Comparative assessment of Ni–Co coatings obtained from a deep eutectic solvent, choline chloride-ethylene glycol, and water by electroplating

Abstract

Alloy electroplating using deep eutectic solvents (DES), compared to aqueous electrolytes, has essential benefits in a wide potential range, the high solubility of metal salts (including chlorides and oxides), and an environmentally friendly alternative. This research aimed to compare the coatings obtained by electrolysis of the Ni–Co alloy conventionally from an aqueous solution against the electroplating obtained in 2:1 ethylene glycol-choline chloride. The electrochemical behavior was studied through potentiodynamic polarization kinetic analysis carried out complying with Abner’s rules for alloy deposits; hydrodynamic conditions were modified, keeping the temperature at 60 °C and the salt concentration in both baths constant. As a result, nickel electrolysis has been carried out successfully by taking advantage of the benefits of using DES in energy consumption with 80% efficiency compared to water as a solvent under the same conditions. The composition and morphology of Ni–Co alloy coatings were characterized by scanning electron microscopy (SEM/EDS), and corrosion resistance was investigated by potentiodynamic polarization and electrochemical impedance (EIS). Coatings were obtained for both electrolytic baths with a chemical composition within the range of the alloy but with a higher cobalt content in the deposits obtained in water; in contrast, the distribution of the Ni–Co alloy was more homogeneous with changes in morphology and crystallization in the deposits obtained from the DES bath. The coatings’ anti-corrosion performance showed that the Co content difference increases the corrosion resistance of the Ni–Co alloy obtained from aqueous electrolytes compared to deposits obtained from DES.