The Passivity of Pure Nickel in Alkaline Solution under Different Temperatures: Electrochemical Verification and First-Principles Calculation

Properties of a passive film formed on pure nickel in an anaerobic alkaline solution are investigated by a first-principles calculation and electrochemical experiments in this work, and both results show agreement with each other. The formation energy of nickel vacancies is lower than that of oxygen vacancies in the NiO film, which is consistent with the deduction of the point defect model in which nickel vacancies impart p-type semiconducting character to the passive film, as confirmed by Mott–Schottky analysis. The density of nickel vacancies (approximately 1021 cm−3) in the passive film increases with temperature but decreases with the film-formation potential. The thickness of the passive film increases linearly with the film-formation potential, as verified both by Auger electron spectroscopy and electrochemical impedance spectroscopy. The diffusion coefficient of the nickel vacancies increases from 10−18 to 10−16 cm2/s as the temperature rises from 298 to 348 K, respectively, in experiments using high-field equations and first-principles calculation.