An electrochemical impedance study of the electrochemical doping process of platinum phthalocyanine microcrystals in non-aqueous electrolytes

The electrochemical doping process of platinum phthalocyanine (PtPc) microc rystalline films in acetonitrile electrolyte has been investigated using el ectrochemical impedance spectroscopy (EIS). The system shows the impedance behaviour expected for a conductive polymer-that is, the appearance of a se parate Randles circuit, a Warburg section and purely capacitive behaviour a t low frequencies, An equivalent circuit is developed which provides a good fit to experimental impedance data over a wide frequency range of 1 MHz-0. 05 Hz. The kinetic parameters of the electrochemical doping process depend strongly upon the doping potential. Analysis of the conductivity of the PtP c film suggests that a percolation effect is responsible for the first-scan discrepancy. At low doping levels, the rate of the first electrochemical s tep is slow and determined by the conductivity of the microcrystalline film , Once the film becomes conductive, the electrochemical reaction is acceler ated abruptly giving rise to a sharp peak. Further increases in doping pote ntial trigger another slow oxidation process. The potential dependence of t he diffusion-migration capacitance suggests strong interactions between cha rge carriers within the microcrystalline film. (C) 2001 Published by Elsevi er Science B.V.