In situ ATR-FTIR- and Raman-investigations on the polymerization of 2,2′-thienylpyrrole and the redox behaviour of thin film poly(thienylpyrrole) electrodes in aqueous electrolytes

The polymerization of 2,2′-thienylpyrrole and the redox behaviour of the resulting polymer film electrodes were studied in order to improve the stability and the response time of miniaturized thin film pH-sensors based on this polymer. The polymerization process was studied in aqueous solutions of different pH containing NaClO4, LiClO4 and NaBF4. In electrolytes containing perchlorate ions dense and homogeneous poly(thienylpyrrole) films were produced, exhibiting a conductivity ranging between 0.1 and O.3S.cm−1. During in situ FTIR-ATR experiments, the detection of oligomeric structures was not possible. The polymerization of the monomer starts in a very narrow potential range quite rapidly and by in situ Raman spectroscopy an intermediate state was detectable during potentiostatic polymerization. The poly(thienylpyrrole) films exhibit in perchlorate containing electrolytes in the pH range 1 to 8 a relatively reversible and similar redox behaviour. In contrast to poly(thienylpyrrole) films produced in non-aqueous electrolytes, the films polymerized in aqueous media show at higher redox cycles (> 1000) a reduced stability connected with a reduced degree of reversibility.