A Pyridinic Fe-N4 Macrocycle Effectively Models the Active Sites in Fe/N-Doped Carbon Electrocatalysts

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum in fuel cells, but their active site structures are poorly understood. A leading postulate is that iron active sites in this class of materials exist in an Fe-N4 pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N4 catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen2N2)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for oxygen reduction to a prototypical Fe-N-C material and iron octaethylporphyrin, (OEP)Fe, a prototypical pyrrolic iron macrocycle. N 1s XPS signatures for coordinated N atoms in (phen2N2)Fe are positively shifted relative to (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen2N2)Fe are distinct from those of (OEP)Fe, and are remarkably similar to those of Fe-N-C with compressed Fe–N bond lengths of 1.97 Å in (phen2N2)Fe that are similar to the average 1.94 Å length in Fe-N-C. Electrochemical data indicate that the iron center in (phen2N2)Fe is relatively electropositive, with an Fe(III)-OH/Fe(II)-OH2 potential at 0.59 V vs the reversible hydrogen electrode (RHE), ~300 mV positive of (OEP)Fe. This correlates with a 300 mV positive shift in the onset of ORR catalysis for (phen2N2)Fe with a corresponding 1400-fold increase in TOF relative to (OEP)Fe. Consequently, the ORR onset for (phen2N2)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe, (phen2N2)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H2O2 production, comparable to Fe-N-C materials. This study establishes a pyridinic iron macrocycle that effectively models Fe-N-C active sites and provides a rich platform for constructing high-performance Fe-based oxygen reduction catalysts.

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A Pyridinic Fe-N4 Macrocycle Effectively Models the Active Sites in Fe/N-Doped Carbon Electrocatalysts

10.26434/chemrxiv.10008545.v2 ◽

2020 ◽

Author(s):

Travis Marshall-Roth ◽

Nicole J. Libretto ◽

Alexandra T. Wrobel ◽

Kevin Anderton ◽

Nathan D. Ricke ◽

...

Keyword(s):

Oxygen Reduction ◽

Active Sites ◽

Catalytic Properties ◽

Reduction Reaction ◽

Iron Phthalocyanine ◽

Electrochemical Studies ◽

Onset Potential ◽

Nitrogen Doped Carbon ◽

Iron Active Sites

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum in fuel cells, but their active site structures are poorly understood. A leading postulate is that iron active sites in this class of materials exist in an Fe-N4 pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N4 catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen2N2)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for oxygen reduction to a prototypical Fe-N-C material, as well as iron phthalocyanine, (Pc)Fe, and iron octaethylporphyrin, (OEP)Fe, prototypical pyrrolic iron macrocycles. N 1s XPS signatures for coordinated N atoms in (phen2N2)Fe are positively shifted relative to (Pc)Fe and (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen2N2)Fe are distinct from those of both (Pc)Fe and (OEP)Fe, and are remarkably similar to those of Fe-N-C with compressed Fe–N bond lengths of 1.97 Å in (phen2N2)Fe that are close to the average 1.94 Å length in Fe-N-C. Electrochemical studies establish that both (Pc)Fe and (phen2N2)Fe have relatively high Fe(III/II) potentials at ~0.6 V, ~300 mV positive of (OEP)Fe. The ORR onset potential is found to directly correlate with the Fe(III/II) potential leading to a ~300 mV positive shift in the onset of ORR for (Pc)Fe and (phen2N2)Fe relative to (OEP)Fe. Consequently, the ORR onset for (phen2N2)Fe and (Pc)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe and (Pc)Fe, (phen2N2)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H2O2 production, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data establish (phen2N2)Fe as a pyridinic iron macrocycle that effectively models Fe-N-C active sites, thereby providing a rich molecular platform for understanding this important class of catalytic materials.

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Treasure Map for Nonmetallic Catalyst: Optimal Nitrogen and Fluorine Distribution of Biomass-Derived Carbon Materials for High-Performance Oxygen Reduction Catalysts

Journal of Materials Chemistry A ◽

10.1039/d1ta05485f ◽

2021 ◽

Author(s):

Yaling Zhao ◽

Yang Liu ◽

Ye Chen ◽

Xupo Liu ◽

Xiaoge Li ◽

...

