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Density Functional Theory Method for Study of the Mechanism of C–H Bond Formation on Finite-Sized Graphene Surface

The structures and electronic states of hydrogenated graphenes with a finite size have been investigated by a density functional theory (DFT) method. Five graphenes of various sizes (n=2, 4, 7, 14, and 19, where n indicates the number of benzene rings in graphene) were examined as models of a hydrogenated graphene system. The harmonic vibrational frequency corresponding to a C–H stretching mode showed a linear relationship between the frequency and the C–H bond length. The C–H bond formed by the addition of hydrogen atoms was completely polarized as Cδ-–Hδ+ in an equilibrium structure. It was found that the activation barrier is formed by hybridization from sp2 to sp3 in the transition region. The mechanism of C–H bond formation on a graphene surface was discussed on the basis of theoretical results.