Electrochemical preparation and redox/ion exchange properties of polypyrrole in aqueous sodium hexafluoroaluminate (original) (raw)
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Journal of Electroanalytical Chemistry, 2012
a b s t r a c t EQCM gravimetry in a (10 À8 , 10 À6 ) g range was used for measurements of time processes of the potentiostatic deposition and redox state switching of polypyrrole in aqueous sodium hexafluoroaluminate. Time/potential dependencies of molar mass to charge factors determined from EQCM chronoamperometry and EQCM cyclic voltammetry were considered to reveal how the electrodeposition potential affects composition and ion-exchange properties of the resulting polymer film. Polypyrrole was synthesized at constant potentials, from +0.55 V to +0.80 V vs. SCE. The redox switching and accompanying ionexchange were monitored in (+0.6, À0.6) V and (+0.6, À1.2) V vs. SCE potential windows.
Effects of the secondary counterions in the electrochemistry of polypyrrole
Journal of Electroanalytical Chemistry, 1997
Thin polypyrrole layers (thickness: 0.2 to 0.3 lzm) on gold were studied in aqueous solutions of sodium hexafluoroaluminate, sodium hexafluorosilicate, sodium hexafiuorophosphate, and sodium chloride. Polypyrrole was prepared by the t~,lectrochemical oxidatiort of pyrrole in the chloride solution. The systems were examined by cyclic voltammetry and impedance spet~roscopy. Transport/redox capacitances, effective charge diffusion coefficients, and charge transfer resistances were determined at several d.c. potentials of the polymer electrodes in a region of the reversible change of the redox/conductivity state of polypyrrole: the redox capacitance values of the oxidized polypyrrole are in the range of (0.7 to 0.9)x 103Fcm -3, and the diffusion coefficients are ia the range of 10 -s to 10 -9 cm 2 s-i; the charge transfer resistances are higher for the secondary connterion systems than for the primary counterion system. Contributions from the bulk and interfacial phenomena of the polymer electrode to the electrochemical characteristics were separated and the overall mechanisms of the redox process of polypyrrole in studied electrolyte solutions are postulated. The thin layer polypyrrole electrode was found to respond more slowly to the electrical perturbations when working in the secondary counterion systems. The significance of the polycation-counterion-co-ion interactions in the mechanism of the transport and transfer of charges in the polymer electrode is pointed out. A contribution of sodium ions to the charge transport in the polypyrrole-hexafluoroaluminate system is postulated. © 1997 Elsevier Science S.A.
Ion-exchange voltammetry at polymer-coated electrodes: Principles and analytical prospects
Electroanalysis, 1995
This review describes principles and analytical applications of ion-exchange voltammetry (IEV) at polymer modified electrodes. Results of mechanistic studies which are relevant to the development and optimization of IEV methods are discussed. Useful examples of IEV determinations of traces of inorganic and organic electroactive ions of interest for environmental, biomedical or pharmaceutical analysis are given along with future prospects for this technique.
The Journal of Physical Chemistry, 1992
This study concerns the growth, redox behavior, and analysis of poly(pyrro1e chloride) films ranging in thickness from -0.5 to -1.5 pm. Changes in the electrolyte pH from radical-coupling reactions during the oxidation of pyrrole lead to estimates of the polymerization efficiency in 0.1 M KCI which vary from 82% to 92% depending on the charge consumed. These values are compared with the Coulombic efficiency computed earlier in this laboratory using electrochemical quartz crystal microgravimetry (EQCM). The EQCM technique was combined with coulometry and in situ pH and K-ion-selective elactrode measurements for reexamining the extent of permselectivity of polypyrrole with respect to the chloride ion in aqueous elcctrolyta. Chloride ions contribute -75-8596 to the transport of the total charge during the redox of polypyrrole in 0.1 M KC1. The residual charge is partitioned between H+ and K+ depending on the initial pH of the electrolyte, which was varied from -1 to -7 in this study. Potassium ion transport was further verified by X-ray photoelectron spectroscopy. The extent of permselectivity is also dependent on the nature of the electrolyte cation, the bulky tetraethylammonium ion showing the most ideal behavior in this regard. Redox cycling of polypyrrole in 0.1 M CsCl and 0.1 M HCl was accompanied by a m b l e cation movement especially at potentials below ~-3 0 0 mV (vs Ag/AgCl). Finally, the ion transport during the redox of poly(pyrro1e chloride) was found to be intrinsically asymmetric in two related respects: first, the redox charge monitored via chronocoulometry in the two switch directions, i.e., oxidized/reduced, was not identical. Second, the measured redox charge was only 27-3596 of that theoretically expected from the polymer doping level for the 0.1 M KCl electrolyte. These data underline the inadequacy of the chronocoulometry/voltammetry procedure for assay of the doping level in conducting polymers such as polypyrrole, especially for rather thick (>a few hundred nanometers) polymer films.
