Identification of the Electronic and Structural Dynamics of Catalytic Centers in Single-Fe-Atom Material

Li, Xuning; Cao, Changsu; Hung, Sung‐Fu; Lü, Ying; Cai, Weizheng; Rykov, Alexandre I.; Miao, Shu; Xi, Shibo; Yang, Hongbin; Hu, Zehua; Wang, Junhu; Zhao, Jiyong; Ercan, E.; Xu, Wei; Chan, Ting Shan; Chen, Haoming; Xiong, Qihua; Xiao, Hai; Huang, Yanqiang; Li, Jun; Zhang, Tao; Liu, Bin

doi:10.1016/j.chempr.2020.10.027

Cited by 255 publications

(221 citation statements)

References 63 publications

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“…For the Fe‐N‐C obtained at 700°C, its out‐of‐plane FeN 4 sites with a small degree of Fe–N bond contraction that were identified as sites with optimal ORR performance (Onset potential [E onset ] of 0.98 V vs. RHE, half‐wave potential [ E 1/2 ] of 0.84 V vs. RHE, 0.5 M H 2 SO 4 ), even though contraction strain about FeN 4 is not energetically favorable for the catalyst. The N coordination number can also be varied to form defective MN x ( x = 2, 3, or 5) sites, leading to central metals with different electronic structures and different ORR activities 20,44–47 . However, it remains unclear whether FeN x ( x = 2, 3, or 5) structure with nitrogen vacancies or excess nitrogen relative to the traditional FeN 4 coordination can enhance ORR activity.…”

Section: Control Over Fen X Active Sites In Fe‐n‐c Materialsmentioning

confidence: 99%

“…Fe‐N‐C materials free from metallic Fe nanoparticles 14,15 demonstrate outstanding ORR activity and durability, with the active Fe determined to exist in a porphyrin‐like N coordination environment (FeN 4 ) using advanced physical methods, including Mössbauer spectroscopy, X‐ray absorption spectroscopy (XAS), and high‐angle annular dark‐field scanning transmission electron microscope. Density functional theory calculations (DFT) added further evidence that FeN 4 sites were indeed very active sites for ORR 14,16–22 . Although deeper knowledge is emerging about the true active site of Fe‐N‐C material for ORR (i.e., porphyrin‐like iron single‐atom sites), the ORR performance of Fe‐N‐C materials remains generally inferior to commercial Pt/C catalysts 23,24 .…”

Section: Introductionmentioning

confidence: 99%

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Engineering local coordination environments and site densities for high‐performance Fe‐N‐C oxygen reduction reaction electrocatalysis

et al. 2021

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Fe‐N‐C catalysts represent very promising cathode catalysts for polymer electrolyte fuel cells, owing to their outstanding activity for the oxygen reduction reaction (ORR), especially in alkaline media. In this review, we summarize recent advances in the design and synthesis of Fe‐N‐C catalysts rich in highly dispersed FeN x active sites. Special emphasis is placed on emerging strategies for tuning the electronic structure of the Fe atoms to enhance the ORR activity, and also maximizing the surface concentration of FeN x sites that are catalytically accessible during ORR. While great progress has been made over the past 5 years in the development of Fe‐N‐C catalyst for ORR, significant technical obstacles still need to be overcome to enable the large‐scale application of Fe‐N‐C materials as cathode catalysts in real‐world fuel cells.

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Section: Control Over Fen X Active Sites In Fe‐n‐c Materialsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Engineering local coordination environments and site densities for high‐performance Fe‐N‐C oxygen reduction reaction electrocatalysis

et al. 2021

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“…[ 10–13 ] Single atoms of iron coordinated with nitrogen (e.g., FeN 4 ) moieties in a carbon matrix are commonly recognized as the real active sites for absorbing O 2 and catalyzing the subsequent ORR kinetics. [ 14–19 ] The FeNC materials can be prepared by the high‐temperature pyrolysis of C‐, N‐ and Fe‐containing precursors. [ 2,20–25 ] Nanocrystals of zeolitic imidazolate frameworks (ZIF‐8) modified with Fe have proven as highly promising precursors of FeNC electrocatalysts due to their ability to yield FeN 4 sites and generate porous nanostructures.…”

Section: Introductionmentioning

confidence: 99%

FeNC Electrocatalysts with Densely Accessible FeN₄ Sites for Efficient Oxygen Reduction Reaction

