γ-MgH2 induced by high pressure for low temperature dehydrogenation

Abstract

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 degrees C) than α-MgH2, which desorbs at temperatures above 300 degrees 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.