Light-induced halogen defects as dynamic active sites for CO₂ photoreduction to CO with 100% selectivity

Dynamic defects on halide perovskite materials, caused by ion dissociation and migration under light illumination, typically result in undesirable energy dissipation and limited energy conversion efficiency. However, in this work, we demonstrated that dynamic halogen defects generated by the same process in bismuth oxyhalide (Bi₅O₇Cl) materials can act as active sites to promote charge separation and photocatalytic efficiency. Mechanistic studies and density functional theory calculations revealed that dynamic Cl defects affected the electronic structure of Bi₅O₇Cl and photocatalytic CO₂ reduction process. As active sites, these defects promoted charge transfer, leading to the activation of adsorbed CO₂ molecules and reduction of the energy barrier of the rate-determining step. Thus, CO₂ was spontaneously converted into COOH^- intermediate and finally reduced to CO with a high efficiency of 108.60 μmol g^-1 and selectivity of 100% after 4-h of CO₂ photoreduction. This work is highly instructive and valuable to the exploration of dynamic defects on halide-containing materials applied in solar energy conversion.