Influence of dopants Ti and Ni on dehydrogenation properties of NaAlH ₄: Electronic structure mechanisms

We report on a study of influence of dopants (Ti and Ni) on the dehydrogenation properties of NaAlH₄ using the ab initio density functional method. Calculations show that the influence of dopants on the electronic structure is much localized; only the electronic structures of atoms in the vicinity of the dopants were changed. The mechanisms by which Ti improves the dehydrogenation properties of NaAlH₄ are sensitive to the occupation of Ti in NaAlH₄. If Ti substitutes for an Al atom, it may form Ti-Al intermetallics, and if it occupies an interstitial site, it may "capture" H atoms to form TiH₂ phase. In both cases, the [AlH₄] groups were dramatically distorted, which is the main reason why Ti dopant improves the dehydrogenation properties of NaAlH₄. The influence of Ni on the dehydrogenation properties of NaAlH₄ is relatively in weak comparison to the Ti dopant, mainly because the Ni only affects the electronic distribution in its vicinity, and so no significant changes of the [AlH₄] groups were observed in Ni doped systems.