Hydriding and Dehydriding Features of a Titanium-Added Magnesium Hydride Composite

Abstract

Magnesium has excellent hydrogen-storage properties except low hydriding and dehydriding rates. In the present work, titanium (Ti) was chosen as an additive to increase the hydriding rate of Mg and the dehydriding rate of MgH2. 15 wt.% Ti was added to MgH2 by milling in hydrogen (reactive mechanical grinding). The hydriding and dehydriding features of the Ti-added MgH2 composite (named 85 MgH2 + 15 Ti) were investigated. At the first cycle (n = 1), 85 MgH2 + 15 Ti absorbed 2.96 wt.% H for 2.5 min and 5.51 wt.% H for 60 min at 593 K in 12 bar H2, having an effective hydrogen-storage capacity of 5.51 wt.%. β-MgH2, γ-MgH2, TiH1.924, MgO, and MgTi2O4 were formed during reactive mechanical grinding. Reactive mechanical grinding of MgH2 with Ti is believed to create imperfections, produce cracks and clean surfaces, and decrease particle sizes. The phases formed during reactive mechanical grinding and their pulverization during reactive mechanical grinding are believed to make these effects stronger. Since the γ-MgH2 phase is believed to be decomposed at n = 1, the existence of the γ-MgH2 phase in the milled sample does not contribute to the improvement of the sorption behavior of Mg.