Heterointerfaces regulating the 3d-orbital electronic structure of FeN4 for enhanced oxygen reduction electrocatalysis

Optimizing the oxygen reduction reaction (ORR) kinetics requires precise control of intermediate adsorption at active sites, which can be achieved through orbital engineering by regulating the electronic structure. This study addresses the challenge by exploring how modulation of the 3d-orbital electronic structure of FeN4 active sites influences ORR electrocatalysis. To realize this, a catalyst composed of Fe3C nanoparticles and FeN4 single atoms anchored on carbon black (Fe3C-FeN4/CB) was synthesized via a synergistic strategy of spatial confinement and atmosphere control. This unique heterostructure creates interfaces between Fe3C and FeN4 that modulate the electronic configuration of the FeN4 center, transforming its geometry from square-planar to quasi-octahedral. Spectroscopic characterizations and theoretical calculations reveal that this orbital modulation results in a downward shift of the Fe d-band center, altering the reaction pathway and lowering the energy barrier for ORR. Consequently, the Fe3C-FeN4/CB catalyst exhibits outstanding ORR activity, four-electron selectivity, excellent methanol tolerance, and remarkable electrochemical stability. When applied in a zinc-air battery, it achieves a peak power density of 178.4 mW cm−2 and superior cycling stability compared to commercial Pt/C catalysts. This work provides valuable insights into heterointerface-induced orbital modulation as a promising design principle for high-performance ORR electrocatalysts.