KINETICS OF THE CHARGE DISCHARGE PROCESS IN CONDUCTING POLYMERS - SLOW RELAXATION AND HYSTERESIS EFFECTS - INVESTIGATIONS ON POLYANILINE BY MILLIMETRIC AND ULTRAMICROELECTRODES

In cyclovoltammetry experiments, the oxidation wave of a conducting polymer depends on the wait-time it has been left in its insulating state. This relaxed wave differs in shape and peak position from the steady-state wave, that is, the wave obtained by repetitive cycling. This relaxation effect was studied with millielectrodes for scan rates between 2 and 200 mV/s and wait-times in the range 10-3 X 10(3) s, and with ultramicroelectrodes (5-mu-m diameter) with scan rates between 10(2) and 2 X 10(5) V/s for wait-times down to 0.2 ms. In both cases, it is shown that the shift in peak potential is logarithmic as a function of both wait-time and scan rate. The steady-state wave can thus be defined as a relaxed wave for a particular wait-time. On this basis, part of the hysteresis between oxidation and reduction comes from the relaxation effect. Ultramicroelectrodes provide a means of estimating the kinetic rate constant of polyaniline. The relaxation of polymethylthiophene is also briefly considered.