Fabrication of a ZnO/Au/WO₃ indirect Z-scheme thin film for PEC water oxidation

The indirect Z-scheme heterojunction is an advanced charge-transfer configuration that couples two semiconductors through a mediator, enabling efficient separation of electrons and holes while preserving strong redox potential. Such a heterojunction has proven highly effective for photoelectrochemical (PEC) water splitting. Most reported studies on Z-scheme systems have focused on powder-based photocatalysts, which often suffer from limited stability, aggregation, and poor reproducibility. In contrast, this work demonstrates for the first time an indirect Z-scheme thin-film approach, which enables stronger adhesion to substrates and improved stability under PEC operating conditions. In particular, ZnO/Au/WO₃ Z-scheme heterojunctions were fabricated via sequential DC magnetron sputtering of W, Au, and ZnO, followed by post-annealing at 600 °C. Comprehensive characterizations were performed to investigate their structural, morphological, chemical, and optical properties. Under 460 W illumination in 0.5 M Na (Formula presented) SO(Formula presented), the optimized electrode achieves a peak photocurrent density of 1.54 ± 0.5 mA/cm (Formula presented) at 1.4 V vs. RHE, nearly threefold higher than pristine WO₃, and maintains stability over 3000 s. EIS indicates a significant decrease in charge-transfer resistance upon Au and ZnO incorporation. This study highlights the advantages of thin-film Z-scheme engineering, providing a scalable and stable pathway for efficient PEC water oxidation and hydrogen production.