Investigation of Lithium Complex Hydrides Li2MH5 (M = B, Al) as Hydrogen Storage materials; A theoretical study

Lithium complex hydrides Li2MH5 (M= B, Al) in are potential hydrogen storage material because of their high capacity of (10, 6.5 wt. % respectively) H2. However, their high thermodynamic stability is unfavorable for dehydrogenation processes. Understanding the bonding nature of Al-H, B-H and Li-H are essential for predicting their dehydrogenation mechanism and then improving their dehydrogenation performance. Quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of compounds. In this work the charge density distribution in Li2AlH5 and Li2BH5 was compared. Thus using calculated Nuclear Quadrupole Coupling Constants (NQCC) of 2H nuclei, the electronic structure of Li2AlH5 and Li2BH5 was studied. The results show that between two proposed dehydrogenation mechanisms for Li2MH5, hetro phase dehydrogenation is preferred than partial dissociation to LiMH4. Furthermore easier condition for hetro phase dehydrogenation is expected in Li2AlH5. The electric field gradient (EFG) of quadrupolar nuclei were calculated to obtain NQCC parameters. All calculations performed using Gaussian 03 at MP2/6-311G** level of theory. The selected level and basis set give the rather acceptable qualitative NQCCs of hydrogen atoms.

کلیدواژه ها:

Nuclear quadrupole resonance (NQR) ، Lithium complex hydrides ، Hydrogen ، Ab initio calculations ، Nuclear Quadrupole Coupling Constant (NQCC)