Oxygen Reduction on Transition‐Metal Porphyrins in Acid Electrolyte I. Activity

The oxygen reduction characteristics of metalloporphyrins adsorbed at monolayer levels on a high surface area carbon, Norit BRX, have been studied in 8 N H 2 SO 4 and also in 6N KOH. In an acid, oxygen reduction activity is found to be correlated with the Me II /Me III redox potential. Most Co complexes have too high a redox potential, while too low a redox potential is observed for Fe, Ru, Os, Mn, and Cr. Ir porphyrins have the highest activity. In KOH, Ru porphyrins show the best performance. A heat treatment improves activity and stability strongly in an acid, but only mildly in an alkaline solution. A mechanism is proposed for oxygen reduction on transition metal chelates, both in acid and in alkaline solutions.