Hydrogen storage in mechanically milled Mg–LaNi5 and MgH2–LaNi5 composites

Abstract

Magnesium and magnesium hydride were mechanically milled with LaNi5 to make a Mg–Ni–La ternary alloy for hydrogen storage. Mechanical milling of MgH2+LaNi5 or milling of Mg+LaNi5 followed by a full hydrogenation leads to a composite of MgH2+LaH3+Mg2Ni. Upon hydrogen absorption/desorption cycling, a mixture of Mg+LaH3+Mg2Ni phases is obtained in both cases, but with different powder sizes. The powder size is greatly reduced by using MgH2 instead of Mg in the milling process. The reduction in powder size gives faster absorption kinetics, and slower desorption kinetics. Adding both Ni and La to Mg-based alloys produces a synergetic effect on the hydrogen absorption/desorption. The ternary Mg–Ni–La alloy showed much better absorption and desorption kinetics than the binary alloys Mg–La and Mg–Ni. Lanthanum hydride has strong catalytic effects on absorption of Mg, but weak effects on desorption. Mg2Ni has better catalytic effect than lanthanum hydride at temperatures above 373 K.