One-Step Dry Coating of Hybrid ZnO-WO 3 Nanosheet Photoanodes for Photoelectrochemical Water Splitting with Composition-Dependent Performance.

In this study, the potential of zinc oxide (ZnO), tungsten oxide (WO 3 ), and their composites (ZnO-WO 3 ) as photoanodes for photoelectrochemical (PEC) water splitting was investigated. ZnO-WO 3 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 post-processes. Different compositions of ZnO-WO 3 NCs were optimized to enhance the kinetics of the PEC water-splitting reaction. Surface morphology analysis revealed the transformation of microsized particle nanosheets (NS) powder into nanosized particle nanosheets (NS) across all photoanodes. The optical characteristics of ZnO-WO 3 photoanodes were scrutinized using diffuse reflectance and photoluminescence emission spectroscopy. Of all the hybrid photoanodes tested, the photoanode containing 10 wt.% WO 3 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 WO 3 content in ZnO-WO 3 NCs, which is attributed to improved charge transfer kinetics and carrier segregation. The maximum photocurrent for a NC, i.e., 10 wt.% WO 3 , was recorded at 0.133 mA·cm -2 at 1.23V vs. a reversible hydrogen electrode (RHE). The observed improvement in photocurrent was nearly 22 times higher than pure WO 3 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-WO 3 ratio in the hybrid NCs.