First-principle study of the effects of Nb and Ti doping on the dehydrogenation properties of Ca(BH4)2

The electronic structures of Ca(BH4)2 and Ca(BH4)2-M (M = Ti or Nb) are studied by first principles density functional theory calculations, and the dehydrogenation mechanism of Ti, Nb doping is also intensively investigated. The formation energy of dopants suggests that both Ti, Nb tend to occupy the interstitial sites. The electronic structure analysis indicates that the interactions of Nb (Ti) and atoms in [BH4] groups generate intermediate phases which are conducive to the decomposition of Ca(BH4)2. The electronegativity calculation and Bader analysis also indicate Nb and Ti have good catalytic behaviors. By analyzing electron localized functions, the calculations indicate that [BH4] groups restructure after Ti or Nb is doping, and the catalytic function of Ti is weaker than that of Nb. The calculated results are consistent with catalytic dehydrogenation experiments of Ca(BH4)2.