First-Principles Prediction of the Optoelectronic, Mechanical, Thermodynamic and Hydrogen Storage Attributes of Double Perovskite Rb2NaXH6 (X = Al, In) Hydrides

Abstract

Solid-state technology is considered the most affordable, secure and volumetrically efficient technique to store green energy. The key role of hydrogen storage in renewable energy lies in its ability to effectively capture, store, and distribute excess energy produced by intermittent sources such as solar and wind, therefore ensuring a dependable and sustainable energy provision. Perovskite hydrides have shown great promise in storing the hydrogen energy effectively. In this manuscript we have assessed the hydrogen storage potential for Rb₂NaXH₆ (X = Al, In). Using the FP-LAPW approach which is implanted in Wien2K computational code, the physical traits of Rb₂NaXH₆ (X = Al, In) are assessed in detail. The structural parameters are analyzed via volume optimization curves and tolerance factor, while for the assessment of the thermal stability, formation energies are computed. The mechanical properties for Rb₂NaXH₆ (X = Al, In) are evaluated by using the elastic constants computed by the Thomas Charpin method. The directional sound velocities regarding each crystallographic plane are also analyzed using these computed elastic constants. Indirect bandgaps for Rb₂NaXH₆ (X = Al, In) are reveled from the electronic properties. The optical properties assessed via Kramer-Kronig equations revealed significant absorption and scattering for both hydrides in the UV region. To assess the potential of both hydrides for efficient hydrogen storage, the gravimetric and volumetric ratios are also analyzed. Furthermore, the Gibb’s free energy equation is employed to evaluate the desorption temperatures for both studied hydrides. The attained results favor the use of Rb₂NaXH₆ (X = Al, In) in optoelectronic and hydrogen storage applications.