Investigation of KMnH3 and KFeH3 perovskite hydrides via ab-initio for hydrogen storage

Materials of the perovskite type could be a good option for applications involving the storage of hydrogen. In this work, the structural, electrical, mechanical, hydrogen storage, and thermodynamic characteristics of cubic perovskite-type hydride compounds KXH3 (X = Mn, Fe) were examined using the density functional theory (DFT). KXH3 compounds have been optimized in cubic crystal structure and the lattice constants have been obtained as 3.8834 & Aring; and 3.7283 & Aring; for KMnH3 and KFeH3, respectively. The structural optimization results show also that both compounds have negative formation energies of -0.722 eV and -0.557 eV for KMnH3 and KFeH3, respectively, indicating their thermodynamic stability. Their mechanical stability was also confirmed through the computation of the elastic constants and other polycrystalline mechanical properties like bulk modulus, Poisson's ratio, etc. Both compositions exhibit metallic behavior, according to the electronic band structure and density of states. Thermodynamic properties, such as entropy, specific heat at constant volume, Gr & uuml;neisen parameter and Debye temperature were assessed using the quasi-harmonic Debye model over a temperature range of 0 to 1000 K and pressure range of 0 to 25 GPa. These compounds show gravimetric hydrogen storage capacities of 3.021 wt % for KMnH3 and 2.994 wt% for KFeH3, with desorption temperatures of 532.994 K and 411.188 K, respectively. These properties are of considerable interest for solid hydrogen storage materials.