3D Space-Confined Pyrolysis of Double-Network Aerogels Containing In-Fe Cyanogel and Polyaniline: A New Approach to Hierarchically Porous Carbon with Exclusive Fe-Nx Active Sites for Oxygen Reduction Catalysis

Iron and nitrogen co-doped carbon (Fe-N/C) nanomaterials are promising non-Pt catalysts toward the oxygen reduction reaction (ORR). Both spectroscopy and density functional theory studies reveal that Fe-N-x accounts for the ORR activity. However, Fe-N/C catalysts prepared by traditional high-temperature pyrolysis always contain less active Fe or Fe3C nanoparticles, and it remains a great challenge to obtain Fe-N/C catalysts with high-content Fe-N-x active sites. Herein, a 3D space-confined strategy for the pyrolysis of double-network aerogels is reported, to obtain Fe-N/C network catalysts with exclusive Fe-N-x active sites without the generation of Fe or Fe3C nanoparticles. The as-prepared Fe-N/C network exhibits more positive half-wave potential, higher diffusion-limited current density, and better selectivity for the ORR than catalysts derived from single aerogels and commercial Pt/C. Additionally, the ORR activity measured in potassium thiocyanate (KSCN) poisoned electrolyte corroborates that Fe-N-x is the active site. This work opens a new guideline for designing the M-N/C catalysts with exclusive active sites in porous carbon matrices for boosting energy electrocatalysis.