Impedance Study of the Charge-Transfer Interaction Between the Polyaniline Chain and Redox Pair in Solution

Abstract

Conductivity, electrochromism, chemical sensing, and electroluminescence are the most interesting and promising properties of conducting polymers. 1 All of those are based on the peculiar chemical structure of the polymer chain, which can change its electronic and conformational structure under external conditions. These conditions may be: chemical environment, i.e., active chemical species, pH, or different solvent; electric field, i.e., polarization in electrochemical or solid-state conditions; and other conditions that can introduce variations favorable to the polymer, for instance, optical excitation or magnetic field.Polyaniline (PANI) is one of the most stable conducting polymers and much work has gone into understanding its chemical and electronic properties. 2-5 At present it is largely accepted that insulator-metal transition of PANI is based on the acid-base chemistry of amine and imine groups. In strong mineral (and organic) acids imine groups become protonated, and their positive charges are delocalized over several monomer units along the polymer chain. Scheme I shows the chemical structures of polyaniline in its nonconductive emeraldine base (PANI-EB) and conductive emeraldine salt (PANI-ES) forms. The contranions (i.e., anions of the strong acid) are not involved in delocalization, so, their chemical nature is secondary. 6 It was recently proposed from a study of the electrochemical behavior of the quinone-hydroquinone (Qui-Hqui) redox pair on the PANI electrode in strong acid solution (1 M H 2 SO 4 ) that protonated centers of the polymer are directly involved in the charge transfer to/ from an organic acceptor. 7,8 Scheme II shows the internal and external redox transformation of/on the PANI electrode in those conditions.In our work 8 we have also proposed and discussed the structures of the reaction center (CT complex), assuming it to be the protonated imine group and Hqui (Qui) molecule with a hydrogen junction (H bridge) between them, Scheme III. While the charge-transfer process takes place through this bridge, the electrochemical kinetics of the Hqui oxidation (Qui reduction) would show a first-order dependence on the quantity of PANI deposited on the Pt electrode as was observed in Ref. 8.Following this hypothesis we have proposed that in less acid electrolytes, Hqui molecules could interact with the PANI-EB to form H bonds and in that way they themselves would protonate imine centers of the polymer electrode. Obviously, this will happen when there are not quite enough free protons in the electrolyte, i.e., when pH is above a given level.This assumption could also be valid for the polymer-molecular mixture PANI-EB ϩ Hqui prepared from an inert solvent, for instance N-methylpyrrolidinone. When the CT complex is formed between EB and Hqui, the latter has to accept a negative charge andThe impedance method was used to study the charge-transfer interaction between the polymer conducting chain (emeraldine form of polyaniline, PANI) and active molecules in solution (tetrafluorohydroquinone, 4F-Hq...

The Formation of Polypyrrole at Iron from 1-Butyl-3-methylimidazolium Hexafluorophosphate

“…Indeed, such high capacitance values have been attributed previously to the intrinsic redox charging of conducting polymer films in aqueous media. 18,19 These impedance data show clearly that the polypyrrole coating formed at the iron electrode is conducting, in agreement with the voltammetry data presented in Fig. 7.…”

“…17 These studies have all been conducted with inert electrodes. Although conducting polymers have been deposited at corrosion susceptible electrodes, from aqueous solutions, 18,19 there are no reports on the preparation of conducting polymers at these substrates using ionic liquids as the solvent system. In this paper, results are presented and discussed on the electropolymerization of pyrrole from an ionic liquid at iron to generate adherent and stable conducting polypyrrole films.…”

Analysis of high-frequency distortions in impedance spectra of conducting polyaniline film modified Pt-electrode measured with different cell configurations

“…2b, however, some distortions of impedance spectra are at the highest frequencies seen as unexpected shifts of phase angle parts from zero [9,10,12,13,[16][17][18]. For impedance spectra A-1 and B-1 measured in conventional three-electrode cell, increase of log |Z| at the highest frequencies [16][17][18] can also be observed in Fig. 2b.…”

“…material(s), overall design (geometry) and environment of the cell. In already presented impedance spectra of low impedance and highly capacitive WE such as conducting form of polyaniline (PANI) film modified electrodes and/or PANI membranes in acidic solutions, relatively high extent of distortions could be noticed in high frequency parts of impedance spectra measured in either conventional three-electrode cell [16][17][18], in three-electrode cell with RE connected with pseudo-reference electrode (PRE) [9,10,12,13], or in four-electrode cell with two RE's [17,19]. Since in the case of highly capacitive and low impedance WE, presence of parasitic impedances and/or reflections of RE and CE in measured impedance spectra could hardly be avoided, even after using PRE placed close to RE [9,10,12,13], it seems to be of high importance to distinguish and separate their frequency response from the frequency response of impedance branch containing conducting PANI film WE.…”

The electrochemical synthesis of polypyrrole at a copper electrode: corrosion protection properties

“…R 1 represents the ionic and electronic resistance of the polymer film. These resistance terms have been analysed by several authors [19,20]. It is generally assumed that in the conducting state the polymer film resistance is considered as negligible compared to the electrolyte resistance.…”