Defect-Driven Surface and Electronic Structure Modulation in Alloyed Bismuth Chalcogenide Nanosheets for CO 2 Reduction

The modulation of defects and edge site reactivity significantly influences the activity of catalysts in various electrochemical processes. However, the role of these factors in bismuth-based electrocatalysts for the CO₂ reduction reaction (CO₂RR) has not been adequately realized. To elucidate the effects of these phenomena on the CO₂RR, we synthesize Bi₂Se_3-xTe_x (x = 0, 1, 1.5, 2, 3) alloyed nanosheets by varying the composition of selenium (Se) and tellurium (Te). Our approach simultaneously modifies their surface morphology and electronic structure, effectively regulating the CO₂RR activity. The presence of rich defects in the alloyed nanosheets leads to the formation of a high density of vertically aligned edges. The chalcogen vacancies in the alloyed nanosheets introduce localized defect states within the bandgap, which facilitates the accumulation of electrons at the active sites and significantly lowers the kinetic barriers for CO₂RR. These defect-induced geometric and electronic modifications optimize the CO₂RR performance, achieving a high Faradaic efficiency for formate. Furthermore, when alloyed nanosheets are coupled with a photoanode, the integrated photoelectrochemical CO₂RR device exhibits an average applied bias photon-to-current efficiency of up to 12.1% for formate over 50 h of operation. Our study offers a promising pathway for designing high-performance CO₂RR catalysts through chalcogen alloying.