Identification of durable and non-durable FeNx sites in Fe–N–C materials for proton exchange membrane fuel cells

Li, Jingkun; Sougrati, Moulay Tahar; Zitolo, Andrea; Ablett, James; Oğuz, Ismail Can; Mineva, Tzonka; Matanović, Ivana; Atanassov, Plamen; Ying, Hai; Zenyuk, Iryna V.; Cicco, Andrea Di; Kumar, Kavita; Dubau, Laëtitia; Maillard, Frédéric; Dražić, Goran; Jaouen, Frédéric

doi:10.1038/s41929-020-00545-2

Cited by 412 publications

(550 citation statements)

References 68 publications

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“…Thus, these catalysts should encompass the efficient active sites to optimize oxygen species adsorption for low overpotential, desirable pore organization to enhance active sites exposure and mass transport, as well as a predictable structure to unveil the ORR mechanism. [5][6][7] Due to maximized atom efficiency, single atom catalysts (SACs) have been regarded as promising substitute for Ptbased catalysts in heterogeneous ORR catalysis. [8] Over the last few years, the graduated escalation in catalytic activity of SACs has been attained, with single-atom Fe-N 4 site presenting the best one among vast metal-nitrogen (M-N x ) sites.…”

Section: Introductionmentioning

confidence: 99%

A Versatile Approach to Boost Oxygen Reduction of Fe‐N₄ Sites by Controllably Incorporating Sulfur Functionality

Shao

Zhang

et al. 2021

Adv Funct Materials

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Although atomically dispersed Fe-N 4 on carbon materials (Fe-NC) have enormous potential for the oxygen reduction reaction (ORR), precise control over the electronic structure of Fe to enhance the catalytic performance and a full understanding of the catalytic mechanism remain elusive. Herein, a novel approach is designed to boost the kinetic activity of single Fe-N 4 centers by controlling S-doped content and species (namely, thiophene-like S and oxidized S). Due to confinement and catalysis effects, the innovative strategy of combining a Mg(OH) 2 template with KOH activation preferentially generates oxidized S and simultaneously constructs porous carbon with a high Fe loading (2.93 wt%) and hierarchical pores. Theoretical calculations suggest that neighboring S functionalities can affect the electronic configurations of Fe-N 4 sites and increase the electron density around Fe atoms, thereby optimizing the adsorption energy of intermediates and substantially accelerating reaction kinetics, following the trend: oxidized S doped > thiophenelike S doped > pristine Fe-N 4 . Benefiting from high activity and accessibility of Fe-N 4 sites, the optimal FeNC-SN-2 electrode displays impressive ORR activity with large power density while maintaining outstanding durability in Zn-air batteries and microbial fuel cells. The work paves the way to prepare stable single-atom metal-N x sites with heteroatom-doping for diverse highperformance applications.

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Section: Introductionmentioning

confidence: 99%

A Versatile Approach to Boost Oxygen Reduction of Fe‐N₄ Sites by Controllably Incorporating Sulfur Functionality

Shao

Zhang

et al. 2021

Adv Funct Materials

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“…In brief, for the synthesis of metal COP- performed on a Nicolet 8700/Continuum XL with wavenumber from 2200 to 500 cm − 1 . Solid-state nuclear magnetic resonance (NMR) spectra were measured on a Burker 400M spectrometer operating at 10 kHz for 13 C. Chemical compositions and elemental oxidation states of the samples were investigated by X-ray photoelectron spectroscopy (XPS, ThermoFischer, ESCALAB). The elemental spectra were all corrected concerning C1s peaks at 284.8 eV.…”

Section: Methodsmentioning

confidence: 99%

“…[3][4][5][6][7][8] It has exhibited catalytic activity approaching that of platinum in acids media as well as inspiring performance in PEMFCs. [9][10][11][12] Recently, some advanced characterization techniques such as Mössbauer spectra [13][14][15] , X-ray absorption near-edge structure (XANES) 10,14,16 or annular dark-eld scanning transmission electron microscope (ADF-STEM) analysis 8,11,17,18 have enabled identi cation for Fe-N-C atomic structure as well as determination towards its correlation with catalytic properties. Meanwhile, ab initio investigations have also deciphered the root of high instinct activity of MN x C y moieties from the perspective of electron states based on descriptor-based approach.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, Frédéric et al have also demonstrated that their durability is inconsistent in the oxygen reduction process: the FeN 4 C 12 moiety with a high-spin eventually inverted into iron oxides; whereas FeN 4 C 10 moiety with low-or intermediate-spin remained unvaried after 50 hours operation. 13 Moreover, Wu et al 9,29 and Wang et al 30 have together demonstrated that FeN 4 C 8 and FeN 4 C 12 moieties are more apt to absorb oxygen and proceed four proton-electron transfer in oxygen reduction by electrochemical measurement coupled with density functional theory (DFT), compared to FeN 4 C 10 moiety. These studies implicitly indicate the carbon matrix connected to FeN 4 sites has a nonnegligible effect on instinct activity of active sites.…”

Section: Introductionmentioning

confidence: 99%

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Identify the impact of the covalent-bonded carbon matrix to FeN4 sites for acidic oxygen reduction

