In this review, results of recent studies on the electrochemical stability and degradation properties of poly (3,4-ethylenedioxythiophene)

Electrochemical and morphological properties of thin poly(3,4-ethylenedioxy-thiophene) (PEDOT) films deposited on gold were investigated in aqueous sulfuric acid solutions. X-ray diffraction and electron microscopy were used for monitoring the morphological changes and structure evolution caused by overoxidation. The diffraction peaks of PEDOT became sharper and more intensive during the subsequent oxidation cycles. This indicates that besides the degradation of the PEDOT film, its crystallinity was gradually improved with increasing the number of oxidation cycles. These changes may result in the appearance of novel properties that may be advantageous for specific applications.

Many electrochemical systems are intrinsically nonstationary and are affected by timedependent phenomena. The requirement of stationarity in the classical version of impedance spectroscopy appears to be in conflict with the essential properties of the object, therefore a post-experimental mathematical/analytical procedure is necessary for the reconstruction of the "true" impedance values. In this study, it has been shown that the 4-dimensional analysis method, originally proposed by Stoynov, can not only be used for the correction of existing (experimentally measured) impedance data, but it also opens up the possibility of the estimation of impedance spectra outside the time interval of the measurements. As an illustrative example the method has been applied for the determination of the charge transfer resistance (Rct) of poly(3,4-ethylenedioxytiophene) (PEDOT) modified electrode as a function of time, including the Rct value corresponding to the time instant just after overoxidation of the polymer film. After the overoxidation the charge transfer resistance decreased continuously with experiment time to a value somewhat higher than the R ct of the pristine electrode. The results imply that a "healing process" may occur at the film/substrate interface. A better understanding of this effect may have an impact on practical applications.

Electrochemical, mechanical and morphological properties of thin poly (3,4-ethylenedioxy-thiophene)

Note that although the impedance is usually complex, we do not put a "hat" on Z. Eq. (5) means that the complex voltage and current obey the linear relationÛ ¼Î � Z, which is the complex generalization of Ohm's lawThe impedance can also be given in the form [Eq.