Assessing the CO2 Capture and Electro-Reduction in Imidazolium-Based Ionic Liquids: Role of the Ion Exchange Membrane

The electrochemical CO2 reduction (eCO2RR) to valuable chemicals offers a promising method to combat global warming by recycling carbon. Among the possible products, syngas—a CO and H2 mixture—is especially valuable for industrial reactions. The use of Room Temperature Ionic Liquids (RTILs) electrolytes presents a promising pathway for eCO2RR because of the lower overpotential required and the increased CO2 solubility with respect to the aqueous ones. Ensuring a constant CO/H2 production is essential, and it relies on both the catalyst and reactor design. This study explores eCO2RR in RTIL mixtures of 1-butyl-3-methyl imidazolium trifluoromethanesulfonate (good for CO2 conversion) and 1-butyl-3-methyl imidazolium acetate (good for CO2 capture), with various amounts of water as a proton source. We evaluated syngas production stability across different electrochemical cells and ion exchange membranes after determining the appropriate electrolyte mixture for a suitable CO/H2 ratio near 1:1. The two-chamber cell configuration outperformed single-cell designs by reducing oxidative RTILs degradation and by-products formation. Using a bipolar membrane (BPM) in forward mode led to catholyte acidification, causing an increase of HER relative to eCO2RR over time, confirmed by Multiphysics modeling. Conversely, an anionic exchange membrane (AEM) maintained constant syngas production over extended periods. This work offers guidelines for syngas generation in RTIL-based systems from waste-CO2 reduction, which can be useful for other green chemical synthesis processes.