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 spectroscopy at various depth of discharge (DOD) in 6M KOH solution at room temperature. The dependence of impedance versus DOD is apparently presented in the form of 3D impedance plots. An equivalent circuit has been worked out by simulating experimental impedance dispersion, and all parameters in the proposed equivalent circuit were determined. The rate-determining step (RDS) of the dehydriding reaction for this alloy electrode was found to change with DOD, from mixed-controlled at the initial stage of the discharge process to diffusion-controlled at the last stage of the discharge process. (C) 1998 Elsevier Science S.A.