Synergies of Fe Single Atoms and Clusters on N-Doped Carbon Electrocatalyst for pH-Universal Oxygen Reduction.

Single atomic metal-N-C materials have attracted immense interest as promising candidates to replace noble metal-based electrocatalysts for the oxygen reduction reaction (ORR). The coordination environment of metal-N-C active centers plays a critical role in determining their catalytic activity and durability, however, attention is focused only on the coordination of metal atoms. Herein, Fe single atoms and clusters co-embedded in N-doped carbon (Fe/NC) that deliver the synergistic enhancement in pH-universal ORR catalysis via the four-electron pathway are reported. Combining a series of experimental and computational analyses, the geometric and electronic structures of catalytic sites in Fe/NC are revealed and the neighboring Fe clusters are shown to weaken the binding energies of the ORR intermediates on Fe-N sites, hence enhancing both catalytic kinetics and thermodynamics. This strategy provides new insights into the understanding of the mechanism of single atom catalysis.