Electrochemical Reduction of Carbon Dioxide in a Monoethanolamine Capture Medium

The electrocatalytic reduction of CO2 in a 30% (w/w) monoethanolamine (MEA) aqueous solution was undertaken at In, Sn, Bi, Pb, Pd, Ag, Cu and Zn metal electrodes. Upon the dissolution of CO2, the non-conducting MEA solution is transformed into a conducting one, as is required for the electrochemical reduction of CO2. Both an increase in the electrode surface porosity and the addition of the surfactant cetyltrimethylammonium bromide (CTAB) suppress the competing hydrogen evolution reaction; the latter has a significantly stronger impact. The combination of a porous metal electrode and the addition of 0.1% (w/w) CTAB results in the reduction of molecular CO2 to CO and formate ions, and the product distribution is highly dependent on the identity of the metal electrode used. At a potential of -0.8V versus the reversible hydrogen electrode (RHE) with an indium electrode with a coralline-like structure, the faradaic efficiencies for the generation of CO and [HCOO](-) ions are 22.8 and 54.5%, respectively compared to efficiencies of 2.9 and 60.8% with a porous lead electrode and 38.2 and 2.4% with a porous silver electrode. Extensive data for the other five electrodes are also provided. The optimal conditions for CO2 reduction are identified, and mechanistic details for the reaction pathways are proposed in this proof-of-concept electrochemical study in a CO2 capture medium. The conditions and features needed to achieve industrially and commercially viable CO2 reduction in an amine-based capture medium are considered.