Research On The Electrochemical Behaviour Of Conducting Polypyrrole

Due to the special structure and the excellent physical chemical properties, conducting polymers have attracted great interest in many applied fields such as metal protection, energy, optoelectronic devices, molecular devices, electromagnetic shielding, stealth technology etc. The electrochemical properties of conducting polymers are very complex and have not yet been fully understood, and thus are still open for further investigation. Polypyrroly (PPy) is one of the most studies and promising candidates among these conducting polymers, due to outstanding electrochemical characteristics. In this work, PPy films have been electrodeposited on stainless steel in 0.06 mol L-1 pyrrole + 0.1 mol L-1 sodium dodecylbenzenesulfonate solution, and prepared a PPy free-standing film electrode. The electrochemical properties of PPy have been investigated by methods such as potentiodynamic polarisation curve, voltammetry curve, open circuit potential-time curve, electrochemical impedance spectroscopy, Chronopotentiometry and infrared spectrum etc.Galvanic Anodic Protection of stainless steel in 1 mol L-1 H2SO4 solution by the PPy film electrode is investigated.when the galvanic coupling interaction between the PPy film electrode and stainless steel, the area ratio of PPy film and stainless steel must be made up of large cathode - small Anode configuration, and it might be protect stainless steel. If the area ratio is large enough (above 201:1), the PPy film can passivate stainless steel and maintain it in passivation area more time.The influence of electrode potential on the redox of PPy in 3.5% NaCl solution is investigated. Results show that electrode reaction is not diffusion control; PPy films were firstly polarized at -0.8 V for 10 min to reach full reduce state, then potentiostatic anodic polarizations were performed. It is found that film resistance evolution as a function of time shows exponential decay. The relation equation between film resistance and time was analyzed in theory, Rf = Rf0 + Aexp(-t / k). the more higher the potential, the shorter the half-life, the lower the resistance of PPy. The potentiometric responses are affected by the concentration of redox reactants. According to the linear fitting calculation, it is proved that the redox reaction of PPy is bipolaron mechanism.The effect of anion and cation on the electrochemical behavior of PPy in aqueous solution have been studied by cyclic voltammetry, and the concentration of Na+ affects on the electrode potential of PPy films. Results show that the kind of anions are not influencing the ion-exchange process on the PPy film basically, the shape and evolution of the voltammograms during cycling depend strongly on the kind of cations. In PPy films the transport of cations like Na⁺ or NH₄⁺ is dominant, but the larger the volume and steric hindrance of cations, the more difficulty the ion-exchange. The redox response of PPy cycled in cetyltrimethyl ammonium chloride solution is due to the transport of Cl^-. The potential of PPy was a Nernst response to Na+ concentration between 1×10^-4 mol L^-1 and 1 mol L-1 NaCl solution. According to the linear fitting calculation, it is further proved that the redox reaction of PPy is bipolaron mechanism.The influences of pH value on properties for PPy film in 1 mol L^-1 NaCl were investigated. Results show that line slope of potential-pH curve is -0.029 V/pH for pH < 11, and is -0.083 V/pH for pH > 11.it is proved that In acidic solution, proton-acid doping occurs and film conductivity increases, While in alkaline solution, PPy films are de-protonated and confronted over-oxidization thereby becoming less conductivity by infrared spectrum, EIS, voltammetry curve. The higher the value of pH is, the more positive the initial potential and peak potential are. Infrared spectrum also shows that parts of PPy film were over-oxidized and dodecylbenzenesulfonate was inserted in PPy film during electropolymerization process.