Abstract
This study investigated the electrochemical behavior of pure nickel in sub-molten KOH at 200 °C and the structure of surface films formed at different anodic polarization potentials. Potentiodynamic polarization measurements showed an active-to-passive transition followed by transpassivity. Unlike aqueous alkaline solutions, surface films created in active, far passive, and transpassive regions are few microns thick. Grazing-incidence x-ray diffraction (GI-XRD), Raman, and x-ray photoelectron spectroscopy (XPS) measurements revealed that a thick and defective layer of NiO forms during polarization in the active region. Polarization into the passive regime reduces the thickness and number of defects of NiO and promotes passivity. With the formation of +3 valent nickel at far passive region, a thick, flaky adlayer of potassium-intercalated γ-NiOOH is produced. At high transpassive potentials, the flake-like morphology deteriorated with the high rate of oxygen evolution reaction (OER). The micrometer thick electroactive anodic surface films formed during active, far passive, and transpassive region became a few micrometers thick because of the high dissolution rate of Ni and the high viscosity of the sub-molten KOH.
Original language | English |
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Article number | 101963 |
Journal | Surfaces and Interfaces |
Volume | 31 |
DOIs | |
Publication status | Published - Jul 2022 |
Bibliographical note
Publisher Copyright:© 2022
Funding
The authors are grateful for the financial support by the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement number 764977. In addition, the authors sincerely acknowledge the support of Dr. Barış Yağcı, Koç University, and Assoc. Prof. Uğur Ünal, Koç University, for the XPS analysis.
Funders | Funder number |
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H2020 Marie Skłodowska-Curie Actions | 764977 |
Horizon 2020 |
Keywords
- Alkaline sub-molten KOH
- Anodic oxidation
- NiO
- γ-NiOOH