Building Fe atom-cluster composite sites using a site occupation strategy to boost electrochemical oxygen reduction

The high-temperature pyrolysis process for preparing M-N-C single-atom catalyst usually results in high heterogeneity in product structure concurrently contains multiscale metal phases from single atoms (SAs), atomic clusters to nanoparticles. Therefore, understanding the interactions among these components, especially the synergistic effects between single atomic sites and cluster sites, is crucial for improving the oxygen reduction reaction (ORR) activity of M-N-C catalysts. Accordingly, herein, we constructed a model catalyst composed of both atomically dispersed FeN4 SA sites and adjacent Fe clusters through a site occupation strategy. We found that the Fe clusters can optimize the adsorption strength of oxygen reduction intermediates on FeN4 SA sites by introducing electron-withdrawing -OH ligands and decreasing the d-band center of the Fe center. The as-developed catalyst exhibits encouraging ORR activity with half-wave potentials (E1/2) of 0.831 and 0.905 V in acidic and alkaline media, respectively. Moreover, the catalyst also represents excellent durability exceeding that of Fe-N-C SA catalyst. The practical application of Fe(Cd)-CNx catalyst is further validated by its superior activity and stability in a metal-air battery device. Our work exhibits the great potential of synergistic effects between multiphase metal species for improvements of single-atom site catalysts. We designed Fe(Cd)-CNx catalysts composed of Fe single atoms and adjacent Fe clusters. The interaction between Fe clusters and satellite FeN4 sites drives the catalyst to exhibit ultrahigh ORR activity and durability in acidic and basic media. Zinc-air cells in a liquid or flexible solid state with Fe(Cd)-CNx as the cathode exhibit high power density and long-term stability. image