DFT-based first-principles calculations of new NaXH[formula omitted] (X = Ti, Cu) hydride compounds for hydrogen storage applications

Abstract

Density functional theory (DFT) was employed to perform an ab-initio study of new hydrogen storage materials NaXH3 (X = Ti, Cu) using the Generalized Gradient Approximation (GGA) and CASTEP package. The structural, electronic, elastic, optical, and hydrogen storage properties of NaTiH3 and NaCuH3 were calculated within the Pm3̄m cubic-perovskite phase. The thermodynamic stability of both structures was ensured by their negative formation energy. The dynamic stability has been investigated through phonon dispersion, and it has been proven that these compounds are stable. The calculations of elastic constants confirm the mechanical stability of these materials. Furthermore, bulk modulus, shear modulus, and Poisson’s ratio have been derived by employing the obtained elastic constants. NaXH3 hydrides were found to be elastically anisotropic and brittle. The electronic band structures turn out metallic behavior in NaXH3 perovskites. The optical characteristics demonstrate that both compounds exhibit their highest absorption and conductivity levels within the ultraviolet wavelength range. The calculation of gravimetric hydrogen storage capacities for NaTiH3 and NaCuH3 was performed and found to be ≈3.932 and 3.266 wt%, respectively. The hydrogen desorption temperature was identified as 637 and 563 K for NaTiH3 and NaCuH3, respectively. The current DFT results highlight that NaXH3 (X = Ti, Cu) hydrides have considerable potential as candidates for H2 storage purposes.