First-Principles Study of Hydrogen Binding Property in Alkaline-Earth (Be, Mg, Ca) Metal-Doped Closo-Boranes

Using the first-principles method based on density functional theory (DFT), we investigate the stability of alkaline-earth (AE) metal-doped (AE = Be, Mg, and Ca) dodecaborane(12) and the interactions of H₂ molecules with the B₁₂H₁₂Be, B₁₂H₁₂Mg, and B₁₂H₁₂Ca clusters. Our calculated results show that the metal sites carry a partial negative/positive charge. The binding energies of metal cations and the boron framework are calculated to be 28.21, 21.92, and 18.79 eV, respectively, which are large enough to prevent metal atoms clustering and ensure the stability toward recyclability. These charge surfaces created at the metal site, which can induce a dipole in the molecular hydrogen, can bind to the hydrogen molecule through the ion-quadrupole as well as through ion-induced dipole interactions. The results show that B₁₂H₁₂Mg and B₁₂H₁₂Ca complexes can store up to 3.52 and 5.26wt% hydrogen, respectively. These studies may provide guidance for designing new 3D hydrogen storage materials with the icosahedra twelve-member boron cluster doped with AE metals as the building blocks.