Electronic interaction and band alignment between Cu sub-nanometric clusters and ZnIn2S4 nanosheets towards selective photoreduction of CO2 to CO

•ZnIn2S4 nanosheets supported Cu sub-nanometric clusters catalyst was fabricated toward efficient photoreduction CO2 to CO.•Strong metal-support interaction and band alignment were realized between Cu sub-nanometric clusters and ZnIn2S4 nanosheets.•The Cu atoms with diverse chemical states would promote both CO2 activation and protonation process.•The established Ohmic contact facilitate the charge transfer from ZnIn2S4 to Cu sub-nanometric clusters. Engineering the electronic properties of heterogeneous photocatalysts with charge transfer regulated is an effective strategy to boost their CO2 reduction activity. Here, we drew inspiration from the strong metal-support interaction effect, and fabricated ZnIn2S4 supported-Cu sub-nanometric clusters photocatalyst. Within this catalyst, the formed CuS bond would redistribute interfacial charge, resulting in diverse chemical states of Cu atoms and the establishment of Ohmic contact between ZIS and Cu. The built-in electric field of such Ohmic contact benefited the migration of photoexcited electrons from ZIS to Cu. Further mechanistic studies unveiled the crucial role of positively charged Cu atom near the interface in facilitating H2O dissociation, and its adjacent Cu atom at the top-surface adopting a distinct chemical state could activate linear CO2 molecule into a bent configuration. These features substantially lowered energy barriers for CO2 adsorption and subsequent *COOH formation, and Cu-ZIS, accordingly, exhibited a remarkable CO production rate of 60.2 μmol g-1h−1, approximately 20.8-fold enhancement compared to ZIS counterpart.