Hydrogen-storage performance of an Mg–Ni–Fe alloy prepared by reactive mechanical grinding

Abstract

The 71.5%Mg–23.5%Ni–5%Fe alloy prepared by reactive mechanical grinding for 4 h does not need activation. The activated sample has the hydriding rate of 0.494 wt%/min for 5 min and absorbs 3.32 wt% for 60 min at 593 K under 1.2 MPa H₂. It has the dehydriding rate of 0.330 wt%/min for 5 min and desorbs 2.42 wt%H for 20 min at 593 K 0.1 MPa H₂. The XRD pattern of 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe after reactive mechanical grinding exhibits MgH₂ in addition to starting elements Mg, Ni, and Fe. 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe after hydriding–dehydriding cycling contains Mg, Mg₂Ni, MgO, and Fe. The reactive mechanical grinding of Mg with Ni and Fe is considered to facilitate nucleation by creating many defects on the surface and in the interior of Mg, by the additive acting as active sites for the nucleation and shorten diffusion distances of hydrogen atoms by reducing the particle size of Mg. The MgH₂ formed in the as-milled 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe alloy is considered to lead to the creation of more defects and finer particle size.