DFT studies of hydrogen storage properties of Mg 0.75Ti 0.25

Abstract

Absorption energies of hydrogen in Mg 0.75Ti 0.25 alloys as a function of the hydrogen concentration were calculated using Density Functional Theory. Four types of structures of alloys and their hydrides including TiAl 3, ZrAl 3, AuCu 3, and segregated types of structures were considered. The stability of the configurations, and the structural and electronic bonding properties were studied. The hydrogenation properties depend highly on the structure of the alloys. The ordered alloys have very similar properties to that of pure Mg. For segregated alloys, the hydrogenation properties can be divided to Ti-like, ordered alloy-like and Mg-like from low to high hydrogen concentration. The formation energies show that for the four structures, segregated Mg 0.75Ti 0.25 is favored for alloys, whereas TiAl 3 type of Mg 0.75Ti 0.25H 2 are favored for hydrides. Therefore hydrogen induced structural rearrangement of the intermetallic structures of the Mg 0.75Ti 0.25 might occur upon hydrogen cycling. For the non-homogenous Mg–Ti–H system, further phase segregation of Ti in Mg might occur. Partial dehydrogenation with some hydrogen remaining in the Ti-rich region may improve reversibility.