Redox mediation and permeation processes at deactivated poly(o-aminophenol) films. A study applying Rotating Disc Electrode Voltammetry and Electrochemical Impedance Spectroscopy

R. TUCCERI

J. Electroanalytical Chemistry

Elsevier

Lugar: Ansterdam; Año: 2009 vol. 633 p. 198 - 206

0022-0728

The objective of this work was to deactivate poly(o-aminophenol) (POAP) films andthen study how their permeation and electron-transport processes are modified by thedegree of deactivation. POAP films were deactivated by soaking in a ferric cationsolution. The degree of deactivation (qc) was assessed by employing CyclicVoltammetry within the potential region where POAP exhibits its maximalelectroactivity (-0.2 V < E < 0.5 V versus SCE). Rotating Disc Electrode Voltammetry(RDEV) and ac impedance measurements were applied in the interesting case wherePOAP films contact a redox active solution containing the pbenzoquinone/hydroquinone redox couple and a mediation reaction occurs at thepolymer|electrolyte interface. RDEV applied at potential values E < 0.0 V versus SCEallowed obtaining a diffusion coefficient value, De. It was observed that De decreaseswith increasing qc. This effect was attributed to the existence of inactive gaps within theredox site configuration of a deactivated film, which causes an increase in the hoppingdistance for electron conduction. The existence of inactive gaps seems to be related tothe hindrance to accept protons by some redox sites in a deactivated film. This fact wasproved by increasing the pH of the external solution contacting a non-deactivated POAPfilm. Impedance diagrams of deactivated films show an increase in the charge-transferresistance at the metal|polymer interface, which is consistent with the presence ofinactive zones within the redox site distribution of a deactivated film. Some deactivatedPOAP films were reactivated by treatment with an ammonium solution and it wasobserved that electron conduction can only be partially recovered. The permeationprocess at potential values where hydroquinone is able to diffuse through POAP wasalso analyzed on deactivated films. It was found that the rate of diffusion ofhydroquinone decreases as the degree of deactivation increases. This effect wasattributed to unfavourable partition equilibrium at the polymer|solution interface for theelectroactive species in a deactivated film, as compared with a non-deactivated film.This work could be interesting due to the wide range of practical applications of POAPrecently reported. In this sense, although in practical applications of POAP it isnecessary to maintain its conducting properties unaltered, the polymer is subjected toextreme conditions that can cause its partial deactivation. Thus, it seems to be importantto know at least how the charge-transport process changes at POAP films with theirdeactivation.