Evaluation of Physicochemical Properties and Metal Electrodeposition from Deep Eutectic Mixtures based on Choline Chloride and Cobalt Chloride Hexahydrate

Deep Eutectic Solvents (DESs) are a class of liquid mixtures exhibiting tunable physicochemical properties as a function of the nature and ratio of their components. In this paper, we present the preparation, characterization, and application of mixtures with different molar ratios of choline chloride – cobalt chloride hexahydrate, a system that is reported to form a DES. To assess the eutectic nature of the mixtures, their phase transitions have been studied in detail by Differential Scanning Calorimetry (DSC) and the eutectic composition was found to be close to the molar ratio choline chloride : CoCl2∙6H2O 2:1. Further characterizations of the systems are also included: thermal stability, electrical conductivity, viscosity, density, and electrochemical window are reported as a function of temperature and mixture composition. Conductivities as high as 4.8 S m-1 were recorded and the electrochemical window was found to vary depending on the mixture composition. Electrodeposition of uniform layers of cobalt was achieved by chronoamperometry with very low content of impurities and displayed different morphologies depending on mixture composition and applied overpotential.