Electrochemical impedance spectroscopy study of the metal hydride alloy/electrolyte junction

The behaviour of the LaNi3.55Mn0.4Al0.3Co0.75 alloy, used as a negative electrode in the Ni-MH batteries, was studied by the electrochemical impedance spectroscopy (EIS), measured at different potentials. The modeling of the EIS spectra allows us to model the interface electrolyte/Ni-MH electrode by a succession of interfaces electrolyte/corrosion film/alloy particles. The various processes and the physics parameters of each interface are discussed and evaluated. When the potential shifts to more negative values, two reactions are in competition: the hydrogen molecular evolution and the hydrogen atomic absorption. The hydrogen diffuses in the bulk of the alloy and the diffusion is not the limiting factor for the hydrogen absorption.