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

## TL;DR

This paper investigates how different chemical precursors and chloride addition affect the performance of WO3 electrodes in photoelectrochemical applications.

## Contribution

The study reveals how precursor choice and Cl incorporation influence the structural and photoelectrochemical properties of WO3 films.

## Key findings

- AMT/NH4Cl-derived WO3 films showed the highest initial photocurrent density under UV light.
- Cl-rich areas in WO3 films were identified as responsible for enhanced performance but were oxidatively exhausted over time.
- WO3 films synthesized with WCl6 exhibited smooth and uniform surfaces.

## 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.

Long-term chronoamperometry under irradiation (AM 1.5 (1 sun)) of WO3 films at 1.4 V vs. Ag/AgCl. The decrease of photocurrent is explained by the oxidative exhaustion of Cl− rich areas present in WO3 films as proved by EDS analysis.