A parameter study on the impedance of poly(3-methylthiophene) film electrodes

Poly(3-methylthiophene) films (PMT), polymerised galvanostatically (i = 1.0 mAcm(-2)) in propylene carbonate + 0.03 M TBAPF(6) + 0.2 M 3-methylthiophe ne solution, were characterised by cyclic voltammetry and coulometry combin ed with gravimetrical measurements and Electrochemical Impedance Spectrosco py (EIS). The de electronic and ionic conductivities of PMT-films were meas ured on free-standing membranes as function of the electrode potential. Fro m these measurements, the mobilities and diffusivities of electrons and ion s were determined at T = 298 K (mu(e) = 0.21 cm(2) V-1 s(-1), mu(i) = 6.3 x 10(-8) cm(2) V-1 s(-1) and D-e = 5.6 x 10(-3) cm(2) s(-1), D-i = 1.6 x 10( -9) cm(2) s(-1)). EIS measurements on Pt/PMT-film electrodes were carried o ut in the monomere free propylene carbonate solution in dependence of the f ollowing parameters: PMT-film thickness i, supporting electrolyte concentra tion c, temperature T and polarisation potential E. The low frequency part of the impedance spectra could be fitted by a simple cylindrical pore model . The dependence of the fit parameters on the system parameters favours the assumption that the PMT-film is porous and the pores are filled with the b athing electrolyte. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.