Amine-based CO2 capture has been widely explored and applied in CO2-intensive sites, but the energy consumption of amine thermal regeneration is still relatively large due to the presence of strong N-C bond in amine-CO2 adducts. Instead, amine-mediated CO2 electrochemical conversion, which integrates CO2 capture and electrochemical conversion processes, has the potential to reduce the energy penalties in amine regeneration and CO2 utilization or storage. The feasibility of such a process has been proven by a Li-based nonaqueous electrochemical system, containing dimethyl sulfoxide (DMSO) solvent, alkali (Li+, Na+, K+)-PF6- salts and 2-ethoxyethylamine (EEA). However, a further exploration is needed to understand the detailed influences of EEA and EEA-CO2 adducts (EEA-COOH, EEA-COO-, EEA-H+) on electrolytes. Thus, we conducted molecular dynamics simulations to study the solvation structure and transport properties of ions in this system. The results show that, compared with pure DMSO electrolytes, the mobility of Li+ decreases slightly faster when LiPF6 concentration increases from 0.1 M to 1.1 M, with adding EEA to the electrolytes. Besides, EEA-COOH significantly enhances the mobility of Na+. In addition, the ionic conductivities of electrolytes containing EEA-COO- and EEA-H+ show an obvious increase, the potential of mean forces between alkali cations and EEACOO- demonstrate the stability of cation-EEACOO- contact ion pairs (CIP) decreases gradually with the increase of cation ionic radius, and K+ has the minimal transitional energy barrier to form CIP with EEACOO- from the solvent assisted ion pairs, followed by Li+ and Na+. Moreover, the spatial distribution functions of EEA-DMSO and EEA-CO2-DMSO account for the mobility of EEA-CO2 decreasing 66% from that of EEA. This work serves as a fundamental exploration for designing electrolytes in amine-mediated CO2 electrochemical conversion.

Solvation structure and transport properties of electrolytes in amine-mediated CO2 conversion

ACS Fall 2021

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