Engineering Favorable Morphology and Structure of Fe‐N‐C Oxygen‐Reduction Catalysts through Tuning of Nitrogen/Carbon Precursors

Abstract

Structures and morphologies of Fe-N-C catalysts are believed to be crucial because of the number of active sites and local bonding structures governing the overall catalyst performance for the oxygen reduction reaction (ORR). However, the knowledge how to rationally design catalysts is still lacking. By combining different nitrogen/carbon precursors, including polyaniline (PANI), dicyandiamide (DCDA), and melamine (MLMN), we aim to tune catalyst morphology and structure to facilitate the ORR. Instead of the commonly studied single precursors, multiple precursors were used during the synthesis; this provides a new opportunity to promote catalyst activity and stability through a likely synergistic effect. The best-performing Fe-N-C catalyst derived from PANI+DCDA is superior to the individual PANI or DCDA-derived ones. In particular, when compared to the extensively explored PANI-derived catalysts, the binary precursors have an increased half-wave potential of 0.83 V and an enhanced electrochemical stability in challenging acidic media, indicating a significantly increased number of active sites and strengthened local bonding structures. Multiple key factors associated with the observed promotion are elucidated, including the optimal pore size distribution, highest electrochemically active surface area, presence of dominant amorphous carbon, and thick graphitic carbon layers with more pyridinic nitrogen edge sites likely bonded with active atomic iron.

Binary Nitrogen Precursor-Derived Porous Fe-N-S/C Catalyst for Efficient Oxygen Reduction Reaction in a Zn-Air Battery

“…The synergetic effects of N, S co-doping would significantly improve the ORR activity by reducing the electron localization around the Fe centers, and improve the interaction with oxygen, facilitating the four-electron pathway [34]. The high-resolution Fe 2p spectrum of Fe/NS/C-g-C 3 N 4 /TPTZ-1000 presents two major peaks at around 711 and 724 eV, corresponding to Fe 2p 1/2 and Fe 2p 3/2 , respectively (Figure 6f) [15,35]. The dominant peak at 711 eV can be assigned to Fe 3+ or Fe 2+ coordinated with N, which are suggested to be the ORR active centers [15,36].…”

“…The high-resolution Fe 2p spectrum of Fe/NS/C-g-C 3 N 4 /TPTZ-1000 presents two major peaks at around 711 and 724 eV, corresponding to Fe 2p 1/2 and Fe 2p 3/2 , respectively (Figure 6f) [15,35]. The dominant peak at 711 eV can be assigned to Fe 3+ or Fe 2+ coordinated with N, which are suggested to be the ORR active centers [15,36]. The peak at 718.5 eV is a satellite peak indicating the co-existence of Fe 3+ and Fe 2+ in the Fe/NS/C-g-C 3 N 4 /TPTZ-1000 [35].…”

Anchoring CoFe2O4 Nanoparticles on N‐Doped Carbon Nanofibers for High‐Performance Oxygen Evolution Reaction

“…It is well‐established that the D band arises from the disordered or defect carbon and the G band originates from the sp 2 ‐hybridized graphitic carbon. The intensity ratio between D band and G band ( I D / I G ) generally reflects the graphitization degree of carbon materials and a lower value to I D / I G indicates a higher graphitization degree 34, 35, 36, 37, 38. Here the I D / I G ratio of CoFe 2 O 4 @N‐CNFs is calculated to be 0.83, suggesting a well‐crystallized graphitic carbon in the carbon nanofibers.…”

N,P Co‐Coordinated Manganese Atoms in Mesoporous Carbon for Electrochemical Oxygen Reduction

“…Therefore, numerous carbon‐based nanomaterials have been developed to replace the Pt based composites . Among them, the nitrogen species coordinated first‐row transition metal (e.g., Co, Ni, and Fe) atoms in carbons (M–N–C) are widely considered as promising electrocatalysts for ORR . The M–N–C materials are usually recognized as single‐atom catalysts (SACs), since isolated N‐bonded metals atoms are embedded in carbons.…”