Spectroscopic and electrochemical studies of charge transfer in modified electrodes

Abstract

Experimental results from electrochemical e.s.r. on electrodes modified with conducting polymers such as polyaniline, polypyrrole and polythiophene are presented. The results show that the polymer exists in two forms, one stable when it is insulating ( a ) and the other ( p ) when it is conducting. In the conducting region the kinetics of the transformation of the metastable a form into the / 3 form can be followed by e.s.r. It is further shown that in the lightly oxidised films there is a one-to-one correlation between charge injected and e.s.r. spins. These results are explained by a chemical redox model as opposed to a delocalised band.Results from a.c. impedance studies are presented. These results are explained by an equivalent circuit which includes a novel transmission line with differential resistances. Theoretical impedance plots are derived. Experimental results show that the polymer resistance and the resistance of the aqueous pores are equal. Reasons for this finding are discussed.There has been considerable controversy over the nature and dynamics of the charge carriers in conducting polymers. Models range from that of a doped organic semiconductor with well developed bands"* to more chemical models which emphasise the redox chemistry between localised species on the polymer chain.3 In this paper we are concerned with conducting polymers such as polypyrrole, polythiophene and polyaniline. The main experimental techniques we have used are in situ electrochemical e.s.r. and a.c. impedance studies. We will show that the behaviour of the different polymers is similar and may be explained by a chemical model involving localised redox species with two possible conformations of the polymer. A modified transmission line is used to explain the ac data.

Electrochemical Characterisation of Polypyrrole Doped with p‐Sulfonatocalix[4]arene

“…As the potential increases and the film is oxidised the capacitance also increases reaching a maximum near the peak oxidation potential of the film. This observation was consistent with the idea that the capacitance of a PPy film is related to its faradaic process [43,48]. That is, the capacitance of the film mainly arises from the charge separation between the oxidised PPy backbone and the doping counteranions.…”

“…The impedance of a PPy film is classically interpreted using a dual rail transmission line in which the motion of electrons along the polymer chains is described by one resistance rail (R e ), while the motion of the counterions in the pores is described by a second resistance rail (R ion ). A distributed capacitance connects the two rails and models the faradaic capacitance (C f ) of the polymer [43,44]. To the best of our knowledge this is the first electrochemical impedance study of PPy doped with a sulfonated calixarene.…”

Nanocomposites of Polyaniline and a Layered Inorganic Acid Host: Polymerization of Aniline in the Layers, Conformation, and Electrochemical Studies

“…Generalized transmission line equivalent circuit is compatible with a variety of different physical and theoretical models for discussing the electrochemical properties of conducting hybrids. [38] In the present work, the intercalated nanocomposite was first regarded as a kind of "porous electrolyte" and modeled by using the equivalent circuit. Nyquist plots of HNb 3 O 8 , bulk PANI salt (doped by HCl), and nanocomposites are shown in Figure S2 (Supporting Information), and the fitted impedance parameters are listed in Table 1.…”

Electrochemical impedance spectroscopy of dodecylsulphate doped polypyrrole films in the dark and under illumination

“…Albery and cols 15 proposed equations to describe the responses of transmission line type for oxidised polypyrrole. In such case the polymeric electronic (R E ) and ionic (R I ) resistances and the resistance of the solution (R S ) could be determined from the complex plane representation, using the following equations: …”