One-Step Rapid and Scalable Flame Synthesis of Efficient WO₃ Photoanodes for Water Splitting

Photoelectrochemical water splitting is a promising approach for the carbon-free production of hydrogen using sunlight. Here, robust and efficient WO₃ photoanodes for water oxidation were synthesized by the scalable one-step flame synthesis of nanoparticle aerosols and direct gas-phase deposition. Nanostructured WO₃ films with tunable thickness and band gap and controllable porosity were fabricated by controlling the aerosol deposition time, concentration, and temperature. Optimal WO₃ films demonstrate superior water oxidation performance, reaching a current density of 0.91 mA at 1.24 V vs. reversible hydrogen electrode (RHE) and an incident photon-to-current conversion efficiency (IPCE) of ca. 61 % at 360 nm in 0.1 m H₂SO₄. Notably, it is found that the excellent performance of these WO₃ nanostructures arises from the high in situ restructuring temperature (ca. 1000 °C), which increases oxygen vacancies and decreases charge recombination at the WO₃/electrolyte interface. These findings provide a scalable approach for the fabrication of efficient photoelectrodes based on WO₃ and other metal oxides for light-driven water splitting.