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

Abstract

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–Nx 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–Nx 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–Nx 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–Nx 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.

Thermal Sugar Bubbling Preparation of N‐Doped Porous Carbon for High‐Performance Solid‐State Zn‐Air Batteries

“…The increasing intensity suggests the enhanced graphitic degree with increasing pyrolysis temperature, which would improve the electronic conductivity of carbon skeleton. X‐ray photoelectron spectroscopy (XPS) was utilized to analyze the chemical composition of NPC samples . The survey XPS of samples (Figure b and S3) exhibit the presence of carbon, nitrogen, and the adsorbed oxygen, which is in good agreement with the elemental mapping analysis.…”

Recent Advances on Non‐precious Metal Porous Carbon‐based Electrocatalysts for Oxygen Reduction Reaction

“…In which, metal‐nitrogen‐carbon (M−N−C, M=Fe, Co, etc) catalysts were considered as the most promising ORR electrocatalysts, and have attracted the most enormous interest of researchers in the past few years . Previous research revealed that the ideal ORR performance of M−N−C catalysts contributed to the exclusive active sites of surface nitrogen assorted with metal ,. What's more, the ORR activity of M−N−C catalysts were also influenced by carbon source, nitrogen source, the type of metal salt and the pyrolysis temperature, etc .…”

Towards High‐Performance Electrocatalysts for Oxygen Reduction: Inducing Atomic‐Level Reconstruction of Fe‐Nx Site for Atomically Dispersed Fe/N‐Doped Hierarchically Porous Carbon

“…[45] This result implied that the D3 site in Fe-N-HPC was probablyt ransformed into D1 and D2 sites for Fe-N-HPC-A during the acid-washing process. Althoughi ntensivei nvestigations have shown that post-treatment (i.e.,t he acid-washing and second heat-treatment)c an lead to an improvement of ORR activity, [46][47][48] the original reasonf or the enhanced activity is still ambiguous. [20] It may explaint he slightly inferior or almostu nchanged ORRa ctivity for Fe-N-HPC-A as compared with Fe-N-HPC.…”

“…[12,21] Besides, no obvious peak corresponding to the Fe-based crystalline phases( e.g.,F ea nd Fe 3 C) and less-activeD 2s ite were detected, suggesting the predominant presenceo fa ctive D1 andD 3s ites for Fe-N-HPC-AH. Althoughi ntensivei nvestigations have shown that post-treatment (i.e.,t he acid-washing and second heat-treatment)c an lead to an improvement of ORR activity, [46][47][48] the original reasonf or the enhanced activity is still ambiguous. In this work, we speculate that the significantly improved ORR activity is primarily attributed to the atomic-levelr econstruction of Fe-N 4 moieties with formation of absolutep resence D1 and D3 sites, inducedb ythe acid-washing and second heat-treatment.…”