A Pyrene-Substituted Tris(bipyridine)osmium(II) Complex as a Versatile Redox Probe for Characterizing and Functionalizing Carbon Nanotube- and Graphene-Based Electrodes

Abstract

We report the functionalization of nanostructured graphene-based electrode with an original (bis(2,2'-bipyridine)(4,4'-bis(4-pyrenyl-1-ylbutyloxy)-2,2'-bipyridine]osmium(II) hexafluorophosphate complex bearing pyrene groups. Graphene oxide (GO) and chemically reduced graphene oxide (c-RGO) paper electrodes were prepared by the flow-directed filtration method. After film transfer via the soluble membrane technique, the homogeneous and stable GO electrode was electrochemically reduced in water to achieve electrochemically reduced graphene oxide (e-RGO) film on the electrode. The electrochemical properties of GO, c-RGO, and e-RGO electrodes were characterized by scanning electron microscopy and electrochemistry. Cyclic voltammetry of the Ru(NH3)6(2+/3+) redox probe underlines the important influence of the RGO preparation method on electrochemical properties. We finally achieved the flexible functionalization of graphene-based electrodes using either supramolecular binding of the Os(II) complex bearing pyrene groups or its electropolymerization via the irreversible oxidation of pyrene. The properties of these functionalized graphene paper electrodes were compared to glassy carbon (GC) and multiwalled carbon nanotube (MWCNT) electrodes. Thanks to its divalent binding sites, the Os(II) complex constitutes a useful tool to probe the π-extended graphitic surface of RGO and MWCNT films. The Os(II) complex interacts strongly via noncovalent π-π interactions, with π-extended graphene planes, thus acting as a marker to quantify the electroactive surface of both MWCNT and RGO electrodes and to illustrate their ease of functionalization.