PCT Curve and Cycling Performance of MgH2-Ni-NaAlH4-Ti Alloy Milled under H2

In this study, MgH2 was used as a starting material instead of Mg. A sample with a composition of 86 wt% MgH2-10 wt% Ni-2 wt% NaAlH4-2 wt% Ti (designated MgH2-10Ni-2NaAlH4-2Ti) was prepared by reactive mechanical grinding. Its Pressure-Composition-Temperature (PCT) curve measurement, hydriding-dehydriding cycling performance measurement, and microstructure observation were then performed. The desorption PCT curve at 593 K for MgH2-10Ni-2NaAlH4-2Ti at the first cycle exhibited a long plateau at around 2.6 bar, and a short plateau at about 3.6 bar, which correspond to equilibrium plateau pressures of Mg-H and Mg2Ni-H systems, respectively. The hydriding rate at 593 K under 12 bar H2 increased as the number of cycles, n, increased from 1 to 4, and it decreased from n=4 to n=15. At n=14, MgH2-10Ni-2NaAlH4-2Ti absorbed 3.02 wt% H for 2.5 min, 3.36 wt% H for 5 min, 3.51 wt% H for 10 min, and 3.58 wt% H for 30 min, which is 93.0% of the hydrogen absorbed for 30 min at n=4.