Pyrolysis-Mediated Polycyano Strategy for Directed Construction of Fe3C-Synergized Fe─N Carbon Nanotubes Heterostructure Toward High-Efficiency Oxygen Reduction Reaction.

Precise modulation of the coordination environment of Fe─Nx sites is crucial yet challenging for enhancing the intrinsic activity of single-atom Fe/N-codoped carbon catalysts toward the oxygen reduction reaction (ORR). Herein, N-doped carbon nanotubes embedded with Fe3C nanoparticles with abundant pyridinic-N and Fe─Nx active sites are prepared by simple pyrolysis of precursors containing Zn2+/Fe2+ and cyano groups. The optimized Fe3C/FeN@CNT-900 catalyst exhibits a remarkable ORR half-wave potential (E1/2) of 0.89 V versus RHE, along with exceptional methanol tolerance and SCN- resistance. The power density of the zinc-air battery with this cathode achieves 1.65 times of that of the battery using the Pt/C+RuO2 catalyst. Experimental and theoretical analyses reveal that these enhancements arise from tailored electronic structures and optimized intermediate adsorption at Fe active centers. Synergistic catalysis between atomic Fe─Nx sites and Fe3C nanoparticles lowers the energy barrier of the ORR rate-determining step by facilitating interfacial electron transfer, as evidenced by density functional theory calculations. This work provides a rational strategy for designing high-performance dual-active sites in metal-nitrogen-carbon electrocatalysts and highlights the critical role of atomic-nanoparticle interactions in advanced energy conversion systems.