Stable Solar Water Splitting Enabled in Anodic W/WO₃ Nanorod Based Electrodes by Hydrothermal Engineering

The stability of WO₃ photoelectrodes in neutral media remains a significant challenge, particularly for those fabricated by anodic W oxidation. We report a simple, one-step hydrothermal treatment that transforms porous anodic WO₃ into nanorods with a dispersed FeWO₄ phase. This morphological evolution combines the advantages of high-aspect-ratio structures for improved light absorption with reduced charge recombination losses. The treatment also promotes preferential WO₃ growth along the monoclinic (002) planeknown to favor water splitting. The modified electrodes exhibited considerable photoluminescence quenching, significantly enhanced charge separation efficiency, and higher photon-to-current conversion, resulting in a photocurrent density that was ∼1.8 times higher at 1.0 V vs RHE. Additionally, oxygen vacancy formation during operation likely contributes to charge redistribution, mitigating surface degradation in sodium sulfate and enabling rapid stabilization of the photocurrent over several hours. Electrochemical impedance spectroscopy reveals evidence of p-n heterojunction due to integration of the tungstate phase with WO₃, extended charge carrier lifetimes, and enhanced charge transfer. This scalable surface engineering approach offers a promising route to enhance the performance and durability of anodic WO₃ for practical solar-driven water oxidation.