Catalysts for the oxygen reduction reaction (ORR) were prepared on carbon black (C) using Fe(II)phthalocyanine (FePc) and CI-Fe(III)tetramethoxyphenylporphyrin (CIFeTMPP), as Fe precursors with and without a pyrolysis step at 800 degrees C. CO poisoning of the ORR catalytic sites for all these Fe/N/C electrocatalysts was attempted at pH 1 and 13, but to no avail, even if an iron ion is known to occupy the center of the active sites in at least the unpyrolyzed FePc/C or CIFeTMPP/C. The exact nature of the active center of these Fe-based heat-treated catalysts may still be a subject of debate but, in light of the absence of CO poisoning for unpyrolyzed FePc/C and CIFeTMPP/C, resistance to CO poisoning by the heat-treated catalysts cannot be used as evidence that the active center of their catalytic site is devoid of iron. (c) 2010 Elsevier B.V. All rights reserved.