Importance of Hydride-Hydride Interaction in the Stabilization of LiH, NaH, KH, LiAlH₄, NaAlH₄, and Li₃AlH₆ as Solid-State Systems for Hydrogen Storage

摘要

The solid-state structures of LiH, NaH, KH, LiAlH_(4), NaAlH_(4) and Li_(3)AlH_(6) have been explored in details as potential hydrogen-storage materials using computational electron density methods; the full-potential linearized augmented plane wave (FPLAPW) method plus local orbital (FPLAPW+lo) embodied in the WIEN2k package code. Topological analysis of their DFT-computed electron densities in tandem with Bader’s Atoms in Molecules (AIM) theory reveals a plethora of stabilizing interactions some of which are really strong. With the exception of NaH and KH, which do not contain the hydride-hydride bonding, the rest of the metal hydrides; LiH, LiAlH_(4), NaAlH_(4) and Li_(3)AlH_(6) show an increasing number of hydride-hydride interactions that contribute to the stabilization of their three-dimensional (3-D) solid-state structures. Even though these hydride-hydride interactions are weaker compared to the M-H counterparts, their multiplicity greatly contributes to the stability of these metal hydrides. Results from their electron density studies reveal that the number of hydride-hydride interactions in these binary and complex metal hydrides increase with the complexity of the solid-state structures. LiAlH_(4) is more stable compared to NaAlH_(4), Li_(3)AlH_(6), and LiH. NaH and KH were seen to be the least stable solid-state structures. It is suggested that the presence of these hydride-hydride interactions play a significant role in the mediation or understanding of the reaction mechanism leading to the release of hydrogen from these solid-state systems.