Zhou

Chen

Wang

et al. 2021

Adv Funct Materials

125

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The development of iron and nitrogen co‐doped carbon (FeNC) electrocatalysts for the oxygen reduction reaction (ORR) in proton‐exchange membrane fuel cells (PEMFCs) is a grand challenge due to the low density of accessible FeN4 sites. Here, an in situ trapping strategy using nitrogen‐rich molecules (e.g., melamine, MA) is demonstrated to enhance the amount of accessible FeN4 sites in FeNC electrocatalysts. The melamine molecules can participate in the coordination of Fe ions in zeolitic imidazolate frameworks to form FeN6 sites within precursors. These FeN6 sites are then converted into atomically dispersed FeN4 sites during a pyrolytic process. Remarkably, the FeNC/MA exhibits a high single‐atom Fe content (3.5 wt.%), a large surface area (1160 m2 g−1), and a high density of accessible FeN4 sites (45.7 × 1019 sites g−1). As a result, FeNC/MA shows a much enhanced ORR activity with a half‐wave potential of 0.83 V (vs the reversible hydrogen electrode) in a 0.5 m H2SO4 electrolyte solution and a good performance in a PEMFC system with an activity of 80 mA cm−2 at 0.8 V under 1.0 bar H2/air. This work offers a promising approach toward high‐performance carbon‐based ORR electrocatalysts.

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“…Liu et al reported the N-FeN 4 C 10 moiety as an active site by the spin-crossover-involved ORR mechanism. [6] FrØdØric Jaouen et al showed low or intermediate spin FeN 4 C 10 sites are more durable after al ong time operation in the fuel cell. [7] Spin configurations may be as ap ossible catalytic descriptor linking the catalyst structure and the electrocatalytic activity.…”

Section: Introductionmentioning

confidence: 99%

Unraveling the Origin of Sulfur‐Doped Fe‐N‐C Single‐Atom Catalyst for Enhanced Oxygen Reduction Activity: Effect of Iron Spin‐State Tuning

et al. 2021

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Heteroatom doped atomically dispersed Fe 1 -NC catalysts have been found to show excellent activity toward oxygen reduction reaction (ORR). However,t he origin of the enhanced activity is still controversial because the structurefunction relationship governing the enhancement remains elusive.Herein, sulfur(S)-doped Fe 1 -NC catalyst was obtained as amodel, which displays asuperior activity for ORR towards the traditional Fe-NC materials. 57 Fe Mçssbauer spectroscopy and electron paramagnetic resonance spectroscopyr evealed that incorporation of Si nt he second coordination sphere of Fe 1 -NC can induce the transition of spin polarization configuration. Operando 57 Fe Mçssbauer spectra definitively identified the low spin single-Fe 3+ -atom of C-FeN 4 -S moiety as the active site for ORR. Moreover,DFT calculations unveiled that lower spin state of the Fe center after the Sd oping promotes OH* desorption process.T his work elucidates the underlying mechanisms towards Sd oping for enhancing ORR activity, and paves aw ay to investigate the function of broader heteroatom doped Fe 1 -NC catalysts to offer ageneral guideline for spin-state-determined ORR.

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Identification of the Electronic and Structural Dynamics of Catalytic Centers in Single-Fe-Atom Material

Cited by 255 publications

References 63 publications

Engineering local coordination environments and site densities for high‐performance Fe‐N‐C oxygen reduction reaction electrocatalysis

Engineering local coordination environments and site densities for high‐performance Fe‐N‐C oxygen reduction reaction electrocatalysis

FeNC Electrocatalysts with Densely Accessible FeN₄ Sites for Efficient Oxygen Reduction Reaction

Unraveling the Origin of Sulfur‐Doped Fe‐N‐C Single‐Atom Catalyst for Enhanced Oxygen Reduction Activity: Effect of Iron Spin‐State Tuning

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Identification of the Electronic and Structural Dynamics of Catalytic Centers in Single-Fe-Atom Material

Cited by 255 publications

References 63 publications

Engineering local coordination environments and site densities for high‐performance Fe‐N‐C oxygen reduction reaction electrocatalysis

Engineering local coordination environments and site densities for high‐performance Fe‐N‐C oxygen reduction reaction electrocatalysis

FeNC Electrocatalysts with Densely Accessible FeN4 Sites for Efficient Oxygen Reduction Reaction

Unraveling the Origin of Sulfur‐Doped Fe‐N‐C Single‐Atom Catalyst for Enhanced Oxygen Reduction Activity: Effect of Iron Spin‐State Tuning

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FeNC Electrocatalysts with Densely Accessible FeN₄ Sites for Efficient Oxygen Reduction Reaction