Abstract
The primary objectives of the work described in this paper were to evaluate the concentration and diffusion coefficient of 
in a commercial perfluorosulfonate ionomer (Nafion) and to assess the effect of a film of this ionomer on the rate of 
reduction at a substrate Pt electrode surface. Electrochemical experiments at Nafion film‐coated electrodes were used to obtain these data. A high temperature film‐casting procedure, which has been shown to yield high quality solution‐cast Nafion films, was used to prepare the Nafion‐coated electrodes. The Nafion film‐coated electrodes were equilibrated with and exposed to 
during the electrochemical experiments; it was of particular interest to compare the diffusion, solubility, and kinetic data obtained at the film‐coated electrode to analogous data obtained at a bare electrode, exposed to this electrolyte. We have found that the diffusion coefficient is lower in Nafion than in the electrolyte solution but that the solubility and oxygen reduction rate are higher.