Effect of TiH₂–Induced Strain on Thermodynamics of Hydrogen Release from MgH₂

MgH2 is a prototypical light metal hydride, but it is too stable for use in practical hydrogen storage applications. Experiments with ball-milled MgH2–0.1TiH2 have shown that the enthalpy of reaction of MgH2 in this mixture is lower than for bulk MgH2 (Lu, J. et al. J. Am. Chem. Soc.2009,131, 15843). We have explored the mechanism for this phenomenon using first-principles density functional theory calculations of MgH2/TiH2 interfaces. We found that epitaxial contact between MgH2 and TiH2 can be formed with strongly favorable interface formation energies. Similar epitaxial interfaces also exist for Mg and TiH2. The strain induced by TiH2(111) on MgH2 and Mg in these interfaces can reduce the enthalpy for H2 release from MgH2.