Z-scheme assisted ZnO/Cu₂O-CuO photocatalysts to increase photoactive electrons in hydrogen evolution by water splitting

Multi-component photocatalysts have been considered as promising candidates to overcome fast charge recombination phenomena in solar water splitting process, which improve electron utilizations in reductive hydrogen generation. However, most reported multi-component systems have been rarely fabricated by aids with z-scheme type components. Thus, cuprous and cupric oxides are proposed as an excellent example for a z-scheme system with ZnO base materials. The ZnO particles are firstly synthesized by a precipitation method, and CuS components are added on the ZnO particle surfaces in various compositions. The ZnO/CuS materials are then thermally treated under controlled oxygen atmosphere to form cuprous and cupric oxides. To enhance photoactive electrons for reductive water splitting in conduction bands of the photocatalyst system, optimum content of cuprous oxides in the z-scheme components is a critical factor. At the optimum cuprous content (14.3%) in the copper oxides, the highest hydrogen production rate of 1092.5 μmolg^-1h^-1 is achieved at about 3% apparent quantum yield under the standard solar irradiation.