Reactive capture and electrochemical conversion of CO2 with ionic liquids and deep eutectic solvents

Abstract

Ionic liquids (ILs) and deep eutectic solvents (DESs) have tremendous potential for reactive capture and conversion (RCC) of CO₂ due to their wide electrochemical stability window, low volatility, and high CO₂ solubility. There is environmental and economic interest in the direct utilization of the captured CO₂ using electrified and modular processes that forgo the thermal- or pressure-swing regeneration steps to concentrate CO₂, eliminating the need to compress, transport, or store the gas. The conventional electrochemical conversion of CO₂ with aqueous electrolytes presents limited CO₂ solubility and high energy requirement to achieve industrially relevant products. Additionally, aqueous systems have competitive hydrogen evolution. In the past decade, there has been significant progress toward the design of ILs and DESs, and their composites to separate CO₂ from dilute streams. In parallel, but not necessarily in synergy, there have been studies focused on a few select ILs and DESs for electrochemical reduction of CO₂, often diluting them with aqueous or non-aqueous solvents. The resulting electrode–electrolyte interfaces present a complex speciation for RCC. In this review, we describe how the ILs and DESs are tuned for RCC and specifically address the CO₂ chemisorption and electroreduction mechanisms. Critical bulk and interfacial properties of ILs and DESs are discussed in the context of RCC, and the potential of these electrolytes are presented through a techno-economic evaluation.