Strain engineering, ionic substitution and co-substitution: Pathways to enhanced hydrogen storage performance of KMgH3

This study examines the hydride perovskite KMgH₃, using the density functional theory (DFT) calculations via WIEN2k to evaluate its potential for solid-state hydrogen storage. The compound's thermodynamic stability, structural, electronic, and hydrogen storage properties were explored. Furthermore, this study investigated the influence of triaxial tensile and compressive strain, as well as the partial substitution of potassium (K) and magnesium (Mg) with lithium (Li) and beryllium (Be), respectively, and the combined effect of co-substitution on the material's hydrogen storage performance. Remarkably, applying −8 % triaxial compressive strain improved the volumetric storage density from 38.1 to 49.0 gH₂/l at −8 %. Substituting K and Mg significantly improved the gravimetric hydrogen capacity from 4.55 wt% to 5.66 wt% and 4.89 wt%, respectively. Co-substitution delivered even more promising results, surpassing the US Department of Energy (DOE). These findings highlight candidates with strong potential to advance next-generation hydrogen storage technologies.