Hydrogen sorption kinetics and mechanism of Mg2Fe(1-x)NixH6

This work aims to optimize the content of Ni substitution for Fe in Mg2FeH6 to form the quaternary in-termetallic 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 opti-mized composition of x similar to 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. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This work aims to optimize the Ni substitution in Mg2FeH6 and form the quaternary intermetallic hydrides of Mg2Fe(1-x)NixH6 with the best kinetics and reversibility. The degree of Ni substitution is enhanced by increasing the Mg2NiH4 content, resulting in improved dehydrogenation kinetics and reversible hydrogen capacities. The structures and dehydrogenation energies of Mg2Fe(1-x)NixH6 with different Ni-substituted contents are simulated and calculated to explain the role of Ni substitution.