Electroreduction of CO₂ and Quantification in New Transition-Metal-Based Deep Eutectic Solvents Using Single-Atom Ag Electrocatalyst

Abstract

Deep eutectic solvents (DESs) are efficient media for CO 2 capture, and an electroreduction process using the deterministic surface of single-atom electrocatalysts is a facile way to screen gas absorption capacities of novel DESs. Using newly prepared transition-metal-based DESs indexed as TDESs, the interfacial mechanism, detection, quantification, and coordination modes of CO 2 were determined for the first time. The CO 2 has a minimum detection time of 300 s, whereas 500 s of continous ambient CO 2 saturation provided ZnCl 2 /ethanolamine (EA) (1:4) and CoCl 2 /EA (1:4) TDESs with a maximum CO 2 absorption capacity of 0.2259 and 0.1440 mmol/L, respectively. The results indicated that CO 2 coordination modes of η 1 (C) and η 2 (O, O) with Zn in ZnCl 2 /EA (1:4) TDESs are conceivable. We found that the transition metals in TDESs form an interface at the compact layer of the electrocatalyst, while CO 2 •– /CO 2 reside in the diffuse layer. These findings are important because they provide reliable inferences about interfacial phenomena for facile screening of CO 2 capture capacity of DESs or other green solvents.

Bifunctional Ionic Deep Eutectic Electrolytes for CO2 Electroreduction

“…From −1.7 to 0.9 V, there is no observable Faradaic activity, implying that the electrochemical stability window is 2.6 V versus Ag/AgCl. Usually, DESs have a low electrochemical potential window, but this result indicates the significance of cathodic limits for the prospective viability of DESs in electroreduction reactions similar to the previous report …”

“…The corresponding current responses of CO 2 •– in DEACl–DEA were transformed to concentration for estimating the equivalent amount of CO 2 utilized during the process. The DEACl–DEA ionic deep eutectic electrolyte is unlike our previous study that used transition metal-based DESs with a pseudocapacitive attribute, in which case CO 2 saturation therein further increased the double layer capacitance . Instead, DEACl–DEA has a different double layer capacitance features upon CO 2 saturation.…”

“…The ionic DESs were synthesized through constant mixing of known mole ratios (1:2, 1:3, 1:4, 1:5, and 1:6) of HBA (DEACl) and HBD (DEA) components at 70 °C for 8 h using a similar method reported previously. , Then, the DESs were dried and aged to observe the best mole ratio that maintained its fluidity without recrystallization.…”

“…The CO 2 solubility in ionic DESs was measured with the chronoamperometry module at −1.5 V versus Ag/AgCl similar to the previous procedure . In a typical experiment, an electrochemical cell of 10 mL volume was filled to 1/4 capacity with dried ionic DESs and sparged with CO 2 at 5 bar, as illustrated in Figure S1.…”

“…The amine-based DESs are only common for CO 2 capture, , but recently DESs such as methyl diethanolamine hydrochloride methyl diethanolamine (MDEAHCl-MDEA) and zinc chloride ethanolamine (ZnCl-EA), have facilitated ECO 2 R to CO and CO 2 •– , respectively. The MDEA stores CO 2 in the form of bicarbonate rather than carbamate, which has a higher theoretical CO 2 -capturing capability than MEA .…”