Quantum Chemical Investigation on the Material Properties of Al-Based Hydrides XAlH (X = Ca, Sr, Sc, and Y) for Hydrogen Storage Applications.

Aluminum-hydrogen compounds have drawn considerable interest for applications in solid-state hydrogen storage. The structural, hydrogen storage, electronic, mechanical, phonon, and thermodynamic properties of XAlH (X = Ca, Sr, Sc, Y) hydrides are investigated using density functional theory. These hydrides exhibit negative formation energies in the hexagonal phase, indicating their thermodynamic stability. The gravimetric hydrogen storage capacities of CaAlH, SrAlH, ScAlH, and YAlH are calculated to be 1.41 wt%, 0.94 wt%, 1.34 wt%, and 0.93 wt%, respectively. Analysis of the electronic density of states reveals metallic characteristics. Furthermore, the calculated elastic constants satisfy the Born stability criteria, confirming their mechanical stability. Additionally, through phonon spectra analysis, dynamical stability is verified for CaAlH and SrAlH but not for ScAlH and YAlH. Finally, we present temperature-dependent thermodynamic properties. This research reveals that XAlH (X = Ca, Sr, Sc, Y) materials represent promising candidates for solid-state hydrogen storage, providing a theoretical foundation for further studies on XAlH systems.