Effects of additives on the electrodeposition of ZnSn alloys from choline chloride/ethylene glycol-based deep eutectic solvent

The effects of additives on the electrodeposition of ZnSn alloy from aqueous electrolyte have been the subject of considerable interest in the literature; however, to date there has been little consideration of their effects on alloy electrodeposition from Deep Eutectic Solvents (DESs). This work will show, for the first time, the effects of boric acid, ammonium chloride and nicotinic acid on the electrodeposition of ZnSn alloys on copper from a DES consisting of a stoichiometric 1:2 mix of choline chloride and ethylene glycol (Ethaline 200). Cyclic voltammetry has been used to study the electrochemical properties of the ZnSn electrolyte, and the resultant surface morphologies, composition and roughness of the ZnSn coating were revealed via SEM/EDX and AFM, demonstrating that boric acid and nicotinic acid function as very effective brighteners, producing highly uniform and smooth ZnSn deposits. It was found that these additives strongly affect the morphology, composition, and roughness of the ZnSn coating. XRD was also used to examine the crystal structure of ZnSn coatings, where it was found that the phase composition of the deposits depends on the additive(s) used. In addition, corrosion of the ZnSn alloy in salty media was measured using the Tafel method.