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Some FeTPP−Cl/carbon electrocatalysts, heat-treated at temperatures up to 800 °C, have been studied with cyclic voltammetry, x-ray photoelectron spectroscopy, extended X-ray absorption fine structure, and in situ Mössbauer 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 O2 but that they operate according to the well-known redox mechanism.
Bouwkamp-Wijnoltz et al. (Wed,) studied this question.