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, TiH_1.924, 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.