Quantum Chemical Investigation on the Material Properties of Al-Based Hydrides XAl2H2 (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 XAl2H2 (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 CaAl2H2, SrAl2H2, ScAl2H2, and YAl2H2 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 CaAl2H2 and SrAl2H2 but not for ScAl2H2 and YAl2H2. Finally, we present temperature-dependent thermodynamic properties. This research reveals that XAl2H2 (X = Ca, Sr, Sc, Y) materials represent promising candidates for solid-state hydrogen storage, providing a theoretical foundation for further studies on XAl2H2 systems.