Oxygen-Vacancy-Modulated Cu ₂ O/NiCo ₂ O ₄ Heterojunction Enables Highly Selective Photocatalytic CO ₂ Reduction to CH ₄

Constructing heterojunction photocatalysts with abundant defect sites represents an effective strategy to enhance photocatalytic CO 2 reduction. Herein, a Cu 2 O/NiCo 2 O 4 heterojunction enriched with oxygen vacancies is rationally constructed via an in-situ synthesis route. When employed for photocatalytic CO 2 reduction using H 2 O as the proton source, the resulting catalyst delivers a high CH 4 production rate of 74.58 μmol g −1 h −1 with an exceptional electron selectivity of 98.62%, outperforming pristine Cu 2 O and NiCo 2 O 4 by folds of 177.57 and 21.19, respectively. The remarkable enhancement in activity and selectivity originates from the synergistic effect between the p-n type band alignment and oxygen-vacancy-rich interfaces, which jointly facilitate charge separation and directional electron transfer. X-ray photoelectron spectroscopy and electron paramagnetic resonance analyses reveal pronounced interfacial charge redistribution and abundant surface oxygen vacancies. Importantly, in situ Fourier transform infrared spectroscopy (in situ FTIR) enables continuous identification of key reaction intermediates, allowing the CO 2 -to-CH 4 conversion pathway to be elucidated. This study reveals the underlying mechanism and offers a feasible design strategy for the fabrication of high-efficiency photocatalysts applied in solar-powered CO 2 conversion.