BiOCl Nanoflowers with High Levels of Oxygen Vacancy for Photocatalytic CO₂ Reduction

CO2 photoreduction products, such as CO and CH4, have the potential to be further processed into valuable products and fuels, making this process a promising, environmentally friendly, and economically viable energy conversion technology. In this study, uniform BiOCl hierarchical nanoflowers with tunable thickness and abundant oxygen vacancies (OVs) were synthesized using a poly(vinylpyrrolidone)/ethylene glycol-assisted self-assembly method. The OV-rich BiOCl nanoflower (BiOCl-3) showed a 4-fold increase in photocatalytic conversion of CO2 to CO compared to BiOCl nanosheets (BiOCl-1). Density functional theory (DFT) calculations and energy band analysis reveal anisotropy in the CO2 reduction activity across different crystal facets, and the morphology can affect both the conduction band (CB) and band gap, resulting in a more negative CB edge for BiOCl compared to the reduction potential of CO2 photoreduction to CO. This work provides a comprehensive analysis and explanation of the OV-rich BiOCl photocatalytic CO2 reduction from both experimental and theoretical perspectives.