Investigation on the demetallation of Fe-N-C for oxygen reduction reaction: The influence of structure and structural evolution of active site

Xu, Xinlong; Zhang, Xiaoming; Kuang, Zhichong; Xia, Zhangxun; Rykov, Alexandre I.; Yu, Shansheng; Wang, Junhu; Wang, Suli

doi:10.1016/j.apcatb.2022.121290

Cited by 30 publications

(14 citation statements)

References 59 publications

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“…In situ Raman spectroscopy of the NC-1000 catalyst (Figure c) shows that only the two peaks at 1133 and 1519 cm –1 appeared at negative potentials. After a long-time potential cycling in O 2 -saturated 0.1 M HClO 4 , the ORR activity of the FeNC-1000 catalyst in 0.1 M KOH significantly degraded (Figure S4a), which is largely related with Fe demetallation. , Accordingly, the peak intensity at 1064 cm –1 substantially weakened in the in situ Raman spectra at low potentials (Figure S4b). In addition, selective poisoning of the Fe–N x active site in the FeNC-1000 catalyst by SCN – leads to an obvious activity loss in 0.1 M KOH (Figure S4c).…”

Section: Results and Discussionmentioning

confidence: 99%

Probing the Oxygen Reduction Reaction Intermediates and Dynamic Active Site Structures of Molecular and Pyrolyzed Fe–N–C Electrocatalysts by In Situ Raman Spectroscopy

et al. 2022

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While FeN 4 species are widely suggested as the active sites of noble-metal-free Fe−N−C oxygen reduction reaction (ORR) electrocatalysts, the ORR mechanism, particularly the rate-determining steps (RDSs) at the Fe centers, and the likely contribution of co-existed C−N active site remain disputed. Moreover, the dynamic structures of the FeN 4 active sites during ORR electrocatalysis also remain elusive. By in situ (isotope-labeled) Raman spectroscopy of molecular Fe phthalocyanine (FePc) model catalysts and pyrolyzed Fe−N−C catalysts, we achieve direct, simultaneous spectral identification of the ORR intermediates/RDSs at different active sites under different pH conditions, from which their intrinsic activities and ORR mechanisms can be quantitatively decoupled. Besides the single-atomic Fe−N x site, two kinds of C−N sites were pinpointed and clarified as separate active sites in pyrolyzed Fe−N−C catalysts, showing different ORR intermediates (*O 2 − and *OOH) and RDSs. Furthermore, from the FePc model catalyst, we reveal a pH-dependent structural switching of the FeN 4 between planar and non-planar structures during ORR electrocatalysis, which provides important insights into their pH-dependent ORR activity (RDS) and stability.

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Section: Results and Discussionmentioning

confidence: 99%

Probing the Oxygen Reduction Reaction Intermediates and Dynamic Active Site Structures of Molecular and Pyrolyzed Fe–N–C Electrocatalysts by In Situ Raman Spectroscopy

et al. 2022

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Section: Resultsmentioning

confidence: 99%

“…51 Moreover, previous research has ascribed D1 to low-spin FeN 4 C 8 or high-spin FeN 4 C 12 moieties, and it is thought to have exceptionally high ORR activity but fast demetallation. 51,52 However, it was only recently discovered that the hydroxyl axial ligand could spontaneously form on D1 in the electrolyte, thereby promoting ORR kinetics. 8 D3 can be attributed to a high-spin Fe 2+ species that is ve-coordinated similar to the structure of cytochrome c oxidase enzymes, and it is highly active and stable.…”

Section: Elucidation Of Active Sites and The Anti-poisoning Mechanismmentioning

confidence: 99%

Axial ligand promoted phosphate tolerance of an atomically dispersed Fe catalyst towards the oxygen reduction reaction

et al. 2022

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“…It is essential to use the ab initio molecular dynamics (AIMD) to simulate the interaction of O 2 with Fe-N-C under diverse conditions further helping to exposit the structural evolution during ORR. Recently, to reveal the above-mentioned relationship, and poor stability reason, Xu et al [143] minutely analyzed the dynamic evolution of the active sites in Fe-N-C catalysts during ORR in PEMFCs via in-situ Mössbauer spectroscopy, DFT and AIMD. As shown in in-situ 57 Fe-N-C Mössbauer spectra (Fig.…”

Section: Inferring Reaction Mechanism By Associating In-situ Studies ...mentioning

confidence: 99%

A Review of In-Situ Techniques for Probing Active Sites and Mechanisms of Electrocatalytic Oxygen Reduction Reactions

et al. 2022

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Electrocatalytic oxygen reduction reaction (ORR) is one of the most important reactions in electrochemical energy technologies such as fuel cells and metal–O2/air batteries, etc. However, the essential catalysts to overcome its slow reaction kinetic always undergo a complex dynamic evolution in the actual catalytic process, and the concomitant intermediates and catalytic products also occur continuous conversion and reconstruction. This makes them difficult to be accurately captured, making the identification of ORR active sites and the elucidation of ORR mechanisms difficult. Thus, it is necessary to use extensive in-situ characterization techniques to proceed the real-time monitoring of the catalyst structure and the evolution state of intermediates and products during ORR. This work reviews the major advances in the use of various in-situ techniques to characterize the catalytic processes of various catalysts. Specifically, the catalyst structure evolutions revealed directly by in-situ techniques are systematically summarized, such as phase, valence, electronic transfer, coordination, and spin states varies. In-situ revelation of intermediate adsorption/desorption behavior, and the real-time monitoring of the product nucleation, growth, and reconstruction evolution are equally emphasized in the discussion. Other interference factors, as well as in-situ signal assignment with the aid of theoretical calculations, are also covered. Finally, some major challenges and prospects of in-situ techniques for future catalysts research in the ORR process are proposed.

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Investigation on the demetallation of Fe-N-C for oxygen reduction reaction: The influence of structure and structural evolution of active site

Cited by 30 publications

References 59 publications

Probing the Oxygen Reduction Reaction Intermediates and Dynamic Active Site Structures of Molecular and Pyrolyzed Fe–N–C Electrocatalysts by In Situ Raman Spectroscopy

Probing the Oxygen Reduction Reaction Intermediates and Dynamic Active Site Structures of Molecular and Pyrolyzed Fe–N–C Electrocatalysts by In Situ Raman Spectroscopy

Axial ligand promoted phosphate tolerance of an atomically dispersed Fe catalyst towards the oxygen reduction reaction

A Review of In-Situ Techniques for Probing Active Sites and Mechanisms of Electrocatalytic Oxygen Reduction Reactions

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