Interfacial charge separation of nickel tungstate anchored on g-C3N4 heterojunction stimulates visible-light driven direct Z-scheme photoelectrochemical hydrogen evolution

Active photocathodes are required for the photo(electro)chemical hydrogen evolution re-action (PEC-HER) in a highly efficient solar-to-hydrogen fuel conversion process aided by solar assisted water splitting. Here, we used a simple one-pot solvothermal method to prepare NiWO4/g-C3N4 nanocomposites for PEC-HER using low-cost, metal-free photo-catalysts such as graphitic carbon nitride (g-C3N4) and nickel tungstate (NiWO4). Subse-quently, the physicochemical and optoelectronic nature of the as-synthesized materials were studied by spectroscopic methods. As part of a direct Z-scheme heterogeneous mechanism, the photoactive module, g-C3N4 was blended with NiWO4 in varying ratios to enhance the efficiency of charge separation in PEC-HER. As expected, the established NiWO4/g-C3N4 nanocomposite demonstrates an enhanced photo(electro)catalytic activities compared to the single components. It is firmly due to the presence of intimate interfacial interaction between g-C3N4 and NiWO4, which further supports the existence of electrons in the conduction band of g-C3N4 and holes in the valence band of NiWO4. The prepared NiWO4/g-C3N4 nanocomposite with 15 wt% of g-C3N4 showed an enhanced photocurrent density of 167.81 mA cm-2, which is higher than that of other prepared photo(electro) catalysts and confirms its excellent charge separation efficiency as well as very low electron-hole recombination rate. Besides, the photoelectrochemical activities of the pre-pared materials were analysed through a PEC-HER, revealing that the developed NiWO4/g-C3N4 nanocomposite as photocathode requires a low overpotential of 0.048 V to reach the current density of 10 mA cm-2 and a Tafel slope of 43 mV dec-1, indicating the superiority of the photo(electro)catalyst. In addition, the NiWO4/g-C3N4 photocathode exhibits excel-lent performance for PEC-HER with higher stability.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.