Improvement in dehydrogenation performance of Mg(BH4)2·2NH3 doped with transition metal: First-principles investigation

•The doping of Ti, Ni and Nb facilitate B–H bonds dissociation in Mg(BH4)2·2NH3.•The doping of Ti, Ni and Nb inhibit the release of NH3 during the dehydrogenation.•The substitutions reduce the energy barrier and favor H diffusion in Mg(BH4)2·2NH3.

The electronic structures, dehydrogenation properties and diffusion path of an H atom in pure and transition metal substituted Mg(BH4)2·2NH3 were investigated using the first-principles calculations. The occupation energies of dopants indicate that substituting Ti for an Mg1 atom is the easiest, while Ni and Nb substitutions are somewhat difficult. The electronic density of states and the topological analysis of electron density reveal the covalent characteristics of the N–H and B–H bonds and the weak ionic interaction between M (the metal atoms) and the NH3 and BH4 groups. The substitutions of Ti, Ni and Nb increase the interaction between metal and N atoms, which stabilize the NH3 groups and inhibit the release of ammonia during dehydrogenation. The hydrogen removal energies indicate that Ti, Ni or Nb doping weakens the interactions between B and H atoms, thereby facilitating the dissociation of B–H bonds in Mg(BH4)2·2NH3. The minimum energy paths of H diffusion demonstrate that the substitutions can reduce the energy barrier and thus favor H diffusion in the bulk phase. Thus, substitution is an effective technique for improving the hydrogenation/dehydrogenation performance of Mg(BH4)2·2NH3 hydrogen storage material.

Graphical abstractThe results of first-principles calculations show that the transitional metal (Ti, Ni and Nb) doping is an effective technique to improve the hydrogenation/dehydrogenation performance of Mg(BH4)2·2NH3 hydrogen storage material.Figure optionsDownload full-size imageDownload as PowerPoint slide