Electrochemical transformation of Fe-N-C catalysts into iron oxides in alkaline medium and its impact on the oxygen reduction reaction activity

Sgarbi, Ricardo; Kumar, Kavita; Saveleva, Viktoriia A.; Dubau, Laëtitia; Chattot, Raphaël; Martin, Vincent; Mermoux, Michel; Bordet, Pierre; Glatzel, Pieter; Ticianelli, Édson Antônio; Jaouen, Frédéric; Maillard, Frédéric

doi:10.1016/j.apcatb.2022.121366

Cited by 27 publications

(45 citation statements)

References 80 publications

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“…During O 2 -AST-2k, 3.4% of Fe and 34% of PD were lost (see Figure S7B and C), which is similar to the degradation of another Fe 3 C@N−C species-rich Fe−N−C catalyst in an RDE setup, after 10k cycles of similar potential limits and step duration to those used in this work. 12 Herein, as the initial relative amount of FeN x C y sites is minor, the loss of FeN x C y sites could not be conclusively determined by either XANES or XPS. For example, in the XPS N 1s spectra (see Figure 4A), the intensity at the N−Fe peak (399.5 eV) barely drops.…”

Section: Methodsmentioning

confidence: 94%

“…In all cases in this study, it was not observed that the dissolved Fe species reprecipitate as Fe oxide, in contrast to a recent study performed under RDE conditions and for two other Fe−N−C catalysts, one rich in Fe 3 C@N−C and the other rich in atomically dispersed FeN x C y sites. 12 The different tendencies of reprecipitation of leached Fe might be attributed to the different CL structures, ranges of current densities, and/ or temperature. Although Fe dissolution is observed during Ar-AST-2k, the polarization curve and XPS N 1s and C 1s spectra barely change (see Figures S7, 4A and B).…”

Section: Methodsmentioning

confidence: 99%

“…The dissolution of different Fecontaining species initially present in Fe−N−C catalysts could lead to various types and degrees of degradation. 12 For instance, Fe leaching from atomically dispersed FeN x C y sites, which catalyze ORR in both acidic and alkaline media, will result in a decreasing active site density (SD). The TOF of active sites may also be modified.…”

Section: Introductionmentioning

confidence: 99%

“…With regard to durability and longevity of Fe–N–C catalysts in this environment, many questions remain however open. In particular, an understanding of Fe x + leaching and, consequently, an implementation of mitigation strategies to its suppression are considered main challenges. ,,− …”

Section: Introductionmentioning

confidence: 99%

“…While it is likely that several degradation mechanisms are operative and the extent of each mechanism is different depending on the FC operating conditions, the Fe–N–C structure and morphology, and the active layer design, a fundamental understanding of the stability of Fe–N–C catalysts is still lacking. The dissolution of different Fe-containing species initially present in Fe–N–C catalysts could lead to various types and degrees of degradation . For instance, Fe leaching from atomically dispersed FeN x C y sites, which catalyze ORR in both acidic and alkaline media, will result in a decreasing active site density (SD).…”

Section: Introductionmentioning

confidence: 99%

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Oxygen Reduction Reaction in Alkaline Media Causes Iron Leaching from Fe–N–C Electrocatalysts

Ehelebe

Hutzler

et al. 2022

J. Am. Chem. Soc.

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The electrochemical activity of modern Fe–N–C electrocatalysts in alkaline media is on par with that of platinum. For successful application in fuel cells (FCs), however, also high durability and longevity must be demonstrated. Currently, a limited understanding of degradation pathways, especially under operando conditions, hinders the design and synthesis of simultaneously active and stable Fe–N–C electrocatalysts. In this work, using a gas diffusion electrode half-cell coupled with inductively coupled plasma mass spectrometry setup, Fe dissolution is studied under conditions close to those in FCs, that is, with a porous catalyst layer (CL) and at current densities up to −125 mA·cm–2. Varying the rate of the oxygen reduction reaction (ORR), we show a remarkable linear correlation between the Faradaic charge passed through the electrode and the amount of Fe dissolved from the electrode. This finding is rationalized assuming that oxygen reduction and Fe dissolution reactions are interlinked, likely through a common intermediate formed during the Fe redox transitions in Fe species involved in the ORR, such as FeN x C y and Fe3C@N–C. Moreover, such a linear correlation allows the application of a simple metricS-numberto report the material’s stability. Hence, in the current work, a powerful tool for a more applied stability screening of different electrocatalysts is introduced, which allows on the one hand fast performance investigations under more realistic conditions, and on the other hand a more advanced mechanistic understanding of Fe–N–C degradation in CLs.

