The Structures and Properties of Y-Substituted Mg₂Ni Alloys and Their Hydrides: A First-Principles Study

Abstract

The structures and properties of Y-substituted Mg 2 Ni alloys and the corresponding hydrides are investigated by a first-principles plane-wave pseudopotential method within density functional theory. Results show that Mg 2 Ni has the best structural stability when Y atom occupies the Mg(6f) lattice sites. The calculated enthalpies of formation for Mg 2 Ni , Mg 2 NiH 4 and Mg 15 YNi 8 H 32 are -51.612, -64.667 and -62.554 kJ/mol, respectively. It is implied that the substitution of Y alloying destabilizes the stability of the hydrides. Moreover, the dissociated energies of H atoms are decreased significantly, indicating that Y alloying benefits the improvement of the dehydrogenating properties of Mg 2 Ni hydrides. The calculation and analysis of the electronic structures suggest that there is a stronger interaction between H and Ni atoms than the interaction between H and Mg atoms in Mg 2 NiH 4 . However, the Ni-H bond is weakened by the substitution of Y. Therefore, the substitution is an effective technique to decrease the structural stability of the hydrides and benefit for hydrogen storage.