Advanced Electrochemical Strategies for Optimizing the Electrodeposition of Nickel, Zinc, and Zinc-Nickel Alloys

This review addresses the challenges in the electrodeposition (ED) of nickel, zinc, nickel-zinc alloys, and Ni-Zn metal-matrix composites (MMCs) to achieve high-performance metallic coatings (corrosion-resistant, conductive, and reflective) while minimizing energy consumption. All related terminology and fundamentals of the advanced ED of Ni, Zn, and Ni-Zn alloys in the absence and presence of organic additives and eco-friendly ionic liquids (ILs) have been discussed. A summary and discussion of the reported studies in the literature, with representative figures and correlations, show that the coating performance (adhesion, cohesion, continuity, non-porosity, brightness, compactness, and uniform thickness) depends on the proper pre-treatment of the metal object and the electroplating bath (electrolyte composition, throwing power (T.P.), and buffer capacity). Complete cathodic current efficiency (CCE) is achieved by eliminating the undesired electrode reactions, using a chloride anti-passivator to dissolve oxide films from the anode surface, and descaling the cathode surface. The activation overvoltage of the cathodic reaction controls the kinetics of ED. The additives adsorb onto the coating surface and can modify (increase or decrease) the surface roughness. ILs synergistically reinforce the performance of the additives. The optimum operating conditions were a current of 10 mA cm -2 , a temperature of 27°C, a rotation speed of 100 rpm, a pH range of 2-4, and an electrical conductivity of approximately 200 µS. The properties of the MMCs are greatly enhanced by incorporating the elements Co, W, and Zr.