Investigating the essential physical and hydrogen storage properties of Mg ₂ QH ₆ (Q = Cr, Mn) hydrides: Prospects for hydrogen storage applications

Hydrogen is a possible clean energy solution to mitigate the global energy problem and environmental issues. The Mg 2 QH 6 (Q= Cr, Mn) hydrides have attracted interest due to their substantial hydrogen storage capabilities and advantageous characteristics. The pressure-induced physical characteristics of Mg 2 QH 6 (Q= Cr, Mn) have been methodically examined by density functional theory (DFT) to assess their viability for hydrogen storage and energy-related applications. A comprehensive examination of their structural stability, hydrogen storage properties, electronic band structures, optical absorption characteristics, elastic constants, mechanical stability, and thermodynamic aspects was conducted at applied pressures from 0 to 40 GPa. The gravimetric hydrogen storage capacities of Mg 2 CrH 6 and Mg 2 MnH 6 are determined to be 5.67 and 5.52 wt%, demonstrating their significant prospects for practical hydrogen storage applications. The electronic structure simulations validate the metallic characteristics of both Mg 2 CrH 6 and Mg 2 MnH 6 hydrates over the whole pressure spectrum, signifying exceptional electrical conductivity, beneficial for electrochemical and catalytic applications. The imaginary component of the dielectric function displays pronounced peaks at 8.682 eV (40 GPa) for Mg 2 CrH 6 and 8.335 eV (40 GPa) for Mg 2 MnH 6 , indicating robust optical activity. Thermodynamic analysis confirms the stability of both substances under pressure. The elastic and mechanical evaluations validate their stability and ductility under compression, affirming their dependability under highpressure conditions. These theoretical findings offer significant insights into the pressure-tunable properties of Mg 2 QH 6 hydrides, underscoring their potential for complex hydrogen storage systems and multifunctional optoelectronic devices.