Self-Templated Hierarchically Porous Carbon Nanorods Embedded with Atomic Fe-N₄ Active Sites as Efficient Oxygen Reduction Electrocatalysts in Zn-Air Batteries

Iron-nitrogen-carbon materials are being intensively studied as the most promising substitutes for Pt-based electrocatalysts for the oxygen reduction reaction (ORR). A rational design of the morphology and porous structure can promote the accessibility of the active site and the reactants/products transportation, accelerating the reaction kinetics. Herein, 1D porous iron/nitrogen-doped carbon nanorods (Fe/N-CNRs) with a hierarchically micro/mesoporous structure are prepared by pyrolyzing the in situ polymerized pyrrole on the surface of Fe-MIL-88B-derived 1D Fe₂O₃ nanorods (MIL: Material Institut Lavoisier). The Fe₂O₃ nanorods not only partially dissolve to generate Fe³⁺ for initiating polymerization but serve as templates to form the 1D structure during polymerization. Furthermore, the pyrrole coated Fe₂O₃ nanorod architecture prevents the porous structure from collapsing and protects Fe from aggregation to yield atomic Fe-N₄ moieties during carbonization. The obtained Fe/N-CNRs display exceptional ORR activities (E_1/2 = 0.90 V) and satisfactory long-term durabilities, exceeding those for Pt/C. Furthermore, the unprecedented Fe/N-CNRs catalytic performance is demonstrated with Zn-air batteries, including a superior maximum power density (181.8 mW cm⁻²), specific capacity (998.67 W h kg⁻¹), and long-term durability over 100 h. The prominent performance stems from the unique 1D structure, hierarchical pore system, high surface area, and homogeneously dispersed single-atom Fe-N₄ moieties.