Abstract
Transient of current in thin layer formation on nickel electrode was investigated during an anodic potential step in 0.1 M NaOH aqueous solution. The current was shown to have a time-dependency of i(t)=i0[1+(t/τ)]-1/2 which was derived from ionic migration under potential drop through the surface thin film. In the equation, the initial current, i0, and the time constant, τ, after the potential step were estimated from the slope and the intercept on the 1/i2 vs. t plot, respectively. From a plot of i02τ vs. φ, the oxide layer thickness at the potential, φ0, before the step and an average ionic mobility in the oxide film were calculated. The oxide layer was found to grow from the potential of 0.02 V vs. SCE and to saturate in thickness at 1.3 nm at the potential range between 0.2 and 0.4 V. The average mobility was estimated to be μ=9.9×10-20m2V-1s-1.
