γ-MgH_2 induced by high pressure for low temperature dehydrogenation

摘要

The formation of metastable gamma-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 alpha-MgH2 converted to gamma-MgH2 during compression. This resulted in the onset of hydrogen desorption at 60 degrees C under vacuum. Our findings thus show that application of ultra-high pressure can facilitate the formation of gamma-MgH2, which has a lower dehydrogenation temperature (= 200 degrees C) than alpha-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 gamma-MgH2 as a future hydrogen storage material. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.