γ-MgH₂ induced by high pressure for low temperature dehydrogenation

The formation of metastable γ-MgH₂ upon application of ultra-high pressure and its dehydrogenation properties were studied. Magnesium-nickel alloy (14 wt.% Ni) was hydrogenated and compressed at ultra-high pressures of 2.5 and 4 GPa. The phase composition and desorption properties of the products were investigated. Powder X-ray diffraction indicated that some α-MgH₂ converted to γ-MgH₂ during compression. This resulted in the onset of hydrogen desorption at 60 °C under vacuum. Our findings thus show that application of ultra-high pressure can facilitate the formation of γ-MgH₂, which has a lower dehydrogenation temperature (≤200 °C) than α-MgH₂, which desorbs at temperatures above 300 °C. The metastable phase possessed a high hydrogen storage capacity of at least 4.5 wt.%. These properties revealed the potential of γ-MgH₂ as a future hydrogen storage material.