Electrochemical behavior of methyl viologen at graphite electrodes modified with Nafion sol-gel composite

Electrodes were prepared by spin-coating spectroscopic graphite rods with a Nafion doped sol. Coating solutions consisting of Nafion:TEOS (tetraethoxysilane) ratios of 3:1 and 4:1 gave smooth films on the electrode surface. These modified electrodes were evaluated and compared with Nafion modified and bare spectroscopic graphite electrodes using methyl viologen (MV2+) as a representative cationic electroactive probe. Substantial partitioning of MV2+ into the Nafion:sol-gel matrix to the electrode surface was observed by cyclic voltammetry and square wave voltammetry. Cyclic voltammograms of MV2+ in 0.1 M NaCl at Nafion:sol-gel 4:1 modified electrodes showed a reversible reduction to MV+ with E-0'=-0.695 V vs. Ag/AgCl. Results of scan rate variation showed the wave to be characterized by semi-infinite diffusion for scan rates in the range 50-500 mV/s. Slowing the scan rate below 50 mV/s resulted in a transition to thin-layer behavior. MV2+ partitioned much more quickly into the sol-gel-Nafion modified electrodes compared to pure Nafion modified electrodes. Reversibility of the MV2+-loaded modified Nafion-doped sol-gel coatings on electrodes was obtained by soaking in 1 M NaCl solution. Concentration calibration plots for MV2+ at the sol-gel-Nafion modified electrodes were nonlinear. Substantial enhancement of current signal at low concentrations was observed by square wave voltammetry. (C) 1998 Elsevier Science B.V. All rights reserved.