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 CO 2 involves employing electrochemical CO 2 reduction reactions (ECO 2 RR). Within this context, the ECO 2 RR 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 H 2 during the electroconversion of CO 2 . In this regard, Bi-MOFs and their derivatives, such as N-doped carbon-supported α-Bi 2 O 3 –CN x and Bi NPs/NC, were examined as potential electrocatalysts for ECO 2 RR. In an aqueous bicarbonate electrolytic solution, the α-Bi 2 O 3 –CN x -600 composites demonstrated a remarkable Faradaic efficiency of 93.8% at −0.79 V vs RHE, with minimal H 2 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-Bi 2 O 3 –CN x -600 composites in 0.5 M KHCO 3 (−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-Bi 2 O 3 within the carbon frameworks (CN x ), providing abundant active sites. Moreover, a higher content of N-doping in the α-Bi 2 O 3 –CN x -600 lattice likely facilitated *OCHO generation. Density functional theory calculations were also utilized to scrutinize the reaction mechanism underlying the CO 2 reduction reaction to formic acid (HCOOH) over α-Bi 2 O 3 (−120) monoclinic and Bi(012) rhombohedral composites. The computed Gibbs free energy changes associated with the reduction of CO 2 to HCOOH and hydrogen (H 2 ) formation on the α-Bi 2 O 3 catalyst suggest a potential suppression of the hydrogen evolution reaction (HER), aligning with experimental findings. Hence, these findings suggest that the prepared α-Bi 2 O 3 –CN x -600 catalysts hold significant potential for the efficient electrochemical reduction of CO 2 to fuels.