First principle study of physical aspects and hydrogen storage capacity of magnesium-based double perovskite hydrides Mg₂XH₆ (X = Cr, Mn)

Hydrogen's potential as a clean energy source has propelled hydrogen storage into a pivotal realm of contemporary research. Cutting-edge double perovskite compounds have become a central focus for exploring hydrogen storage applications. The aim is to scrutinize their structural, mechanical, electronic, magnetic, thermoelectric, and hydrogen storage properties. The negative value of enthalpy of formation and approaching value of tolerance factor confirm the thermodynamic and structural stability of studied compositions, leading to the calculation of ground state lattice parameters. The high value of Curie temperature (310 K), particularly for Cr-based composition, exhibits the viable application of this composition at room temperature. Metallic behavior in the spin-up channel and semiconducting nature in the spin-down channel are witnessed in the band structure that ascertains the half-metallic behavior of both compositions, ensuring 100% spin polarization, an essential feature for spintronic devices. Furthermore, employing the BoltzTraP code to analyze thermoelectric characteristics with heightened Seebeck coefficients and reduced thermal conductivity reveals their suitability for thermoelectric devices. Moreover, investigation into the hydrogen storage characteristics of Mg₂XH₆ (X = Cr, Mn) exhibits notable hydrogen storage capacities of 5.60 wt% for Mg₂CrH₆ and 5.51 wt % for Mg₂MnH₆. This study marks the pioneering examination of Mg₂XH₆ (X = Cr, Mn) double perovskite-type hydrides, promising significant contributions to future research endeavours in hydrogen storage applications.