Hydrogen Storage Behaviours of Nanocrystalline and Amorphous Mg20-xLaxNi10(x=0-6) Hydrogen Storage Alloys

Mg2Ni-type hydrogen storage alloys with nominal composition Mg20-xLaxNi10 (x = 0, 2, 4, 6) were prepared by melt spinning. The microstructures of the alloys were studied by XRD, SEM and HRTEM. It is found that no amorphous phase formed in the as-spun La-free alloy, but the as-spun alloys containing La mainly held a major amorphous phase. When La content x≤2, the major phase in the as-cast alloys is Mg2Ni phase, but with the further increase of La content, the major phase of the as-cast alloys changes into (La, Mg)Ni3+LaMg3 phases. The hydrogen absorption and desorption kinetics of the as-cast and spun alloys were measured using an automatically controlled Sieverts apparatus, indicating that the hydrogen absorption and desorption capacity and the kinetics of the x = 2 alloy clearly increase with rising of spinning rate, but a contrary result is obtained for x = 6 alloy. The electrochemical measurement shows that the discharge capacity of the x = 2 alloy grows with rising of spinning rate, but it is a completely contrary result for x = 6 alloy. The melt spinning significantly improves the cycle stability of the x = 2 and 6 alloys.