Fresh Look at Transport in Perfluorosulfonate Ionomers: Ultramicroelectrode Investigations of Nafion and Dow Ionomers

摘要

Chronoamperometry at ultramicroelectrodes is a powerful and convenient technique for the determination of apparent diffusion coefficients and concentrations of electroactive cations ion-exchanged into Nafion and Dow perfluorosulfonate films. This technique offers tremendous advantages over the conventional electrochemical methods which employ film coated macro sized electrodes. These advantages stem from the elimination of iR distortion at the ultramicroelectrode and from the ability to determine both the concentration and apparent diffusion coefficient of the electroactive cation from a single experiment. Further improvements over the conventional approach were achieved by eliminating coupled diffusion and migration contributions to the measured current response. Under these conditions, charge is transported via ionic diffusion rather than through electron hopping. Furthermore, the apparent diffusion coefficients decrease with increasing concentration of the electroactive cation in the film. Keywords: Perfluorosulfonate ionomers; Microelectrode; Nafion; Dow ionomers; Chronoamperometry; Apparent diffusion coefficients, Sulfonates. (mjm)