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.