Journal
JOURNAL OF SOLID STATE ELECTROCHEMISTRY
Volume 21, Issue 11, Pages 3155-3167Publisher
SPRINGER
DOI: 10.1007/s10008-017-3634-z
Keywords
Niobium; Anodic dissolution; Hydrofluoric acid; Mechanistic analysis
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Funding
- Department of Science and Technology, India
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The dissolution of niobium electrode in anodic regime in hydrofluoric acid was studied using electrochemical techniques. In the active region, complex plane plots of the impedance spectra exhibited mainly two capacitive loops. In the passive region, the spectra exhibited a mid-frequency pseudo-inductive loop and a low-frequency negative resistance. X-ray photoelectron spectroscopic analysis showed that the surface contains Nb2+ and Nb5+. The impedance data were analysed using equivalent circuit with Maxwell elements as well as mechanistic modelling. A four-step mechanism with a chemical and electrochemical dissolution step is proposed to explain the results. The results show that Nb with an oxidation state of 2 is likely to be an intermediates species. The simulations predict that at low over potentials, the surface is covered mainly with bare metal, whereas at high over potentials, the surface is entirely covered by passivating Nb5+ film.
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