Selective Photocatalytic Reduction of CO2 to CH4 Modulated by Chloride Modification on Bi2WO6 Nanosheets

Solar-driven photocatalytic CO2 reduction into CH4 with H2O is considered to be a promising way to alleviate the energy crisis and greenhouse effect. However, current CO2 photoreduction technologies tend to overlook the role of photooxidation half reaction as well as the effect of the protons produced by water oxidation on CH4 generation, resulting in low CO2 conversion efficiency and poor CH4 selectivity. In the present study, a series of chloride-modified Bi2WO6 nanosheets were constructed in view of chloride-assisted photocatalytic water oxidation. The results show that the CH4 yield of the synthesized sample can be enhanced up to about 10 times compared to that with no Cl- modification. Besides, the selectivity of CH4 can be regulated by the loading amount of chloride, varying from 51.29% for Bi2WO6 to 94.98% for the maximum. The increase of product yield is attributed to chloride modification, which not only changed the morphology of the catalyst, but also modified the pathway of water oxidation. Further studies on intermediate products and the density functional theory calculation confirm that the Cl- ions on Bi2WO6 nanosheets not only promote H2O oxidation, but also lower the energy barrier for intermediate *CHO generation, thus facilitating CH4 production. The results gained herein may provide some illuminating insights into the design of a highly selective photocatalyst for efficient CO2 reduction.