Anodic polarization and galvanostatic investigation of a metal hydride alloy electrode

Hydrogen diffusion in the metal hydride dominates the high-rate discharge c apability of the metal hydride electrode in a nickel metal hydride (Ni/MH) battery. In this study, an AB(5)-type hydrogen-absorbing alloy was used as the metal hydride electrode material. The oxidation and the rate-determinin g mass transfer reactions in the metal hydride electrode were studied and a nalyzed using anodic polarization measurements. The diffusion coefficient o f hydrogen in the metal hydride alloy was determined using both anodic pola rization measurements at varying hydrogen concentrations and a galvanostati c technique. The diffusion coefficient of hydrogen in the MH alloy is of th e order of 10(-11) cm(2) s(-1) assuming that the average radius of the allo y particles is 5 mum. The anodic polarization performance of an electrode w ithout hydrogen in the alloy is related both to the oxidation of the alloy powder and to the formation of a passive layer on the surface of the alloy powder. (C) 2000 International Association for Hydrogen Energy. Published b y Elsevier Science Ltd. All rights reserved.