Electrodeposition of a mirror zinc coating from a choline chloride-ethylene glycol-based deep eutectic solvent modified with methyl nicotinate

A number of studies have reported the effects of additives on metal coatings electrochemically deposited from deep eutectic solvents (DESs). However, no previous study has investigated the influences of methyl nicotinate (MN) as an additive on the electrodeposition of zinc on a copper substrate from a DES. The results of this investigation show that MN significantly develops the Zn deposition in this system compared to the corresponding system in its absence. This is the first study to date to show that a mirror zinc coating can be obtained on a copper substrate using such a mechanism. Various electrochemical methods such as cyclic voltammetry, chronocoulometry, and chronoamperometry have been used to understand the electrochemical properties of Zn electrolytes in the absence and presence of MN. These experiments found that the redox reaction currents decline when the additive was included in the Zn electrolyte, and that Zn deposition followed an instantaneous nucleation mechanism in the absence of the additive while in its presence the mechanism was closer to that of progressive growth. Further, the current efficiency decreased from 98.99% in the absence of additive to approximately 82% as a result of including the additive in the Zn plating bath, according to electrochemical quartz crystal microbalance (EQCM) data. The resultant roughness, thickness and surface morphology of the deposited zinc were characterised using atomic force microscopy, scanning electron microscopy, and X-ray diffraction, indicating that methyl nicotinate, as an additive, functions as a highly influential brightener that allows the formation of highly homogeneous and flat zinc deposits.