Probing the Electrolyte Transfer in Ultrathin Polypyrrole Films by In Situ Xray Reflectivity and Electrochemistry (original) (raw)
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Influence of ion-exchange on the electrochemical properties of polypyrrole films
Electrochimica Acta, 2014
Cyclic voltammetry, X-ray microanalysis (EDS), FTIR, and AFM were applied for the systematic examination of the influence of self-exchange and potential stimulated ion-exchange on the electrochemical properties of polypyrrole (PPy) films prepared in the presence of benzene sulfonate (BS), para-toluene sulfonate (pTS), and naphthalene-1, 5-disulfonate (NDS) anions. All electrochemical experiments were carried out in aqueous solutions. It was established that small inorganic anions, like NO 3 − , Cl − , ClO 4 − can relatively easily replace an essential part of the sulfonates in PPy/BS and PPy/pTS films simply during a 10 min polarization at 0.4 V. A single potentiodynamic cycle increases the completeness of the exchange of the anions remarkably. The EDS analysis carried out before and after the anion exchange showed that 5-15% of the sulfonate anions still remain in the PPy films. The ability of the double-charged SO 4 2− anions to replace sulfonate anions is even more pronounced as the exchange process does not need additional electrochemical activation. The quantum chemical model calculations have shown that the interaction of the sulfate anions with charged pyrrole oligomers is essentially stronger compared to other anions under the study. The redox capacitance and the corresponding electrochemical doping level of the redoped PPy films are remarkably higher than those before ion-exchange, showing that the PPy matrix formed in the presence of sulfonate anions does not collapse after ion-exchange and it creates favorable conditions for increased mobility of inorganic anions.
Electrochemistry Communications, 2007
For many years, polypyrrole films have appeared to be the most studied conducting polymer. Unfortunately, shadows still remain concerning the electrochemical mechanisms of these films and in particular, the aspect which concerns the limiting step which governs the electrochemical response. Different possibilities are available such as the transport of ionic species in the film, the electron transfer at the electrode/film or the electron motion in the film, the ionic exchanges at the film/interface electrolyte. Classical electrochemical methods do not permit to discriminate between these effects. Ac-electrogravimetry technique was used here to demonstrate that the electrochemical behaviour of thin pPy films is governed by the ionic insertion without any doubt. Particular parameters were modified as the ionic atomic weight or the electrolyte concentration to corroborate this idea.
Electrochemical and X-ray diffraction studies on polypyrrole films
Materials Chemistry and Physics, 1996
The redox behaviour of polypyrrole (PPY) films doped with perchlorate (Clod-) or p-toluene sulfonate (TsO-) anions was studied by cyclic voltammetry. The values of the kinetic parameters I,, crA and cyc (exchange current density, anodic and cathodic transfer coefficients) were obtained using Tafel equations. We report a decrease in the lo value after each redox scan, in contrast with the cu, and cu, values, which remain almost constant. We attribute this variation of the I,, value to the irreversible trapping of cations (Li+ or H+) in the polymer layer, after the reduction process. X-ray diffraction measurements evidenced an anisotropic molecular organization of PPY (TsO-), in contrast with PPY (ClO,-), which exhibits an isotropic structure.
Mn-modified polypyrrole thin films for supercapacitor electrodes
Synthetic Metals, 2014
Thin film Mn-modified polypyrrole (PPy) composite electrodes have been prepared by chronoamperometric electrodeposition and characterized in terms of their physico-chemical and electrochemical properties and performance. Analysis of the chronoamperometric data shows that electrodeposition of the thin film results in a relative increase in electrochemically active surface area of up to 30 times. This finding was supported by transmission electron microscopy (TEM), atomic force microscopy (AFM) and profilometry analysis of the films. Electrochemical quartz crystal microbalance (EQCM) studies have allowed for the direct determination of electrode mass, both during deposition and electrochemical performance evaluation, which has enabled analysis of electrode properties, including film growth (up to 26 µg/cm 2), density (~2 g/cm 3), and the charge storage during electrochemical cycling, including the rates of mass uptake/removal with charge.
Lancet, 2011
Polypyrrole films were electrosynthesized on conductive tin oxide substrates by potentiostatic deposition in various aqueous electrolyte solutions including p-toluenesulfonate, naphthalenesulfate, nitrate, tetrafluoroborate, and perchlorate anions. Electrical and structural characteristics (morphology, roughness and thickness) were determined using Van der Pauw method, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Optical Profilometry (OP). Experimental parameters including the electrolyte, applied electrodeposition potential, and pyrrole concentration were shown to affect the morphologies and conductivities of so-prepared polypyrrole films. The p-toluenesulfonate doped polypyrrole film showed the highest conductivity whereas the perchlorate doped one showed the lowest conductivity of all the films. On the contrary, the film thickness did not affect the electrical conductivity. Concerning the morphology, globular-shaped topographic structures were obtained for nearly all the polymer films, but with different sizes of globules and aggregates. Both roughness and morphological features were also proved to be very dependent from the electropolymerization parameters.
