Hydrogen transport through LaNi4.7Al0.3Hx porous electrode in the coexistence of two hydride phases (alpha- and beta-phases): current transient analysis

Abstract

The hydrogen transport through a LaNi4.7Al0.3Hx porous electrode in the coexistence of two hydrogen-poor phase alpha-LaNi4.7Al0.3Hx and hydrogen-rich phase beta-LaNi4.7Al0.3Hx has been investigated during the hydrogen discharging from the electrode by analysing current decay transients supplemented by a cyclic polarization curve and open-circuit potential transients. From the occurrence of three-staged current decay transients, the beta-LaNi4.7Al0.3Hx patches were sporadically embedded in the alpha-phase matrix during the hydrogen charging into the electrode at the overpotentials between -0.01 and -0.03 V (RHE) and the beta-LaNi4.7Al0.3Hx layer was completely embedded in matrix below -0.03 V (RHE). The hydrogen transport through the spherical symmetric LaNi4.7Al0.3Hx particle proceeded by the same mechanism of the "up-hill diffusion" coupled with interface-controlled phase boundary movement, as did the hydrogen transport through the plane symmetric Pd foil electrode. The current decay transient technique employed in this work proved to be a more informative approach to evaluation of the charge-discharge performance of the metal hydride electrode in practical use of the nickel/metal hydride secondary battery. (C) 1997 Published by Elsevier Science Ltd.