Evolution Pathway from Iron Compounds to Fe<sub>1</sub>(II)–N<sub>4</sub> Sites through Gas-Phase Iron during Pyrolysis

Li, Jingkun; Li, Jiao; Wegener, Evan C.; Richard, Lynne Larochelle; Liu, Ershuai; Zitolo, Andrea; Sougrati, Moulay Tahar; Mukerjee, Sanjeev; Zhao, Zipeng; Huang, Yu; Yang, Fan; Zhong, Sichen; Xu, Hui; Kropf, A. Jeremy; Jaouen, Frédéric; Myers, Deborah J.; Jia, Qingying

doi:10.1021/jacs.9b11197

Cited by 226 publications

(188 citation statements)

References 38 publications

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“…[46][47][48] An important step toward a better understanding of this promising substitution material for platinum electrodes is to clarify the structure and electronic properties of the active site. [39,43,49,50] The current consensus in the literature is that the catalytically active iron ion is surrounded by 2-4 nitrogen donor atoms embedded in a graphene sheet that may have structural or electronic defects and possibly an additional axial ligand. [39,49,51,52] The sketch shown in Figure 1A attempts to summarize the types of environment discussed in the literature.…”

Section: Introductionmentioning

confidence: 99%

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Gallenkamp

Kramm

Proppe

et al. 2020

Int J of Quantum Chemistry

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Single-atom catalysts with iron ions in the active site, known as FeNC catalysts, show high activity for the oxygen reduction reaction and hence hold promise for access to low-cost fuel cells. Because of the amorphous, multiphase structure of the FeNC catalysts, the iron environment and its electronic structure are poorly understood. While it is widely accepted that the catalytically active site contains an iron ion ligated by several nitrogen donors embedded in a graphene-like plane, the exact structural details, such as the presence or nature of axial ligands, are unknown. Computational chemistry in combination with Mössbauer spectroscopy can help unravel the geometric and electronic structures of the active sites. As a first step toward this goal, we present a calibration of computational Mössbauer spectroscopy for FeN 4-like environments. The uncertainty of both the isomer shift and the quadrupole splitting prediction is determined, from which trust regions for the Mössbauer parameter predictions of computational FeNC models are derived. We find that TPSSh, B3LYP, and PBE0 perform equally well; the trust regions with B3LYP are 0.13 mm s −1 for the isomer shift and 0.36 mm s −1 for the quadrupole splitting. The calibration data is made publicly available in an interactive notebook that provides predicted Mössbauer parameters with individual uncertainty estimates from computed contact densities and quadrupole splitting values. We show that a differentiation of common FeNC Mössbauer signals by a separate analysis of isomer shift and quadrupole splitting will most likely be insufficient, whereas their simultaneous evaluation will allow the assignment to adequate computational FeNC models.

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Section: Introductionmentioning

confidence: 99%

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Gallenkamp

Kramm

Proppe

et al. 2020

Int J of Quantum Chemistry

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“…Kumar et al reported that iron-containing particles also show moderate initial ORR activity in acidic electrolyte besides the atomic distributed Fe-N-C catalyst [ 12 ]. Other groups showed much lower activities for iron particles in acidic media compared to atomic Fe-N x sites [ 13 , 14 ]. This is the reason why unprotected iron-containing particles are commonly removed by an additional step of acid leaching after pyrolysis [ 5 ].…”

Section: Introductionmentioning

confidence: 99%

Relevant Properties of Carbon Support Materials in Successful Fe-N-C Synthesis for the Oxygen Reduction Reaction: Study of Carbon Blacks and Biomass-Based Carbons

et al. 2020

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Fe-N-C materials are promising non-precious metal catalysts for the oxygen reduction reaction in fuel cells and batteries. However, during the synthesis of these materials less active Fe-containing nanoparticles are formed in many cases which lead to a decrease in electrochemical activity and stability. In this study, we reveal the significant properties of the carbon support required for the successful incorporation of Fe-N-related active sites. The impact of two carbon blacks and two activated biomass-based carbons on the Fe-N-C synthesis is investigated and crucial support properties are identified. Carbon supports having low portions of amorphous carbon, moderate surface areas (>800 m2/g) and mesopores result in the successful incorporation of Fe and N on an atomic level and improved oxygen reduction reaction (ORR) activity. A low surface area and especially amorphous parts of the carbon promote the formation of metallic iron species covered by a graphitic layer. In contrast, highly microporous systems with amorphous carbon provoke the formation of less active iron carbides and carbon nanotubes. Overall, a phosphoric acid activated biomass is revealed as novel and sustainable carbon support for the formation of Fe-Nx sites. Overall, this study provides valuable and significant information for the future development of novel and sustainable carbon supports for Fe-N-C catalysts.

