The hydrogenation of Mg0.8125Ti0.1875 was investigated by density functional calculations, using a model where Ti was segregated into nano-clusters. Introducing small amounts of hydrogen resulted in significant stabilization, with the mixing enthalpy (cohesive energy relative to standard state elements) becoming negative for hydrogen contents exceeding 0.07 H per metal. H prefers sites on the interface between Mg and Ti, with hydrogenation energies down to –115 kJ/(mol H2). Trapping of H on these very stable sites is proposed as an alternative explanation to why the reversibility of Mg-Ti thin films, which are initially meta-stable, can be preserved over many cycles of hydrogenation.
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