Modulating the Iron Microenvironment for a Cooperative Interplay Between Fe-N-C Single Atoms and Fe 3 C Nanoclusters on the Oxygen Reduction Reaction

The coexistence of single atoms and nanoparticles is shown to increase the oxygen reduction performance in Fe-N-C electrocatalysts, but the mechanisms underlying this synergistic effect remain elusive. In this study, model Fe-N-C electrocatalysts with controlled ratios of FeN sites and Fe C nanoclusters is systematically designed and synthesized. Experiments and density functional theory (DFT) computations reveal that Fe C nanoclusters near FeN sites modulate the electron density of the Fe single-atom microenvironment through an electron withdrawing effect. This substantially alters the oxygen reduction reaction (ORR) mechanisms and boosts the catalytic performance of FeN sites. This study provides fundamental insights into the dynamic catalytic impact of single atoms and nanoparticle coexistence in advanced Fe-N-C electrocatalysts for the ORR, paving the way for further refinement through various combinations.