WO3 electrodes by spray pyrolysis for photoelectrochemical applications: impact of W precursor and Cl incorporation

Abstract

This study explores the influence of various precursors including ammonium metatungstate (AMT) and peroxotungstic acid (PTA) in water, and tungsten hexachloride (WCl₆ in MeOH or EtOH), as well as the role of ammonium chloride incorporation on the structural, morphological, and photoelectrochemical characteristics of WO₃ layers synthesized by spray pyrolysis. X-ray diffraction (XRD) analysis revealed that films annealed at 550 °C crystallized in the monoclinic phase of WO₃ with a polycrystalline structure without amorphous parts. Different morphological features of the samples were identified by scanning electron microscopy (SEM): dense grains for films formed using PTA, aggregated grains for films synthesized from AMT, smooth and uniform surfaces for films based on WCl₆, and porous architectures resulting from NH₄Cl incorporation. Photoelectrochemical measurements under UV and simulated solar illumination demonstrated that AMT/NH₄Cl – derived WO₃ films significantly enhanced the initial photocurrent density, reaching values of up to ∼3 mA cm⁻² under UV light. Topological energy dispersive spectroscopy (EDS) revealed the existence of Cl rich areas responsible for this effect. With prolonged exposition to light and bias, Cl in these areas was oxidatively exhausted and average current densities as in samples obtained with other precursors were obtained. These findings highlight the critical role of precursor selection and doping in determining the photoelectrochemical performance of spray-deposited WO₃ photoanodes.