Tuning the chemical reactivity of carbon materials through electronic state modification

The chemical reactivity of carbon materials is primarily governed by edge sites; however, this reactivity may also depend on the energy levels of π-electrons, specifically the Fermi level. To verify this hypothesis, experiments must be conducted using carbon materials with consistent structural and functional group compositions, while varying only the Fermi level. In this study, we prepared carbon thin films with thicknesses of several nanometers via chemical vapor deposition on Al2O3 nanoparticles. The structure, as well as the quantity and quality of edge sites in the carbon films, remained constant regardless of the number of carbon layers—except in the case of a single layer. In contrast, work function measurements showed that the Fermi level varied depending on the number of carbon layers. When cobalt was supported on these carbon thin films, and the reduction and carbonization behavior of cobalt were examined, the composition of cobalt species was found to change with the number of carbon layers. These results indicate that the Fermi level of carbon influences the chemical reactivity between the carbon support and cobalt, providing new insights into tuning the reactivity of carbon materials through Fermi-level control.