Effect of the Structure of Nonuniform Conducting Polymer Films on Their Electrochemical Impedance Response (original) (raw)
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Electrochemical Analysis of Conducting Polymer Thin Films
International Journal of Molecular Sciences, 2010
Polyelectrolyte multilayers built via the layer-by-layer (LbL) method has been one of the most promising systems in the field of materials science. Layered structures can be constructed by the adsorption of various polyelectrolyte species onto the surface of a solid or liquid material by means of electrostatic interaction. The thickness of the adsorbed layers can be tuned precisely in the nanometer range. Stable, semiconducting thin films are interesting research subjects. We use a conducting polymer, poly(p-phenylene vinylene) (PPV), in the preparation of a stable thin film via the LbL method. Cyclic voltammetry and electrochemical impedance spectroscopy have been used to characterize the ionic conductivity of the PPV multilayer films. The ionic conductivity of the films has been found to be dependent on the polymerization temperature. The film conductivity can be fitted to a modified Randle's circuit. The circuit equivalent calculations are performed to provide the diffusion coefficient values.
Journal of the Brazilian Chemical Society, 2000
Efeitos de morfologia, espessura, oxidação e iluminação dos filmes de polipirrol dopados com dodecilsulfato podem ser observados qualitativamente por EIS e consistem de variações de valores de resistências e capacitâncias de um circuito equivalente proposto, presentes nas interfaces e no interior do material. O circuito se ajusta bem para filmes sintetizados com densidade de carga de 190 mC cm -2 . Para filmes mais finos os valores calculados por espectroscopia de impedância eletroquímica (EIS) apresentam desvios provavelmente pela ausência de efeitos difusivos. A oxidação dos filmes causa uma diminuição geral da impedância em toda a faixa de freqüências medidas. Os efeitos de morfologia também são observados em todas as freqüências. Os efeitos de iluminação são reversíveis e aparecem, como esperado, apenas quando o polímero está na forma reduzida. A iluminação diminui a resistência interna e a capacitância de carga espacial e aumenta a resistência de transferência de carga e a capacitância de dupla camada.
Bulletin of the Chemical Society of Ethiopia, 2006
Polypyrrole (PPy) films of different thickness were characterized by electrochemical impedance spectroscopy (EIS) measurements in acetonitrile and aqueous solutions, containing 0.1 M NaClO4 or sodium dodecylsulfate as the dopant. The PPy films were electrochemically deposited on Pt, and their electrochemical properties studied by cyclic voltammetry. Impedance spectra were obtained at potentials ranging from 0 to 0.8 V/SCE. The EIS data were fitted using two different equivalent electrical circuits (depending on the nature of the dopant). They involve a diffusive capacitance, which increased with the passing charge during electrosynthesis (i.e. film thickness) for ClO4-doped PPy, but was practically unaffected by the film thickness in the case of SDSdoped PPy. Also, a double-layer capacitance was found only in the circuit of ClO4-doped PPy. It increased with the film thickness, and showed a minimum near the open-circuit potential. Finally the charge-transfer resistance (Rct) obtained with SDS is nearly 200-fold higher than that obtained with ClO4in the same solvent (H2O). With the same dopant (ClO4-), Rct is about five times higher in acetonitrile relative to water. All these EIS results of the different types of PPy suggest a relation with the wettability of the polymer.
Conductivity measurements of electrodeposited polypyrrole
Journal of Applied Electrochemistry, 1987
Thick, freestanding, flexible films of polypyrrole have been prepared from propylene carbonate solutions of pyrrole monomer containing tetra-ethyl ammonium p-toluene sulphonate electrolyte. The conductivity of the films was found to vary with orientation of the sample, deposition temperature and time. Conductivities of up to 338.4 S cm-1 were attained with samples prepared at 0~ XRD analyses have revealed a difference in structure with sample orientation which affects the conductivity of the material significantly.
Application of a distributed impedance model in the analysis of conducting polymer films
Electrochemistry Communications, 2000
The problem analysed is whether the electrochemical transfer in the doping of conducting polymer electrodes must be described as a macroscopic resistance localised at the outer boundaries of the polymer layer, or by a distributed process inside the film region. Impedance measurements of poly(thiophene-3-acetic acid) film in its oxidised state are reported for various values of pH in solution. The analysis shows that the observed response consists on the coupling, throughout the polymer film, of the transfer resistance with other conduction and polarisation processes. This is interpreted as evidence of a distributed charge-transfer resistance in the internal polymer/solution interface.
