Optimal oxidation of Cu_xZn_1-xS photocatalysts for enhanced solar H₂ production by efficient charge separations

Solar water splitting is a promising way of producing H₂ from the renewable natural resources, and heterostructure photocatalysts have been widely investigated in photocatalytic applications. In this work, flower-shaped Cu_xZn_1-xS composite photocatalysts were prepared with various copper contents and then further thermally oxidized under controlled oxygen atmosphere. The oxidized composite catalysts formed the Z-scheme assisted type-II heterosystem, which resulted in efficient photo-generated charge transfer. The maximum H₂ production rate was determined as 595 μmol/g/h from the optimally oxidized Cu_xZn_1-xS photocatalyst. This could be mainly attributed to the highest Cu₂O crystal fraction in the total copper oxides phases as confirmed by XRD measurement. High light absorption and low charge recombination in heterostructure system were crucial points to improve solar harvesting efficiency in water splitting reactions. Therefore, overall photocatalytic efficiency of the oxidized composite photocatalysts can be enhanced by optimizing their atomic compositions and crystalline phase fractions.