Preparation of Fe–N–C catalysts with FeN<sub>x</sub> (<i>x</i> = 1, 3, 4) active sites and comparison of their activities for the oxygen reduction reaction and performances in proton exchange membrane fuel cells

Li, Yongcheng; Liu, Xiaofang; Zheng, Lirong; Shang, Jia‐Xiang; Wan, Xin; Hu, Riming; Guo, Xu; Hong, Song; Shui, Jianglan

doi:10.1039/c9ta08532g

Cited by 185 publications

(138 citation statements)

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“…Among all FeN x active sites, Fe-N 4 has the most proper EMSI between Fe and support, which results in the lowest formation energy and the highest ORR activity. [36] Other than the common coordination (i.e., C and N), there are also some new coordination such as O, S, P, and so on. Wang et al prepared a series of SACs containing metal-S sites such as Fe-N 4 S 2 , Ni-N 3 S 1 , and Co-N 3 S 1 (Figure 2d).…”

Section: M-dnmentioning

confidence: 99%

Electronic Metal–Support Interaction of Single‐Atom Catalysts and Applications in Electrocatalysis

et al. 2020

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between the electronic structure and catalytic efficiency of heterogenous catalysts. Dating back to 1930s, the concept of "electronic factor" was proposed by G. M. Schwab to describe the influence of electronic interaction on catalytic behavior of supported catalyst and divided the interaction into two parts, structural and synergetic ones. [4] Electrons transferring between the metal and the support was first under consideration when it came to the catalysis. After that, S. J. Tauster used the term of "strong metal-support interaction" (SMSI) to describe the chemisorption properties of group VIII elements supported by a metal oxide (e.g. SiO 2 , MgO) in 1978. [5] Later the concept was broadened to interaction between any metallic species and support, based on the experimental phenomena. [6] Till that time, based on the early characterization of surface science, researchers had realized that the active site might change during the process from metallic to an SMSI state, which was indicated to be covered or encapsulated by the support. [7] Among many hypotheses concerning the mechanism of SMSI, electron transfer between the metal and the support has been adapted by many researchers, and was confirmed by Rodriguez based on X-ray crystallography and UV photoemission spectroscopy in 1990s. [8] Then almost at the same time that the term of SACs was formally put forward, C. T. Campbell proposed the concept of "electronic metal-support interaction" (EMSI). As Campbell described, the chemical and catalytic properties might be affected by the electronic perturbations (i.e., shifts in the energy of d-band center) due to the EMSI. [9] In other words, the EMSI gave a much more detailed explanation of the enhanced properties of supported catalysts than SMSI, indicating that the study on catalysis was finally pushed to the electronic scale after so many years. [9b,c,10] Unfortunately, for metal particles or clusters, the accurate identification of electronic state is often difficult or even impossible. [11] The most reliable way to overcome the barrier above is to develop the catalyst based on single-atom metal that avoids intrinsic metal effects, including the electronic quantum size effect as well as structure-sensitivity geometrical effect. [12] Therefore, the rise of SACs provides a nearly perfect model to study the EMSI. As the supported metal species downsize to the single atom, the interaction between active site and support is always uniform, which can be much easier to be characterized by both experiment and theoretical calculation. [13] With the help of advanced techniques, for instance, X-ray absorption spectroscopy (XAS), the information about electronic The electronic metal-support interaction (EMSI), which acts as a bridge between theoretical electronic study and the design of heterogenous catalysts, has attracted much attention. Utilizing the interaction between the metal and the support is one of the most essential strategies to enhance electrocatalytic efficiency due to structural and synergetic promotion. To ...

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Section: M-dnmentioning

confidence: 99%

Electronic Metal–Support Interaction of Single‐Atom Catalysts and Applications in Electrocatalysis

et al. 2020

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“…Obviously, P‐coordination is more capable of trapping O 2 than N‐coordination. Besides, the formation of in‐plane M−N 4 sites in a carbon matrix is energetically favorable over the formation of M−N 2 sites at the edge [31–33] …”

Section: Theoretical Advancesmentioning

confidence: 99%

Recent Advances in Phosphorus‐Coordinated Transition Metal Single‐Atom Catalysts for Oxygen Reduction Reaction

et al. 2020

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Carbon‐supported heteroatom‐coordinated metal single‐atom catalysts (SACs) are promising electrocatalysts for oxygen reduction reaction (ORR) due to their low cost and tunable catalytic activity. Adjusting the electronic structure of the active center is an effective way to improve the activity of SACs. Compared with the intensively studied nitrogen‐coordinated transition metal atoms (e. g. Fe, Co and Mn), phosphorus‐coordinated and nitrogen‐phosphorus dual‐coordinated ones exhibit different electronic structures, which changes the reaction energy barrier and enhances the catalytic activity. This review summarizes recent advances in phosphorus coordination SACs for ORR in terms of theoretical study, site structure determination, synthesis method and catalytic activity. Further research is called for to explore the precise synthesis of phosphorus coordination SACs in a controllable manner and check the SACs under actual working conditions.

