DFT Study of the Physical Properties of X2MgTiH6 (X = Rb, Cs) Double Perovskite Hydrides for Hydrogen Storage Applications

Hydrogen is attracting considerable interest as a clean and environmentally friendly energy carrier. This is why hydrogen storage technologies have been the subject of intensive research for several decades. In this field, the development of new storage materials remains a major challenge. Our study focuses specifically on the physical properties of X2MgTiH6 (X = Rb and Cs), which we analyze systematically using density functional theory (DFT) to assess their potential for hydrogen storage. Both compounds have a cubic crystal structure, with lattice constants calculated at 8.13 Å and 8.16 Å for X = Rb and X = Cs, respectively. Phonon dispersion calculations confirm the dynamic stability of these two hydrides. Analysis of the electronic band structure reveals a metallic character for both materials. Moreover, calculations of optical properties indicate favorable characteristics for hydrogen storage applications. Notably, the predicted gravimetric hydrogen storage capacities of X2MgTiH6 (X = Rb, Cs), although below current DOE targets, highlight the hydrogen storage potential of this family of compounds and motivate further investigation of their structural and thermodynamic properties.