Covalent Grafting of Redox-Active Molecules to Vertically Aligned Carbon Nanofiber Arrays via "Click" Chemistry

Electrochemically active ferrocene groups were covalently linked to vertically aligned carbon nanofibers (VACNFs) in a simple and efficient manner via the Cu(I)-catalyzed azide alkyne cycloaddition (CuAAC), one form of "click" chemistry. The VACNFs were terminated with azide groups followed by the attachment of ethynylferrocene through a 1,4-disubstituted 1,2,3-triazole linkage. Our results show that the CuAAC reaction goes to completion in one hour and provides highly stable attachment of electrochemically active ferrocene groups to the nanofibers. X-ray photoelectron spectroscopy measurements of the density of surface-bound ferrocene molecules are in good agreement with those determined by cyclic voltammetry. The rates of electron transfer were found to be slightly faster than those measured previously through alkyl linkages to the VACNF surface. Stability tests show that the covalently grafted ferrocene groups are stable for more than 1500 repeated cyclic voltammograms and over a potential window of > 1.5 V, limited by the solvent. These results suggest that the use of "click" chemistry with VACNFs provides a facile route toward synthesis of high-surface-area electrodes with high stability and tailored electrochemical properties.