Electrochemical surface oxidation of carbon nanofibers

Carbon nanofiber (CNF) surfaces were functionalized with oxygen-bearing groups through electrochemical oxidation. The electrode was prepared without a binder, allowing easy separation of the functionalized CNFs for subsequent applications. The relationships between the applied potential and the CNF structure with the resulting O/C atomic ratio and the distribution of oxygen functional groups were investigated. Surface groups were identified and characterized by elemental analyses, X-ray photoelectron spectroscopy, micro-attenuated total reflectance FTIR, and cyclic voltammetry. The oxidation of herringbone CNFs was initiated at a relatively low potential at both the anodic and cathodic electrodes, while the O/C atomic ratio remained relatively constant within the range of potentials investigated. The relative concentration of carbonyl and hydroxyl groups increased with increasing potential while the amount of carboxylic groups decreased. The structure of the CNF was important in determining the O/C atomic ratio, which was especially dependent on the spatial arrangement of graphene layers. Tubular CNFs exhibited low O/C atomic ratios while herringbone CNFs, which have a higher surface area, exhibited the largest ratios. The dispersion of the CNFs in water was much more homogeneous following electrochemical oxidation.