Electronic and Ionic Transport Properties of Electrodeposited Polypyrrole Films
Le Journal de Physique Colloques, 1983
Rdsum6-Des films de polypyrrole ont dtB dBposBs par voie dlectrochimique sur des Blectrodes d'inox. Les conditions d'obtention du ddpat sont prdcisdes (densit6 de courant, tempdrature). Le rapport de la conductivitd Blectronique dans le sens parallele B la surface du film sur la conductivitd dlectronique le long de la surface du film est 3 inferieur 3 10. La variation du coefficient de diffusion des ions perchlorates dans le film correspond une dnergie d'activation de 30 kJ/mole.
XPS characterization of nanosized overoxidized polypyrrole films on graphite electrodes
Analyst, 1999
X-Ray photoelectron spectroscopy (XPS) analysis was used to verify the structure of nanosized overoxidized polypyrrole (OPPy) films that were grown on glassy carbon. The films were electrochemically grown to ca. 1.2-1.6 nm thickness from acetonitrile with tetrabutylammonium perchlorate (TBAP) and from water with adenosine triphosphate (ATP) as dopant. The films have been previously characterized by electrochemical methods, but this represents the first study of the ultrathin films by XPS. XPS analysis verifies that the key structural features of nanosized OPPy films are the same as those of much thicker films previously studied by XPS on metal substrates, where differential charging effects are much less severe. Some differences between the microstructures of OPPy and OPPy/ATP films are highlighted by the results. In addition, XPS results confirm a two-domain model of the polymer films that has been proposed from previous studies of PPy and OPPy. The results show that XPS can be used to characterize nanosized films on graphite, after correction for differential charging. Graphite represents a substrate of choice for the fabrication of permselective ultrathin membranes for biosensors from materials such as OPPy.
Charging process in polypyrrole films: effect of ion association
Journal of Electroanalytical Chemistry, 1998
Cyclic voltammetric (CV) response of polypyrrole (PPy) films in contact with tetraphenylborate (TPB) acetonitrile (AN) solutions has demonstrated pronounced anomalies compared to the CV for the usual anions. The redox activity of the film is considerably reduced and both the anodic and cathodic waves consist of two peaks whose positions are strongly dependent on the ionic strength of the solution. The diminution of the charging ability has been related to a much lower maximum concentration of the doping anions (TPB) inside the film due to their large size. The observed splitting of the waves into two peaks cannot be attributed to two different electronic processes like the successive generation of 'polarons' and then 'bipolarons'. On the other hand, the hypothesis that ions inside the film may be in two different forms, 'free' and 'bound', has allowed us to reproduce all the experimental features, in particular, two separated peaks at lower electrolyte concentrations, their shift in the opposite directions with 960 mV slope versus logarithm of the ionic strength, independence of the peak heights or shapes of the concentration, merging of the peaks at higher ionic strengths. The same concept has been able to explain an observed separation of the broad peak for polyaniline (PANI) films in contact with mixed perchlorate-polyanion solutions into two narrower peaks upon diminishing the perchlorate content. This conclusion is in conformity with our analysis of data for the charging process of PPy in perchlorate solutions obtained earlier by in situ electrochemical quartz-crystal microbalance studies (EQCM). Experimental plots for mass versus its charge have quite different shapes for films polymerised at high or low potentials. In particular, those curves in the latter case possess opposite slopes at low and high film charges as well as a pronounced hysteresis. These observations have also been interpreted successfully within the framework of the above model of two forms of ions inside the polymer phase. The comparison has also provided evidence that 'bound' ions can be exchanged gradually with their 'free' form during the cyclic voltammetry process. This process results in a complicated shape for the mass versus charge plots including a crossing of the anodic and cathodic branches as well as a loop within the range of low charges. All these predictions of the model are in conformity with the above experimental results. The theory considers 'immobile' ions as associated with neutral sites of the polymer matrix, either due to the formation of a bond, or the ion binding by micro-cavities. An alternative approach assumes the anions to form a complex with positively charged electronic species (like 'polarons' or 'bipolarons'). However, the latter is unable even to provide a qualitative explanation of the above data, e.g. opposite signs of the slope for low and high charge ranges.
Electrochemical properties of cation sensitive polypyrrole films
Journal of Electroanalytical Chemistry, 1998
The peculiarity of polypyrrole/sulphate (PPy/SO4) films redox behaviour has been investigated by cyclic voltammetry and electron probe microanalysis. The changes in PPy/SO4 film ionic composition during the redox process, especially the influence of electrolyte cations on its redox properties, were studied in detail. It was established that in the solutions of double charged metal-or bulky tetraalkylammonium cations the redox activity of PPy/SO4 film is suppressed, its mechanism is speculated on the basis of the film's morphological peculiarity (compact structure), hydration radii and energy of moving ions, also the aggravations to effective charge balanced intermediate states during redox cycling are taken into account. In the case of tetraalkylammonium ions instead of the charge compensation problem the hydrophilic nature of PPy/SO4 film, and on the other hand the hydrophobicity of cations, causes additional kinetical aggravations or even suppression of film electroactivity. 0 1997 Published by Elsevier Science Ltd