Abstract
Fe-based catalysts for the reduction of oxygen were synthesized by wet-impregnation of FeII acetate or FeIII-porphyrin on pristine carbon black followed by pyrolysis in ammonia or argon. The catalysts were characterized using RDE and RRDE voltammetry in both acid and alkaline electrolytes. The results support the presence of two types of active sites for oxygen reduction in these catalysts: (i) the Fe-N4/C type, with a structure resembling the central porphyrin moiety, and (ii) the Fe-N2+2/C type, hosted in the micropores of the carbon support. Fe-N4/C sites are poorly active in acid but highly active in alkaline, whereas Fe-N2+2/C sites are highly active in both electrolytes.
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