Oxygen reduction on Nafion-coated thin-film palladium electrodes

The electrochemical reduction of oxygen on thin Pd films with a nominal thickness of 0.25–10 nm was studied in alkaline and acidic solution using the rotating disk electrode (RDE) method. The Pd films on glassy carbon electrodes were prepared by electron beam evaporation and coated with a Nafion layer. The surface morphology of the films was examined by transmission electron microscopy (TEM). In 0.1 M KOH the electrocatalytic activity of Pd electrodes towards oxygen reduction was high and the specific activity (SA) did not depend on the film thickness. In 0.05 M H2SO4 the activity was lower and a decrease of SA with decreasing film thickness was observed. The oxygen reduction reaction on thin Pd films predominantly followed a four-electron pathway in both solutions and the reduction mechanism was similar to that on bulk Pd, the first electron transfer being the rate-limiting step.