Enhancement of UV-responsive photocatalysts aided by visible-light responsive photocatalysts: Role of WO3 for H2 evolution on CuCl

[Display omitted] •WO3 absorbs visible light but inactive for photocatalytic H2 evolution.•We found visible-excitation of WO3 can assist H2 evolution on UV-active CuCl photocatalysts.•Activity of CuCl/WO3 increased 1.7 fold by the addition of visible light than UV only.•Z-schematic recombination takes place at WO3/CuCl to elongate the lifetime of electrons in CuCl.•Inactive narrow-band gap materials can be use to enhance wide-band gap photocatalysts. WO3 is one of the most popular materials for visible-light photocatalysts. However, its conduction band minimum is too low for water reduction. Here, we found that WO3 can assist water reduction by using visible light in a CuCl2 aqueous solution. Photoirradiation of WO3 in CuCl2 reduces Cu2+ to form indissoluble CuCl adducts, and as-produced CuCl/WO3 was active for H2 evolution under UV-light. This composite has very low reactivity under visible light (>400 nm), but visible-light assisted H2 evolution was observed with simultaneous irradiation with UV light: the activity was increased ∼1.7 fold. Transient absorption measurements revealed that Z-schematic recombination initially takes place between photogenerated electrons in WO3 and holes in CuCl. As a result, the lifetime of electrons in CuCl was increased, enhancing H2 evolution. These results demonstrate that inactive narrow-band gap materials can be used to enhance the activity of wide-band gap materials under sunlight illumination.