A Review About the Charge Conduction Process at Poly(o-aminophenol) Film Electrodes

ABSTRACT

This review, which is divided into two parts, concerns charge-transport and charge-transfer processes at poly(oaminophenol) film electrodes. The first part deals with the case where the solutions contacting poly(o-aminophenol) films only contain ions that do not possess a redox activity (“background electrolyte”). The second part refers to the transport properties of poly(o-aminophenol) films contacting redox active solutions. In the first part, I have attempted to document the most significant evidence, which proves that the electrochemical behaviour of poly(o-aminophenol) can be explained on the basis of a chemical reaction coupled with a reversible electron-transfer process. In this connection, it was demonstrated that the response of poly(o-aminophenol) is highly dependent on the solution pH. This indicates that protons and electrons take part in the electrode reaction of the polymer. Different studies about the charge conduction across poly(oaminophenol) films indicate the existence of a diffusion-limited charge-transport process. It was suggested that the transport process might be electron hopping-assisted by the corresponding counterion motion. In this regard, transport parameters, such as apparent or effective diffusion coefficients, have been employed to characterise the whole charge conduction process at poly(o-aminophenol) film electrodes. In some papers, electron and ion movements have been separately treated through electron and ion diffusion coefficients. It was found that these transport parameters depend not only on the type and concentration of the electrolyte solution contacting the polymer film but also on polymer film thickness. With regard to the electrochemical behaviour of poly(o-aminophenol) in the presence of solutions containing redox active couples, it has been reported that at negative potentials (-0.250 V versus SCE) the polymer can act as a mediator in electron-transfer reactions at the polymer solution interface. However, at positive potentials (higher than 0.8 V versus SCE) the species dissolves into the polymer with a partition equilibrium at the film solution interface.

At the end of this review (Section 4) I have tried to collect common and different viewpoints on the charge conduction process at poly(o-aminophenol) film electrodes reported in the literature. In Section 5 I describe some critical aspects related to charge-transport parameter values extracted from different electrochemical models applied to studying the polymer. Finally in Section 6, emphasis is laid on the effects of conduction and permeation processes at poly(o-aminophenol) on some of its practical applications, such as those where the polymer acts as an electrochemical sensor.

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