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

Carbon dioxide (CO) activation by effective electrons has been regarded as the rather necessary first-step for a CO reduction reaction (CORR). 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 CORR. 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 CORR 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, are firstly confirmed by the electron density difference based on density functional theory calculations. Next, the CORR 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, 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, 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 photoreduction on the BiOBr(001) surface and provide new perspectives for better understanding the structure-performance relationship at the molecular level.