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Efficient, durable, and inexpensive electrocatalysts are recommendable for accelerating the kinetics of oxygen reduction reaction and achieving high performance. Herein, with predesigned hierarchically porous silica nanorods as a hard template, hierarchically macro-bimodal meso/microporous 3D carbon interwoven nanorod networks containing a high content of single-atom FeNx species (Fe/RNC) were prepared by melting of precursors and confined pyrolysis within the pores of the hard template. What distinguishes the use of silica nanorods as a hard template is that it not only provides a porous texture for confined pyrolysis of the precursors but also the interwoven texture of the nanorods gives rise to a macroporous mesh-like morphology. Benefiting from the ultrahigh iron content (5.69 wt %) of the FeNx sites, a 3D porous network configuration with high accessibility of active centers, as well as a high specific surface area of 793 m2g–1, the as-prepared Fe/RNC exhibited superior activity and durability for ORR and zinc–air batteries. For comparison, the catalyst Fe/NC-MCM, which was prepared with a similar procedure but with unimodal mesoporous silica MCM-41 nanoparticles as the hard template, possesses a less porous structure and active accessibility and thus exhibits inferior ORR activity. This work provides an effective design/nanoengineering for electrocatalysts in ORR and zinc–air batteries and will inspire more research on accessibility of active sites in non-noble carbon-based electrocatalysts.

Heteroatom-doped carbon-based transition-metal single-atom catalysts (SACs) are promising electrocatalysts for oxygen reduction reaction (ORR). Herein, with the aid of hierarchically porous silica as hard template, a facile and general melting perfusion and mesopore-confined pyrolysis method was reported to prepare single-atomic Fe/N-S-doped carbon catalyst (FeNx/NC-S) with hierarchically porous structure and well-defined morphology. The FeNx/NC-S exhibited excellent ORR activity with a half-wave potential (E1/2) of 0.92 V, and a lower overpotential of 320 mV at a current density of 10 mA cm-2for OER under alkaline condition. The remarkable electrocatalysis performance can be attributed to the hierarchically porous carbon nanospheres with S doping and high content of Fe-Nx sites (up to 3.7 wt% of Fe), resulting from the nano-confinement effect of the hierarchically porous silica spheres (NKM-5) during the pyrolysis process. The rechargeable Zn-air battery with FeNx/NC-S as a cathode catalyst demonstrated a superior power density of 194.5 mW cm-2charge-discharge stability. This work highlights a new avenue to design advanced SACs for efficient sustainable energy storage and conversion.