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Section: Methodsmentioning

confidence: 94%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Oxygen Reduction Reaction in Alkaline Media Causes Iron Leaching from Fe–N–C Electrocatalysts

Ehelebe

Hutzler

et al. 2022

J. Am. Chem. Soc.

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Identification and Understanding of Active Sites of Non‐Noble Iron‐Nitrogen‐Carbon Catalysts for Oxygen Reduction Electrocatalysis

Yang

Chen

Zhang

et al. 2023

Adv Funct Materials

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Non-noble iron-nitrogen-carbon (Fe-N-C) catalysts have been explored as one type of the most promising alternatives of precious platinum (Pt) in catalyzing the oxygen reduction reaction (ORR). However, their catalytic ORR activity and stability still cannot meet the requirement of practical applications. Active sites in such catalysts are the key factors determining the catalytic performance. This review gives a critical overview on identification and understanding of active sties of non-pyrolytic and pyrolytic Fe-N-C catalysts in terms of design strategies, synthesis, characterization, functional mechanisms and performance validation. The diversity and complexity of active sites that greatly dominate the progress of Fe-N-C catalysts include Fe-containing sites (Fe-based nanoparticles and single-atom Fe-species) and metalfree sites (heteroatoms doping and defects). Meanwhile, synergistic effects are also discussed in this review with emphasis on the interaction among multiple active sites. Although substantial endeavors have been devoted to develop the efficient Fe-N-C catalysts, some challenges still remain. To facilitate further research on Fe-N-C catalysts toward practical applications, some research perspectives are prospected in the aspects of innovative synthesis methods, active-sites modulation strategies, high-resolution ex situ/in situ/ operando characterization techniques, theoretical calculations, and so on. This review may provide a guideline for identifying and understanding activesites for developing high-performance Fe-N-C catalysts.

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Straightforward Synthesis Methodology for Obtaining Excellent ORR Electrocatalysts From Biomass Residues Through a One Pot‐High Temperature Treatment Approach

Alemany‐Molina,

Pabón‐Román,

Chinchilla

et al. 2024

Advanced Sustainable Systems

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Materials prepared from biomass residues are potential candidates to substitute the Pt‐based commercial electrocatalysts in oxygen reduction reaction (ORR). Although some investigations have reported activity and durability comparable to Pt/C using biomass‐derived catalysts based on Fe─N─C sites, it remains a challenge to decrease the environmental impact of the production of these materials. A straightforward procedure is developed to obtain excellentORR electrocatalysts from biomass residues which requires a single high‐temperature treatment. The final washing step is avoided by optimizing the initial amount of Fe precursor (FeC2O4). Besides the formation of iron oxide nanoparticles, a highly dispersed Fe phase is detected by High Angle Annular Dark Field Scanning Transmission Electron Microscopy and Energy Dispersive X‐Ray Spectroscopy (HAADF‐STEM‐XEDS) analysis as well as graphitic carbon structures. The best performance for almond shell‐based electrocatalysts is achieved for the sample containing 4.6 wt. % of Fe. The procedure developed is also applied to oceanic posidonia and eucalyptus residues, also showing excellent ORR behavior. The best sample is studied in a primary Zn‐air battery (ZAB) obtaining a maximum power density of 59 mW cm−2 and 755 mAh gZn−1 capacity.

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Electrochemical transformation of Fe-N-C catalysts into iron oxides in alkaline medium and its impact on the oxygen reduction reaction activity

Cited by 27 publications

References 80 publications

Oxygen Reduction Reaction in Alkaline Media Causes Iron Leaching from Fe–N–C Electrocatalysts

Oxygen Reduction Reaction in Alkaline Media Causes Iron Leaching from Fe–N–C Electrocatalysts

Identification and Understanding of Active Sites of Non‐Noble Iron‐Nitrogen‐Carbon Catalysts for Oxygen Reduction Electrocatalysis

Straightforward Synthesis Methodology for Obtaining Excellent ORR Electrocatalysts From Biomass Residues Through a One Pot‐High Temperature Treatment Approach

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