One-pot electrosynthesis of ultrathin overoxidized poly(3,4-ethylenedioxythiophene) films

Abstract

In an aqueous electrolyte under an anodic polarization, most of the conductive polymers could undergo an overoxidation due to the hydroxyl radicals formed during water oxidation. Regarding poly(3,4-ethylenedioxythiophene) (PEDOT) only a few reports studied its overoxidation. In this paper, we propose a facile and rapid strategy to prepare an ultrathin (15 nm), pinhole-free and non-conductive overoxidized PEDOT film by electropolymerization of EDOT under potentiostatic conditions in the presence of solely weak-acid anions in the monomer solution. The influence of the pH of this solution as well as the applied potential was studied notably by electrochemical impedance spectroscopy. It was pointed out that the PEDOT film is overoxidized when its electrosynthesis is performed in an aqueous monomer solution of pH 10.5, at 1.1 V/SCE, the monomer solution containing only weak-acid ions as anions (phosphates or carbonates). XPS analyses show that some C and S atoms of the film are oxidized leading to a break of the polymer conjugation and therefore to a decrease of its electronic conductivity. Finally, after adding in the monomer phosphate solution of pH 10.5 perchlorate ions that allow to avoid total overoxidation of the film formed at the very beginning of the process, PEDOT nanowires were obtained.