Optimizing the Carbon Dioxide Reduction Pathway through Surface Modification by Halogenation.

Facilitating the charge separation of semiconductor photocatalysts to increase the photocatalytic CO2 reduction activity has become a great challenge for sustainable energy conversion. Herein, the surface halogen-modified defect-rich Bi2 WO6 nanosheets have been successfully prepared to address the aforementioned challenge. Importantly, the modification of surface with halogen atoms is beneficial for the adsorption and activation for CO2 molecules and charge separation. These properties have been analyzed by experimental and theoretical methods. DFT calculations revealed that the modification of the Bi2 WO6 surface with Br atoms can decrease the formation energy of the *COOH intermediate, which accelerates CO2 conversion. All halogen-modified defect-rich Bi2 WO6 nanosheets showed an enhanced photocatalytic CO2 reduction activity. Specifically, Br-Bi2 WO6 exhibited the best CO generation rate of 13.8 μmol g-1 h-1 , which is roughly 7.3 times as high as the unmodified defect-rich Bi2 WO6 (1.9 μmol g-1 h-1 ). Moreover, in the presence of a cocatalyst (cobalt phthalocyanine) and a sacrificial agent (triethanolamine), Br-Bi2 WO6 exhibited an even further improved CO generation rate of 187 μmol g-1  h-1 . This finding provides a new approach to optimize the CO2 reduction pathway of semiconductor photocatalysts, which is beneficial to develop highly efficient CO2 reduction photocatalysts.