X-ray diffraction. Structural characterizations of the hydride phases after RBM were carried out by X-ray powder diffraction (XRD) using the laboratory D8 advance Bruker instrument (Cu K α radiation λ = 1.5406 Å, Bragg-Brentano geometry) in a 2θ range from 10 to 90 • . Energy Dispersive X-Ray Spectroscopy. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) measurements on MgTiVZrNbHf, MgTiVCrNb and MgAlTiVCr phases before and after hydrogen cycling were performed on a Jeol JSM-7600F thermal field emission scanning electron microscope equipped with an Oxford X-Max detector and operated at 10 and 15 kV. The samples were deposited onto aluminum stubs using doublesided carbon tape.