Charge transfer and mass transfer reactions in the metal hydride electrode

Charge transfer reaction across the electrode/electrolyte interface and hyd rogen diffusion in the negative MH alloy electrode dominate the high-rate d ischarge capability of the metal hydride electrode in a nickel metal hydrid e (Ni/MH) battery. The mass transfer process in the MH electrode mainly inv olves hydrogen diffusion in the bulk MH alloy. The charge transfer reaction in the negative electrode reflects the capability of hydrogen reduction an d oxidation reactions at the surface of the MH alloy powder. In this study, an AB(5)-type hydrogen-absorbing alloy was used as the negative electrode material. The rate-determining mass transfer process in the bulk MH alloy e lectrode was studied and analyzed using anodic polarization measurements Th e exchange current density, which is related to the charge transfer reactio n, was analyzed by using the hydrogen equilibrium pressure. The estimation of hydrogen diffusion coefficient in the MH alloy is strongly dependent on the value of the effective reaction area of charge transfer reaction at the surface of the alloy powder. (C) 2000 International Association for Hydrog en Energy. Published by Elsevier Science Ltd. All rights reserved.