Nature of Ti Species in the Li-Mg-N-H System for Hydrogen Storage: A Theoretical and Experimental Investigation

With the properties of the Li-Mg-N-H system improved by the doped Ti species, the activation energies of these systems were estimated by an Arrhenius plot, and this elucidated a slightly decreased value with doped TiF3. To explore the nature of Ti species in the Li-Mg-N-H system, the crystal structure of Li2MgN2H2 with doped Ti was calculated and determined as Li7TiMg4(N2H2)(4) by a first principle approach. As a result, the Li-N and N-H bonds in Li7TiMg4(N2H2)(4) were markedly weakened, which were evaluated by the energies of Li/H vacancy formation. Moreover, the weakened Li-N bonds indicated a considerable improvement in hydrogen absorption of Li2MgN2H2 with doped Ti, which was close to the experimental results. Otherwise, the weakened N-H bonds indicated a theoretical possibility that Li2MgN2H, could be destabilized for further hydrogen desorption at an elevated temperature.