Construction of Fe Nanoclusters/Nanoparticles to Engineer FeN4 Sites on Multichannel Porous Carbon Fibers for Boosting Oxygen Reduction Reaction

Abstract Fe–N–C catalysts are emerging as promising alternatives to Pt‐based catalysts for the oxygen reduction reaction (ORR), while they still suffer from sluggish reaction kinetics due to the discontented binding affinity between the Fe‐N 4 sites and oxygen‐containing intermediates, and unsatisfactory stability. Herein, a flexible multichannel carbon fiber membrane immobilized with atomically dispersed Fe‐N 4 sites and neighboring Fe nanoclusters/nanoparticles (FeN 4 ‐Fe NCP @MCF) is synthesized. The optimized geometric and electronic structures of the Fe atomic sites brought by adjacent Fe nanoclusters/nanoparticles and hierarchically porous structure of the carbon matrix endow FeN 4 ‐Fe NCP @MCF with outstanding ORR activity and stability, considerably outperforming its counterpart with FeN 4 sites only and the commercial Pt/C catalyst. Liquid and solid‐state flexible zinc–air batteries employing FeN 4 ‐Fe NCP @MCF both exhibit outstanding durability. Theoretical calculation reveals that the Fe nanoclusters can trigger remarkable electron redistribution of the FeN 4 sites and modulate the hybridization of central Fe 3 d and O 2 p orbitals, facilitating the activation of O 2 molecules and optimizing the adsorption capacity of oxygen‐containing intermediates on FeN 4 sites, and thus accelerating the ORR kinetic. This work offers an effective approach to constructing coupling catalysts that have single atoms coexisting with nanoclusters/nanoparticles for efficient ORR catalysis.