Anodic polarization and galvanostatic investigation of a metal hydride alloy electrode

Hydrogen diffusion in the metal hydride dominates the high-rate discharge capability of the metal hydride electrode in a nickel metal hydride (Ni/MH) battery. In this study, an AB5-type hydrogen-absorbing alloy was used as the metal hydride electrode material. The oxidation and the rate-determining mass transfer reactions in the metal hydride electrode were studied and analyzed using anodic polarization measurements. The diffusion coefficient of hydrogen in the metal hydride alloy was determined using both anodic polarization measurements at varying hydrogen concentrations and a galvanostatic technique. The diffusion coefficient of hydrogen in the MH alloy is of the order of 10−11 cm2 s−1 assuming that the average radius of the alloy particles is 5 μm. The anodic polarization performance of an electrode without 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.