This study developed a porous tungsten-doped TiO2 coating on a titanium substrate using plasma electrolytic oxidation, followed by ZnO decoration and subsequent heat treatment. The ZnO-decorated coating significantly improved electrocatalytic and photoelectrocatalytic efficiencies for methylene blue degradation under visible light, increasing from 8.6 to 62% and from 29.7 to 84.4%, respectively. However, photocatalytic efficiency declined from 53.4 to 43.1% after ZnO decoration, primarily due to an increase in the bandgap (2.87 to 3.00 eV) and reduced light absorption caused by ZnO coverage. Elemental analysis revealed ZnO accumulation is near the inner coating layer, with partial pore filling which was further verified by increased inner layer resistance and elevated Warburg values in the EIS study. The inner layer of the coating, enriched with ZnO, supported electrocatalytic activity, while the outer layer mainly facilitated photocatalytic reactions. This improvement was mainly attributed to extended charge carrier lifetime resulting from the n-n heterojunction effect at the interface of ZnO and TiO2 semiconductors, as deduced from CV and EIS data. Reusability tests revealed stable photoelectrocatalytic performance over six cycles, with only a 22.5% efficiency reduction. This study highlights the potential of the fabricated ZnO/W-TiO2 coatings as durable and effective photoanodes for wastewater treatment and other industrial applications.
