Modeling the structural, magnetic, electronic, optical and mechanical performance in Ca₃XH₈ (X= Cr, Mn and Fe)...

To move towards sustainable energy options, we need safe and effective ways to store hydrogen. In this paper, we do an extensive first-principles analysis of Ca₃XH₈ (X = Cr, Mn, Fe) perovskite hydrides to assess their potential for enhanced solid-state hydrogen storage. We used Density Functional Theory (DFT) computations in the CASTEP framework to look into their structural, electronic, magnetic, optical, mechanical, and thermodynamic characteristics. The optimized structures show cubic symmetry (Pm-3m) and meet both thermodynamic and dynamic stability requirements, as shown by negative formation energies and phonon spectra that don't have imaginary modes. Ab initio molecular dynamics simulations further demonstrate structural integrity at 800 K, hence validating their heat resilience. The electronic band structure and density of states exhibit metallic characteristics, suggesting advantageous electronic conductivity and effective charge transfer during hydrogen adsorption and desorption processes; however, the kinetics of hydrogen diffusion are not explicitly measured in this study. Spin-polarized investigations demonstrate that all compounds have antiferromagnetic ordering, significantly impacting their electronic and magnetic properties. Optical tests show that these materials have high reflectivity, substantial absorption coefficients, and a strong dielectric response. This suggests that they might be used in optoelectronic devices as well as for storing hydrogen. Mechanical investigation shows that the material meets Born stability standards, and its predicted elastic moduli and brittle character are good for hydrogen absorption and desorption. The gravimetric hydrogen storage capacities were found to be 3.25, 3.20, and 3.15 wt% for Ca₃CrH₈, Ca₃MnH₈, and Ca₃FeH₈, respectively. The volumetric storage capacities ranged from 76.4 to 82.3 gH₂/L, and the desorption temperatures were between 868 and 1313 K. These findings offer the initial theoretical insights into Ca₃XH₈ hydrides, showcasing their structural integrity, metallic conductivity, and potential for hydrogen storage, thereby establishing them as intriguing candidates for forthcoming sustainable energy applications.