Microstructure and electrochemical performances of La0.7Mg0.3Ni2.55-xCo0.45Mx (M = Cu, Cr, Al; x=0-0.4) hydrogen storage alloys prepared by casting and rapid quenching

In order to improve the cycle stability of La-Mg-Ni system (PuNi3-type) hydrogen storage alloy, Ni in the alloy was partly substituted by Cu, Cr and Al. respectively. La-Mg-Ni system hydrogen storage electrode alloys La0.7Mg0.3Ni2.55-Co0.45Mx (M = Cu, Cr, Al; x = 0, 0. 1, 0.2, 0.3, 0.4) were prepared by casting and rapid quenching. The microstructures of the as-cast and quenched alloys were systematically determined by XRD, SEM and TEM. The obtained results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni-3 phase and the LaNi5 phase as well as the LaNi2 phase. The element substitution and rapid quenching have an inappreciable influence on the phase composition of the alloys, but both change the phase abundance of the alloys obviously. The results obtained by the electrochemical measurement indicated that the substitution decreased the discharge capacities of the as-cast and quenched alloys, whereas it improved the cycle stability, and the effect of three kinds of substitution elements on the cycle life of the alloys increased in the sequence Al > Cr > Cu. The rapid quenching significantly enhanced the cycle stability of the alloys. but it notably decreased the discharge capacity of the alloys. (C) 2007 Elsevier B.V. All rights reserved.