Keyword(s):

Fuel Cells ◽

Oxygen Reduction Reaction ◽

Oxygen Reduction ◽

High Throughput ◽

Porous Carbon ◽

High Performance ◽

Carbon Materials ◽

Reduction Reaction ◽

Oxygen Reduction Catalysts ◽

Reduction Catalysts

Heteroatom-doped porous carbon materials have shown promising prospects in the field of Zn-air batteries (ZABs) and fuel cells. However, the high-throughput preparation and instant screening of excellent oxygen reduction reaction...

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Conversion of straw to nitrogen doped carbon for efficient oxygen reduction catalysts in microbial fuel cells

RSC Advances ◽

10.1039/c5ra15235f ◽

2015 ◽

Vol 5 (109) ◽

pp. 89771-89776 ◽

Cited By ~ 23

Author(s):

Lang Liu ◽

Qi Xiong ◽

Chungen Li ◽

Yan Feng ◽

Shuiliang Chen

Keyword(s):

Oxygen Reduction ◽

Microbial Fuel Cells ◽

Freeze Drying ◽

Reduction Reaction ◽

Nitrogen Doped ◽

High Efficient ◽

Oxygen Reduction Catalysts ◽

Nitrogen Doped Carbon ◽

Reduction Catalysts ◽

Oxygen Reduction Reaction Catalyst

Nitrogen-doped carbon with high nitrogen content was prepared from rice straw through a three-step process, including hydrothermal, freeze drying and heat-treatment in NH3, and was used as a high-efficient oxygen reduction reaction catalyst in MFCs.

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A Pyridinic Fe-N4 Macrocycle Effectively Models the Active Sites in Fe/N-Doped Carbon Electrocatalysts

10.26434/chemrxiv.10008545 ◽

2020 ◽

Author(s):

Travis Marshall-Roth ◽

Nicole J. Libretto ◽

Alexandra T. Wrobel ◽

Kevin Anderton ◽

Nathan D. Ricke ◽

...

Keyword(s):

Oxygen Reduction ◽

Active Sites ◽

Catalytic Properties ◽

Reduction Reaction ◽

Iron Phthalocyanine ◽

Electrochemical Studies ◽

Onset Potential ◽

Nitrogen Doped Carbon ◽

Iron Active Sites

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum in fuel cells, but their active site structures are poorly understood. A leading postulate is that iron active sites in this class of materials exist in an Fe-N4 pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N4 catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen2N2)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for oxygen reduction to a prototypical Fe-N-C material, as well as iron phthalocyanine, (Pc)Fe, and iron octaethylporphyrin, (OEP)Fe, prototypical pyrrolic iron macrocycles. N 1s XPS signatures for coordinated N atoms in (phen2N2)Fe are positively shifted relative to (Pc)Fe and (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen2N2)Fe are distinct from those of both (Pc)Fe and (OEP)Fe, and are remarkably similar to those of Fe-N-C with compressed Fe–N bond lengths of 1.97 Å in (phen2N2)Fe that are close to the average 1.94 Å length in Fe-N-C. Electrochemical studies establish that both (Pc)Fe and (phen2N2)Fe have relatively high Fe(III/II) potentials at ~0.6 V, ~300 mV positive of (OEP)Fe. The ORR onset potential is found to directly correlate with the Fe(III/II) potential leading to a ~300 mV positive shift in the onset of ORR for (Pc)Fe and (phen2N2)Fe relative to (OEP)Fe. Consequently, the ORR onset for (phen2N2)Fe and (Pc)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe and (Pc)Fe, (phen2N2)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H2O2 production, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data establish (phen2N2)Fe as a pyridinic iron macrocycle that effectively models Fe-N-C active sites, thereby providing a rich molecular platform for understanding this important class of catalytic materials.

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Microbe-engaged synthesis of carbon dot-decorated reduced graphene oxide as high-performance oxygen reduction catalysts

Journal of Materials Chemistry A ◽

10.1039/c6ta01662f ◽

2016 ◽

Vol 4 (19) ◽

pp. 7222-7229 ◽

Cited By ~ 33

Author(s):

Lihua Zhou ◽

Peng Fu ◽

Yueqiang Wang ◽

Lihua Sun ◽

Yong Yuan

Keyword(s):

Graphene Oxide ◽

Oxygen Reduction ◽

Reduced Graphene Oxide ◽

High Performance ◽

Reduction Reaction ◽

Microbial Reduction ◽

Carbon Dot ◽

Reduced Graphene ◽

Oxygen Reduction Catalysts ◽

Reduction Catalysts

A carbon dot-decorated reduced graphene oxide catalyst for the oxygen reduction reaction is developed via a combination of microbial reduction and hydrothermal treatment.

