A study on time-dependence of the oxygen evolution reaction on nickel by FFT impedance measurement

The degradation and rejuvenation of the oxygen evolution reaction (OER) on nickel electrodes in 1 mole dm^-3 KOH solution were studied by electrochemical techniques, especially by an impedence method using the first Fourier transform (FFT) which is able to measure the frequency-dispersion for the time-dependence of the reaction because of its short measuring time. The impedance behaviour for the OER was well explained by equivalent circuits for the low and the high overpotential regions, respectively. OER rejuvenation by anodization at 0.6 V was pursued by the capacitance component of the equivalent circuit for the high overpotential region. This rejuvenation by anodization was assumed to produce a transformation of oxide layers corresponding to the capacitance component and also grow poorly conductive oxide films.