Electrochemical impedance studies of methanol electro-oxidation on Pt/C thin film electrode

Anodic processes of methanol oxidation on Pt/C thin film electrodes are carefully examined using electrochemical impedance spectroscopy. The influence of the electrode potential on the impedance pattern is studied and a quantitative explanation for the impedance behavior of methanol oxidation is achieved using a newly derived mathematical model. Theoretical derivations agree well with the experimental results, both of which show that the impedance patterns are strongly dependent on the electrode potential. At potentials higher than 0.30 V (vs. Ag/AgCl), a pseudoinductive'' behavior is observed. At potentials higher than 0.42 V (vs. Ag/AgCl), the impedance pattern is reversed to the second and third quadrants. The conditions required for the reversing of impedance pattern are delineated with the use of the impedance model. (C) 2002 The Electrochemical Society.