Kinetics of electron transfer between Fe(CN) 63−/4− and poly(3,4-ethylenedioxythiophene) studied by electrochemical impedance spectroscopy

Abstract

The electron transfer between the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and the Fe(CN) 6 3−/4− redox couple in aqueous solution was investigated by electrochemical impedance spectroscopy (EIS). PEDOT was electrochemically deposited on platinum from aqueous solutions containing 0.01 M 3,4-ethylenedioxythiophene (EDOT) and 0.1 M poly(sodium 4-styrenesulfonate) (NaPSS) as supporting electrolyte. Pt/PEDOT(PSS) electrodes with polymer films of different thickness were investigated at different concentrations of the redox couple in 0.1 M KCl background electrolyte solution. Impedance spectra were obtained at the dc-potential corresponding to the formal redox potential of Fe(CN) 6 3−/4− ( E°′≈220 mV) where the polymer is in the oxidized and electrically conducting state. The EIS data for the electrodes were fitted to an equivalent electrical circuit. The standard rate constant ( k o) for electron-transfer between Pt/PEDOT(PSS) and Fe(CN) 6 3−/4− was determined by calculations based on the Butler–Volmer equation. The diffusion coefficient ( D) of the redox couple was also calculated from the EIS data.