Nowadays, deep eutectic solvents (DESs) are one of the most recognized and studied as novel plating solutions [1,2]. However, the majority of them are based on choline chloride with the consequent high concentration of aggressive species in the solution. Chlorides, in fact, may be a problem for both metal electrodes and the surrounding experimental apparatus, due to their strong corrosive nature. Moreover, the possible contamination of the electrodeposited film has to be taken into account together with the consequent side effects on its properties. In the present work, we propose an organic solution based on ethylene glycol, without the employment of choline chloride [3,4,5,6]. The electrochemical characterization of the solutions was performed by means of cyclic voltammetry (CV) and linear scan voltammetry (LSV); both galvanostatic and potentiostatic deposition approaches were investigated. Morphology (SEM) and thickness of the films (XRF) were evaluated for different deposition parameters for both Hull cell and standard two-electrodes cell configurations. On the other hand, potentiostatic depositions were carried out starting from the knowledge gained in the LSV investigations: the films were subjected to the same characterization considered for the galvanostatic depositions. In both cases, high faradaic efficiencies were reported, higher than 85% in most of the experimental conditions. All the electrodeposition experiments were carried out at 70°C considering also the employment of a supporting electrolyte. The Zn deposits were analyzed by means of X-Ray diffraction (XRD), showing the hexagonal microstructure typical of zinc. No diffraction peaks belonging to oxides or hydroxides were detected; the result was confirmed also by scanning electron microscopy (SEM) investigation, showing a compact film with no traces of oxygen (EDX). Finally, polarization tests were carried out to evaluate the corrosion performances.

References

[1] Abbott, A. P., et al. "Deep eutectic solvents formed between choline chloride and carboxylic acids: versatile alternatives to ionic liquids." Journal of the American Chemical Society 126.29 (2004): 9142-9147.

[2] Abbott, A. P., et al. "Electrodeposition of zinc–tin alloys from deep eutectic solvents based on choline chloride." Journal of Electroanalytical Chemistry 599.2 (2007): 288-294.

[3] Panzeri, G., et al. " E Electrodeposition of high-purity nanostructured iron films from Fe(II) and Fe(III) non-aqueous solutions based on ethylene glycol." Electrochimica Acta, Available online 28 March 2018, ISSN 0013-4686.

[4] Vorobyova, T. N., and O. N. Vrublevskaya. "Electrochemical deposition of gold–tin alloy from ethylene glycol electrolyte." Surface and Coatings Technology 204.8 (2010): 1314-1318.

[5] Nguyen, H. P., et al. "Electrodeposition of bismuth telluride thermoelectric films from a nonaqueous electrolyte using ethylene glycol." Electrochimica Acta 68 (2012): 9-17.

[6] Neuróhr, K., et al. "Electrodeposition of Ni from various non-aqueous media: the case of alcoholic solutions." Journal of The Electrochemical Society 162.7 (2015): D256-D264.