Voltammetric modeling of the kinetics involved in the nickel deposition onto nickel

A comprehensive physicochemical model is used to account for the nickel electrodeposition in sulfate media employing a rotating disk electrode. The model accounts for the nickel deposition, H⁺ and water reduction. These reactions involve the reduction of Ni(II) by two consecutive 1-electron transfer steps and the H⁺ and water reduction via the two-step Volmer-Tafel mechanism. Diffusion and convection are considered in the mass-transport balances. Reasonable fits of the model to the experimental data were obtained at different NiSO₄ concentrations. Further insights of this system show that the reduction process starting from the open circuit potential to more negative potentials occurs in the following order: H ⁺ reduction, nickel deposition and water reduction. The computation of other variables involved in the model such as the surface pH and concentrations provide additional support to those finds elucidated with the model.