Charge-transfer and charge-transport parameters of deactivated poly(o-aminophenol) film electrodes. A study employing electrochemical impedance spectroscopy

Poly(o-aminophenol) (POAP) films were deactivated and then reactivated, and dependences of the different charge-transport and charge-transfer parameters on the degree of deactivation (θc) were obtained by employing electrochemical impedance spectroscopy. These dependences were extracted when the polymer contacts an electroactive solution and a mediation reaction occurs at the polymer|electrolyte interface. While some parameters, such as interfacial metal-film and film-solution resistances (Rm|f, Ref|s,Rif|s), the high-frequency capacitance (CH) and the redox capacitance (Cp) exhibit a continuous variation without hysteresis between deactivation and reactivation processes within the whole θc range, others, such as electron and ion diffusion coefficients (De, Di), show hysteresis between consecutive deactivation and reactivation processes. On the basis of these findings it was considered that while some parameters of the polymer only depend on the amount of redox active sites, others (De and Di) depend on both the quantity and distribution of redox active sites.

Graphical abstractDiffusion coefficients for electron and ion transport at poly(o-aminophenol) decrease as the degree of deactivation (θc) increases. Both dependences exhibit a univocal correspondence during deactivation and subsequent reactivation, for degrees of deactivation lower than 0.4. Slower electron transport with the increase of the degree of deactivation was attributed to the increase of the electron hopping distance caused by the presence of inactive sites in the redox site configuration of a deactivated film. Decrease of the ion diffusion coefficient with the increase of the degree of deactivation up to 0.4 was associated with the inhibition of nitrogen-containing groups that provide the binding of hydrogen ions that contribute to film conductivity. Both dependences show a change of slope for degrees of deactivation higher than 0.5 together with the existence of hysteresis after reactivation. The less pronounced decrease of the electron diffusion coefficient with a higher degree of deactivation (θc) was attributed to a redistribution of the redox site configuration to maintain the electron hopping distance constant. In the case of the ion diffusion coefficient, the effect was attributed to inhibition of nitrogen-containing groups that immobilize protons that do not participate in the diffusion process. These findings seem to indicate that electron and ion conduction of a deactivated poly(o-aminophenol) film can only be completely recovered by reactivation when its degree of deactivation is lower than 0.4. However, a permanent loss of conductivity is observed for degrees of deactivation higher than 0.5.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Deactivation of poly(o-aminophenol) film electrodes. ► Dependences of charge transport parameters on the degree of deactivation. ► Electron and ion diffusion coefficients show hysteresis between consecutive deactivation and reactivation processes. ► Some transport parameters depend on the distribution of redox site inside the polymer film.