High-Performance Fe-N-Doped Graphene Electrocatalysts with pH-Dependent Active Sites for the Oxygen Reduction Reaction

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 99mV more positive in KOH and 34mV 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.