ELECTROCHEMICAL IMPEDANCE STUDY ON THE KINETICS OF HYDROGEN EVOLUTION AT AMORPHOUS METALS IN ALKALINE-SOLUTION

The mechanism of the hydrogen evolution reaction on the amorphous metals Ni78Si8B14 and Fe60Co20Si10B10 in 1M KOH at T = 298 K has been studied by electrochemical impedance spectroscopy in the frequency range 10 mHz less-than-or-equal-to f less-than-or-equal-to 65 kHz. Comparative measurements were carried out on polycrystalline Ni and Pt electrodes. Analysis and discussion of the data is based on a theoretical transfer function derived for the Volmer-Tafel reaction mechanism. Formal rate constants could be obtained from a nonlinear least squares fit of the impedance data and were compared with previous results obtained from an analysis of steady-state polarization curves. Participation of surface and/or bulk diffusion steps of H atoms at low overpotentials is indicated on Fe60Co20Si10B10 by a time constant arising at low frequencies in the impedance spectra.