A theoretical study of high-pressure-induced phases of LiAlH4 using calculated NQCC parameters

Abstract

Quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of compounds. Lithium alanate (LiAlH₄) is a potential hydrogen storage material because of its high capacity of 10.5 wt % H₂. However, the drawbacks of its dehydrogenation process are the relatively high temperatures and the slow dehydrogenation kinetics; furthermore, its reversibility is rather poor. Understanding the bonding nature of Al and H is essential for improving its dehydrogenation performance. In this work the charge density distribution in LiAlH₄ is studied. Thus using calculated nuclear quadrupole coupling constants of hydrogens (²H-NQCCs), the electronic structure of α-LiAlH₄ with high pressure forms of LiAlH₄, (β- and γ-LiAlH₄) were compared. The results show that easier condition for dehydrogenation is expected in β-LiAlH₄. Comparison of calculated dehydrogenation enthalpies of LiAlH₄ phases verifies this prediction. The electric field gradient (EFG) of quadrupolar nuclei were calculated to obtain NQCC parameters. All calculations performed using Gaussian 03 at B3LYP/6-31G* level of theory.