Ants Alumaa

Electrochemical properties of polypyrrole/sulphate films

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 films 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

Nature of ion sensitivity of polypyrrole electrodes

The ion sensitivity of polypyrrole (PPy) films deposited electrochemically onto Pt, glassy carbon and SnO2 substrate was studied by potentiometric measurements. The influence of electrochemical (overoxidation, reduction and potentiodynamic cycling) and chemical (alkaline solution) pre-treatment on the potentiometric behaviour of PPy electrodes was determined. The dependence of the potential of the PPy electrode after long-term conditioning on the log of electrolyte activity of conditioning solution is characterised by low negative (solutions of NaSCN, NaNO3, KCl, or NaF) and low positive (Cs2SO4, Na2SO4 or Li2SO4) slopes. The exceptionally low exchange rate of anions between sulphate-doped PPy films and solution was established by electron probe microanalysis. Short-term (2–5 min) potential responses of PPy electrodes to the change of composition and concentration of electrolyte were studied. PPy electrodes conditioned in NaSCN, NaNO3, KCl, and NaF solutions possess anion sensitivity, and electrodes conditioned in Cs2SO4, Na2SO4 and Li2SO4 solutions, cation sensitivity, independent of the composition of the solution used for the preparation of the PPy film. The short-term response is generally not selective and depends on the arrangement of the ions in the Hofmeister lyophilic series. This potential response is interpreted as the result of asymmetric movement of anions or cations through the PPylsolution boundary.

Redox properties of polypyrrole bilayers

The spatially separated bilayers of polypyrrole (PPy) doped with anions of limited (dodecylsulfate (DDS) and sulfate) and good mobility (chloride) have been prepared by consecutive electrodeposition. The perfect coverage of PPy in the inner layer was obtained already at a very low effective thickness (<0.05 μm) of the outer layer. The peculiarity of the redox behavior of PPy bilayers has been investigated by cyclic voltammetry (CV) and electron probe microanalysis (EPMA). Ion transport through the outer PPy film has been characterized. The cation permeability in the mainly reduced outer component of PPy/DDS/Cl bilayer is limited and increases in the sequence of decreasing hydrated ion radii. The transport of the chloride dopant ions in the course of the reduction process of the inner layer of PPy/Cl/DDS and PPy/Cl/SO4 bilayers through the hydrophobic PPy/DDS and even through the dense but less hydrophobic PPy/SO4 film proceeds relatively easily. The penetration of the anions of the test solution during the reoxidation process of the PPy/Cl inner layer through the PPy/DDS outer layer is, on the contrary, essentially hindered. The reason for the high resistance to ion movement is the hydrophobic character of the PPy/DDS outer layer in which the amount of the electrolyte test solution is too low in order to initiate the anion migration process. Ion transport under conditions of simultaneous redox process in the outer and inner layer is characterized.

Electrochemical properties of dodecylsulphate doped polypyrrole films

Abstract The electrochemical behavior of dodecylsulphate (DDS) as a surfaceactive dopant of conducting polymer was studied. High selectivity of incorporation of the DDS into the growing polypyrrole film during the anodic polymerization was observed. The DDS ions are firmly fixed and cannot escape from the film and as the oxidation state of the polypyrrole is changed, other ions migrate into or out of the film. Extremely high kinetic resistance of the first reduction process is typical of the DDS doped polypyrrole. The incorporation of cations during the first cycle drastically changes the electrochemical properties of the film.