Boron-Doped Oxidized Carbon Black Hybridizing Bismuth Oxide for Electrocatalytic CO₂ to Formate at a Large Current Density

The electrochemical CO₂ reduction reaction (CO₂RR) is a feasible green route for chemical production, but the design of an efficient catalyst is still challenging to fulfill the requirement of an industrial current. In this study, we reported a hybrid material Bi@BOC composed of boron-doped oxidized carbon black and bismuth oxide for the conversion of the CO₂ to formate under a large current density. Bi@BOC underwent an irreversible in situ reconstruction during the CO₂RR process to form a Bi₂O₃/Bi₂O₂CO₃ composite as the active sites that facilitated the production of formate across a broad current range of 300-800 mA cm^-2, e.g. achieving a Faradaic efficiency of formate (FE_formate) > 95% at 800 mA cm^-2. Additionally, Bi@BOC maintained the FE_formate above 80% at 100 mA cm^-2 for 12 h in a membrane electrode assembly (MEA) reactor. Operando X-ray absorption fine structure (XAFS) spectra and in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) confirmed the structural reconstruction into Bi₂O₂CO₃ and unraveled the roles of hybridizing B-doped carbon with bismuth: 1) promotion of the abundant Bi₂O₂CO₃ formation with high stability for the reversible valence variation of the Bi species; 2) improvement of the conductivity to accelerate the charge transfer; and 3) provision of the better hydrophobicity to inhibit the hydrogen evolution side reaction.