Although Mg 2 FeH 6 has drawn significant attention for storing hydrogen, its sluggish kinetics during hydrogenation and poor reversibility hinder practical uses. In this work, the replacement of Fe atoms in Mg 2 FeH 6 with Ni atoms is attempted and the material properties are investigated. A detailed study of the de/rehydrogenation kinetics and reaction mechanisms of the Ni-doped Mg 2 FeH 6 is carried out. The effects of Ni-loading contents on kinetic properties and behaviors as well as reversibility and reaction pathways are characterized. In addition, the crystal structure of a new Ni-substituted Mg 2 FeH 6 phase is confirmed. • Experimental confirmation for the first time of Ni substitution for Fe in Mg 2 FeH 6. • Studying the effects of Ni-loading contents on desorption kinetics and reversibility. • Alteration of de/rehydrogenation pathways with different Ni-loading contents. • Enhancement of Mg 2 FeH 6 reversibility via the formation of Mg 2 Fe 0.75 Ni 0.25 H 6. [ABSTRACT FROM AUTHOR]