Catalysing electropolymerization: High-quality polythiophene films for electrochemical sensors by the utilization of fluorine based Lewis acid catalysts

Abstract

Polythiophene and other conductive polymers can be obtained by electropolymerization from various solvents, of which boron trifluoride diethyl etherate (BFEE) is preferably used. In this solvent, electropolymerization can be performed at significantly lower potentials and therefore milder conditions, from which polymers with improved properties result. However, their quality cannot easily be reproduced. We discovered the mechanism behind the decreased initial oxidation potential of thiophene in BFEE and transferred it onto stable solvents by the utilization of fluorine based Lewis acid catalysts. By exemplarily utilizing zinc fluoride in acetonitrile, we found that the catalysis allows for lower oxidation potentials, higher selectivity of polymerization, and smoother film surface morphology – in a reproducible manner. The presented polythiophene films constitute a promising substrate material for the fabrication of electrochemical sensors. Films were deposited by cyclic voltammetry, chronoamperometry, and chronopotentiometry, and characterized by electrochemical impedance spectroscopy and Raman spectroscopy. Surface morphology and elemental composition were analysed with white light interferometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. We propose a number of alternative catalysts that can be utilized in various solvents, not just for thiophene electropolymerization, but for various other conductive polymers. The presented catalysis can therefore serve as a universal tool for the synthesis of high quality conductive polymer films for innovative and trendsetting applications.