First-principles insight of hydrogen storage properties of mixed perovskite hydrides Na_1–xK_xMgH₃ ($\user2{ x} \le 0.75\user2{ })$

Abstract

The potential of hydrogen as an energy carrier has been widely recognized due to concerns about climate change, environmental degradation and energy security. However, the storage and transportation of hydrogen remain significant challenges. Hydrides with a perovskite crystal structure can store large amounts of hydrogen in a small volume, and they are relatively easy to produce hydrogen. Among them, the ternary perovskite hydride NaMgH₃ is distinguished by its relatively high theoretical hydrogen storage densities and reversibility of hydrogen absorption and desorption. In this study, first-principles calculations within the framework of density functional theory were employed to investigate the effect of substituting Na⁺ by K⁺ on the structural, electronic and hydrogen storage properties of Na_1–xK_xMgH₃ ($x \le 0.75 )$. The results show that the substitution of Na⁺ by K⁺ induces a slight decrease in the lattice parameters and an increase in the cell volume, and the MgH₆ octahedron becomes more distorted, which is a good indicator of destabilization of the host material, ultimately leading to a decrease in decomposition temperature from 560.1 to 489.6 K, which is beneficial for hydrogen storage applications.