Preparation and Electron-Transfer Properties of Self-Assembled Monolayers of Ferrocene on Carbon Electrodes

In this article, ferrocene is used as a redox-active species to study the electron-transfer properties of self-assembled monolayers (SAMs) on carbon. Glassy carbon electrodes were modified using different compositions of alkyl amine SAMs having various chain lengths and diluent chemistries. An amide coupling reaction was carried out to attach ferrocenecarboxylic acid to the amine-terminated SAMs. We investigated the role defect sites in the SAMs play in effecting electron transfer to the appended ferrocene molecules by modifying the SAMs with ZnO electrodeposits. There is a significant change in the electron-transfer rates as a function of SAM linker length only when the SAM defect sites are blocked with ZnO electrodeposits. These findings imply that defect-driven direct electron transfer occurs on ferrocene-modified SAMs on heterogeneous carbon electrodes in contrast to the alkyl linker tunneling mechanism that is known for well-ordered SAMs on Au electrodes. Finally, we demonstrate that the surface modification protocols used here are amenable to a wide range of carbon electrodes.