IMPEDANCE SPECTROSCOPY AND CYCLIC VOLTAMMETRY AT BARE AND POLYMER COATED GLASSY-CARBON ELECTRODES

Influence of electrochemical pretreatment of a glassy carbon electrode on electrochemical parameters of the charge transfer is investigated. The couple ferro/ferricyanide serves as a model system. Parameters are calculated from data obtained from impedance spectroscopy and cyclic voltammetry measurements supposing a pure quasireversible case. By electrochemical pretreatment the heterogeneous charge transfer constant is enhanced from the range of 0.0001 up to higher than 0.01 cm s-1. The diffusion coefficient has been evaluated to be about 8 x 10(-6) cm2 s-1. When the electrode is coated by styrene-maleic anhydride copolymer, the polymer swells in aqueous medium until signals similar to bare electrodes are obtained. They can be attributed to the pinhole diffusion of the electrode substrate. It can be shown that parameters, determined from impedance measurements, fit experimental data very well.