Covalent functionalization and electron-transfer properties of vertically aligned carbon nanofibers: The importance of edge-plane sites

The use of covalently bonded molecular layers provides a way to combine the outstanding stability and electrochemical properties of carbon-based structures with the unique properties of molecular structures for applications such as electrocatalysis and solar conversion. The functionalization of vertically aligned carbon nanofibers (VACNFs) with 1-alkenes, using ultraviolet light, was investigated as a potential way to impart a variety of different functional groups onto the nanofiber sidewalls. We report how variations in the nanofiber growth rate impact both the amount of exposed edge-plane sites and the resulting electrochemical activity toward Ru(NH₃)₆^3+/2+ and Fe(CN)₆^3-/4- redox couples. Measurements of the distribution of surface oxides show that surface oxides are unaffected by the grafting of alkenes to the nanofibers. Carbon nanofiber reactivity was also compared to multiwalled and single-walled carbon nanotubes. Our results demonstrate that edge-plane sites are preferred sites for photochemical grafting, but that the grafting of molecular layers only slightly reduces the overall electrochemical activity of the nanofibers toward the Ru(NH ₃)₆^3+/2+ couple. These results provide new insights into the relationships between the chemical reactivity and electrochemical properties of nanostructured carbon materials and highlight the crucial role that exposed edge-plane sites play in the electrochemical properties of carbon nanotubes and nanofibers.