Correlation between hydrogen storage properties and structural characteristics in mechanically milled magnesium hydride MgH 2

Abstract

In this work, we clarified the correlation between hydrogen storage and crystallographic properties in nanostructural magnesium hydride MgH 2 prepared by mechanical milling under hydrogen gaseous atmosphere. At the early stage within 2 h milling, the amount of desorbed hydrogen decreases ∼16% from 7.3 to 6.1 wt.% and the onset temperature of dehydrogenation decreases by 70 K from 670 K, while both the powder size and the crystallite size in powder decrease with increasing the milling time down to 1 μm and 15 nm, respectively, and the lattice strain of 0.3% is rapidly introduced. At the middle stage with longer milling time than 2 h, however, the crystallite size hardly change, but the lattice strain is once released at 2–5 h milling and again increases for longer milling time than 5 h. On the other hand, the amount of desorbed hydrogen suddenly increases from 2 to 5 h, and again decreases with a little increase of lattice strain during 5–80 h milling. At the final stage, the hydrogen capacity and desorption temperature reach to saturation of, respectively, 6.5 wt.% and 600 K, whereas the crystallite size and lattice strain reach to saturation of ∼7 nm and 0.2%, respectively. The results obtained indicate that the reduction of crystallite size as well as the introduction of lattice strain in MgH 2 during milling gives rise to the decrease in hydrogen storage capacity.