EIS Study of Nickel Deposition in Borate–Sulfate Solutions

Abstract

A physicochemical model for nickel deposition on a nickel rotating disk electrode is statistically fit to experimental electrochemical impedance spectroscopy (EIS) data obtained in borate–sulfate solutions containing 0.05, 0.1, and 0.2 M over a range of electrode potentials and to steady-state polarization curves in the same solutions. The model accounts for the simultaneous evolution of hydrogen and for the adsorption–desorption of borate, as well as the transport of dissolved species to the electrode surface. The kinetic parameters are estimated by minimization of the sum-of-squares error between the model and measurements using a genetic algorithm. An analysis of the model provides supporting evidence that the first step of Ni(II) reduction controls the rate of deposition and that the intermediate is rapidly consumed by the second step of the reaction. Fitting the model to the experimental EIS spectra shows that the system is sensitive to certain kinetic parameters but is insensitive to others. Furthermore, it is not possible for the model to satisfactorily fit all of the EIS spectra with a unique set of kinetic parameters. By contrast, the model is shown to fit very well the steady-state polarization curves obtained at different concentrations with a single set of parameters.