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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. [ABSTRACT FROM AUTHOR]

Eutectic solvents are tunable for targeted applications through the functional groups in their hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) components, as well as the HBA : HBD composition ratio. This study examines the properties of choline-based eutectics containing imidazole, phenol, pyrrole-2-carbonitrile, and 1,2,4-triazole HBAs, and ethylene glycol, 1,2-propylene glycol, and ethanolamine HBDs. The viscosity, conductivity, degree of hydrogen bonding, thermal stability, and solvatochromic properties are examined as a function of HBA, HBD, and the composition. These studies revealed a predominant dependence of physical properties on the HBD and determined that the strong hydrogen bonding in phenol and imidazole-based systems lead to higher viscosities and lower conductivities – critical parameters for CO2 capture and electrochemical conversion. The developed eutectic solvents were further evaluated in terms of their CO2 capture capacities and electrochemical stabilities. Solvatochromic properties were found to correlate with CO2 capacities, demonstrating the tunability of these solvents for CO2 capture. The quantitative structure–property relationship (QSPR) analysis demonstrated the ability to predict viscosities and CO2 capture capacities (<25% deviation) through a multi linear regression method utilizing five molecular descriptors. This work highlights the role of functionalized HBAs and HBDs in the physical, thermal, and electrochemical properties of eutectic solvents as they relate to CO2 capture and electrochemical processes. [ABSTRACT FROM AUTHOR]

Choline-based sorbents derived from imidazole (ImH), phenol (PhOH), pyrrole-2-carbonitrile (CNpyrH), and 1,2,4-triazole (TrzH) are developed for CO2 capture to enable alternative regeneration approaches over aqueous amines. During synthesis, the equilibrium between [Ch]+[OH]− and Ch± dipolar in water shifts to support the formation of Ch±ImH and Ch±PhOH in the presence of ImH and PhOH upon drying. In contrast, salts of [Ch]+[CNpyr]− and [Ch]+[Trz]− were obtained with CNpyrH and TrzH, as confirmed by NMR and FTIR spectroscopy. Density functional theory (DFT) calculations support a spontaneous proton transfer from CNpyrH and TrzH to Ch±, while they show an energy barrier in the case of ImH. These sorbents formed eutectic solvents upon mixing with ethylene glycol (EG) where deprotonation of EG and subsequent binding of CO2 contributed to capacities up to 3.56 mol CO2 kg−1 at 25 °C and 1 bar of CO2. The regenerability of the eutectic solvents was demonstrated by dielectric heating via microwaves (MWs) in support of renewable energy utilization. This study shows the impact of proton sharing on the CO2 capacity and regenerability of eutectic sorbents as molecular design guidance. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) and deep eutectic solvents (DESs) have tremendous potential for reactive capture and conversion (RCC) of CO 2 due to their wide electrochemical stability window, low volatility, and high CO 2 solubility. There is environmental and economic interest in the direct utilization of the captured CO 2 using electrified and modular processes that forgo the thermal- or pressure-swing regeneration steps to concentrate CO 2 , eliminating the need to compress, transport, or store the gas. The conventional electrochemical conversion of CO 2 with aqueous electrolytes presents limited CO 2 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 CO 2 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 CO 2 , 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 CO 2 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.

Choline-based sorbents derived from imidazole (ImH), phenol (PhOH), pyrrole-2-carbonitrile (CNpyrH), and 1,2,4-triazole (TrzH) are developed for CO 2 capture to enable alternative regeneration approaches over aqueous amines. During synthesis, the equilibrium between [Ch] + [OH] - and Ch ± dipolar in water shifts to support the formation of Ch ± ImH and Ch ± PhOH in the presence of ImH and PhOH upon drying. In contrast, salts of [Ch] + [CNpyr] - and [Ch] + [Trz] - were obtained with CNpyrH and TrzH, as confirmed by NMR and FTIR spectroscopy. Density functional theory (DFT) calculations support a spontaneous proton transfer from CNpyrH and TrzH to Ch ± , while they show an energy barrier in the case of ImH. These sorbents formed eutectic solvents upon mixing with ethylene glycol (EG) where deprotonation of EG and subsequent binding of CO 2 contributed to capacities up to 3.56 mol CO 2 kg -1 at 25 °C and 1 bar of CO 2 . The regenerability of the eutectic solvents was demonstrated by dielectric heating via microwaves (MWs) in support of renewable energy utilization. This study shows the impact of proton sharing on the CO 2 capacity and regenerability of eutectic sorbents as molecular design guidance.

CO 2 separations from cabin air and the atmospheric air are challenged by the very low partial pressures of CO 2 . In this study, a facilitated transport membrane (FTM) is developed to separate CO 2 from air using functionalized ionic liquid (IL) and poly(ionic liquid) (PIL) carriers. A highly permeable bicontinuous structured poly(ethersulfone)/poly(ethylene terephthalate) ( b PES/PET) substrate is used to support the PIL-IL impregnated graphene oxide thin film. The CO 2 separation performance was tested under a mixture feed of CO 2 /N 2 /O 2 /H 2 O. Under 410 ppm of CO 2 at 1 atm feed gas, CO 2 permanence of 3923 GPU, and CO 2 /N 2 and CO 2 /O 2 selectivities of 1200 and 300, respectively, are achieved with helium sweeping on the permeate side. For increased transmembrane pressure (>0 atm), a thicker PIL-IL/GO layer was shown to provide mechanical strength and prevent leaching of the mobile carrier. CO 2 binding to the carriers, ion diffusivities, and the glass transition temperature of the PIL-IL gels were examined to determine the membrane composition and rationalize the superior separation performance obtained. This report represents the first FTM study with PIL-IL carriers for CO 2 separation from air.