Covalent Grafting of Ferrocene to Vertically Aligned Carbon Nanofibers: Electron-transfer Processes at Nanostructured Electrodes
By Landis, Elizabeth C. & Hamers, Robert J.
Published in The Journal of Physical Chemistry C
2008
Abstract
Ferrocene was used as a model system to understand the electron-transfer properties of redox-active molecules covalently linked to the surface of vertically aligned carbon nanofibers. Ultraviolet-initiated grafting of organic alkenes was used to prepare carboxylic acid-terminated layers, and ferrocene was then linked to these layers via amide groups. The electrical properties of the resulting layers were measured using cyclic voltammetry and electrochemical impedance spectroscopy. Standard rate constants for electron transfer (kapp) of approximately 1.0-1.3 s-1 were found for ferrocene covalently linked to the nanofiber surfaces, compared to about 3 s-1 on glassy carbon surfaces. Measurements of the electron-transfer rates through molecular layers of different length show no significant change. Similarly, no significant changes were observed in electron-transfer rate constants or peak width upon dilution of the ferrocene-containing molecules. Our results show that molecular layers grafted to carbon nanofibers are sparse and disordered compared with those commonly studied on planar surfaces. A model based on preferential grafting to exposed graphitic edge planes is proposed to explain the results.