Study of hydrogen diffusion in alpha- and beta-phase hydrides of Mg2Ni alloy by microelectrode technique

A new microelectrode technique was developed for studying hydrogen diffusio n in Mg2Ni alloy electrodes during charging and discharging in 6 M KOH solu tion based on a spherical core shrink model. The diffusion coefficients of hydrogen in alpha- and beta -phase hydrides were measured on a single parti cle electrode using the potential-step method. It was found that the diffus ion of hydrogen in the beta -phase of the hydride occurs more slowly than i n the alpha -phase. This effect is attributed to formation of a beta -phase hydride layer beneath the particle surface during charging which retards h ydrogen transport and results in incomplete charging. This leads to an extr emely low electrochemical capacity. The diffusivity of hydrogen in magnesiu m alloy powders measured by the microelectrode technique was also compared with those evaluated by a porous plate electrode. (C) 2001 Elsevier Science B.V. All rights reserved.