Study of the New Mg2H3X (X = Br, Cl) Compounds: Hydrogen Storage Applications

This work tackles the structural and electronic features of the tetragonal compounds Mg₂H₃X (X = Br, Cl) using LSDA + mBJ within the framework of density functional theory (DFT). For Mg₂H₃Cl structural optimization gave a₀ = 3.894 Å, c₀ = 7.745 Å and a₀ = 3.870 Å, c₀ = 7.839 Å for Mg₂H₃Br. Differences of ionic radii are the reasons for explaining the changes of lattice parameters for these compounds. Mg₂H₃Br and Mg₂H₃Cl were found to have semiconducting properties with indirect band gaps of 1.374 eV and 1.755 eV, respectively. Their small band gaps suggest possible use in optoelectronic devices. These results indicate that Mg₂H₃Br may be suitable for low energy applications such as infrared detectors, while Mg₂H₃Cl may be useful in high energy applications such as photovoltaics. The calculated hydrogen gravimetric densities for Mg₂H₃Br and Mg₂H₃Cl are 2.300 wt% and 3.470 wt%, respectively. This indicates Mg₂H₃Cl has higher hydrogen storage capacity than Mg₂H₃Br. The results of the total and partial density of states are analyzed and these results can help understand how the constituent atoms shape the electronic structure. Moreover, the optical features of these compounds highlight their importance for hydrogen storage, electronic devices, and sophisticated optoelectronic materials. This information is important for understanding the prospects of developing advanced technologies based on Mg₂H₃Br and Mg₂H₃Cl.