Ions transfer mechanisms during the electrochemical oxidation of poly(3,4-ethylenedioxythiophene) in 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide ionic liquid

Abstract

The cyclic voltammetry and the electrochemical impedance spectroscopy responses of p-doped poly(3,4-ethylenedioxythiophene) (PEDOT) electrodeposited on platinum electrode surface were studied in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (EMITFSI). The influence of adding salt, lithium bis((trifluoromethyl)sulfonyl)amide (LiTFSI, Li(CF 3SO 2) 2N), was studied. When PEDOT was prepared in acetonitrile, the cyclic voltammograms displayed two distinct anodic peaks indicating at least two redox reaction mechanisms. Results indicated that for one of these mechanisms 1-ethyl-3-methylimidazolium cation was the exchanged species during the oxidation, and at the same time bis((trifluoromethyl)sulfonyl)amide anion could be viewed as immobile ions trapped in the polymer film. The impedance responses were analyzed within two parallel diffusion paths that reflected the non-uniformity of the electroactive polymer film. The variation of the two time diffusion constants as a function of potential followed the same trend as the kinetic parameters determined by a potential step method. The total capacitance form electrochemical impedance spectroscopy was in agreement with that has obtained with cyclic voltammetry. Results showed also the importance of the electrodeposition conditions on the electrochemical behavior of PEDOT.