AC-IMPEDANCE STUDIES OF THE DISCHARGE PROCESS OF A MG2NI-TYPE HYDROGEN STORAGE ALLOY ELECTRODE IN 6M KOH SOLUTION

The discharge process of Mg2Ni-type hydrogen storage alloy electrode, consisting of Mg-Ni-AI-V, was characterized by AC impedance spectrosco py at various depth of discharge (DOD) in 6M KOH solution at room temp erature. The dependence of impedance versus DOD is apparently presente d in the form of 3D impedance plots. An equivalent circuit has been wo rked out by simulating experimental impedance dispersion, and all para meters in the proposed equivalent circuit were determined. The rate-de termining step (RDS) of the dehydriding reaction for this alloy electr ode was found to change with DOD, from mixed-controlled at the initial stage of the discharge process to diffusion-controlled at the last st age of the discharge process. (C) 1998 Elsevier Science S.A.