The Effect of Strain on Hydrogen StorageCharacteristics in K2NaAlH6  double Perovskite Hydride through First-principles method

Today hydrogen is considered one of the most credible options for a non-polluting, carbon-free energy carrier. Hydrogen can be obtained or produced by different means from different renewable energy sources and can be stored in solid, liquid, or gaseous form. Storing hydrogen in complex hydrides in solid form is one of the most efficient methods of storage because they are secure, offer high hydrogen capacity, and demand optimal functioning conditions. Complex hydrides give a large gravimetric capacity that allows large amounts of hydrogen to be stored. This study examined the effects of uniaxial and biaxial strains on the properties of the Perovskite-type compound K 2 NaAlH 6 . The analysis was conducted through first principales calculations using the full potential linearized augmented plane waves ( FP-LAPW ) approach. The results showed that both compressive and tensile strains led to significant structural deformation in the K 2 NaAlH 6 crystal structure, which became more pronounced as the magnitude of the strain increased or decreased. This deformation reduced the stability of the compound, resulting in a marked decrease in its dehydrogenation enthalpy and decomposition temperature. The values under maximal biaxial compression strain of ε ≈ 5% were -40.14 KJ/mol.H 2 and 308.72 K, respectively, compared to the original values of -62.98 KJ/mol.H 2 and 484.52 K . The analysis of the densities of states showed that changes in the dehydrogenation and structural properties of K 2 NaAlH 6 were closely linked to the Fermi level value of the total densities of states. These findings provide valuable insights into the potential of K 2 NaAlH 6 as a hydrogen storage material.