The activity of Pt supported on Vulcan XC-72R carbon catalyst for oxygen reduction in the absence and presence of dissolved Fe in 0.5 M H2SO4 was measured. The Pt/C catalyst in sulfuric acid with dissolved Fe in the electrolyte was far more active for oxygen reduction than those without dissolved Fe. The activity of Pt/C for oxygen reduction in 0.5 M H2SO4 in the presence of 100 ppm dissolved Fe is doubled at 70 degrees C, O-2 at 0.6 V vs. a standard hydrogen electrode. The mechanism of enhancement is due to the reaction of dissolved Fe and H2O2 to form Fe(III) hydroperoxy complexes, followed by the heterogeneous decomposition on Pt to release O-2.