On an Easy Way To Prepare Metal–Nitrogen Doped Carbon with Exclusive Presence of MeN<sub>4</sub>-type Sites Active for the ORR

Kramm, Ulrike I.; Herrmann-Geppert, Iris; Behrends, Jan; Lips, K.; Fiechter, S.; Bogdanoff, Peter

doi:10.1021/jacs.5b11015

Cited by 437 publications

(372 citation statements)

References 52 publications

(127 reference statements)

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“…In contrast, high PRR current on FeNC‐dry‐0.5 demonstrates that FeN x C y moieties are PRR‐active. This is a first major finding of the present study, enabled by the synthesis of Fe‐N‐C catalysts free of Fe particles 10b, 15…”

supporting

confidence: 53%

“…We also demonstrated that FeN x C y moieties and Fe@N‐C species are moderately active toward PRR, proving their possible roles in both direct (major path) and indirect 4 e − ORR pathways. Since the synthesis of Fe‐N‐C catalysts with only FeN x C y moieties,10b, 15 only Fe@N‐C particles,10a or their combination3b,3d, 17 is now controllable, the understanding of the nature of active sites for PRR provided herein offers new insights for the rational design of advanced Fe‐N‐C catalysts with high selectivity and expectedly improved durability in polymer electrolyte fuel cells. …”

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confidence: 99%

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Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe‐N‐C Catalysts

et al. 2017

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Fe‐N‐C catalysts with high O2 reduction performance are crucial for displacing Pt in low‐temperature fuel cells. However, insufficient understanding of which reaction steps are catalyzed by what sites limits their progress. The nature of sites were investigated that are active toward H2O2 reduction, a key intermediate during indirect O2 reduction and a source of deactivation in fuel cells. Catalysts comprising different relative contents of FeNxCy moieties and Fe particles encapsulated in N‐doped carbon layers (0–100 %) show that both types of sites are active, although moderately, toward H2O2 reduction. In contrast, N‐doped carbons free of Fe and Fe particles exposed to the electrolyte are inactive. When catalyzing the ORR, FeNxCy moieties are more selective than Fe particles encapsulated in N‐doped carbon. These novel insights offer rational approaches for more selective and therefore more durable Fe‐N‐C catalysts.

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confidence: 53%

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confidence: 99%

Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe‐N‐C Catalysts

et al. 2017

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“…A significant advantage of SACs is that the well-defined single atomic site could allow precise understanding of the catalytic reaction pathway, and rational design of targeted catalysts with tailored activity (in a manner similar to homogeneous catalyst design). However, this perceived advantage has been investigated theoretically 23,24 , but has not yet been demonstrated experimentally in M-N-Cs, largely because existing M-N-Cs were generally obtained through pyrolysis of metal-, nitrogen-and carbon-containing molecular or polymeric precursors and the as-synthesized materials Articles Nature Catalysis are typically highly heterogeneous, concurrently containing single atomic metals along with crystalline particles, and crystalline and amorphous carbon [25][26][27][28] . Such structural and compositional heterogeneity poses a key obstacle to unambiguously identifying the exact atomistic structure of the active sites and to further establishing a definitive correlation with the catalytic properties that can guide the subsequent design of future generations of SACs.…”

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confidence: 99%

General synthesis and definitive structural identification of MN4C4 single-atom catalysts with tunable electrocatalytic activities

et al. 2018

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E fficient and cost-effective electrocatalysts play critical roles in energy conversion and storage [1][2][3] . Homogeneous and heterogeneous catalysts represent two parallel frontiers of electrocatalysts, each with their own merits and drawbacks 4,5 . Homogeneous catalysts are attractive for their highly uniform active sites, tunable coordination environment and maximized atom utilization efficiency, but are limited by their relatively poor stability and recyclability. Heterogeneous catalysts are appealing for their high durability, excellent recyclability, and easy immobilization and integration with electrodes, but usually have rather low atom utilization efficiency due to the limited surface sites accessible to reactants. To this end, considerable efforts have been devoted to developing nanoscale heterogeneous catalysts that can increase the exposed surface atoms 3 . However, the inhomogeneity in the distribution of particle sizes and facets poses a serious challenge for controlling active sites and fundamental mechanistic studies 6,7 . In contrast, homogeneous catalysts typically exhibit the well-defined atomic structure with tunable coordination environment that is essential for deciphering the catalytic reaction pathway and rational design of targeted catalysts with tailored catalytic properties 8 . Single-atom catalysts (SACs) with monodispersed single atoms supported on solid substrates are recently emerging as an exciting class of catalysts that combine the merits of both homogeneous and heterogeneous catalysts [9][10][11][12][13][14] . However, most SACs studied to date employ metal oxides (for example, TiO 2 , CeO 2 and FeO x ) as supporting substrates to prevent atom aggregation [15][16][17][18] , which cannot be readily applied in electrocatalytic applications due to their low electrical conductivity and/or poor stability in harsh liquid-phase electrolytes (for example, strong acid or base). Atomic transitionmetal-nitrogen moieties supported in carbon (M-N-Cs) represent a unique class of SACs with high electrical conductivity and superior (electro)chemical stability for electrocatalytic applications 19 . In particular, Fe-based M-N-Cs have been extensively studied as electrocatalysts towards the oxygen reduction reaction (ORR) with demonstrated activity and stability approaching those of commercial Pt/C catalysts 20,21 . In addition, as suggested by numerous theoretical studies, M-N-Cs are promising candidates for catalysing a wide range of electrochemical processes, such as hydrogen reduction/oxidation 22 , CO 2 /CO reduction 23 and N 2 reduction 24 . A significant advantage of SACs is that the well-defined single atomic site could allow precise understanding of the catalytic reaction pathway, and rational design of targeted catalysts with tailored activity (in a manner similar to homogeneous catalyst design). However, this perceived advantage has been investigated theoretically

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“…Studies of ORR-active materials show the presence of both metallic Fe and Fe–N species16242728. ORR catalysts containing a preponderance of either type of site have been recently synthesized, with catalysts suggested to feature FeN 4 species exhibiting the highest activity to date26293031. However, the active species in the vast majority of reported NPM catalysts remains unknown due to the heterogeneity present.…”

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confidence: 99%

Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts

Varnell¹,

Tse²,

Schulz³

et al. 2016

Nat Commun

281

177

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The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites.

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On an Easy Way To Prepare Metal–Nitrogen Doped Carbon with Exclusive Presence of MeN₄-type Sites Active for the ORR

Cited by 437 publications

References 52 publications

Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe‐N‐C Catalysts

Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe‐N‐C Catalysts

General synthesis and definitive structural identification of MN4C4 single-atom catalysts with tunable electrocatalytic activities

Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts

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On an Easy Way To Prepare Metal–Nitrogen Doped Carbon with Exclusive Presence of MeN4-type Sites Active for the ORR

Cited by 437 publications

References 52 publications

Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe‐N‐C Catalysts

Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe‐N‐C Catalysts

General synthesis and definitive structural identification of MN4C4 single-atom catalysts with tunable electrocatalytic activities

Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts

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On an Easy Way To Prepare Metal–Nitrogen Doped Carbon with Exclusive Presence of MeN₄-type Sites Active for the ORR