Electrochemical\nCO<sub>2</sub> Reduction in Deep Eutectic\nSolvent: Effect of Water and Organic Diluents

Deep eutectic solvents (DESs) are promising media for\nCO<sub>2</sub> electroreduction because of their high CO<sub>2</sub> solubility,\nlow cost, and eco-friendliness. However, the high viscosity and poor\nionic conductivity severely limit their applications. In this study,\nlow-viscosity polar aprotic solvents, propylene carbonate (PC) and\nsulfolane (SL), were used as diluents in Ethaline (ChCl:2EG) to prepare\nmixed electrolytes for electrochemical CO<sub>2</sub> reduction. Raman\nand infrared spectra indicate that PC and SL can participate in the\neutectic network of Ethaline through intermolecular hydrogen bonding,\nthereby decreasing the viscosity. The current density of the Ag cathode\nincreases from 1.7 to 8.0 and 5.3 mA/cm<sup>2</sup> with the addition\nof PC and SL, respectively. The two diluents also result in improved\nCO faradaic efficiency (FE<sub>CO</sub>) and suppressed HER because\nthe CO and SO bonds in the molecular frameworks of\nPC and SL can disrupt the hydrogen bonds of accumulated water molecules\nduring electrolysis. At −2.0 V, FE<sub>CO</sub> increases from\n63% to over 90% upon the addition of PC and SL. This study provides\nnew insights into the design of high-performance DES electrolytes\nfor CO<sub>2</sub> electroreduction.