Electrochemical synthesis and characterization of poly(3,4-ethylenedioxythiophene)in ionic liquids with bulky organic anions

摘要

The electrochemistry of poly(3,4-ethylenedi-oxythiophene)(PEDOT)was studied in two ionic liquids with bulky organic anions,i.e.,l-butyl-3-methylimi-dazolium(BMIM)diethylene glycol monomethyl ether sulfate(MDEGSO_4)and BMIM octyl sulfate(OctSO_4).BMIM-MDEGSO_4 is a liquid,while BMIM-OctSO_4 is in solid form at room temperature.Electrosynthesis of PEDOT in BMIM-MDEGSO_4 with an EDOT concentration of 0.1 M and in BMIM-MDEGSO_4/EDOT 1/1(w/w)solution resulted in no polymer at all or a very limited amount of polymer on the electrode surface,as determined by cyclic voltammetry in 0.1 M KCl(aq)solution.In contrast,electrosynthesis of PEDOT in BMIM-OctSO_4/EDOT 1/1(w/w)resulted in a high yield of electroactive material on the electrode surface.Furthermore,electrosynthesis.of PEDOT in ionic liquid-water solution(C_(ionic liquid)= 1.5 M)containing 0.1 M EDOT was also found to give a relatively high yield of electroactive material on the electrode surface,both for 1.5 M BMIM-MDEGSO_4(aq)and 1.5 M BMIM-Oc-tSO_4(aq).The PEDOT electrodes showed an anionic potentiometric response in 10~(-5)-10~(-1)M KCl(aq)solution,indicating a predominant anion transfer at the polymer-solution interface despite the relatively bulky anions(MDEGSO_4~-or OctSO_4)incorporated as counterions in PEDOT during electropolymerization.On the basis of electrochemical impedance spectroscopy,the charge(ion)transport properties of the polymer film were strongly influenced by the water content of the ionic liquid(C_(lonic Uquid)= 0.05-2.0 M).