Confined ComplexationInduced Size Control of Fe/Fe₂O₃/Fe₅C₂ Multicomponent NanoparticlesEmbedded in Fe, N‑Doped Mesoporous Carbon toward EfficientOxygen Electrocatalysis

Controlling particle size and phase hybridization in metal-compound-based catalysts is crucial for optimizing oxygen catalytic activity in zinc-air batteries (ZABs), yet precise regulation remains a substantial challenge. In this work, a novel confined complexation-calcination method is explored to synthesize a series of size-controllable Fe/Fe₂O₃/Fe₅C₂ multicomponent nanoparticles embedded in Fe, N-doped mesoporous carbon (Fe–N–C). By modulation of the size of nitrogen-source ligands during confined complexation, the particle size and dispersion of Fe/Fe₂O₃/Fe₅C₂ are precisely regulated, resulting in varied oxygen electrocatalytic performances. Notably, the electrocatalyst synthesized using a medium-sized nitrogen-source ligand 1,10-phenanthroline (Fe/Fe₂O₃/Fe₅C₂/Fe–N–C (PEN)) demonstrates the smallest particle size (∼19 nm) and superior dispersion of Fe/Fe₂O₃/Fe₅C₂, which not only increases the exposure of active sites but also enhances charge/mass transfer efficiency. The optimized Fe/Fe₂O₃/Fe₅C₂/Fe–N–C (PEN) shows excellent catalytic activity for oxygen reduction reaction with a half-wave potential of 0.835 V vs RHE. In addition, high stability and good activity for oxygen evolution reaction are also demonstrated, establishing it as an ideal bifunctional catalyst for secondary ZABs. The assembled ZAB achieves a peak power density of 148.9 mW cm^–2, surpassing that of its Pt/C-based counterpart. This work provides new insights into precise particle size control of advanced electrocatalysts for sustainable energy applications.