Optimized tungsten-copper oxide Z-schemes for efficient water splitting

ABSTRACT In this study, we report the synthesis and optimization of photo responsive Z-scheme heterostructures composed of tungsten oxide (WO 2.9 ) nanostructures synthesized via hot wire chemical vapor deposition (HWCVD) on the top of cuprous oxide (Cu 2 O) thin films on copper substrates for efficient, bias-free solar water splitting. The engineered WO 2.9 /Cu 2 O heterostructures leverage the electronic properties of both intrinsic semiconductors to enhance light absorption, charge separation, and photocatalytic performance. Morphological evolution from rod-like to cauliflower-like WO 2.9 nanostructures was achieved by tuning the volume of tungsten oxide. Structural and compositional analysis using X-ray diffraction (XRD), and Raman spectroscopy confirmed the high crystallinity and chemical composition of each compound. Our findings reveal that solar-to-hydrogen (STH) efficiency is highly sensitive to the WO 2.9 volume, with volume-dependent synthesis influencing charge carrier dynamics. Electrochemical characterizations, including cyclic voltammetry and electrochemical impedance spectroscopy, demonstrated a substantial change in photo-current density and charge transfer kinetics under simulated solar illumination. The resultant WO 2.9 /Cu 2 O photocatalyst with an optimized W/Cu ratio shows high and stable photocurrent density. The optimized heterostructures achieved maximum current density and STH efficiency of −0.42 Am -2 and 1%, respectively, which demonstrates good photochemical stability and highlights its strong potential for scalable and sustainable green hydrogen production.