First principles study of AlH3 vacancy mediated mechanism in dehydriding of NaAlH4.

First-principles calculations were performed to study the performance of AlH 3 vacancy in the early stage of the dehydrogenation reaction of NaAlH 4 . AlH 3 vacancy tends to exist on the (001) surface rather than in the interior of NaAlH 4 . The migration of AlH 3 vacancy from the subsurface layer to the surface layer is an exothermic process, with an energy barrier of 0.33 eV. The result suggests that enhancing the mobility of AlH 3 vacancy along the surface (001) is a feasible approach to facilitate the dehydrogenation reaction of NaAlH 4 . Al H 6 3 − anion is observed in this work by importing two AlH 3 vacancies, which exists stably at T = 300 K, but decomposes when the temperature increases to 400 K. The formation mechanism of Al H 6 3 − is that two neighboring Al H 4 − units form two AlH 3 vacancies and two remaining H − anions firstly, and then the two remaining H − anions are attracted to Al H 4 − unit to form Al H 6 3 − anion. [ABSTRACT FROM AUTHOR]