Ionic liquids are studied intensively for electrochemical applications and more specifically for the electrodeposition of metals. In this paper the electrochemical stability of a deep-eutectic solvent based on choline chloride and ethylene glycol is studied over longer periods of electrolysis. The formation of several decomposition products such as 2-methyl-1,3-dioxolane was observed. Possible mechanisms for the formation of these products are given: some products involve a reaction at either the anode or the cathode, while others can be explained by consecutive reactions of reaction products formed at both electrodes. A range of chlorinated products like chloromethane, dichloromethane and chloroform could be detected as well. This is remarkable as evolution of chlorine gas at the anode is not observed. The formation of the chlorinated products is ascribed to the existence of the Cl 3 ion in the solution. The presence of the Cl 3 ion was observed photometrically. The presence of chlorinated products gives rise to a larger environmental impact and higher risks for health and safety, and it questions the "greenness" of these ionic liquid analogues. To reduce the decomposition of the solvent, water and easily oxidizable acids were added as 'sacrificial agents'. Their influence on the formation of 2-methyl-1,3-dioxolane was quantified. However, the addition of the sacrificial agents did not improve the stability of the solvent. Addition of formic acid reduced the formation of 2-methyl-1,3-dioxolane but chlorinated products could still be detected. Water reduced the formation of chlorinated products.

A deep-eutectic solvent with the properties of an ionic liquid is formed when choline chloride is mixed with copper(II) chloride dihydrate in a 1:2 molar ratio. EXAFS and UV-vis-near-IR optical absorption spectroscopy have been used to compare the coordination sphere of the cupric ion in this ionic liquid with that of the cupric ion in solutions of 0.1 M of CuCl(2)·2H(2)O in solvents with varying molar ratios of choline chloride and water. The EXAFS data show that species with three chloride ions and one water molecule coordinated to the cupric ion as well as species with two chloride molecules and two water molecules coordinated to the cupric ion are present in the ionic liquid. On the other hand, a fully hydrated copper(II) ion is formed in an aqueous solution free of choline chloride, and the tetrachlorocuprate(II) complex forms in aqueous choline chloride solutions with more than 50 wt % of choline chloride. In solutions with between 0 and 50 wt % of choline chloride, mixed chloro-aquo complexes occur. Upon standing at room temperature, crystals of CuCl(2)·2H(2)O and of Cu(choline)Cl(3) formed in the ionic liquid. Cu(choline)Cl(3) is the first example of a choline cation coordinating to a transition-metal ion. Crystals of [choline](3)[CuCl(4)][Cl] and of [choline](4)[Cu(4)Cl(10)O] were also synthesized from molecular or ionic liquid solvents, and their crystal structures were determined.

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The theory of the potentiostatic transient for 3D nucleation with diffusion-controlled growth is discussed. It is shown that the theoretical model of Mirkin and Nilov [J. Electroanal. Chem., 283 (1990) 35] and Heerman and Tarallo [J. Electroanal. Chem., 470 (1999) 70] predicts too high values of the current, which becomes very apparent for high values of the site density and low values of the nucleation rate constant (progressive nucleation). For example, the model then predicts that the current in the limit of long times will be higher than the Cottrell limit by a factor of 4/3 which is physically unacceptable. Therefore, a modification to this model is proposed which is based on a careful analysis of the Kolmogorov-Avrami theorem. The ''extended area'' in the KolmogorovAvrami theorem includes contributions from ''phantom nuclei'' that are born inside already existing zones but do not exist physically. This is necessary to preserve the randomness of the system and allows the correct calculation of the appearance rate of the nuclei and the nucleus saturation density. The ''extended current'', defined in analogy with the ''extended area'', then also attributes current to the phantom nuclei. It follows that the ratio j ex ðtÞ=h ex ðtÞ which appears in the model of Mirkin and Nilov and Heerman and Tarallo does not correspond to the actual number of nuclei formed on the electrode. Therefore, the ''extended quantities'' in this ratio must be replaced with quantities that relate directly to the real number of clusters (this implies what is fairly obvious, that the appearance rate of the clusters must be calculated first). This makes it is possible to derive an equation that predicts correctly the current in the limits of both short and long times which is directly linked to the N a ðtÞ vs. time relation (where N a ðtÞ is the actual number of nuclei on the electrode). Experiments for the nucleation of silver on glassy carbon electrodes, with the simultaneous recording of both jðtÞ vs. time and N a ðtÞ vs. time relations, are described. The experimental results obtained from the transients and the direct visual counting of nuclei are compared with the theoretical predictions.