Thermodynamic and kinetic aspects of charge transfer inside conducting polymer films (original) (raw)
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Theoretical analysis of distributions of electric potential and concentrations of electronic and ionic species across metal/polymer/solutlon system has shown existence o$ insulating (at very low charging degrees) and conductive states of the film. In the latter case the ratio of cations and anions in the film is a function o$ the doping degree and bulk electrolyte concentration as well as of ionic solvatlon properties o$ the film. Phenomena within the strong colon expulsion regime have been analyzed, including quasiequilibrium charging curves (at various compositions of electronic species in the film), reaction kinetics at polymer/solutlon interface, low-amplltude impedance.
Electrochimica Acta, 2013
In the paper, we have considered possible causes responsible for the fact that CV-curves of electrodes modified by polymer metal complexes with the Schiff bases possess some shoulders or split into two peaks, while the total electrode process has a one-electron character. This study includes a quantitative analysis of voltammetric responses of electrodes, the modifying films of which contain, beside mobile charge carriers (counter-ions), two kinds of immobile ones. Three cases of polymer films are the object of the corresponding description, namely systems combining such charge carriers formed either independently of each other or due to some conversions between them. The obtained results are in a qualitative agreement with those observed in experimental conditions.
On the Processes of the Charge Transfer in the Electrical Conducting Polymer Materials
Chemistry & Chemical Technology, 2013
The analysis of charge transfer processes in the electrical conducting solid polymer systems has been carried out. The processes in these systems are divided to two types. The first type is the process of charge transfer between electrodes and particles while the second onethe process of the charge transfer between conductive particles. The description of medium is carried out using Green temperature functions of polarization operators for the molecular medium. It permits taking into account the effects of frequency and space dispersion. The analytical expressions for kinetic parameters of the charge transfer processes from electrodes to particles and between particles in condensed matter have been obtained. The comparison of the general theoretical dependence of the current in electric conducting polymer composites (ECPC) on the average distance between conducting particles with analogical dependence for some real ECPC are presented in the paper.
Charging process in electron conducting polymers: dimerization model
Electrochimica Acta, 2001
Theory of the charging and discharging process in electron-conducting polymer films at an electrode surface has been presented. It is based on the concept of two coexisting subsystems at the polymer matrix, 'usual' sites P which can exchange with the electrode by the electronic charge in a quasi-reversible manner, and sites D where intermolecular bonds between neighboring polymer molecules can be formed. The charging and discharging of the latter subsystem may be realized along different reaction pathways, e.g. via the bond formation after the generation of two cation radicals within such site D in the course of the anodic scan while the bond dissociation may take place via a partially discharged state of the intermolecular bond. This difference leads to a hysteresis in cyclic voltammograms, first of all to a significant mutual shift of the anodic and cathodic peaks of the current originated from the redox transformations of D sites. An important feature of the P sites extracted from experimental CV data is their broad energetic inhomogeneity (dispersion of their redox potentials) responsible for plateaus of the current observed at high charging levels in both directions of the potential scan. Several approaches to the numerical integration of the kinetic equations for the sites' states have been analyzed, and qualitative predictions of the theoretical model have been illustrated.
Journal of Solid State Electrochemistry, 1998
Electrochemical investigations on oligomeric model compounds (β-carotenoids) of polyacetylene varying the chain length in the range between 5 and 23 double bonds provide deeper insights into the redox properties of such systems. Furthermore, cyclic voltammetric studies of α,ω-diphenylpolyenes and phenylenevinylenes give clear evidence that the formation of the radical ions is followed by a rapid reversible dimerization between the oligomeric chains. The thermodynamic and kinetic parameters of the chemical reaction are presented. Applying these results to the properties of conducting polymers opens up new perspectives for interpreting charge storage and conductivity.
