Development of MgH2-Ni Hydrogen Storage Alloy Requiring No Activation Process via Reactive Mechanical Grinding

Abstract

MgH2 was employed as a starting material instead of Mg in this work. A sample with a composition of 94 wt% MgH2-6 wt% Ni (called MgH2-6Ni) was prepared by reactive mechanical grinding. The hydriding and dehydriding properties were then examined. An MgH2-Ni hydrogen storage alloy that does not require an activation process was developed. The alloy was prepared in a planetary ball mill by grinding for 4 h at a ball disc revolution speed of 250 rpm under a hydrogen pressure of about 12 bar. The sample absorbed 3.74 wt% H for 5 min, 4.07 wt% H for 10 min, and 4.41 wt% H for 60 min at 573 K under 12 bar H2, and desorbed 0.93 wt% H for 10 min, 1.99 wt% H for 30 min, and 3.16 wt% H for 60 min at 573 K under 1.0 bar H2. MgH2-6Ni after reactive mechanical grinding contained β-MgH2 (a room temperature form of MgH2), Ni, γ-MgH2 (a high pressure form of MgH2), and a very small amount of MgO. Reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation, and to reduce the particle size of Mg. Mg2Ni formed during reactive mechanical grinding also increases the hydriding and dehydriding rates of the sample.