A voltammetry study on the diffusion of counter ions in polypyrrole films

Polypyrrole (PPy) films doped with large immobile dodecyl benzene sulfonate (DBS) anions have been cycled in electrolytes of different concentration in an investigation of the diffusion of counter ions in this polymer complex. The diffusion of counter ions determines the speed of response of the films when they are used in artificial muscles or as electrodes in batteries and other devices. For the present study, PPy/DBS films were electro-polymerized on platinum wires and cycled in aqueous solutions of NaCl of concentrations ranging from 0.1 M to 5 M. Significant changes in the redox properties of the films were observed with the increase of the concentration. The effective diffusion coefficients in 0.1 M, 1 M and 3 M NaCl are nearly 3 × 10 −12 m 2 s −1, 20 × 10 −12 m 2 s −1 and 55 × 10 −12 m 2 s −1, respectively. The diffusion coefficient in 3 M NaCl is approximately 18 times the value in 0.1 M NaCl reflecting that the amount of salt and solvent taken up by the polymer is linked to the electrolyte composition by osmotic balances. These findings have implications for the design of polypyrrole based electrodes and actuators that are required to operate at higher frequencies.