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 -0.8 V 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.