Boosting Photocatalytic CO₂ Reduction via Oxygen Vacancy Defective S-Scheme In₂O₃@NiIn₂S₄ Hollow Spheres with Efficient Charge Separation

One of the most promising approaches to carbon neutrality is photocatalytic conversion of CO₂ into chemical fuels. Nevertheless, it continues to face significant challenges in addressing high charge-transfer resistance and sluggish charge-transfer kinetics, substantially limiting its practicality for large-scale deployment. Here, we prepared S-scheme In₂O₃@NiIn₂S₄ hollow spheres (HSs) utilizing an ordinal solvothermal coating of Ni-MOF and a high-temperature sulfidation process of the In(OH)₃-InOOH hollow sphere precursor, which facilitated close contact between the two components. This close contact provides an efficient channel for the smooth transfer of light-induced charges across the heterointerface. The S-scheme In₂O₃@NiIn₂S₄ heterojunction is crucial for boosting the separation of space charges, which promotes the efficiency of multiple photochemical processes. Meanwhile, the oxygen vacancy defects generated in In₂O₃ provide more active sites and promote charge-transfer in the S-scheme heterojunction. The combined benefits of these advantages enable the enhanced S-scheme In₂O₃@NiIn₂S₄ HSs to demonstrate remarkable photocatalytic performance in CO₂ reduction. In situ X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) provide evidence for the S-scheme charge transfer pathway. This research introduces a practical approach aimed at enhancing robust interactions among the various components of heterostructure catalysts, thereby facilitating charge transfer and improving the photocatalytic activity.