The degradation of poly(3,4-ethylenedioxythiophene) (PEDOT) films at an anode in an aqueous solution has been systemically studied. On the basis of results, the anodic processes can be divided into three segments: p-doping region from －0.3 to 0.5 V, transitional region from 0.6 to 1 V and overoxidative region from 1.2 to 1.6 V (all vs. SCE). The behaviors of PEDOT in the three potential regions were studied by electrochemical impedance spectroscopy, cyclic voltammetry, conductivity measurements, electron spin resonance and FT infrared spectroscopy. Conclusively the behaviors of PEDOT in the three potential regions were distinctly different. The process in p-doping region was reversible doping/dedoping process, which kept the conjugated structure, conductivity and functional group. The process in transitional region resulted in the change of functional group but invariation of the conjugated structure and conductivity of PEDOT. The process in overoxidative part was badly destructive, which resulted in the irreversible change of the conjugated structure, conductivity and functional group.

Key words: poly(3,4-ethylenedioxythiophene), anodic degradation, electrochemical impedance spectroscopy, electron spin resonance, FT infrared spectroscopy