Abstract: Sunlight-driven photocatalytic water-splitting for hydrogen (H₂) evolution is a desirable strategy to utilize solar energy. However, this strategy is restricted by insufficient light harvesting and high photogenerated electron-hole recombination rates of TiO₂-based photocatalysts. Here, a graphene-modified WO₃/TiO₂ step-scheme heterojunction (S-scheme heterojunction) composite photocatalyst was fabricated by a facile one-step hydrothermal method. In the ternary composite, TiO₂ and WO₃ nanoparticles adhered closely to reduced graphene oxide (rGO) and formed a novel S-scheme heterojunction. Moreover, rGO in the composite not only supplied abundant adsorption and catalytically active sites as an ideal support but also promoted electron separation and transfer from the conduction band of TiO₂ by forming a Schottky junction between TiO₂ and rGO. The positive cooperative effect of the S-scheme heterojunction formed between WO₃ and TiO₂ and the Schottky heterojunction formed between TiO₂ and graphene sheets suppressed the recombination of relatively useful electrons and holes. This effect also enhanced the light harvesting and promoted the reduction reaction at the active sites. Thus, the novel ternary WO₃/TiO₂/rGO composite demonstrated a remarkably enhanced photocatalytic H₂ evolution rate of 245.8 μmol g^-1 h^-1, which was approximately 3.5-fold that of pure TiO₂. This work not only presents a low-cost graphene-based S-scheme heterojunction photocatalyst that was obtained via a feasible one-step hydrothermal approach to realize highly efficient H₂ generation without using noble metals, but also provides new insights into the design of novel heterojunction photocatalysts.

Key words: Step-like heterojunction, S-scheme heterojunction, S heterojunction, Photocatalyst, Hydrogen generation