title: Electrochemistry at nanoscale electrodes: individual single-walled carbon nanotubes (SWNTs) and SWNT-templated metal nanowires.
abstract: Individual nanowires (NWs) and native single-walled carbon nanotubes (SWNTs) can be readily used as well-defined nanoscale electrodes (NSEs) for voltammetric analysis. Here, the simple photolithography-free fabrication of submillimeter long Au, Pt, and Pd NWs, with sub-100 nm heights, by templated electrodeposition onto ultralong flow-aligned SWNTs is demonstrated. Both individual Au NWs and SWNTs are employed as NSEs for electron-transfer (ET) kinetic quantification, using cyclic voltammetry (CV), in conjunction with a microcapillary-based electrochemical method. A small capillary with internal diameter in the range 30-70 μm, filled with solution containing a redox-active mediator (FcTMA(+) ((trimethylammonium)methylferrocene), Fe(CN)(6)(4-), or hydrazine) is positioned above the NSE, so that the solution meniscus completes an electrochemical cell. A 3D finite-element model, faithfully reproducing the experimental geometry, is used to both analyze the experimental CVs and derive the rate of heterogeneous ET, using Butler-Volmer kinetics. For a 70 nm height Au NW, intrinsic rate constants, k(0), up to ca. 1 cm s(-1) can be resolved. Using the same experimental configuration the electrochemistry of individual SWNTs can also be accessed. For FcTMA(+/2+) electrolysis the simulated ET kinetic parameters yield very fast ET kinetics (k(0) > 2 ± 1 cm s(-1)). Some deviation between the experimental voltammetry and the idealized model is noted, suggesting that double-layer effects may influence ET at the nanoscale.
authors.affiliation: Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kingdom.
authors.forename: Petr V
authors.initials: PV
authors.lastname: Dudin
authors.forename: Michael E
authors.initials: ME
authors.lastname: Snowden
authors.forename: Julie V
authors.initials: JV
authors.lastname: Macpherson
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Unwin
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D017097:Electric Impedance; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008670:Metals / Q000737:chemistry*; D008839:Microelectrodes; D008956:Models, Chemical; D037742:Nanotubes, Carbon / Q000737:chemistry*
chemical_list: D008670:Metals; D037742:Nanotubes, Carbon