DYNAMIC IMPEDANCE MEASUREMENTS ON A THIN-FILM POLY-3-METHYLTHIOPHENE ELECTRODE - MEMORY EFFECTS AND SPACE-CHARGE FORMATION

A new procedure for measuring electrochemical impedance spectra direct ly during potential cycling is presented. The method consists in takin g a series of impedance-potential curves at different potential modula tion frequencies. Then the impedance values at desired electrode poten tials are sampled, and corresponding dynamic impedance spectra are rec onstructed. The method was applied to a thin-film poly-3-methylthiophe ne \Pt (P3MT\Pt) electrode in an acetonitrile solution. The results su ggested that undoping of the polymer at negative potentials gave rise to development of a space-charge region within the film that hindered the polymer doping process unless flat-band conditions were reached. S uch behavior could account for a well-known memory effect observed in conducting polymers. Moreover, our data provide further evidence that illumination of a P3MT electrode at negative potentials results in pho toelectrochemical undoping of the polymer.