Ionic liquids/salts for electrochemical CO₂ capture and separation

Electrochemical CO₂ capture (ECC) is an attractive alternative to thermochemical methods. It can operate at constant temperature, use renewable electricity, and work well at a small scale. In recent years, ionic liquids/salts have gained attention because of their unique properties, such as very low vapor pressure, good ionic conductivity, wide electrochemical windows, and tunable structures. This review focuses on two aspects of ionic liquids/salts for electrochemical CO₂ capture. First, as auxiliary agents, they can serve as solvents, electrolytes, or additives that help redox-active carriers work better through improving solubility of redox-active carriers, stabilizing reaction intermediates, avoiding side reactions, and adjusting the energy needed for CO₂ binding. Second, ionic moieties are attached to redox-active cores, forming active materials themselves. Thereby, the solubility can be increased because of the formation of single components. In some ionic salts, such as viologens and quinone-annulated salts, the cation itself can undergo electron transfer and either bind CO₂ directly or cause pH changes that drive CO₂ capture. Due to these advantages, high CO₂ capacity, high faradaic efficiency, and low energy consumption could be obtained. However, several issues remain, including sensitivity to O₂, a trade-off between solubility and viscosity, and the high cost of fluorinated ionic liquids/salts. Future progress may come from computational screening, combining capture with conversion, and better reactor design. This review offers practical guidance for developing novel processes using ionic liquids/salts for efficient electrochemical CO₂ capture.