Modulating the PCET process via optimizing the local microenvironment of a CdS@NiV-LDH heterojunction for CO2 reduction in tunable green syngas photosynthesis†

Abstract

Photoconversion of CO₂ and H₂O into syngas (CO + H₂) for the Fischer–Tropsch reaction is considered a feasible plan to address global energy requirements in times of global warming. However, the production of syngas with high activity and adjustable proportion is challenging mainly due to the less efficient multi-step proton-coupled electron transfer (PCET) process owing to the unfavorable local microenvironment of photocatalysts. Herein, an S-scheme CdS@NiV-LDH (HNV) heterojunction is constructed through mild wet-chemistry methods, and NiV-LDH nanosheets are uniformly grown in situ on the surface of hollow cubic CdS (HCC). The as-prepared three-dimensional hierarchical architecture of the HNV photocatalyst leads to a controllable CO/H₂ ratio ranging from 0.2 to 1, and the CO and H₂ production rate of the optimal HNV-4 heterojunction can reach 1163.8 μmol g⁻¹ h⁻¹ and 1334.6 μmol g⁻¹ h⁻¹, respectively. X-ray photoelectron spectroscopy, electron spin spectroscopy, and photo-deposition platinum metal test show that the photogenerated charge carriers in HNV follow an S-scheme charge transfer mechanism. This significantly improves the spatial separation of the photogenerated electron–hole pairs via the built-in electric field that modifies the electric field microenvironment of the HNV photocatalyst to accelerate the photoreduction process. Meanwhile, the NiV-LDH nanosheets on the external surface act as CO₂ enricher and H₂O moderator that adjusts the reaction microenvironment to speed up the PCET process by increasing the local CO₂ concentration and facilitating *COOH intermediate generation in the HNV heterojunction. This work opens a new horizon for exploring novel heterogeneous photocatalysts toward enhanced visible-light-driven CO₂ conversion to tunable green syngas.