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“…The metallic Fe (PDF #06-0696) as the predominant phase in F-NCS is also confirmed by XRD ( Figure 3h). The use of 5 vol% H 2 facilitates to form metallic Fe at 200 °C rather than iron oxides, [34,35] Figure 1. Interactive facilitation and stabilization between Rh and Fe.…”

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confidence: 99%

Dual‐Metal Interbonding as the Chemical Facilitator for Single‐Atom Dispersions

et al. 2020

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Dispersing metals to the ultrasmall forms is an effective strategy to increase their usage efficiency and catalytic reactivity. [3,4] Recently, atomic dispersion of metal atoms has been realized over the support to form single-atom catalysts (SACs), [4-8] which attract considerable attention due to their maximized metal usage and improved active site homogeneity. [9,10] Because of the high surface energy, single metal atoms are generally formed with the existence of particles or clusters as the byproducts, prohibiting stable atomic dispersion. [11-14] As a result, it is of great importance to find efficient technologies for increasing atomic dispersion while maintaining high stability and catalytic activity during applications. Typically, two strategies are used to disperse SACs stably. One is the bottom-up method, which conventionally refers to single atoms derived from metal ions. Metal ions are captured in electronic and/or structural defects [15-17] of solid matrix such as metal oxide, [18-22] metal carbides, [23,24] zeolites/metal-organic Atomically dispersed catalysts, with maximized atom utilization of expensive metal components and relatively stable ligand structures, offer high reactivity and selectivity. However, the formation of atomic-scale metals without aggregation remains a formidable challenge due to thermodynamic stabilization driving forces. Here, a top-down process is presented that starts from iron nanoparticles, using dual-metal interbonds (RhFe bonding) as a chemical facilitator to spontaneously convert Fe nanoparticles to single atoms at low temperatures. The presence of RhFe bonding between adjacent Fe and Rh single atoms contributes to the thermodynamic stability, which facilitates the stripping of a single Fe atom from the Fe nanoparticles, leading to the stabilized single atom. The dual single-atom Rh-Fe catalyst renders excellent electrocatalytic performance for the hydrogen evolution reaction in an acidic electrolyte. This discovery of dual-metal interbonding as a chemical facilitator paves a novel route for atomic dispersion of chemical metals and the design of efficient catalysts at the atomic scale. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202003484. Heterogeneous catalysis is pivotal to the modern chemical industry, [1] with many heterogeneous catalysts comprising transition or noble metals deposited over a solid support phase. [2]

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Evolution Pathway from Iron Compounds to Fe₁(II)–N₄ Sites through Gas-Phase Iron during Pyrolysis

Cited by 226 publications

References 38 publications

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Relevant Properties of Carbon Support Materials in Successful Fe-N-C Synthesis for the Oxygen Reduction Reaction: Study of Carbon Blacks and Biomass-Based Carbons

Dual‐Metal Interbonding as the Chemical Facilitator for Single‐Atom Dispersions

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Evolution Pathway from Iron Compounds to Fe1(II)–N4 Sites through Gas-Phase Iron during Pyrolysis

Cited by 226 publications

References 38 publications

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

Relevant Properties of Carbon Support Materials in Successful Fe-N-C Synthesis for the Oxygen Reduction Reaction: Study of Carbon Blacks and Biomass-Based Carbons

Dual‐Metal Interbonding as the Chemical Facilitator for Single‐Atom Dispersions

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Evolution Pathway from Iron Compounds to Fe₁(II)–N₄ Sites through Gas-Phase Iron during Pyrolysis