Iron-based platinum group metal free (PGM-free) carbonaceous catalysts of a type commonly called “Fe-N-C” have high activity metals in the oxidation reduction reaction (ORR) in acid electrolytes. However, the durability of Fe-N-C catalysts is typically low. One puzzling feature of Fe-N-C catalysts is that they often – but not always – exhibit redox peaks near the expected potential of Fe²⁺ à Fe³⁺ + e^- (0.77 V vs. SHE). It has been observed that the absence of these peaks is correlated with improved catalytic performance. While the source of these peaks has not been identified rigorously as iron redox, it has been observed that the peaks appear in the presence of iron and do not appear in voltammograms of either N-C substrate alone or cobalt catalyst analogs (Co-N-C). Furthermore, the redox potential of these peaks shifts when the electrolyte is changed from sulfuric acid to perchloric acid, whereas the halfwave potential of the ORR does not change. What, then, is the source of these peaks? And does the redox event have significance to the catalytic mechanism? The study reported here investigates the effect of a series of acid electrolytes on the observed redox peaks, showing a progressive shift to lower potentials in perchloric, sulfuric, and phosphoric acids. Furthermore, these peaks are demonstrated to be absent in the case of N-C substrate alone. Addition of iron salts to the electrolytes results in the appearance of peaks in the voltammograms of N-C, with associated changes in the capacitance, indicating that the source of the peaks is surface-adsorbed iron salts. Therefore, the appearance of redox peaks is an indicator of the degradation of the catalyst and no change in the halfwave potential would be expected, as the adsorbed salts are not catalytically active.