Closoborate-transition metal complexes for hydrogen storage

Abstract

We report hydrogen uptake capacity of early transition metal (TM) atom (Sc, Ti and V) decorated closoborate (B₆H₆) using density functional theory and second order Møller–Plesset method. Maximum of four hydrogen molecules can be adsorbed on B₆H₆Sc, B₆H₆Ti and B₆H₆V complex with their gravimetric hydrogen uptake of 6.51, 6.36, 6.21 wt% respectively. We have used M06, B3LYP and MP2 methods with 6-311++G** basis set for the study. The Gibbs free energy corrected adsorption energies show that adsorption of four H₂ molecules on B₆H₆Ti and B₆H₆V is energetically favorable whereas it is unfavorable on B₆H₆Sc at 298.15 K at M06/6-311++G** and B3LYP/6-311++G** level. Many-body analysis approach has been used here to study the nature of interaction between adsorbed H₂ molecules and the substrate and that between hydrogen molecules in a complex. The binding energy of B₆H₆Sc(4H₂), B₆H₆Ti(4H₂) and B₆H₆V(4H₂) complex is found to be 39.44, 58.43 and 51.03 kcal mol⁻¹ respectively using M06/6-311++G** level of theory. Interaction between inorganic material-metal complexes with adsorbed H₂ molecules is found to be attractive for all the three complexes. The charge transfer between Ti and adsorbed H₂ molecules is more than that for Sc and V. The HOMO–LUMO gap shows that all the three H₂ adsorbed complexes are kinetically stable. The dimers of TM-closoborate complexes in head-to-tail type configuration and multi-transition metal atom decorated closoborate complexes have also been studied. In both the cases number of H₂ molecules adsorbed per TM atom is not affected neither by dimerization nor multi-transition metal atom decoration.