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Nitrogen-doped carbon with a high degree of graphitization derived from biomass as high-performance electrocatalyst for oxygen reduction reaction

Applied Surface Science ◽

10.1016/j.apsusc.2016.11.073 ◽

2017 ◽

Vol 396 ◽

pp. 986-993 ◽

Cited By ~ 41

Author(s):

Jujiao Zhao ◽

Yanming Liu ◽

Xie Quan ◽

Shuo Chen ◽

Hongtao Yu ◽

...

Keyword(s):

Oxygen Reduction Reaction ◽

Oxygen Reduction ◽

High Performance ◽

Reduction Reaction ◽

Nitrogen Doped ◽

Nitrogen Doped Carbon ◽

High Degree ◽

Degree Of Graphitization

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Identification of Active Sites of Pure and Nitrogen-Doped Carbon Materials for Oxygen Reduction Reaction Using Constant-Potential Calculations

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.0c03951 ◽

2020 ◽

Vol 124 (22) ◽

pp. 12016-12023

Author(s):

Zhiyao Duan ◽

Graeme Henkelman

Keyword(s):

Oxygen Reduction Reaction ◽

Oxygen Reduction ◽

Active Sites ◽

Carbon Materials ◽

Reduction Reaction ◽

Nitrogen Doped ◽

Constant Potential ◽

Nitrogen Doped Carbon

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NaCl protected synthesis of 3D hierarchical metal-free porous nitrogen-doped carbon catalysts for the oxygen reduction reaction in acidic electrolyte

Chemical Communications ◽

10.1039/c9cc02986a ◽

2019 ◽

Vol 55 (61) ◽

pp. 9023-9026 ◽

Cited By ~ 16

Author(s):

Rui Wu ◽

Xiaoju Wan ◽

Jianghai Deng ◽

Xun Huang ◽

Siguo Chen ◽

...

Keyword(s):

Oxygen Reduction Reaction ◽

Oxygen Reduction ◽

High Performance ◽

Porous Metal ◽

Reduction Reaction ◽

Protective Agent ◽

Metal Free ◽

Hierarchical Porous ◽

Carbon Catalysts ◽

Nitrogen Doped Carbon

A high-performance 3D hierarchical porous metal-free N-doped carbon catalyst for oxygen reduction reaction in acidic medium was synthesized with ZnO as a mesoporous template and NaCl as both a macroporous template and a structure protective agent.

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Transition Metal (Fe, Co, Ni) Nanoparticles on Selective Amino-N-Doped Carbon as High-Performance Oxygen Reduction Reaction Electrocatalyst

Nanomaterials ◽

10.3390/nano9050742 ◽

2019 ◽

Vol 9 (5) ◽

pp. 742 ◽

Cited By ~ 9

Author(s):

Seonghee Kim ◽

Shuhei Kato ◽

Takahiro Ishizaki ◽

Oi Lun Li ◽

Jun Kang

Keyword(s):

Transition Metal ◽

Oxygen Reduction Reaction ◽

Oxygen Reduction ◽

High Performance ◽

Reduction Reaction ◽

Metal Nanoparticle ◽

Superior Performance ◽

Pt Catalyst ◽

Hydrogen Electrode ◽

Electrochemical Testing

Metal-air batteries are attracting increasing attention as a superior renewable energy conversion device due to their high performance and strong potential. However, the high cost and low stability of the current Pt catalyst is the main obstacle preventing wide industrial application. In this work, we applied a plasma process to fabricate aniline and a transition metals electrode (Fe, Co, Ni) as the carbon-nitrogen and the metal nanoparticle (NP) precursors, respectively, for selective metal/amino-N-doped carbon catalysts. All three as-synthesized catalysts exhibited dominant amino-N as the major C–N bonding state. In electrochemical testing, Co/amino-N-doped carbon showed positive E1/2 potential (0.83 V vs. Reversible Hydrogen Electrode (RHE)). In addition, the calculated electron transfer number (n) of Co/amino-N-doped carbon at 0.5 V vs. RHE was 3.81, which was only slightly less than that of commercial Pt/C (3.97). This superior performance of transition metal/amino-N-doped carbon promotes it as an economical oxygen reduction reaction (ORR) electrocatalyst to replace expensive Pt/C in metal-air batteries.

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