Oxygen-bridged Schottky junction in ZnO-Ni3ZnC0.7 promotes photocatalytic reduction of CO2 to CO: Steering charge flow and modulating electron density of active sites.

ABSTRACT

Developing carbon dioxide (CO2) photocatalysts from transition metal carbides (TMCs) with abundant active sites, modulable electron cloud density, as well as low cost and high stability is of great significance for artificial photosynthesis. Building an efficient electron transfer channel between the photo-excitation site and the reaction-active site to extract and steer photo-induced electron flow is necessary but challenging for the highly selective conversion of CO2. In this study, we achieved an oxygen-bridged Schottky junction between ZnO and Ni3ZnC0.7 (denoted as Znoxide-O-ZnTMC) through a ligand-vacancy strategy of MOF. The ZnO-Ni3ZnC0.7 heterostructure integrates the photo-exciter (ZnO), high-speed electron transport channel (Znoxide-O-ZnTMC), and reaction-active species (Ni3ZnC0.7), where Znoxide-O-ZnTMC facilitates the transfer of excited electrons in ZnO to Ni3ZnC0.7. The Zn atoms in Ni3ZnC0.7 serve as electron-rich active sites, regulating the CO2 adsorption energy, promoting the transformation of *COOH to CO, and inhibiting H2 production. The ZnO-Ni3ZnC0.7 shows a high CO yield of 2674.80 µmol g-1h-1 with a selectivity of 93.40 % and an apparent quantum yield of 18.30 % (λ = 420 nm) with triethanolamine as a sacrificial agent. The CO production rate remains at 96.40 % after 18 h. Notably, ZnO-Ni3ZnC0.7 exhibits a high CO yield of 873.60 µmol g-1h-1 with a selectivity of 90.20 % in seawater.