Polymer Films on Electrodes. 28. Scanning Electrochemical Microscopy Study of Electron Transfer at Poly(alkylterthiophene) Films (original) (raw)
Related papers
Journal of Electroanalytical Chemistry, 1997
Oxidation of ferrocene at a poly(3-octylthiophene) (POT) f'dm electrode has been investigated by using cycfic voltammetry, rotating disc electrode voltammetry and el~hemical impedance spectroscopy. The POT film electrode was prepared by galvanostatic electropolymerization of 3-octylthiophene on a rotating Pt disc electrode. In the medium used, i.e. 0.1 M LiBF 4 + propylene carbonate, the formal redox potentials of fetrocene and POT are 0.4 and 1.1V vs. AgLAgCI respectively. This makes it possible to study the oxidation of ferrocene at both undoped (semiconducting) POT and at doped (electronically conducting) POT. The voltammetric data show that the oxidation of ferrocene is kinetically controlled at undoped or lightly doped POT while ferrocene is oxidized at a diffusion limited rate at highly doped POT. Impedance dat~ on the POT film electrode in solutions containing different concentrations of supporting electrolyte and ferrocene indicate that the ferrocene oxidation occurs in parallel with the doping process, resulting in a competition between ferrocene and doping ions for the available 'sites' at the polymer[solution interface. The kinetics of electron transfer at the polymerlsolution interface are discussed based on the Butler-Volmer formulation of electrode kinetics. © 1997 Elsevier Science S.A.
Electrochimica Acta, 2017
Many electrochemical systems are intrinsically nonstationary and are affected by timedependent phenomena. The requirement of stationarity in the classical version of impedance spectroscopy appears to be in conflict with the essential properties of the object, therefore a post-experimental mathematical/analytical procedure is necessary for the reconstruction of the "true" impedance values. In this study, it has been shown that the 4-dimensional analysis method, originally proposed by Stoynov, can not only be used for the correction of existing (experimentally measured) impedance data, but it also opens up the possibility of the estimation of impedance spectra outside the time interval of the measurements. As an illustrative example the method has been applied for the determination of the charge transfer resistance (Rct) of poly(3,4-ethylenedioxytiophene) (PEDOT) modified electrode as a function of time, including the Rct value corresponding to the time instant just after overoxidation of the polymer film. After the overoxidation the charge transfer resistance decreased continuously with experiment time to a value somewhat higher than the R ct of the pristine electrode. The results imply that a "healing process" may occur at the film/substrate interface. A better understanding of this effect may have an impact on practical applications.
Electrochemical Properties of Overoxidized Poly-3,4-Ethylenedioxythiophene
Russian Journal of Electrochemistry, 2018
The properties of poly(3,4-ethylenedioxythiophene) (PEDOT) films were studied electrochemically at high positive potentials (from-0.3 to 1.5 V relative to the Ag/AgCl electrode). A cyclic voltammetry (CV) study revealed the range of potentials (up to 1.3-1.5 V) where the cycling leads to significant changes in the electrochemical, structural, and morphological properties of the polymer film due to overoxidation. When the upper cycling potential E up exceeded 1.4 V, the anodic current significantly increased during the first cycle and then decreased, which suggests a loss of the electroactivity of the polymer and degradation of its properties. In the high-frequency region of the impedance spectra of the PEDOT films, a semicircle appears after overoxidation, which indicates a notable increase of the charge transfer resistance in the system, in contrast to the films subjected to potentiodymanic processing in a limited range of potentials from-0.3 to 1.3 V. The effect of overoxidation on the polymer morphology was studied by scanning electron microscopy. The chemical state of elements in the structure of the polymer film was determined by X-ray photoelectron spectroscopy. The obtained data indicate that-S=O groups formed at the thiophene sulfur in the polymer.
Synthetic Metals, 2000
. Ž . Electrochemical oxidation of poly 3,4-ethylenedioxythiophene PEDOT is investigated by cyclic voltammetry combined with ''in situ'' conductivity measurements, UV-vis-NIR and Raman spectroelectrochemical studies. The results seem to indicate that the doping can be adequately described by a heterogeneous ''two-phase'' model in which the doped conducting phase grows on the expense of the undoped, neutral phase. The extension of the scanning potential to 1400 mV vs. AgrAgCl leads to a finite potential window of PEDOT conductivity -the phenomenon reported for the first time in the case of PEDOT. The existence of this potential window can be rationalized within the framework of the ''two-phase'' model of electrochemical doping, assuming the coexistence of percolating conductive and insulating networks. Doping induced changes in Raman spectra of PEDOT indicate that, unlike in other polythiophenes, the ground state of the neutral polymer is quinoid in nature whereas upon doping it is transformed into the benzenoid one. q 2000 Elsevier Science S.A. All rights reserved.
