First-principles study on hydrogen storage properties of the new hydride perovskite XAlH3 (X=Na, K)

Abstract

First-principles were employed to research the hydrogen storage capacities and structure, mechanic, electronic, optical, dynamical, thermodynamic properties of XAlH3 (X = Na, K) compounds. The investigation of elastic constants, formation energy and phonon dispersion curve reveals that the XAlH3 compounds possesses mechanical, thermodynamic and dynamic stability. By calculating the B/G, it is evident that NaAlH3 has ductility and KAlH3 has brittleness. Moreover, the chemical bonding of XAlH3 compounds is ionic. According to the results obtained from the electronic property analysis, these compounds are metal nature. Additionally, the internal charge transfer of the two compounds was studied by Bader partial charge analysis. The optical properties show that the NaAlH3 hydride has higher static dielectric function than that of KAlH3. The thermodynamic properties of these hydrides have been studied, including energy, heat capacity, free energy, and the entropy variation with temperature. Furthermore, NaAlH3 and KAlH3 have high hydrogen storage capacities, which are 5.40 wt% and 4.19 wt%, respectively. This study has revealed for the first time the characteristics of XAlH3 hydrides, bringing new potential options for hydrogen storage materials.