Electrochemical Conversion of CO₂ to Methanol on Boron-Doped Diamond Electrode in Monoethanolamine Aqueous Solution

Amine-based CO2 absorption solutions have attracted increasing attention as promising media for carbon capture and utilization due to their high CO2 absorption capacity. In this study, we demonstrate the electrochemical CO2 reduction reaction (CO2RR) using a monoethanolamine-based CO2 absorption solution (MEA-CO2 solution) with boron-doped diamond (BDD) electrodes. Our approach, which combines a BDD electrode and a bipolar membrane (BPM), enables the selective formation of methanol in an MEA-CO2 solution. In addition to the advantages in corrosion resistance of BDD electrodes, the use of a BPM instead of a conventional cation exchange membrane (CEM) continuously supplies CO2 to the electrode surface through the decomposition of carbamate ions. Furthermore, we identified the reactive CO2-related species and specified the reaction conditions for selective methanol formation. We also discuss the reaction pathway for methanol formation, and our findings indicate that MEA plays multiple roles, including absorbing CO2, stabilizing CO2RR intermediates via C–N bond formation, and catalytically promoting methanol production.