Investigation of nickel electrochemical impedance spectra under conditions of anodic polarization in hydroxide solutions with chloride ion additives.Intстатья
Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 10 апреля 2024 г.
Аннотация:Nickel in a slightly alkaline medium with chloride additives was chosen as a model system forstudying a metal prone to passivation and the formation of point defects during anodicpolarization. For this system, electrochemical impedance spectra were obtained at differentratios of concentrations of sodium hydroxide and chloride under conditions of anodicpolarization. We intended to use them to assess the thickness and uniformity of the passive layeron the metal surface. The existence of two time constants, manifested in the high frequency andlow-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 metalwith 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-frequencypart of the impedance spectrum is due to the Faraday process of solid-phase oxidation of nickelat the oxide and metal interface. As in the previously studied chloride free system, the samepatterns are observed: a power-law dependence of the resistance to ion charge transfer acrossthe oxide layer/solution boundary on the concentration of anions has been established, whichcan be described in terms of the Freundlich isotherm. Moreover, this charge transfer resistanceis practically independent of the potential. The capacitance of the double layer at the sameboundary is directly proportional to the square root of the total concentration of alkali andchloride, which indicates compliance with the classical Gui-Chapman model. With an increasein the anodic potential and the concentration of anions, there is a tendency to decrease theresistance and increase the capacitance factor of the Faraday reaction. According to theresistance values related to the high-frequency part of the impedance spectrum and the overallcapacitance 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.