The determination of kinetics parameters of the hydrogen evolution on Pd–Ni alloys by ac impedance

The hydrogen evolution reaction (HER) at a Pd–Ni electrodeposited alloy electrode has been studied by means of ac impedance spectrum measurements and by dc polarization current behavior in 0.5 mol dm−3 NaOH solution at 25°C. The rate constants of the forward and backward reactions of the corresponding steps were estimated by a nonlinear fitting method. It has been found that the overall reaction proceeds through a Volmer–Heyrovsky mechanism, with Heyrovsky as the rate determining step. The coverage vs potential relation is discussed comparing the results of ac impedance calculations with the same of potential decay determinations.