Exploring the physical properties of sodium hydride for solid-state hydrogen storage: A DFT approach

This work explores the effects of strain on the structural, mechanical, electronic and hydrogen storage properties of NaH hydride using density functional theory (DFT) within the generalized gradient approximation (GGA-PBE). The NaH compound crystallizes in a cubic structure with a lattice constant of 4.87 Å and is confirmed to be both thermodynamically and mechanically stable. Moreover, the calculated elastic parameters, including the anisotropy factor, Pugh’s ratio, and Poisson’s ratio, reveal that NaH displays elastic anisotropy and predominantly brittle behavior. The electronic behavior of NaH was examined under both unstrained and strained conditions. In its relaxed state, NaH shows a semiconducting character with an indirect band gap of 3.77 eV. When compressive strain (ε = -8%) is applied, the band gap increases to 4.23 eV, while tensile strain (ε = +8%) reduces the band gap to 3.40 eV. Furthermore, NaH exhibits a gravimetric hydrogen capacity of 4.20 wt.% and a volumetric capacity of 57.96 g·H 2 /L. The computed hydrogenation enthalpy and dehydrogenation temperature are -48.155 kJ/mol H 2 and 368 K, respectively. Under triaxial strain, these properties improve and fall within the US DOE operating window (233-333 K), making NaH a suitable material for practical hydrogen storage. Overall, these results highlight NaH as a promising candidate for next-generation hydrogen storage systems.