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Abstract

Recently, there has been growing interest in multi-principal element alloys for hydrogen storage. However, most of the papers published so far report compositions based only on transition metal elements, which limit the gravimetric storage capacities due to their densities. Since Mg is a low-density element promising for hydrogen storage, the study of Mg-containing multi-principal element compositions is opportune. In the present work, we report for the first time the structural characterization and hydrogen storage properties of the A₂B type MgTiNbCr_0.5Mn_0.5Ni_0.5 alloy and its derivative Mg_0.68TiNbNi_0.55 alloy. These Mg-containing multi-principal element alloys form major BCC phase (W-type, Im3̅ m) and major FCC hydride (MH₂ with CaF₂-type structure) when synthesized by mechanical alloying (MA) and reactive milling (RM), respectively. Hydrogen is desorbed from both RM samples in two steps, with some overlap, from different hydrides formed during synthesis. The microstructure of the Mg_0.68TiNbNi_0.55 composition is more homogeneous (less secondary phases), but both alloys present a total gravimetric capacity of around 1.6 wt% H₂.