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Tao S.X.,Laboratory of Inorganic Chemistry and Catalysis | Notten P.H.L.,Laboratory of Inorganic Chemistry and Catalysis | Van Santen R.A.,Laboratory of Inorganic Chemistry and Catalysis | Jansen A.P.J.,Laboratory of Inorganic Chemistry and Catalysis
Journal of Alloys and Compounds | Year: 2011

Absorption energies of hydrogen in Mg0.75Ti0.25 alloys as a function of the hydrogen concentration were calculated using Density Functional Theory. Four types of structures of alloys and their hydrides including TiAl3, ZrAl3, AuCu3, 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 Mg0.75Ti0.25 is favored for alloys, whereas TiAl3 type of Mg0.75Ti 0.25H2 are favored for hydrides. Therefore hydrogen induced structural rearrangement of the intermetallic structures of the Mg 0.75Ti0.25 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. © 2010 Elsevier B.V. All rights reserved. Source


Tao S.-X.,Laboratory of Inorganic Chemistry and Catalysis | Notten P.H.L.,Laboratory of Inorganic Chemistry and Catalysis | Van Santen R.A.,Laboratory of Inorganic Chemistry and Catalysis | Jansen A.P.J.,Laboratory of Inorganic Chemistry and Catalysis
Computational Materials Science | Year: 2011

The effect of structural changes in MgH2 induced by contact with TiH2 on the thermodynamics of hydrogen cycling has been studied using DFT calculations. Models of epitaxial (1 0 0) MgH2/TiH 2 multilayers with different layer thicknesses and Mg:Ti ratios have been designed. The hydrogen desorption energy from the MgH2 layer is found to depend on the thickness of the MgH2 layers and the Mg:Ti ratio because the MgH2 structure tends to change from fluorite to rutile with increasing MgH2 thickness and Mg:Ti ratio. Three types of hydrogen can be distinguished: hydrogen in MgH2 layer with desorption energy of 0.44 eV/H2, hydrogen in MgH2/TiH 2 interface with desorption energy of 1.19 eV/H2, hydrogen in TiH2 layer with desorption energy of 0.95 eV/H2. The desorption energy of hydrogen desorption from the fluorite-like MgH2 is 0.23 eV/H2 lower than the bulk rutile MgH2. The structural deformations as well as the interfacial energy differences between the partial hydrogenated and hydrogenated states have been found to be responsible for the tuned hydrogen desorption energy. © 2011 Elsevier B.V. All rights reserved. Source

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