Conducting polymers dedoping

19 Factors Controlling Stability of Polymers Acceptable for Gas Sensor Application 

Additional annealing of doped polymers also accelerates the process of dedoping. Li and Wan (1999) have shown that temporal change in film conductivity of doped poly aniline at room temperature is increased strongly after thermal treatment of doped polymer at 7=150 °C. Results of this research are shown in Fig. 19.6. We need to recognize that the indicated effect limits the application of any thermal treatments during gas sensor fabrication. It was noted that the conductivity of PANICS A and PANI-p-TSA are the most stable below 200 °C, while the stability of PANI films doped with H SO and H PO are much better than the PANI-HCIO and PANI-HCl after thermal treatment at a high temperature (200 °C) (Li and Wan 1999). 

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The doping of the conducting polymer is generally obtained during the electropolymerization of the monomer, with perchlorate or sulphate anions for examples. The doping-dedoping process is essential for the electroactivity of the polymer. Various electro-active anionic species, such as tetrasulphonated metal... 

The adherence of the ECP to the metal, in particular when dedoping has occurred, is also extremely important, and critical for good protection, but, unfortunately, is not always specified. A thin passive interlayer firmly anchored to the metal and to the polymer, generally resulting from a precipitation reaction between the metal ion and the doping anion, may improve the adhesion of the material. Of course, this implies a suitable choice of the electrolyte, which will depend both on the monomer and on the metal. Thus, in the following, a distinction will be made between ferrous and nonferrous metals, but also between the most usual conducting polymers (PPy, PANI, PT, and derivatives). 

The nature of the electrolyte and its interaction with the electrode materials has a strong influence on the pseudocapacitive behavior and thus the pseudocapacitance. Therefore, the pseudocapacitive mechanism is briefly reviewed. As shown in Figure 1.7, there are several types of electrochemical processes that can contribute to the pseudocapacitance, including reversible adsorption of ions from the electrolyte, redox reactions involving ions from the electrolyte for some transition metal oxides, reversible electrochemical doping/dedoping in conductive polymer-based electrodes, and lattice intercalation [11,41,69,71]. 

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