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.