One-step dry coating of hybrid ZnO–WO3 nanosheet photoanodes for photoelectrochemical water splitting with composition-dependent performance

Abstract

In this study, the potential of zinc oxide (ZnO), tungsten oxide (WO3), and their composites (ZnO-WO3) as photoanodes for photoelectrochemical (PEC) water splitting was investigated. ZnO-WO3 nanocomposites (NCs) were deposited on fluorine-doped tin oxide substrates at room temperature using a one-step dry coating process, the nanoparticle deposition system, with no postprocesses. The hybridization composition of ZnO-WO3 NCs was optimized to improve the efficiency of the PEC water-splitting reaction kinetics. The transformation of the microsized particle nanosheets (NS) powder into nanosized particle nanosheets (NS) across all photoanodes was revealed by surface morphology analysis. Diffuse reflectance and photoluminescence emission spectroscopy were employed to investigate the optical characteristics of the ZnO-WO3 photoanodes. Of all the hybrid photoanodes tested, the photoanode containing 10 wt.% WO3 exhibited the lowest bandgap of 3.20 eV and the lowest emission intensity, indicating an enhanced separation of photogenerated carriers and solar energy capture. The photoelectrochemical results showed a 10% increase in the photocurrent with increasing WO3 content in ZnO-WO3 NCs, which is attributed to improved charge transfer kinetics and carrier segregation. The maximum photocurrent recorded vs. the reversible hydrogen electrode (RHE) was 0.133 mA·cm−2 @ 1.23V. The observed improvement in photocurrent was nearly 22 times higher than pure WO3 nanosheets and 7.3 times more than that of pure ZnO nanosheets, indicating the composition-dependence of PEC performance, where the synergy requirement strongly relies on utilizing the optimal ZnO-WO3 ratio in the hybrid NCs.

Keywords: ZnO-WO3 hybrid photoanodes; Charge transfer kinetics; Photoelectrochemical water splitting; Nanoparticle deposition system (NPDS); Nanosheets; Nanocomposites; Bandgap optimization.