Prediction of the structural, phonon, electronic, optical, and hydrogen storage properties of NaXH3 (X = Ga, In) hydride perovskites

Abstract

In this manuscript, we have investigated the hydrogen storage, structural, optical, phonon, and electronic properties of the perovskite hydrides NaXH${}_3$ (X $=$ Ga, In) using first-principles calculations. The calculated formation energies ($-5.33\mathrm{eV}$ for NaGaH${}_3$ and $-5.24\mathrm{eV}$ for NaInH${}_3$) confirm that these compounds exhibit thermodynamic stability. Phonon dispersion analysis reveals that NaInH${}_3$ is dynamically stable, whereas NaGaH${}_3$ exhibits dynamical instability due to the presence of imaginary frequencies. Electronic band structure calculations indicate that both compounds display metallic behavior. Regarding their optical response, they show strong reflectivity in the visible region and significant absorption in the ultraviolet range. The hydrogen storage analysis yields gravimetric capacities of 2.15 wt% for NaInH${}_3$ and 3.16 wt% for NaGaH${}_3$, with corresponding desorption temperatures of 515.76 K and 525.63 K, respectively. These results provide fundamental insights into Na-based hydride perovskites and highlight their potential as promising candidates for the next generation of hydrogen storage technologies.