First-Principles Study on the Physical Properties of Hydrogen Storage Materials X2MgH ₆ (X =Ca, Sr, Ba)

The current focus in harnessing hydrogen energy is finding the ideal hydrogen storage material. In this study, we investigated the electrical, mechanical and optical properties of three novel hydrides X 2 MgH 6 (X[Formula: see text][Formula: see text][Formula: see text]Ca, Sr, Ba) using a first-principles approach. Our results demonstrate that all three hydrides exhibit semiconducting properties with indirect band gaps. The phonon dispersion spectrum shows that Sr 2 MgH 6 and Ba 2 MgH 6 are stable in dynamics. The mechanical properties indicate strong resistance to deformation along the [Formula: see text]-axis and [Formula: see text]-axis, with Ca 2 MgH 6 showing the highest bulk and shear moduli. Optical property analysis demonstrates that these materials have significant absorption and reflection capabilities, particularly in the ultraviolet region. Furthermore, the hydrogen storage capacities were calculated to be 3.77[Formula: see text]wt%, 3.5[Formula: see text]wt% and 1.3[Formula: see text]wt% for Ca 2 MgH 6 , Sr 2 MgH 6 and Ba 2 MgH 6 , respectively, highlighting their potential as efficient hydrogen storage materials. This research provides valuable insights into the design and optimization of hydrogen storage materials, contributing to the advancement of hydrogen-related technologies.