Materials with a greater propensity to store hydrogen have drawn a lot of attention in recent decade because of their possible uses in clean energy systems. By offering effective, sustainable, and eco-friendly substitutes for conventional fossil fuels, these materials are essential in tackling the world’s energy problems. We have analyzed the influence of \(\:{\text{B}}^{{\prime\:}}\) -site vacancy on hydrogen storage abilities of potassium-based K2LiAlH6 double perovskite by employing the first-principles technique. For both K2LiAlH6 and K2LiH6, structural and thermo-dynamical stability is attested by computing their volume optimization, tolerance factors and formation energies. The elastic constants reveal a significant reduction towards the external strains when vacancy is created at \(\:{\text{B}}^{{\prime\:}}\) -site. The mechanical properties imply that K2LiAlH6 with or without the vacancy at \(\:{\text{B}}^{{\prime\:}}\) -site, the material possesses brittle characteristics. The electronic properties elaborates that K2LiAlH6 possesses an indirect bandgap of 4.16 eV, whereas for K2LiH6 metallic nature is observed. K2LiAlH6 reveals stronger polarization in the high energy region, whereas K2LiH6 reports higher dispersion in the IR region as predicated via their optical analysis. The hydrogen storage abilities reveal a significant increase in the gravimetric densities which are evaluated from 4.83 to 6.17 wt% and a modest increase is noticed in volumetric densities, which are computed from 41.85 to 44.76 \(\:\:{\uprho\:}\:\) (gH2/L) with the creation of \(\:{\text{B}}^{{\prime\:}}\) -site vacancy in K2LiAlH6. It ultimately fulfills the United States department of energy criteria and has indicated its capability to be utilized for hydrogen storage.