Charge percolation in electroactive polymer films
Journal of the Chemical Society, Faraday Transactions, 1990
A steady-state dual-electrode ring-disc technique which can be utilised to determine charge-transfer diffusion coefficients in electroactive and electronically conductive polymer films is described. The method has been applied to two different electroactive polymer films: a ruthenium containing redox polymer, [Ru(bpy),(PVP)CI]CI, and the electronically conducting polymer polyaniline. Charge-transfer diffusion coefficients obtained for the redox polymer were of the order of lo-' cm2 s-'. The latter value is at least three orders of magnitude greater than values obtained using cyclic voltammetry or chronoamperometry, and was presumed to correspond to electron-hopping diffusion, rather than couterion motion. In contrast, for the electronically conducting polymer little difference was observed between the diffusion coefficients obtained via the steadystate dual-electrode method (ca. lo-' cm2 s-') and values obtained using transient techniques (chronoamperometry, chronocoulometry) or complex impedance spectroscopy. This observation results in the implication that the counterion and electron diffusion coefficients are equal in magnitude. This proposal has also been confirmed from complex impedance spectroscopy. The shape of the steady-state current-potential response has been examined for both classes of polymers. In particular, the waveshape analysis for polyaniline films has shown that the redox transformation corresponding to the transition from an insulating to a conductive state, involves the transfer of two electrons, but does not conform to the simple Nernst equation. A modified Nernst equation is proposed which specifically considers interactions within the polymer layer. The departure from ideal conditions is quantified in terms of an interaction coefficient, 0, which has its origin in the Brown-Anson interaction theory. Representative cyclic voltammetric data for thin polyaniline layers are also examined, and confirm that the redox switching reaction must be viewed in the context of the Brown-Anson model.
Electrochimica Acta, 2006
To calculate such phenomenological parameters of the polymer film impedance theory, as charge transfer resistances and interfacial capacities, a well-known model of homogeneous electroactive films with two kinds of charge carriers is used. General representations of the electrochemical kinetics are applied to describe the injection processes of charge carriers into the films. The exchange current densities (i.e. inverse values of the charge transfer resistances) and the interfacial capacities are calculated as functions of the electrode potential and the bathing electrolyte solution concentration for films with both cationic and anionic nature of counter-ions. In both cases, the exchange current density of electrons as a function of the electrode potential may have an extremum or be monotonous, depending on particular values of the partition coefficient of electrons, while the capacity of the substrate/film interface is a monotonic function of the potential. On the contrary, the exchange current density of counter-ions is a monotonic function of the electrode potential, whereas the capacity of the film/solution interface might depend on the potential in a non-monotone way. The obtained results can be useful for a quantitative treatment of experimental data on the charge transfer resistance and the double layer capacity often observed in the Nyquist plots of the polymer film impedance. Some restrictions of the model used are also discussed.
Short-range electron-ion interaction effects in charging the electroactive polymer films
Electrochimica Acta, 1994
This paper has analyzed the effects of the polymer/solution interfacial potential as a function of electrode polarization as well as of various short-range interactions between the charged components of the polymer phase, electronic and ionic species. Charging/discharging processes depend crucially on whether the value of interaction parameter is greater (repulsion or weak attraction between the species) or less (sufftciently strong attraction) than its critical value. In the former case it can be realized as a "continuous" transition between the insulative and conductive states of the tilm at sweeping polarixation, the difference between the 6lm charging and discharging ("hysteresis") being solely due to conventional relaxation processes (diffusion, slow interfacial transfer em). Anodic and cathodic current peaks are generally non-symmetrical, due to the film/solution potential variation. In the latter case, two quasi-equilibrium states, low-and high-density ones, coexist within a polarization range separated by a free-energy barrier so that the charging/discharging process has features of a phase transition. It may lead to a considerable hysteresis during the cycling process, even if it is realii in a quasi-equilibrium way. Variable behaviour has been found for the partial interfacial potentials versus electrode polarization, @"P(E) and d@'(E), depending on individual charges of electronic and ionic species, on the value of the global interaction parameter as well as on the ratio of different contributions to the free energy, due to electron-electron, electron-ion and ion-ion short-range interactions. These curves may be of an S-or Z-shape, possess extrema or even a loop with the self-crossing point. Highly narrow peaks are characteristic of these systems with a strong attraction between the species. There is again an asymmetry between the anodic and cathodic peaks as well as with respect to peak potentials, due to the film/solution potential variation. The ratio of anodic and cathodic peak widths depends on the particular type of the rate-determining process, es slow electron or ion interfacial transfer or "droplets" formation.