Oxygen reduction on platinum electrode coated with Nafion

The kinetics of the reduction of oxygen on platinum covered by a Nafion ® film in sulfuric acid (0.5 M) has been studied in order to determine to what extent the solid polymer electrolyte modifies this reaction. As electrode we used a rotating electrode which is particularly well adapted to the measurement of the permeability D f C f (product of the diffusion coefficient and of the oxygen concentration in the film) of oxygen in the Nafion ® film. This product is of the order of 6×10 −12 M cm −1 s −1 whatever the state of division of the platinum, and is of the same order of magnitude as the permeability D s C s of oxygen in the adjacent sulfuric acid solution. It is shown, moreover, that the oxygen concentration in the film is very high, about five times that in the solution.