An advanced model of the impedance of polymer film electrodes
Electrochimica Acta, 1999
A new model for the impedance of polymer ®lm electrodes has been developed in that three mobile charge carriers are considered. It has been observed especially in the case of organic conductive polymer that beside the electron diusion and counterion transport very often hydrogen ions also participate in the charge transport and charge transfer processes in the course of redox transformation of these polymers, i.e. a model describing this case is essential. It has been demonstrated that by the help of reasonable assumptions some of the mathematical problems can be overcome and an analytical solution can be obtained for the complex impedance in the case of low amplitude variation of the electrode polarization. The equations derived for the charge transport and charge transfer impedances are tested by CNLS ®tting data obtained for an Auvpoly(o-phenylenediamine) electrode.
Faradaic impedance behaviour of oxidized and reduced poly (2,5-di-(2-thienyl)-thiophene) films
Journal of Electroanalytical Chemistry, 1997
Poly(2,5-di-(-2-thienyl)-thiophene) films with thickness less than 1.32 /~m were electrogenerated on Pt from 5 mM and 20 mM monomer concentrations in 0.1 M LiCIO4 + acetonitrile at constant current. Cyclic voltammograms recorded between 0 and !. 10 V vs. SSCE in the electrolyte showed a redox couple associated to the reduced and oxidized states. The polymer retains its reduced form until 0.6 V, its oxidized form from 0.8 V and a mixture of both states in the potential region 0.6 to 0.8 V. Faradaic impedance measurements for both states were performed at a constant potential between 0.3 and 1.0 V after reducing the electrogenerated polymer at 0 V. A progressive decrease in impedance was always found with increasing the film thickness and more positive potential. An equivalent circuit involving two complex elements is proposed to simulate adequately the Bode plots, Nyquist diagrams and complex plane admittance diagrams obtained. The film resistance is very high for all polymers, suggesting that the mass transport of CIO~-ions through the polymer is the rate-determining of the oxidation-doping process. The film capacitance is low for the reduced form and gradually il,creases when the polymer is oxidized. Deposits obtained from a 20 mM monomer solution have higher charge-storage capacity than those generated from a 5 mM one, particularly for the oxidized polymer where large amounts of CIO 4 counterions are accumulated.
Resistance of the Polypyrrole/Polyimide Composite by Electrochemical Impedance Spectroscopy
Journal of Porous Materials, 2000
Electrically conducting polymers are promising for applications in polymer based charge storage devices and for membrane applications. Composing polypyrrole with polyimide improves mechanical properties of polypyrrole and affects the electrochemical properties of the composite. In this paper resistance to ion flow of pure polyimide and of the polypyrrole/polyimide composite were studied by electrochemical impedance spectroscopy, comparatively, as a function of applied potentials and of amount of polypyrrole. Electron scanning microscopy and surface mapping were used for surface characterization. Observed behavior was explained with electroactivity of the components of the composite. Conclusions about the effect of polypyrrole on the structure and resistance were made.
2010
Electrochemical synthesis of polypyrrole (PPY), doped with 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPSNa), was carried out using chronoamperometric technique. Cyclic voltammetry measurements showed that the electroactivity of PPY films, doped with AMPSNa, increases with the film thickness. Scanning electron microscopy photographs revealed that the PPY particles are in the nano-scale range and that their size depends on the potential at which the PPY has formed. Electrochemical impedance spectroscopy (EIS), in the potential range of + 1.0 and − 1.0 V, revealed in the PPY film charge transfer domination with a semicircle at high frequencies, and anion diffusion dominance at low frequencies. EIS also showed that the charge transfer resistance of PPY film at − 1.0 V is lower than what is expected and that on increasing the thickness of the PPY films, the overall impedance decreases. The proposed equivalent circuit model, based on the double layer capacity and the Warburg impedance, was replaced by two constant-phase elements to fit the experimental work of this study. The values of the fractional exponent of the first constant phase element at approximately 0.5 indicate that the processes have a diffusion-limited nature.