Unveiling the potential of XInH3 (X = Rb and Cs): A DFT study for solid state hydrogen storage applications

Efficient hydrogen storage materials are essential for the advancement of sustainable energy solutions. This work employs density functional theory (DFT) to examine the capacity of XInH₃ (X = Rb and Cs) as materials for storing hydrogen in solid-state. The crystal structures of RbInH₃ and CsInH₃, which both belong to the space group pm3m, with lattice parameters of 4.35 Å and 4.44 Å, respectively. The formation enthalpies of RbInH₃ and CsInH₃ are −4.29 eV/atom and −6.41 eV/atom, respectively, suggesting that they possess favorable thermodynamic stability. The gravimetric hydrogen storage capacities of RbInH₃ and CsInH₃ are 1.45 % and 1.18 % respectively. An examination of the electronic structure indicates the presence of metallic properties, characterized by the overlapping of the valence and conduction bands. The optical characteristics of RbInH₃ and CsInH₃ demonstrate substantial absorption in the ultraviolet (UV) region, with RbInH₃ having a peak at 20.25 electron volts (eV) and CsInH₃ at 16.92 eV. The mechanical properties demonstrate anisotropic behavior and imply brittle features. The evaluation also includes thermodynamic properties such as the Debye temperature and melting temperatures. These findings suggest that RbInH₃ and CsInH₃, with their favorable structural stability and ease of synthesis, could be integrated into current hydrogen storage technologies, offering a pathway for further optimization to enhance their practical applicability.