Electrochemical studies of self-doped conducting polymers: Verification of the ‘cation-popping’ doping mechanism

Abstract

Cyclic voltammetry in conjunction with X-ray microprobe analysis has been used to investigate the doping mechanism in covalently-bonded-anion (self-doped) conducting polymers. The polymers investigated are the acid and sodium salt forms of poly 3-(4-butanesulfonate) thiophene (P3-BTSH and P3-BTSNa, respectively) and poly 3-(2-ethane sulphonate) thiophene (P3-ETSNa). These water-soluble polymers, whose synthesis is described in detail, were used (in the form of films cast from solution onto ITO glass or platinum sheets) as working electrodes in cyclic voltammetry experiments in which the proton or Na + concentration of the electrolyte was monitored. The results directly verify the proposed doping mechanism: charge injection into the π-electron system of the conjugated polymer accompanied by proton or sodium ion ejection, without incorporation of electrolyte anion, leaving behind the oppositely charge counterion.