Electron Transfer Kinetics in Ethaline/Water Mixtures: An Apparent Non‐Marcus Behavior in a Deep Eutectic Solvent

Abstract

Effects of water on the charge‐transfer (CT) kinetics in deep eutectics solvents (DES) have been investigated in ethaline (1 : 2 choline chloride+ethylene glycol), taken as a prototypical example of a hydrophilic DES. Standard heterogeneous CT rate constants ks were measured for two redox couples: 1,1’‐ferrocene‐dimethanol/1,1’‐ferrocenium‐dimethanol and ferro‐/ferricyanide on a glassy carbon electrode in ethaline as function of the water amount in the DES. Contrarily to the behavior reported in classical solvents and in apparent contradiction with the Marcus Theory, ks values show very little or no variation with the amount of water in the DES or the changes of viscosities or diffusion coefficients that are observed. This unexpected phenomenon is discussed as function of the known physical‐chemistry parameters of ethaline.

Sequential Selective Dissolution of Coinage Metals in Recyclable Ionic Media

“…This assessment was based on a thermodynamic cycle parametrized using DFT calculations with a hybrid cluster/ continuum solvent model (Figure 3) employing the ωB97X-D4 [89] functional and def2-TZVPPD [91][92] basis set as implemented in Orca. The thermodynamic cycle computes the free energy for oxidative dissolution of the metal in ChCl/U, by separating the chemical process into the free energy of dissolution in water and the solubility free energy when the metal ions are transferred from water to ChCl/U (For more information on the computational approach [73][74][75][76][77][78][79][80][81][82][83][84][85][86][87] and details, [88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104][105] see Supporting Information, section 5.). The computational results show that ChCl/U significantly stabilizes Cu 2 + , Ag + , and Au 3 + cations and that oxidative dissolution is exergonic for all three metals with values of À 78.4, À 28.6, and À 44.3 kcal/mol, respectively.…”

Unconventional Electrochemical Behaviors of Cu Underpotential Deposition in a Chloride-Based Deep Eutectic Solvent: High Underpotential Shift and Low Coverage

“…Compared with their analogues ionic liquids (ILs), DESs possess extra merits including a simple synthesis process and low cost, which benefit large-scale production in the field of electrochemistry. Current issues of electrodeposition in aqueous solution, such as toxicity of reagents and low current efficiencies, could be overcome by using DESs. ,− Moreover, metal electrodeposition in DESs is of interest because DESs are featured by wider electrochemical windows, sufficiently large diffusion coefficients, and proper metal ion solvation. , For example, electrodeposition behaviors of Cu and the state of Cu complexes in DESs have been studied since the employment of DESs instead of aqueous electrolytes could avoid CuCl precipitation. − In 2011, Lloyd et al determined the speciation of Cu­(I) and Cu­(II) complexes in ethaline by UV–vis spectroscopy, and the main Cu­(I) and Cu­(II) complexes were found to be [CuCl 3 ] 2– and [CuCl 4 ] 2– , respectively. Subsequently, extended X-ray absorption fine structure spectroscopy was employed to test the complex states of Cu­(I)/Cu­(II) in four types of DESs .…”

Effect of Water On Deep Eutectic Solvents: Structural Properties and Interactions with CO2

“…Several recent computational studies have provided molecular-level insights into the impact of water on DESs; however, most of these studies have focused on ethaline (HBAs = choline cations and chloride anions; HBD = ethylene glycol HBD) 18,21,[46][47][48] and reline (HBAs = choline cations and chloride anions; HBD = urea) [49][50][51][52] , with a handful of studies performed on other DESs 18,50,53,54 . A comprehensive investigation into other classes of DESs would offer a broader perspective and provide insight needed to more globally design DESs for CO2 capture [55][56][57][58] .…”