Abstract
This work aims to optimize the content of Ni substitution for Fe in Mg2FeH6 to form the quaternary intermetallic hydrides of Mg2Fe(1−x)NixH6 with the best kinetics and reversibility. Different degrees of Ni substitution (x) are obtained from varying the mole ratios of Mg2FeH6:Mg2NiH4 used as starting materials. By increasing Mg2NiH4 contents, the degree of Ni substitution enhances from x = 0.26–0.47, which is beneficial to dehydrogenation kinetics and reversible hydrogen capacities. The sample with significant Ni substitution rather decompose into Mg2Ni than Mg, which Mg2Ni reacts with Fe to reproduce Mg2Fe(1−x)NixH6 upon rehydrogenation. During cycling, Ni substitution degree of all samples enhances to the optimized composition of x∼0.5, resulting in the kinetic improvement. Furthermore, the structures of Mg2Fe(1−x)NixH6 with different Ni-substituted contents are simulated and their dehydrogenation energies are calculated to explain the role of Ni substitution on the dehydrogenation of Mg2Fe(1−x)NixH6.
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