Xiang

2021

Preprint

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Atomically dispersed Fe and N co-doped carbon (Fe–N–C) catalysts exhibited superior acid oxygen reduction reaction (ORR) activities and recently been considered as the most promising alternatives to the benchmark Pt-based catalysts for proton exchange membrane fuel cells. The atomic configuration between Fe, N and C is one of the key factors to affect ORR activity. However, the traditional synthetic methods that rely on pyrolysis of the mixtures of Fe, N and C precursors often result in the plurality of local environment for the FeNx site. Unveiling the effect of covalent-bonded carbon matrix to FeNx sites towards ORR activity is important but still a great challenge due to inevitable connection of diverse N as well as random defects during the pyrolysis process. Here, we report a proof-of-concept study on the evaluation of covalent-bonded carbon environment connected to FeN4 sites on their catalytic activity via pyrolysis-free approach. Basing on the closed π conjugated phthalocyanine-based intrinsic covalent organic polymers (COPs) with well-designed structures, we directly synthesized a series of atomically dispersed Fe-N-C catalysts with various pure carbon environment without any N doping directly connected to the same FeN4 sites. Experiments coupled with density functional theory demonstrate that the catalytic activities appear a volcano plot with the increase of degree of delocalized π electrons from the carbon matrix. The delocalized π electrons changed anti-bonding d-state energy level of the single FeN4 moieties, hence tailored the adsorption between active centers and oxygen intermediates and altered the rate-determining step of oxygen reduction reaction.

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“…In this context, the development of PGMfree electrocatalysts for ORR derived from cheap and highly available precursors is a topic of relevant interest, which could have a relevant impact on the future market offuel cells [16,21], metal air batteries [22,23] and electrochemical sensors for O2 detection [24,25]. For this reason, great efforts have been and continue to be made for exploring the use of cheap and abundant biomasses [26,27] as a feedstock to obtain new materials with improved activity [28], selectivity [29,30] and stability [31,32].…”

Section: Introductionmentioning

confidence: 99%

Highly Graphitized Fe-N-C Electrocatalysts Prepared from Chitosan Hydrogel Frameworks

Daniel¹,

Kosmala²,

Brombin³

et al. 2021

Preprint

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The development of platinum group metal-free (PGM-free) electrocatalysts derived from cheap and environmentally friendly biomasses for oxygen reduction reaction (ORR) is a topic of relevant interest, particularly from the point of view of sustainability. Fe-nitrogen-doped carbon materials (Fe-N-C) have attracted particular interest as alternative to Pt-based materials, due to the high activity and selectivity of Fe-Nx active sites, the high availability and good tolerance to poisoning. Recently, many studies focused on developing synthetic strategies, which could transform N-containing biomasses into N-doped carbons. In this paper chitosan was employed as a suitable N-containing biomass for preparing Fe-N-C catalyst in virtue of its high N content (7.1%) and unique chemical structure. Moreover, the major application of chitosan is based on its ability to strongly coordinate metal ions, a precondition for the formation of Fe-Nx active sites. The synthesis of Fe-N-C consists in a double step thermochemical conversion of a dried chitosan hydrogel. In acidic aqueous solution, the preparation of physical cross-linked hydrogel allows to obtain sophisticated organization, which assure an optimal mesoporosity before and after the pyrolysis. After the second thermal treatment at 900 °C, a highly graphitized material was obtained, which has been fully characterized in term of textural, morphological and chemical properties. RRDE technique was used for understanding the activity and the selectivity of the material versus the ORR in 0.5 M H2SO4 electrolyte. Special attention was put in the determination of the active site density according to nitrite electrochemical reduction measurements. It was clearly established that the catalytic activity expressed as half wave potential linearly scales with the number of Fe-Nx sites. It was also established that the addition of the iron precursor after the first pyrolysis step leads to an increased activity because of both an increased number of active sites and of a hierarchical structure, which improves the access to active sites. At the same time, the increased graphitization degree, and a reduced density of pyrrolic nitrogen groups are helpful to increase the selectivity toward the 4e- ORR pathway.

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Identification of durable and non-durable FeNx sites in Fe–N–C materials for proton exchange membrane fuel cells

Cited by 412 publications

References 68 publications

A Versatile Approach to Boost Oxygen Reduction of Fe‐N₄ Sites by Controllably Incorporating Sulfur Functionality

A Versatile Approach to Boost Oxygen Reduction of Fe‐N₄ Sites by Controllably Incorporating Sulfur Functionality

Identify the impact of the covalent-bonded carbon matrix to FeN4 sites for acidic oxygen reduction

Highly Graphitized Fe-N-C Electrocatalysts Prepared from Chitosan Hydrogel Frameworks

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Identification of durable and non-durable FeNx sites in Fe–N–C materials for proton exchange membrane fuel cells

Cited by 412 publications

References 68 publications

A Versatile Approach to Boost Oxygen Reduction of Fe‐N4 Sites by Controllably Incorporating Sulfur Functionality

A Versatile Approach to Boost Oxygen Reduction of Fe‐N4 Sites by Controllably Incorporating Sulfur Functionality

Identify the impact of the covalent-bonded carbon matrix to FeN4 sites for acidic oxygen reduction

Highly Graphitized Fe-N-C Electrocatalysts Prepared from Chitosan Hydrogel Frameworks

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Product

Resources

About

A Versatile Approach to Boost Oxygen Reduction of Fe‐N₄ Sites by Controllably Incorporating Sulfur Functionality

A Versatile Approach to Boost Oxygen Reduction of Fe‐N₄ Sites by Controllably Incorporating Sulfur Functionality