Electrochemical CO2 reduction to CO facilitated by MDEA-based deep eutectic solvent in aqueous solution

Electrocatalytic CO2 reduction (ECO2R) is an environment-friendly way to convert CO2 into profitable products. Amine solution recently has been employed as an electrolyte in ECO2R but suffers from low efficiency. Herein, aqueous solutions containing different amine-based deep eutectic solvents (DESs) were used as electrolytes for CO2 reduction. The effect of different DESs on the CO2 reduction was investigated at Ag, Cu, and Zn metal electrodes. Tafel and electrochemical impedance spectroscopy (EIS) were applied to understand the CO2 reduction. DES in aqueous solution facilitates the CO2 reduction to CO with higher faradaic efficiency of CO (FECO) than amine solutions and a mixture of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD). Both HBD and HBA have an influence on CO2 reduction. [Monoethanolamine hydrochloride] [methyldiethanolamine] ([MEAHCl][MDEA]) gives high FECO, 71% FECO at −1.1 V vs RHE at Ag electrode, 33% higher than [MEAHCl][MEA]. Experimental results and EIS analysis reveal that the facilitation of CO2 reduction to CO probably stems from a synergistic effect of nano-size agglomerate dispersion on Ag-surface, bicarbonate formation, exchange current density, and Cl− ions present in DESs. These findings present a feasible method to employ the aqueous MDEA-based DES solution as an electrolyte for CO2 reduction.