Electrochemistry of Conductive Polymers 48. Electrochemical Polymerization of 3,4-Ethylenedioxythiophene in Ionic Liquids and Propylene Carbonate

Abstract

Systematic studies on the electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) were conducted at gold electrodes in two room temperature ionic liquids (RTILs) sharing the 1-butyl-3-methylimidazolium cation (BMIM+) for one of two anions, BF4- or TFSI- [bis(trifluoro-methylsulfonyl) imide], and in propylene carbonate (PC) containing BF4- or TFSI- for a common t-butylammonium cation. EDOT oxidation in RTILs was shown to undergo a change in charge-transfer mechanism during the potential sweep, which must have led to differences in polymerization reactions in the two media. Differences were noted between poly-EDOT (PEDOT) films prepared in RTILs and those in PC; PEDOT films were characterized using techniques including UV-visible absorption spectroscopic, scanning electron microscopic, and Fourier transform electrochemical impedance spectroscopic experiments. The films prepared in PC and with TFSI- displayed the better electrochemical properties. Differences in electron and mass transfer kinetics in different media led to differences observed for film growth kinetics, chain lengths, and redox characteristics for the PEDOT films. Also revealed was that different oxidation mechanisms are at work in RTILs in different potential regimes.