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“…Latest demonstrations reveal that single metal atoms coordinated with nitrogen forming M-Nx sites serve as the active centers for ORR, particularly Fe and Co-based catalysts [12,13]. Strategies to improve the performance of single-atom catalysts are widely investigated such as increasing the density of active sites, enhancing the intrinsic activity of catalyst by the construction of bi-metal or tri-metal active sites or regulation of coordination environment of active sites [6,[14][15][16][17]. Introduction of intrinsic defects is identified as effective method to tune the coordination structure of single active site [18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Fe atoms anchored on defective nitrogen doped hollow carbon spheres as efficient electrocatalysts for oxygen reduction reaction

Huang

Guharoy

et al. 2020

Nano Res.

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Defective electrocatalysts, especially for intrinsic defective carbon, have aroused a wide concern owing to high spin and charge densities. However, the designated nitrogen species favorable for creating defects by the removal of nitrogen, and the influence of defects for the coordination structure of active site and oxygen reduction reaction (ORR) activity have not been elucidated. Herein, we designed and synthesized a pair of electrocatalysts, denoted as Fe-N/C and Fe-ND/C for coordination sites of atomic iron-nitrogen and iron-nitrogen/defect configuration embedded in hollow carbon spheres, respectively, through direct pyrolysis of their corresponding hollow carbon spheres adsorbed with Fe(acac)3. The nitrogen defects were fabricated via the evaporation of pyrrolic-N on nitrogen doped hollow carbon spheres. Results of comparative experiments between Fe-N/C and Fe-ND/C reveal that Fe-ND/C shows superior ORR activity with an onset potential of 30 mV higher than that of Fe-N/C. Fe-ND sites are more favorable for the enhancement of ORR activity. Density functional theory (DFT) calculation demonstrates that Fe-ND/C with proposed coordination structure of FeN4−x (0<x<4) anchored by OH as axial ligand during ORR, weakens the strong binding of OH* intermediate and promotes the desorption of OH* as rate-determining step for ORR in alkaline electrolyte. Thus, Fe-ND/C electrocatalysts present much better ORR activity compared with that of Fe-N/C with proposed coordination structure of FeN4.

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Preparation of Fe–N–C catalysts with FeN_x (x = 1, 3, 4) active sites and comparison of their activities for the oxygen reduction reaction and performances in proton exchange membrane fuel cells

Abstract: The active sites of Fe–N–C catalysts are nitrogen coordinated iron atoms, FeNx(x = 1–5), that have five possible coordination numbers, corresponding to different ORR activities and PEMFC performances.

Cited by 185 publications

References 49 publications

Electronic Metal–Support Interaction of Single‐Atom Catalysts and Applications in Electrocatalysis

Electronic Metal–Support Interaction of Single‐Atom Catalysts and Applications in Electrocatalysis

Recent Advances in Phosphorus‐Coordinated Transition Metal Single‐Atom Catalysts for Oxygen Reduction Reaction

Fe atoms anchored on defective nitrogen doped hollow carbon spheres as efficient electrocatalysts for oxygen reduction reaction

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Preparation of Fe–N–C catalysts with FeNx (x = 1, 3, 4) active sites and comparison of their activities for the oxygen reduction reaction and performances in proton exchange membrane fuel cells

Abstract: The active sites of Fe–N–C catalysts are nitrogen coordinated iron atoms, FeNx(x = 1–5), that have five possible coordination numbers, corresponding to different ORR activities and PEMFC performances.

Cited by 185 publications

References 49 publications

Electronic Metal–Support Interaction of Single‐Atom Catalysts and Applications in Electrocatalysis

Electronic Metal–Support Interaction of Single‐Atom Catalysts and Applications in Electrocatalysis

Recent Advances in Phosphorus‐Coordinated Transition Metal Single‐Atom Catalysts for Oxygen Reduction Reaction

Fe atoms anchored on defective nitrogen doped hollow carbon spheres as efficient electrocatalysts for oxygen reduction reaction

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Preparation of Fe–N–C catalysts with FeN_x (x = 1, 3, 4) active sites and comparison of their activities for the oxygen reduction reaction and performances in proton exchange membrane fuel cells