Detailed investigation of zinc coating behaviours in various deep eutectic solvents

Determining the optimum conditions of a metal coating is significant for its possible applications in many fields. The present work described the electrodynamic process of zinc coating from six different deep eutectic solvents (DESs), especially type-III DES systems prepared with a quaternary ammonium salt and hydrogen bond type. Non-reversible processes without oxidation were found in DES systems prepared with choline chloride and zinc nitrate salts, and also, propylene glycol and zinc nitrate salts, termed as type-II and type-IV, respectively. The most attracted type-III DES prepared by a mixture of 1 molar choline chloride and 2 molar ethylene glycols, commercially known as Ethaline (E200), were examined for its electronucleation and possible reactions for zinc electrodeposition. For the first time, the Pt working electrode was investigated under high-resolution optical microscopy to visualize the in-situ morphology change during oxidation and reduction in E200. Furthermore, the morphological change during the anodic dissolution of zinc was also investigated in situ under a high-resolution microscope. It was found that insoluble species forming during anodic dissolution blocks the surface. Bulk electrolysis was performed in these solvents to investigate the formed zinc nucleates' morphological differences. XRD analysis was performed to differentiate the crystal planes of each deposition obtained from six DESs. It was found that the type-II and type-IV DESs consisting of zinc nitrates revealed zinc hydroxy nitrate dominated zinc deposition, which can be helpful in various applications.