Voltammetric Response of Water in Deep Eutectic Solvent Based on Choline Chloride and Urea

Abstract

This work investigates the electrochemical role of water in the research of deep eutectic solvent (DES) based on urea and choline chloride. The motivation comes from the growing use of this DES, and on reports where a characteristic voltammetric cathodic pre-wave is observed. However, there has been no direct study to verify if such interpretation of the pre-wave is appropriate. In this regard, cyclic voltammetry has been used in this paper to interrogate the reactions inducing the appearance of the pre-wave. These experiments have been carried out using reline (the eutectic mixture of urea and choline chloride) melts containing different amounts of water, compounds which can be incorporated as impurities from air, or as decomposition products of reline. The analyses showed that a pre-wave in voltammograms in reline originates from water electroreduction accompanied with a subsequent choline hydroxide formation. In this sense, reline behaves like a typical mixture of organic solvent + alkali cation salt + water. The voltammetric signal depends on water content in reline. Importantly, this offers a possibility for in-situ electrochemical determination of water content in reline, provided that a calibration curve is constructed.

Effect of water on the electrodeposition of copper from a deep eutectic solvent

“…In contrast to the results for ethaline, the effect of water on other DES systems, such as reline, can be significant [8,36]. For example, Du [8] reported that the electrochemical window reduced from 2.54 V to 1.03 V at a glassy carbon electrode when the water content was changed from 1 wt% to 12 wt%, similar to the range considered in this work.…”

“…In the absence of water, the anodic and cathodic limits are attributed to the reduction of the choline cation and the oxidation of Clto Cl2, respectively [8,10,36]. With added water, many other reactions are possible [10] and the situation for reline seems particularly complex [36]. It should be noted that even though conventional RTILs can have very large (e.g.…”

A Review of the electrochemical corrosion of metals in choline chloride based deep eutectic solvents

“…In general, water in DES decreases its kinematic viscosity (Figure 5), increases its electrical conductivity, and notably narrows its electrochemical window [82,84], and all these factors contribute to the increase in the corrosion processes rate. Consequently, it was shown in [85] that the corrosion of mild steel in ethaline and reline is significantly enhanced even with the addition of only 10 wt.% of water.…”

The importance of using hydrogen evolution inhibitor during the Zn and Zn-Mn electrodeposition from ethaline

“…11 It is well known that choline chloride based DESs are extremely hygroscopic mixtures, so they contain some percent of water, which is electroreduced at the cathode during the electrodeposition, by the same mechanism as in aqueous electrolytes. 12,13 Therefore, it would be interesting to calculate the pH change in the vicinity of the cathode during the electrodeposition process, and to compare the results for DESs with those for an aqueous solution.…”