Atomic Edge Fe-N₄ Active Sites on N-Doped Porous Carbon Nanosheets Derived from Zeolitic-Imidazolate Frameworks for High-Efficiency Oxygen Reduction

Abstract

Defect and morphology engineering of metalnitrogen codoped carbon (M-N/C) has been proven to be efficacious in promoting the oxygen reduction reaction (ORR) catalytic activity, yet the simultaneous construction of active sites with high intrinsic activity and efficient exposure is a challenge. Herein, an Fe-N/C catalyst consisting of edge Fe-N 4 sites atomically dispersed on porous carbon nanosheets (e-Fe-N/C NS ) is designed for high intrinsic catalytic active as well as efficient utilization. By combining an edge-doping process and an I 2 -etching effect, the edge Fe-N 4 sites are constructed preferentially and the interior active sites are fully exposed. The edge Fe-N 4 sites endow e-Fe-N/C NS with high intrinsic activity, which originated from the local electronic redistribution of the Fe-N 4 configuration induced by the edge carbon, while the enriched porous nanosheet structure enhances the edge Fe-N 4 sites utilization efficiency for high mass activity. The as-synthesized e-Fe-N/C NS exhibits a remarkable halfwave potential (E 1/2 , 0.90 V RHE ) under alkaline conditions. This work provides a novel synthetic method for designing highly active defective sites in catalysts for energy conversion systems.

Iron Monomers or Trimers on Nitrogen-Doped Carbon: Which Is Better for the Electrocatalytic Nitrogen Reduction Reaction?

“…The N 1s signals can be described as three types of nitrogen species, i.e., pyridinic N (398.68 eV), pyrrolic N (400.80 eV), and graphitic N (402.79 eV), , and their relative contents are listed in Table S1. Previous reports have shown that pyridinic N might serve as anchor points for Fe atoms. − Remarkably, we did not detect any Fe 2p signal in the XPS spectra in both Fe 3 ACCs and Fe SACs, likely due to the low Fe loading …”

Regulating the Electronic Configuration of Single-Atom Catalysts with Fe–N5 Sites via Environmental Sulfur Atom Doping for an Enhanced Oxygen Reduction Reaction

“…Owing to their superior catalytic activity, structural stability, and cost-effectiveness, atomically dispersed single-atom catalysts (SACs) with nitrogen-coordinated metal sites (M-N x –C) have been considered the most promising Pt-based alternatives for the ORR among various PGM-free electrocatalysts. − Both the active site density and the intrinsic activity are crucial for acquiring a high catalytic activity of SACs. Recently, significant progresses have been made in achieving high site densities and an increased intrinsic activity of M–N–C catalysts. − Excessive amounts of the metal source were generally added to obtain high-density M-N x sites, which usually led to metal-atom agglomeration and nanoparticle formation during pyrolysis, thus resulting in the low utilization of active sites and an impeded mass transfer for the ORR. , In this respect, the catalyst performance for the ORR could be improved by increasing the catalyst intrinsic activity while ensuring the monoatomic dispersion of M-N x sites. The modulation of coordination environments around the M-N x sites either from the first coordination shell (coordination atoms and coordination numbers) or the peripheral shell (heteroatom doping and local carbon structure) enabled the precise tailoring of the electronic structure of SACs, which influenced their interaction with oxygen intermediates, thus performing an efficient ORR. , …”