Quantum mechanical investigation of structural, optical, electronic and mechanical properties of CaX ₃ H ₈ (X = Cr, Mn, Fe) hydrides toward efficient hydrogen storage applications

Hydrogen is a viable energy transporter, yet finding good solid-state storage materials is still a big problem. In this study, we applied DFT within the CASTEP framework to analyze the structural, electronic, mechanical, optical and hydrogen storage features of CaX 3 H 8 (X [Formula: see text] Cr, Mn, Fe) hydrides. The optimized cubic structures have lattice constants of 4.37, 4.36 and 4.35[Formula: see text]Å and their negative formation enthalpies show that they are thermodynamically stable. Phonon dispersion curves further verify their dynamic stability. Electronic examination demonstrates metallic conductivity, which enables hydrogen diffusion and release. Mechanical stability, confirmed using elastic constants and Pugh’s ratio, suggests that CaCr 3 H 8 and CaFe 3 H 8 are ductile, while CaMn 3 H 8 is brittle. The projected gravimetric hydrogen storage capacities are 3.95%, 3.79% and 3.74% with modest desorption temperatures, confirming their applicability for practical hydrogen storage systems. Overall, the findings highlight CaX 3 H 8 (X [Formula: see text] Cr, Mn, Fe) as stable and efficient options for sustainable hydrogen energy applications.