Single-Crystalline\nα‑Bi<sub>2</sub>O<sub>3</sub> Induced by Nitrogen Doping\nfor Enhanced and Selective CO<sub>2</sub> Electroreduction to Formate\nover a Wide Negative Potential\nWindow

An\nefficient method for reducing atmospheric CO<sub>2</sub> involves\nemploying electrochemical CO<sub>2</sub> reduction reactions (ECO<sub>2</sub>RR). Within this context, the ECO<sub>2</sub>RR to formate\nis recognized as a highly promising pathway to produce value-added\nfuels and chemicals. However, the challenge lies in suppressing the\nevolution of CO and H<sub>2</sub> during the electroconversion of\nCO<sub>2</sub>. In this regard, Bi-MOFs and their derivatives, such\nas N-doped carbon-supported α-Bi<sub>2</sub>O<sub>3</sub>–CN<sub><i>x</i></sub> and Bi NPs/NC, were examined as potential\nelectrocatalysts for ECO<sub>2</sub>RR. In an aqueous bicarbonate\nelectrolytic solution, the α-Bi<sub>2</sub>O<sub>3</sub>–CN<sub><i>x</i></sub>-600 composites demonstrated a remarkable\nFaradaic efficiency of 93.8% at −0.79 V vs RHE, with minimal\nH<sub>2</sub> production. This efficiency was consistently maintained\nat an average of 91.2% over the wide potential range of −0.69\nto −0.99 V vs RHE. Furthermore, high partial current densities\nwere also achieved for α-Bi<sub>2</sub>O<sub>3</sub>–CN<sub><i>x</i></sub>-600 composites in 0.5 M KHCO<sub>3</sub> (−42.59 mA cm<sup>–2</sup> at −0.99 V), displaying\nexcellent durability for over 10 h. The improved catalytic performance\nand selectivity were ascribed to a higher Bi loading as well as well-dispersed\nα-Bi<sub>2</sub>O<sub>3</sub> within the carbon frameworks (CN<sub><i>x</i></sub>), providing abundant active sites. Moreover,\na higher content of N-doping in the α-Bi<sub>2</sub>O<sub>3</sub>–CN<sub><i>x</i></sub>-600 lattice likely facilitated\n*OCHO generation. Density functional theory calculations were also\nutilized to scrutinize the reaction mechanism underlying the CO<sub>2</sub> reduction reaction to formic acid (HCOOH) over α-Bi<sub>2</sub>O<sub>3</sub>(−120) monoclinic and Bi(012) rhombohedral\ncomposites. The computed Gibbs free energy changes associated with\nthe reduction of CO<sub>2</sub> to HCOOH and hydrogen (H<sub>2</sub>) formation on the α-Bi<sub>2</sub>O<sub>3</sub> catalyst suggest\na potential suppression of the hydrogen evolution reaction (HER),\naligning with experimental findings. Hence, these findings suggest\nthat the prepared α-Bi<sub>2</sub>O<sub>3</sub>–CN<sub><i>x</i></sub>-600 catalysts hold significant potential\nfor the efficient electrochemical reduction of CO<sub>2</sub> to fuels.