Electrochimica Acta, 2014
Specific features of voltammetric studies with modified electrodes are subject of the consideration performed in the review. Basing on the approaches developed in preceding works, three groups of problems are discussed. The first one concerns a regular treatment of quasi-equilibrium cyclic voltammograms of modified electrodes. It is emphasized that singular points of such curves and their form depend on the system parameters (charges of immobile charge carriers, binding of counter-ions with the film fragments). As regards the second group of problems, its existence results from possible effects of the film porosity on the rates of reduction/oxidation processes with participation of particles capable to react on the film/solution interface. The main conclusion followed from the performed discussion is in the possibility of appearing the limiting currents not controlled with tested particles diffusion within the adjacent electrolyte. In scope of the third group of problems, the tested particles reactions on the electrodes covered with metal-containing polymer films are considered. As follows from the proper analysis, the current-voltage curves of these processes are described with the well-known equations of the electrochemical kinetics. Validity of the obtained conclusions is illustrated with the corresponding experimental results.
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.
2009
The electrochemical quartz crystal microbalance technique was used to examine the ion exchange behaviour and charge compensation mechanism of polypyrrole (PPy) doped with polystyrene sulfonate (PSS) immersed in electrolytes containing singly, doubly and triply charged metal ions. New insights were obtained concerning the mechanism of charge compensation and ion exchange behaviour of PPy/PSS films in electrolytes with triply and doubly charged transition metal ions. Understanding the ion exchange behaviour of conducting polymers immersed in these types of aqueous media could play a pivotal part in the development of methods for removing toxic metals from water supplies. Charge compensation occurred predominantly by means of cation movement for PPy/PSS films when the electrolyte was KNO 3 , Ca(NO 3 ) 2 , Mn(NO 3 ) 2 or Co(NO 3 ) 2 . After prolonged redox cycling the electroactivity of the polymer decreases slightly, and the charge compensation mechanism becomes complex owing to movement of ions and neutral species in opposite directions. The charge compensation mechanism for PPy/PSS films immersed in aqueous Cr(NO 3 ) 3 and Al(NO 3 ) 3 solutions was also complex, with the ion exchange behaviour shifting towards anion movement to and from the polymer.
Journal of Materials Science, 2011
In this article, important aspects influencing the signal stability of the potentiometric sensors based on various conductive polymers on platinum support are discussed. The initial step is the choice of a suitable cleaning method (mechanical stripping, burning out) of the platinum support. The second point consists in the selection of an appropriate procedure employed to mature the freshly prepared film on the metallic support (soaking, potential treatment, drying). The third crucial stage involves the application of a proper regeneration procedure (pH value of a buffer, anionic surfactant). The mentioned aspects have been tested using polythiophene, polyaniline, polypyrrole, poly(neutral red), poly(5,15-bis(2-aminophenyl)-2,8,12,18tetraethyl-3,7,13,17-tetramethyl-porphyrine), poly(5,15,25, 35-tetrakis(4-hydroxyphenyl)porphyrine) or poly(2,3-bis-(1H-pyrrol-2-yl)-quinoxalin-5-ol) as sensitive layers. The combination of the prepared electrodes into an electrode array (electronic tongue) and the development of a suitable protocol of the measurement allowed us to distinguish the individual brands of the Czech beers, specifically, Bernard 10°, dark Kozel 10°, Kozel 10°, Bráník 10°, Radegast, and Staropramen. Besides the platinum support, the conductive polymers were also deposited on a nonconductive support (membrane). The latter experiments demonstrated that the introduction of a conductive polymer as the outer layer onto poly(vinyl chloride) membranes led to the significant stabilization of their potentiometric response.