Photocatalytic reduction of CO2 over porous ultrathin NiO nanosheets with oxygen vacancies

In recent years, photocatalytic CO₂ reduction reaction has been recognized as a crucial approach to solve the greenhouse effect. However, the low concentration of CO₂ in the atmosphere necessitates a catalyst with excellent CO₂ enrichment capability. Herein, we designed and synthesized a series of NiO nanosheets featuring oxygen vacancies. Under the condition of pure CO₂ and photosensitizer [Ru(bpy)₃]Cl₂, the yield of CO reaches 16.8 μmol/h with a selectivity of 96%. Through characterization and theoretical calculations, we demonstrate that the presence of oxygen vacancies not only enhances the adsorption capacity of catalysts but also induces lattice distortion in NiO, leading to an increased dipole moment and formation of an internal electric field that facilitates photogenerated carrier separation. Furthermore, we conducted CO₂ reduction reactions under atmospheric condition and surprisingly observed a changing of selectivity from CO to CO and CH₄. A series of control experiments showed that [Ru(bpy)₃]Cl₂ acts as a reduction reaction site due to the presence of O₂ in the atmosphere. Simultaneously, oxygen promotes water splitting, which results in abundant proton generation and subsequent changes in carbon products.