Detrimental Effects of Monoethanolamine and Other Amine-Based Capture Agents on the Electrochemical Reduction of CO2

Reactive carbon capture (RCC) is a promising solution for carbon capture and utilization. RCC involves CO2 capture, typically with amine solutions to form carbamate, followed by immediate conversion into value-added chemicals and fuels, typically via electrochemical means. RCC may enhance CO2 reduction (CO2R) by overcoming the inherent limiting low solubility of CO2 in aqueous solutions. In this work, we present a systematic study of the influence of monoethanolamine (MEA) on CO2R performance over an Ag cathode in KHCO3 electrolytes. Contrary to prior work, the study finds no evidence for the direct reduction of carbamate anions. Instead, the presence of MEA suppresses the rate of CO formation while increasing that of H2. These results are supported by a boundary-layer continuum model of mass transport and reaction that correctly predicts experimental trends and demonstrates that MEA reduces the concentration of CO2 near the cathode. Thus, alternative strategies are necessary to achieve RCC in aqueous environments.