Electrochimica Acta, 1992
AIrstract-The small amplitude ac data of the poly(3octylthiophene) electrode-electrolyte system are analysed. The measurements are done at several & potentials for different thicknesses of the polymer fihn and for different electrolyte concentrations (lithium tetrafluoroborate in propylene carbonate). The Ladder type electrical circuit model is found to give best fit of the data. The high frequency double layer capacitance is shown to contain contributions from both sides of of the interface, ie the space charge layer of the polymer semiconductor and the Hehnholtx layer of the electrolyte. The experimental data are compared with calculated data by using a simple model of two capacitors in series, for a potential range including that where the reversible oxidation of the polymer takes place. The adsorption/surface state capacitance is shown to pass through a maximum and the corresponding coverage of surface species is determined. The structure of the double layer, the physical interpretation of the model parameters, and the energy level diagram for the polymer semiconductor electrode are proposed.
Electrochimica Acta, 2003
Poly(3,4-dialkoxythiophene) films with different length of alkyl chain (1,3 and 8 carbon atoms) were obtained on Pt and ITO electrodes from the monomer solutions in acetonitrile by cyclic voltammetry (CV). The properties of the resulting films were studied by electrochemical methods, UV Á/Vis, FTIR and NMR spectra. The CVs were correlated with differential cyclic voltabsorptograms (DCVA) recorded at the absorption maxima to explain the shape of the voltammograms of the polymers studied, dependent on the alkyl-chain length in alkoxy group. The presence of the zones of different crystallinity in the polymer film was postulated. Significant influence of the type of the solvent on asymmetry of the cyclic voltammograms for the polymer doping Á/undoping has been discussed in terms of the solvent interaction with radical cation (polaron) delocalized on the alkoxy side groups. The polaron delocalization was proved by 1 H-NMR spectra. Appearance of infrared activated vibrations (IRAVs) in the range 1500 Á/600 cm (1 and a characteristic electronic band at 3300 cm (1 at the polarization potential '/0.25 V versus Ag/Ag ' and their gradual changes upon further polymer oxidation were interpreted in terms of evolution of different charge carriers in lightly and heavily doped polymer.
Electrochimica Acta, 1994
Abetmet-The spectroelectrochemical (visible rang*VIS) and in situ electron paramagnetic resonance (EPR) measurements were carried out for electroactive polyindole films. Both EPR and absorption VIS spectra were analyzed using the Nernst equation. The number of electrons transferred per monomer unit during the redox process in the polymer (n) as determined from both types of spectra is equal to 0.14 (VIS spectra) or 0.16 (EPR). The applicability of EPR data to determine the n value was verified by measurements for polypyrrole film. It seems that EPR spectra provide more credible values of the number of transferred electrons in redox reactions in the polymer matrix.
Electrochimica Acta, 2006
Synthesis of a titanocene dichloride derivative functionalized with 3,4-etylenedioxythiophene group, Tc1EDOT (Cl 2 TiCpC 5 H 4 (CH 2 ) (3,4ethylenedioxythiophene)) has been described. Redox behavior of the monomer in tetrahydrofuran (THF), dichloromethane (DCM) and acetonitrile (AN) at different scan rates has been discussed in terms of different ability of these solvents to coordination with the reduced titanocene (Tc) complex and the solvation of Cl − anions. Electrooxidation of Tc1EDOT to get a conducting polymer film with immobilized titanocene dichloride centers and electrochemical properties of its polymer matrix in background acetonitrile solution have been compared with those of non-substituted PEDOT and PEDOT-methanol derivative (PEDOTMet), to elucidate the effect of substituents both on polymerization and redox potentials of the matrix. STM and AFM images of p(Tc1EDOT) films obtained with potentiodynamic and potentiostatic regimes are compared to illustrate that the films deposited at constant potential are better ordered and more compact than those obtained by cyclic voltammetry. A comparison of the cyclic voltammograms of p(Tc1EDOT) and poly(titanocene-propyl-pyrrole) (p(Tc3Py)) films in 0.1 TBAPF 6 in THF has shown that the electroactivity of the polymer matrix of p(Tc1EDOT) is extended to more negative potentials in comparison to that of p(Tc3Py). This results in the anodic shift of redox potential of Tc centers immobilized in p(Tc1EDOT) film with respect to that of the centers fixed in p(Tc3Py).