were treated using RTP in air at 650–900 ºC for 60 s, and the results were benchmarked against samples treated for 3 h at 550 ºC in a conventional furnace. Structural analysis revealed comparable crystallinity, phase purity, and morphology across all treatments, indicating minimal structural changes. The optimised RTP treatment at 850 ºC yields a twofold increase in external quantum efficiency (EQE) at 455 nm, and enhances the photocurrent density to 1.9 mA cm2 under 1 sun AM 1.5 G illumination, compared with 1.4 mA cm2 for the furnace-treated sample. Electrochemical impedance spectroscopy (EIS) shows increased effective capacitance (Ceff) and decreased charge-transfer resistance for high-temperature RTP samples (800–900 ºC), consistent with an increased density of shallow donor states that may be associated with subsurface oxygen vacancies. Intensity-modulated photocurrent spectroscopy (IMPS) reveals a correlation between the characteristic frequency (fmin) and steady-state photocurrent, indicating that an increase in vacancy-induced shallow states enhances electron transport through trap-mediated dynamics. Furthermore, RTP lowers energy consumption by around 140-fold relative to conventional annealing. These results highlight RTP as a fast, energy-efficient strategy to enhance photocurrent in WO3 photoelectrodes, providing practical guidelines for the fabrication of high-performance photoanodes.