Studies on the Electrochemical Preparation and Electrochemical Properties of Conducting Polymers——Brief Introduction to the Research Work of Electrochemistry of Conducting Polymers in CAS Key Laboratory of Organic Solids(I)
LI Yong-fange Academy of Sciences, Beijing 100080, China)
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Conducting polymers have drawn much attention since the discovery of conducting polyacetylene in 1977, due to the novelty and curiosity of their structure and properties as well as their promising applications in many aspects. Among the studies of conducting polymers, the electrochemical preparation and electrochemical properties of conducting polymers are of special importance, because the electropolymerization is a main method for preparing conducting polymer films and the electrochemical properties are the basis for their applications in the fields of electrode materials for batteries, electrocatalysis, electrochromic display, etc. We are one of the earliest research groups in the world to perform the studies of electrochemistry of conducting polymers. Starting from 1980s, we mainly studied the electrochemical polymerization processes of pyrrole and the electrochemical properties of conducting polypyrrole. The main achievements we obtained are as follows:In the studies on the electropolymerization processes of pyrrole: 1) An anion-participated electropolymerization mechanism of pyrrole was proposed and a kinetic equation of the electropolymerization was firstly deduced based on the mechanism; 2) Smooth, flexible and strong conducting polypyrrole (PPy) films (tensile strength reaches 127 MPa) were prepared electrochemically in aqueous solution by adding non-ionic surfactant OP_(10); 3) Effects of the electropolymerization conditions (anions, solvents, pH values of the eletropolymerization solutions, and the polymerization current, potential and temperature etc.) on the conductivity and mechanical strength of the as-prepared PPy films were investigated and optimized systematically. It was found that surfactant anions with concentration higher than 0.1 mol/L, low DN (donor number) solvent, acidic aqueous solution, lower temperature, appropriate current (～ 1 mA/cm) are the optimized conditions for the electropolymerization of highly conductive and flexible and strong PPy films. 4) A proton-acid doping structure was proposed and confirmed in the PPy prepared electrochemically, in addition to the doping structure with its oxidized conjugated chain. In the studies on the electrochemical properties of PPy: 1) Two redox processes of PPy corresponding to its two doping structures were observed, and the mechanisms of the electrochemical redox processes in aqueous and organic solutions were studied and elucidated by means of cyclic voltammetry, spectroelectrochemical measurement, electrochemical quartz crystal microbalance (EQCM) etc; 2) The over-potential phenomenon in the first cycle of the cyclic voltammograms of PPy prepared and measured in organic solutions was investigated and elucidated. 3) The electrochemical overoxidation degradation of PPy in aqueous solutions was studied. It was found that the overoxidation potential depends on the pH values of the aqueous solutions, the higher the pH value is, the lower the overoxidation potential will be. The mechanism of the overoxidation was proposed to be related to the oxygen produced by the electrolysis of the aqueous solutions.In addition, the stabilities of conducting polymers in aqueous solutions and in air were elucidated from the electrochemical point of view, and the electrochemical properties of polyaniline (PAn) were also studied and the mechanisms of the redox processes of PAn were elucidated by spectroelectrochemical measurement.