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Ionic and electronic conductivity of the anodic films on nickel

The surface film that forms on pure Ni during potentiostatic anodic polarization in a slightly alkaline solution was investigated by transient electrochemical techniques in combination with cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The Point Defect Model combined with a surface charge approach and interfacial capacity measurements was used to explore correlation between semiconducting properties (electronic conductivity) and kinetics of the film formation (ionic conductivity). Transport of the cation vacancies, as dominant point defects, through the film is the rate-determining step of the overall process of the surface film growth. The diffusion coefficient of the cation vacancies was extracted from the low-frequency EIS data and dc electrochemical measurements. The film formed was found to be a p-type semiconductor. The flat band potential and the carrier density were corrected for the frequency dispersion. The composition of the surface films on nickel, elemental identification and chemical state of elements were obtained using XPS.

nickel; anodic oxide film; diffusivity of point defects; electronic and ionic conductivity; Mott-Schottky analysis

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