Investigation of Electrodeposition Mechanism of Cu/ Ni-P Multilayer Coatings using Chronoamperometry Approach

In this study, the chronoamperometry technique was used to investigate the electrodeposition mechanism of copper/ nickel-phosphor multilayer coatings using the single-bath method. In this regard, the influence of bath components on current transients was studied by fitting two and three-dimensional nucleation and growth models. In the potential range of nickel reduction, hydrogen evolution reaction co-occurs; Therefore, the current contribution of this process, as well as surface absorption and charge of the electric double layer current densities, were considered in these fittings. The reduction mechanism from the final bath was instantaneous nucleation with three-dimensional diffusion-controlled growth. Fitting results reveal that the existence of copper and phosphorus in the bath had an incentive role in the three-dimensional deposition of nickel-rich layers. Although copper-nickel citrate baths are commonly employed for alloy deposition, AAS and EDX analyses revealed that deposition of nickel-rich layers at potentials less than -0.8 V is achievable, and phosphorus co-deposits with nickel. Finally, FE-SEM analysis was used to investigate the morphology of copper-rich and nickel-rich monolayers, which revealed the formation of uniform and spherical deposits, and confirmed the results of the chronoamperometry approach. The potentials of -0.3 and -1.1 V vs. SCE were the most appropriate potentials for generating copperrich and nickel-rich layers, respectively, in terms of particle shape, size, and uniformity.