DFT insights on structural, electronic, optical and mechanical properties of double perovskites X2FeH6 (X = Ca and Sr) for hydrogen-storage applications

Hydrogen has been delivered as a magnificent alternative clean energy source to alleviate the growing energy dilemma and the harmful consequences of traditional energy sources on the environment and the population. This one-of-a-kind energy-efficient technique involves storing hydrogen in solid-state compounds and then releasing it as needed for utilization in possible energy applications. Metal hydrides have shown to be highly effective hydrogen storage mechanisms in this setting. To improve the efficiency of hydrogen storage and release at standard temperatures and pressures, however, the use of metal hydrides with high gravimetric, poor thermodynamic stability and high kinetics is required. X2FeH6 (X = Ca and Sr) has promising promise for hydrogen-storage applications, with gravimetric hydrogen densities of 4.28 wt% and 2.54 wt% weight, respectively. We used the DFT technique inside the GGA + PBE framework to undertake the first comprehensive study of the structural, electronic, optical and mechanical properties of X2FeH6 (X = Ca and Sr). Structural properties indicate that both the compounds are thermodynamically stable. The Ca2FeH6 and Sr2FeH6 are semiconductors with an estimated indirect band gap of 1.67 eV and 1.37 eV, respectively. Dielectric constants, absorption, reflectivity, energy loss functions and refractive indices are among the optical characteristics determined by the calculations. The results of mechanical properties suggest that both of these hydrides fall within the category of brittle materials. These findings are crucial for the future development of metal hydrogen storage materials.