Doping mechanism of PPy/LiDS film in aqueous solutions

We studied electrochemical redox reaction of polypyrrole (PPy) films prepared in an aqueous lithium dodecylsulfate (LiDS) solution by means of cyclic voltammetry, Auger electron spectroscopy, electrochemical quartz crystal microbalance and atomic force microscope, and presented a new doping–dedoping mechanism of PPy/LiDS film associated with the movement of DS−. During a potentiodynamic polymerization of PPy/LiDS, an additional small cathodic peak appeared at −0.37 V in addition to the main redox peaks at −0.81 V. PPy/LiDS film prepared under a galvanostatic condition also showed the additional cathodic peak, too. EQCM results indicated that the main redox peaks were due to the fast movement of small Li+ while the additional peaks were associated with the movement of DS− despite of its large molecular size. In potentiostatic condition the movement of DS− could be found even in negative potential region (−0.8 V) where the movement of Li+ is dominant for potentiodynamic condition. Thus, both cations and anions were involved in the redox process of PPy/LiDS film but the mobility of DS− was controlled by scan rate of potential due to its bulkiness.