Anodic processes on Mn5Si3 electrode in alkaline alectrolyte

  • Igor S. Polkovnikov Perm State University 15, Bukirev str., 614990 Perm, Russian Federation
  • Viktoria V. Panteleeva Perm State University 15, Bukirev str., 614990 Perm, Russian Federation
  • Anatoliy B. Shein Perm State University 15, Bukirev str., 614990 Perm, Russian Federation
Keywords: manganese silicide Mn5Si3,, anodic process,, passivation,, alkaline solution

Abstract

Purpose. The anodic behaviour of a Mn5Si3 electrode in solutions of (0.5–3.0) M NaOH in the region from the E corrosion potential up to the E oxygen evolution potential was studied using the methods of polarization and impedance measurements.

Results. The anodic polarization curves of Mn5Si3 have a weakly expressed region of active dissolution, regions of primary and secondary passivation, separated by a peak at a potential of ≈ 0.2 V (relative to the standard hydrogen electrode), and an area of oxygen evolution. In the first passive region, passivation of silicide is achieved due to the formation of Mn(OH)2 on its surface. In the second passive region it is achieved due to the formation of MnO2. Oxygen evolution is accompanied by the formation of MnO4-ions. Silicon is selectively (chemically and electrochemically) dissolved from the surface layer of silicide. The composition of the films on Mn5Si3 may include small amounts of silicon dioxide and silicates along with the products of metal oxidation.

The impedance spectra of Mn5Si3 at the potentials of the first passive region consist of a capacitive semicircle with an offset centre at high frequencies and an almost vertical straight line at low frequencies. Using the capacitance values corresponding to the low-frequency line of the impedance spectra, we can calculate the magnitude of the change in the thickness of the passivating film with the potential dδ/dE depending on the potential and the concentration of NaOH. The derivative dd/dE varies in the range of 2.1–17.5 nm/V and decreases with increasing electrode polarization and increasing electrolyte concentration.

At the potentials of the second passive region, the slope of the low-frequency line on the impedance spectra is ~ 45°, which corresponds to the diffusion impedance. The formation of MnO2 is accompanied by diffusion control over the mass transfer of the implanted OH--ions into the surface passivating film Mn(OH)2 towards the silicide/film interface.

Conclusion. The process of oxygen evolution on the Mn5Si3 electrode reveals kinetic features that are characteristic for the Mn electrode. The Tafel slope of the E,lgi- curves for silicide is (0.15–0.17) V, the reaction order for OH-- ions is 0.76, and the dependence of the electrode potential on the solution concentration is –0.12 V. The process rate depends on the discharge rate of OH-- ions.

 

CONFLICT OF INTEREST

The authors declare the absence of obvious and potential conflicts of interest related to the publication of this article.

 

 

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Published
2019-03-06
How to Cite
Polkovnikov, I. S., Panteleeva, V. V., & Shein, A. B. (2019). Anodic processes on Mn5Si3 electrode in alkaline alectrolyte. Kondensirovannye Sredy I Mezhfaznye Granitsy = Condensed Matter and Interphases, 21(1), 126-134. https://doi.org/10.17308/kcmf.2019.21/723
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