The effect of C-vacancy on hydrogen storage and characterization of H2 modes on Ti functionalized C60 fullerene a...

Density functional theory calculations were performed to examine the effect of a C vacancy on the physisorption of H(2) onto Ti-functionalized C(60) fullerene when H(2) is oriented along the x-, y-, and z-axes of the fullerene. The effect of the C vacancy on the physisorption modes of H(2) was investigated as a function of H(2) binding energy within the energy window (-0.2 to -0.6 eV) targeted by the Department of Energy (DOE), and as functions of a variety of other physicochemical properties. The results indicate that the preferential orientations of H(2) in the defect-free (i.e., no C vacancy) C(60)TiH(2) complex are along the x- and y-axes of C(60) (with adsorption energies of -0.23 and -0.21 eV, respectively), making these orientations the most suitable ones for hydrogen storage, in contrast to the results obtained for defect-containing fullerenes. The defect-containing (i.e., containing a C vacancy) C(59)TiH(2) complex do not exhibit adsorption energies within the targeted energy range. Charge transfer occurs from Ti 3d to C 2p of the fullerene. The binding of H(2) is dominated by the pairwise support-metal interaction energy E(i)(Cn...Ti), and the role of the fullerene is not restricted to supporting the metal. The C vacancy enhances the adsorption energy of Ti, in contrast to that of H(2). A significant reduction in the energy gap of the pristine C(60) fullerene is observed when TiH(2) is adsorbed by it. While the C( n ) fullerene readily participates in nucleophilic processes, the adjacent TiH(2) fragment is available for electrophilic processes.