Improvement in Hydrogen Desorption from β- And γ-MgH₂ upon Transition-Metal Doping

A thorough study of the structural, electronic, and hydrogen-desorption properties of β- and γ-MgH₂ phases substituted by selected transition metals (TMs) is performed through first-principles calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125% in both the hydrides. This insertion of TMs causes a variation in the cell volumes of β- and γ-MgH₂. The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formation-energy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH₂ phases is exothermic. The selected TMs also influence the stability of both β- and γ-MgH₂ and cause destabilization by weakening the Mg-H bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from β- and γ-MgH₂ at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density-of-states analysis.