Synergistic boron doping and Tin-Bismuth bimetallic interface for lowering the two Free-Energy barriers in electrocatalytic CO2 reduction to formate

Abstract

Bismuth-based catalysts for the electrocatalytic reduction of CO₂ to formate are regarded as a highly promising strategy for the conversion of surplus CO₂ into valuable chemical commodities. Currently, lowering the free-energy barriers of the activation of CO₂ and *OCHO is highly desirable and challenging. In this study, a catalyst rich in boron (B)-doped and Sn-Bi bimetallic interface is constructed. The utilisation of X-ray photoelectron spectroscopy (XPS), Bader charge analysis and projected density of states (PDOS) analysis reveal that the Bi sites adjacent to boron exhibited a positive valence state. This valence characteristic significantly facilitates the adsorption of CO₂ on the surface, resulting in the generation of the *CO₂^– intermediate. Meanwhile, the bismetallic interface between Bi and Sn induces an electron-rich Bi sites, which subtly enhances the interaction between the active sites and the *OCHO intermediate, thereby reducing the free-energy barrier. The synergistic effect of B doping and the bimetallic interface strategically modulates the local electronic structure of Bi to reduce the two free-energy barriers, including the rate-determining step. Comprehensive electrochemical analysis, coupled with corresponding characterization tests and theoretical calculations, demonstrates that it significantly lowers the two free-energy barriers, achieving an impressive maximum Faraday efficiency of 98.4 % at −1.0 V vs. RHE.