REDOX BEHAVIOR OF POLYPYRROLE FILMS IN DIFFERENT SOLVENTS

The redox behavior of polypyrrole (PPy) films has been examined by mea ns of cyclic voltammetry and SEM/EDS. PPy was galvanostatically prepar ed in acetonitrile (AN) containing tetrabutylammonium dodecylsulfate ( TBADS) as an electrolyte. Charge compensation mechanism of PPy films w hich incorporate dodecylsulfate (DS) ions was greatly influenced by th e solvents or electrolyte used in the redox reaction. When the PPy was switched between -0.8 V and 0.5 V in the TBADS/AN solution, bulky DS ions were participated in the redox reaction of the swollen PPy film. In the aqueous solution containing NaDS, on the other hand, Na cations worked as main charge-compensating ions because DS anions with long a lkyl chains were trapped in the contracted PPy and difficult to move d uring the switching process. However, DS ions in the TBADS/water solut ion should be the compensating ions to show higher oxidation potential s. When the free-standing films were reduced for 24 hours at -0.8 V ag ainst an Ag/AgCl reference electrode in the TBADS/AN solution, EDS sul fur concentration profiles showed that DS anions were removed from the films, which lead to a reduction in film thickness to two thirds of t he original thickness but in the aqueous solutions there was no change in film thickness upon reduction. The initial redox reaction in the T BADS/AN solution was most reversible and reactive but long term cyclab ility (electrochemical stability) of the PPy films in AN was inferior to that in water, which resulted from the morphological collapse durin g the repeated redox reaction.