Single-Crystalline α-Bi2O3 Induced by Nitrogen Doping for Enhanced and Selective CO2 Electroreduction to Formate over a Wide Negative Potential Window

An efficient method for reducing atmospheric CO₂ involves employing electrochemical CO₂ reduction reactions (ECO₂RR). Within this context, the ECO₂RR to formate is recognized as a highly promising pathway to produce value-added fuels and chemicals. However, the challenge lies in suppressing the evolution of CO and H₂ during the electroconversion of CO₂. In this regard, Bi-MOFs and their derivatives, such as N-doped carbon-supported α-Bi₂O₃–CN_x and Bi NPs/NC, were examined as potential electrocatalysts for ECO₂RR. In an aqueous bicarbonate electrolytic solution, the α-Bi₂O₃–CN_x-600 composites demonstrated a remarkable Faradaic efficiency of 93.8% at −0.79 V vs RHE, with minimal H₂ production. This efficiency was consistently maintained at an average of 91.2% over the wide potential range of −0.69 to −0.99 V vs RHE. Furthermore, high partial current densities were also achieved for α-Bi₂O₃–CN_x-600 composites in 0.5 M KHCO₃ (−42.59 mA cm^–2 at −0.99 V), displaying excellent durability for over 10 h. The improved catalytic performance and selectivity were ascribed to a higher Bi loading as well as well-dispersed α-Bi₂O₃ within the carbon frameworks (CN_x), providing abundant active sites. Moreover, a higher content of N-doping in the α-Bi₂O₃–CN_x-600 lattice likely facilitated *OCHO generation. Density functional theory calculations were also utilized to scrutinize the reaction mechanism underlying the CO₂ reduction reaction to formic acid (HCOOH) over α-Bi₂O₃(−120) monoclinic and Bi(012) rhombohedral composites. The computed Gibbs free energy changes associated with the reduction of CO₂ to HCOOH and hydrogen (H₂) formation on the α-Bi₂O₃ catalyst suggest a potential suppression of the hydrogen evolution reaction (HER), aligning with experimental findings. Hence, these findings suggest that the prepared α-Bi₂O₃–CN_x-600 catalysts hold significant potential for the efficient electrochemical reduction of CO₂ to fuels.