Tuning hydrogen dissociation behavior of magnesium borohydride (100) surface by transition metal and nonmetal co-substitution

The influences of transition metal Ni and nonmetal N co-substitution for partial metal Mg and nonmetal B elements on the hydrogen dissociation behavior of Mg(BH₄)₂ (100) surface are investigated using the first-principles calculations in this work. The calculations results indicate that the co-substitution of Ni + N is a feasible and effective method for reducing the thermal stability and hydrogen dissociation energy, which helps to enhance the dehydrogenation performance of Mg(BH₄)₂ accordingly. The Ni + N co-substitution causes the hydrogen dissociation energy of the (100) surface to reduce from 2.267 to 1.720 eV/atom because of the co-existence of dual anionic groups NiH₆ and NH₂. The co-existence breaks stable BH₄ group into unstable BH₃ or BH₂ groups. Besides, the first H atom dissociated from the borohydride (100) surface is shifted from the initial B–H bond to a weaker Ni–H bond with a longer bond length. The shift suggests that the hydrogen dissociation process on the (100) surface is facilitated by the Ni + N co-substitution.