Oxygen reduction on a graphite paste and a catalyst loaded graphite paste electrode

Abstract

Oxygen reduction was studied in basic solution at a graphite paste electrode (GPE). The GPE was used as the disk of a rotating ring disk electrode (RRDE) and experiments were done using the voltage scan technique. The enhancements afforded by catalysts applied to the GPE were also studied. Oxygen reduction on a GPE was shown to be a two-electron process resulting in the formation of peroxide. The Tafel slope (plotted as potential versus log(i/sub l/ x i/(i/sub l/ - i))) was 180 mV. The presence of gold, silver, or platinum on the GPE shifted the oxygen reduction wave approximately 800 mV in the anodic direction. Comparison of the data on a metal catalyzed GPE to the solid metal electrode showed that the former electrode produced a greater fraction of peroxide as product than did the latter. Silver and gold catalyzed GPEs gave Tagel slopes of about 120 mV. The intermediate catalysis of iron and cobalt porphyrin was also examined. While the cobalt porphyrin catalyzed oxygen reduction at a more anodic potential than the iron porphyrin, the latter appeared more active in reacting the peroxide formed as the product of the disk reaction.