Advanced Fe–N-doped graphene (FeNG) electrocatalysts are developed for the oxygen reduction reaction (ORR) by annealing a mixture of sustainable and low-cost corn starch, urea, and FeCl₃. The Fe–N coordinations and Fe/Fe₃C nanoparticles can be controllably achieved through space confinement and pyrolysis temperature-induced effects, respectively. Electrochemical tests show that, compared to the commercial Pt/C catalyst, the ORR half-wave potential of FeNG is 99 mV more positive in KOH and 34 mV more negative in H₂SO₄, with higher stabilities in both media. More importantly, the ORR mechanisms of FeNG are demonstrated to be diverse in both KOH and H₂SO₄, owing to the various catalytic centers. The obtained results indicate that the enhanced ORR activity in basic media can mainly be ascribed to quaternary N and Fe/Fe₃C sites, whereas the ORR performance in acidic media originates primarily from Fe–N_X complexes. The electrocatalytic origin of these species is governed, primarily, by their unique electronic structures and specific environments in different pH solutions.