Investigation of nickel electrochemical impedance spectra under conditions of anodic polarization in hydroxide solutions with chloride ion additives

• V.E. Kasatkin, L.P. Kornienko, A.I. Shcherbakov, I.V. Kasatkina, I.G. Korosteleva and V.N. Dorofeeva

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: Nickel in a slightly alkaline medium with chloride additives was chosen as a model system for studying a metal prone to passivation and the formation of point defects during anodic polarization. For this system, electrochemical impedance spectra were obtained at different ratios of concentrations of sodium hydroxide and chloride under conditions of anodic polarization. We intended to use them to assess the thickness and uniformity of the passive layer on the metal surface. The existence of two time constants, manifested in the high frequency and low-frequency regions, was found on the impedance spectra. To process the EIS results, Mansfeld’s equivalent circuit was chosen which corresponds to the physical model of a metal with an oxide layer on the surface. It is shown that at high frequencies, the charge transfer at the interface between the solution and the oxide layer is performed by anions. The low-frequency part of the impedance spectrum is due to the Faraday process of solid-phase oxidation of nickel at the oxide and metal interface. As in the previously studied chloride free system, the same patterns are observed: a power-law dependence of the resistance to ion charge transfer across the oxide layer/solution boundary on the concentration of anions has been established, which can be described in terms of the Freundlich isotherm. Moreover, this charge transfer resistance is practically independent of the potential. The capacitance of the double layer at the same boundary is directly proportional to the square root of the total concentration of alkali and chloride, which indicates compliance with the classical Gui–Chapman model. With an increase in the anodic potential and the concentration of anions, there is a tendency to decrease the resistance and increase the capacitance factor of the Faraday reaction. According to the resistance values related to the high-frequency part of the impedance spectrum and the overall capacitance of the double electric layer, it is not possible to track the change in the thickness of the oxide layer formed on the surface during anodic polarization.

Keywords: nickel, alkaline medium, chloride, electrochemical impedance spectroscopy

Int. J. Corros. Scale Inhib., 2024, 13, no. 2, 683-707
doi: 10.17675/2305-6894-2024-13-2-3

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