On active-site heterogeneity in pyrolyzed carbon-supported iron porphyrin catalysts for the electrochemical reduction of oxygen: An in situ Mossbauer study

Some FeTPP-Cl/carbon electrocatalysts, heat-treated at temperatures up to 800 degreesC, have been studied with cyclic voltammetry, x-ray photoelectron spectroscopy, extended X-ray absorption fine structure, and in situ Mossbauer spectroscopy. It appears that the heat treatment induces considerable site heterogeneity in electronic terms, although structurally the Fe-N4 moiety seems persistent. The data indicate that only part of these Fe-N4 sites contributes to the activity for the electrochemical reduction Of O-2 but that they operate according to the well-known redox mechanism.