New Mg–Mn–Ni alloys as efficient hydrogen storage materials

New ternary Mg–Mn–Ni alloys synthesised by high energy ball milling have been studied as hydrogen storage materials. A new Mg3MnNi2 ternary intermetallic compound of the Ti2Ni type has been identified, its structure was studied by neutron diffraction. It has been shown that in the Mg–Mn–Ni system this intermetallic coexists with Mg, forming two-phase Mg–Mg3MnNi2 alloys. The Mg3MnNi2 compound reversibly absorbs about 1 wt.% of hydrogen already at room temperature and forms interstitial type Mg3MnNi2H∼3 hydride. Substantially higher hydrogenation capacity has been observed in Mg–Mg3MnNi2 alloys with high Mg content, e.g. 5.4 wt.% for the Mg88Mn4Ni8 alloy at 250–350 °C. Hydrogen absorption–desorption kinetics of these alloys are drastically improved compared to undoped magnesium due to catalytic effect of the Mg3MnNi2 phase.