, Volume 19, Issue 3, pp 1211-1225

The effect of C-vacancy on hydrogen storage and characterization of H2 modes on Ti functionalized C60 fullerene A first principles study

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Abstract

Density functional theory calculations were performed to examine the effect of a C vacancy on the physisorption of H2 onto Ti-functionalized C60 fullerene when H2 is oriented along the x-, y-, and z-axes of the fullerene. The effect of the C vacancy on the physisorption modes of H2 was investigated as a function of H2 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 H2 in the defect-free (i.e., no C vacancy) C60TiH2 complex are along the x- and y-axes of C60 (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) C59TiH2 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 H2 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 H2. A significant reduction in the energy gap of the pristine C60 fullerene is observed when TiH2 is adsorbed by it. While the C n fullerene readily participates in nucleophilic processes, the adjacent TiH2 fragment is available for electrophilic processes.

Figure

The effect of a C vacancy on the interaction of H2 with Ti-functionalized C60 fullerene. H2 preferentially orients itself along the x- and y-axes of C60, yielding adsorption energies in the energy window targeted by the DOE. The C vacancy enhances the adsorption energy of Ti, in contrast to that of H2. The role of fullerene is not restricted to supporting the metal. The physicochemical properties investigated in the present work characterize the H2 interaction