Electrochemistry using single multiwalled carbon nanotubes - A step further

We have characterized the electrochemical behavior of single CCVD-grown multiwalled carbon nanotubes (MWCNTs) directly connected to and protruding from the tip of tapered gold wires. Single MWCNTs were connected to gold by electrical breakdown, in absence of binder, under an optical microscope. This procedure minimizes surface contamination in comparison to micromanipulations performed in an electron microscope. The MWCNT-gold adhesive contact was found stable enough to allow immersion of the freely suspended portion of the MWCNT in aqueous electrolytes containing 1 mM 1,1′-ferrocene dimethanol (FeDM) or hexaammine ruthenium ion RuNH363+. Cyclic voltammograms were recorded at various immersion depths, and analyzed using Butler-Volmer (BV) kinetic model to extract transfer coefficient (α) and standard heterogeneous rate constant (k0). The latter was found <0.25 cm/s for FeDM and <0.1 cm/s for RuNH363+, with a large scattering of data suggesting MWCNTs react via inhomogeneous active sites. We also show that complete electrodes terminated by a single MWCNT can be isolated by use of an electrophoretic polymer. Electrochemical activity of the MWCNT can then be partially regenerated over a few microns by electrical breakdown of the polymer layer. Such electrodes could be useful to investigate electrochemical reactions inside micron-sized vesicles.