A study of the hydrogen absorption reaction into alpha- and beta-LaNi5Hx porous electrodes by using electrochemical impedance spectroscopy

Abstract

The hydrogen absorption reaction into alpha- and beta-phase LaNi5Hx porous electrodes in 6 M KOH solution has been investigated as a function of applied potential by analysing the a.c. impedance spectra complemented with cyclic polarization curves. The onset of the hydrogen evolution reaction (HER) can be accounted for in terms of the transition of the Warburg impedance to a capacitive loop at -0.980 V for the alpha-phase porous electrode and at -0.920 V for the beta-phase porous electrode. The charge-transfer resistance, R(ct), values from the beta-LaNi5Hx electrode are much smaller than those from the alpha-LaNi5Hx electrode over the whole applied potential range. The alpha- to beta-phase transition at -0.980 V and the beta to alpha-phase transition at -0.920 V are discussed in terms of the applied potential dependence of R(ct) for the hydrogen absorption reaction.