Electron Transfer Kinetics at Single-Walled Carbon Nanotube Electrodes using Scanning Electrochemical Microscopy

Abstract

An important open question on the electrochemistry of single-walled carbon nanotube (SWNT) electrodes concerns the sites at which electron transfer (ET) occurs. This issue is addressed herein for the case of a simple outer sphere redox couple, (ferrocenymethyl)trimethylammonium (FcTMA+). Using relatively sparse networks (<1% surface coverage) of electrically connected SWNTs, coupled to a scanning electrochemical microscopy (SECM) substrate generation−tip collection setup, we show that high rates of mass transport can be generated to SWNTs, allowing kinetic effects to be observed in the voltammetric waveshape. By developing a numerical model that faithfully represents all aspects of the experimental geometry, highly accurate kinetic data can be obtained. Assuming that all SWNTs are active, a minimum average ET rate constant k0SWNT > 1.0 ± 0.6 cm s−1 is assigned, which is of similar size to other electrode materials and suggests that the sidewall of SWNTs has considerable ET activity.