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

Abstract

New ternary Mg–Mn–Ni alloys synthesised by high energy ball milling have been studied as hydrogen storage materials. A new Mg 3MnNi 2 ternary intermetallic compound of the Ti 2Ni 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–Mg 3MnNi 2 alloys. The Mg 3MnNi 2 compound reversibly absorbs about 1 wt.% of hydrogen already at room temperature and forms interstitial type Mg 3MnNi 2H ∼3 hydride. Substantially higher hydrogenation capacity has been observed in Mg–Mg 3MnNi 2 alloys with high Mg content, e.g. 5.4 wt.% for the Mg 88Mn 4Ni 8 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 Mg 3MnNi 2 phase.