Theoretical insights into effective electron transfer and migration behavior for CO 2 reduction on the BiOBr(001) surfaces.

Carbon dioxide (CO 2 ) activation by effective electrons has been regarded as the rather necessary first-step for a CO 2 reduction reaction (CO 2 RR). In addition, the electron migration and photoreaction selectivity are closely associated with the dominant crystal surface of a catalyst. Therefore, it is very interesting and important to elucidate the electron transfer and charge density effects on the catalyst surface for the CO 2 RR. In this work, the dominant highly-active BiOBr(001) surfaces with Bi-, O- and Br-termination atoms are designed so that their electron distributions and CO 2 RR behaviors can be observed. The electron-rich sites on the BiOBr(001) surfaces, where more effective electrons will migrate to achieve the activation of the adsorbed CO 2 , are firstly confirmed by the electron density difference based on density functional theory calculations. Next, the CO 2 RR pathways at the electron-rich sites are investigated to explore the migration mechanism of effective photo-induced electrons. The results obtained reveal that if a larger number of electrons transfer to CO 2 , then less energy is needed to break the CO bond, and the formation of a *COOH intermediate corresponds to the ability of the surface to take part in protonation. Furthermore, the interface Bi atom can boost the transfer efficiency of effective electrons to CO 2 , but the exposed Br atom with a longer electron transfer distance, because of the steric hindrance of the interface Br atoms, makes it difficult for the electrons to migrate, resulting in it being harder to fracture the CO bond to benefit the formation of the HCOOH product. These findings should give deep insight into the migration behaviors of effective electrons for CO 2 photoreduction on the BiOBr(001) surface and provide new perspectives for better understanding the structure-performance relationship at the molecular level.