Kinetic hydrogenation of the electrode-electrolyte interface for LaY2Ni9 Nickel Metal Hydride accumulators

Impedance spectrum for the hydrogen adsorption-absorption mechanism of LaY2Ni9 electrode was analyzed through an equivalent circuit based on a well understanding of the various processes happening at the interface electrode/electrolyte. The equivalent circuit model takes into account the charge transfer phenomenon, the transition phase of the atomic hydrogen between adsorbed/absorbed states before its diffusion within the alloy. Kinetic parameters such as the specific exchange current density, I0,EIS, the double layer capacitance, Cdl and the adsorption capacitance, Cad, were determined for the LaY2Ni9 electrode versus cycle number using impedance spectroscopy technique. The results of EIS measurements indicate a correlation between the evolution of these kinetic parameters and those determined by other electrochemical techniques. Another correlation is observed between the exchange current density determined by EIS, I0,EIS, and that determined by cyclic voltammetry, I0,CV which related to the applied perturbation type.

I. Introduction

All works on the Ni-MH type of accumulators is devoted to the negative electrode, the latter can be characterized by different electrochemical techniques such as chronopotentiometry, chronoamperometry and cyclic voltammetry but these techniques remain limited to understand all the physical processes involved and in particular the electrode-electrolyte charge transfer mechanism. In this context the electrochemical impedance spectroscopy (EIS) is a very efficacious technique that can reveal the conduct of the physical processes at the electrode-electrolyte interface [1]–[5].