Oxidation-Reduction dynamics in layer-by-layer self-assembled redox polyelectrolyte multilayer modified electrodes

TAGLIAZUCCHI, MARIO; GRUMELLI, DORIS; BONAZZOLA, CECILIA

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY

Año: 2006 vol. 6 p. 1731 - 1740

1533-4880

The oxidation-reduction dynamics of layer-by-layer (LbL) self-assembled redox polyelectrolyte multilayer films on electrodes has been studied by cyclic voltammetry, chrono-amperometry, electrochemical quartz crystal microbalance (EQCM), ellipsometry and Fourier transform reflection-absorption infrared spectroscopy (FTIRRAS). Thin layer electrochemistry with fast electron transfer at the underlying metalfilm interface and charge propagation by electron hopping between adjacent redox sites in the finite thin film has been observed. An almost ideal cyclic voltammetry for a fixed number of redox sites in the thin surface film suggests that the multilayer can be fully oxidized and reduced in the time scale of the experiment (RT/vF ≥ 0.05 sec). Theelectron hopping diffusion coefficient 3 x 10-10 cm2 s-1 was obtained from the chronoamperometric current transient and the ellipsometric thickness. Both cyclic voltammetry and potential step yield a surface osmium bipyridil redox concentration of ΓOs = 4 x 10-10 mol.cm-2 for (PAH-Os)5 (PVS)4 film. Exchange of ions and solvent occur simultaneously to the charge injection as revealed by the EQCM mass change and the ellipsometric thickness change. From the end-to-end mass-to-charge linear relationship, the molar mass of the ionic and neutralspecies exchanged largely exceeds the molar mass of any ions or solvent which suggests an important flux of solvent during redox switching. An initial “break in” effect is observed for the first oxidation-reduction cycles when a newly self-assembled film equilibrates with the electrolyte as charge is injected during the electrochemical perturbation.