REDOX BEHAVIOR OF POLYPYRROLE FILMS IN DIFFERENT SOLVENTS

Abstract

The redox behavior of polypyrrole (PPy) films has been examined by means of cyclic voltammetry and SEM/EDS. PPy was galvanostatically prepared in acetonitrile (AN) containing tetrabutylammonium dodecylsulfate (TBADS) as an electrolyte. Charge compensation mechanism of PPy films which incorporate dodecylsulfate (DS) ions was greatly influenced by the 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 alkyl chains were trapped in the contracted PPy and difficult to move during the switching process. However, DS ions in the TBADS/water solution should be the compensating ions to show higher oxidation potentials. When the free-standing films were reduced for 24 hours at -0.8 V against an Ag/AgCl reference electrode in the TBADS/AN solution, EDS sulfur concentration profiles showed that DS anions were removed from the films, which lead to a reduction in film thickness to two thirds of the original thickness but in the aqueous solutions there was no change in film thickness upon reduction. The initial redox reaction in the TBADS/AN solution was most reversible and reactive but long term cyclability (electrochemical stability) of the PPy films in AN was inferior to that in water, which resulted from the morphological collapse during the repeated redox reaction.