The Effect Of Component Element Substitution On The Hydrogenation Ability Of Mg₂Ni

The electronic structures and thermodynamic stabilities of Mg2Ni1-xMx (M= Ti, V, Cr)and Mg-Ni-Ti-H alloys have been investigated by plane-wave pseudo-potential approach based on the density functional theory. The main conclusions are shown in the followings.1,The influence mechanism of element substitution on the dehydrogenation ability of Mg2NiH4 was investigated. The cell parameters, the density of states, the bond order between atoms and the formation enthalpies were obtained by the calculation. The structural stability of the hydride and the binding nature between atoms were analyzed. With M (M=Ti, V, Cr) substitution, the tendency of the formation enthalpies was consistent with the experiment. The best effect is got by the Ti substitution, which can reduce the structural stability and improve the hydride desorption kinetics of Mg2NiH4. Further analysis of the electronic structures, the interactions of Ni-H and M-H play a dominant role in the structural stability of Mg2NiH4. The substitute element just tries to improve the dehydrogenation ability of Mg2NiH4 by the interactions of M-H.2,The electronic structur and thermodynamic stability of Mg-Ni-Ti-H was studied by the same methord. Results indicate that:the interactions of Ni-H were decreased with the increasing Ti substitution of Mg (8f) in Mg2NiH4. The dehydrogenation ability was improved, but the hydrogen storage capability was decrease. The interactions of Ni-H were also decreased with the increasing Ni substitution of Mg in Mg2NiH4. The formation enthalpies of Mg2NiH4, Mg1.875Ti0.125NiH4, Mg1.75Ti0.25NiH4, Mg2Ti0.125Ni0.875H4, Mg2Tio.25Nio.75H4 were:-55.7kJ/mol,-53.6kJ/mol,-52.4kJ/mol,-54.1 kJ/mol,-52.8 kJ/mol.