Promoting the catalyst performance for oxygen reduction reaction (ORR) in energy conversion devices through controlled manipulation of the structure of catalytic active sites has been a major challenge. In this work, we prepared Fe−N−C single-atom catalysts (SACs) with Fe−N 5 active sites and found that the catalytic activity of the catalyst with shrinkable Fe−N 5 −C 11 sites for ORR was significantly improved compared with the catalyst bearing normal Fe−N 5 −C 12 sites. The catalyst C@PVI-(TPC)Fe-800, prepared by pyrolyzing an axial-imidazole-coordinated iron corrole precursor, exhibited positive shifted half-wave potential (E 1/2 = 0.89 V vs RHE) and higher peak power density (P max = 129 mW/cm 2 ) than the iron porphyrin-derived counterpart C@PVI-(TPP)Fe-800 (E 1/2 = 0.81 V, P max = 110 mW/cm 2 ) in 0.1 M KOH electrolyte and Zn−air batteries, respectively. X-ray absorption spectroscopy (XAS) analysis of C@PVI-(TPC)Fe-800 revealed a contracted Fe−N 5 −C 11 structure with iron in a higher oxidation state than the porphyrin-derived Fe−N 5 −C 12 counterpart. Density functional theory (DFT) calculations demonstrated that C@PVI-(TPC)Fe-800 possesses a higher HOMO energy level than C@PVI-(TPP)Fe-800, which can increase its electron-donating ability and thus help achieve enhanced O 2 adsorption as well as O−O bond activation. This work provides a new approach to tune the active site structure of SACs with unique contracted Fe−N 5 −C 11 sites that remarkably promote the catalyst performance, suggesting significant implications for catalyst design in energy conversion devices.

P-doped PtNi alloy loaded on N,C-doped TiO2 nanosheets (P-PtNi@N,C-TiO2) exhibited excellent activity and durability for oxygen reduction reaction (ORR) in 0.1 M HClO4 solution with mass (4) and specific (6)...

Developing efficient non‐precious metal electrocatalysts to replace Pt‐based noble metal catalysts for oxygen reduction reaction (ORR) in energy conversion devices is highly desirable. Atomically dispersed Fe−N−C catalysts are the most promising alternatives of Pt for ORR; however, enhancing their intrinsic activity via active site modulation is still a challenge. Using an iron porphyrin‐functionalized MOFs as the precursor, we prepared a defects‐rich Fe−N−C catalyst and modulated its intrinsic activity by creating defects near the Fe−Nx sites through decarboxylation reaction. Due to the synergistic effect of the improved porous structure and created defects, the prepared Defects‐FeNC exhibited excellent performance for ORR with half‐wave potential of 0.895 V vs. RHE in alkaline media. The Defects‐FeNC loaded Zn‐Air battery delivered much higher open circuit potential (OCP=1.463 V) and maximum power density (Pmax=151 mW cm−2) than the commercial 20 wt.% Pt/C (OCP=1.441 V; Pmax=119 mW cm−2) under similar experimental conditions. Defects in the catalyst could modulate the electronic structure of the Fe−Nx−C center that further promoted the catalyst catalytic activity for ORR. This work provides a facile active‐sites‐engineering approach for boosting the Fe−N−C catalyst ORR performance, which shows promising implications in energy conversion devices.