scholarly journals A pyridinic Fe-N4 macrocycle models the active sites in Fe/N-doped carbon electrocatalysts

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Travis Marshall-Roth ◽  
Nicole J. Libretto ◽  
Alexandra T. Wrobel ◽  
Kevin J. Anderton ◽  
Michael L. Pegis ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Catalytic Properties ◽  
Molecular Model ◽  
Reduction Reaction ◽  
Electrochemical Studies ◽  
Onset Potential ◽  
Nitrogen Doped ◽  
Nitrogen Doped Carbon ◽  
Excellent Selectivity

Abstract Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site structures remain poorly understood. A leading postulate is that the iron-containing active sites exist primarily in a pyridinic Fe-N4 ligation environment, yet, molecular model catalysts generally feature pyrrolic coordination. Herein, we report a molecular pyridinic hexaazacyclophane macrocycle, (phen2N2)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for ORR to a typical Fe-N-C material and prototypical pyrrolic iron macrocycles. N 1s XPS and XAS signatures for (phen2N2)Fe are remarkably similar to those of Fe-N-C. Electrochemical studies reveal that (phen2N2)Fe has a relatively high Fe(III/II) potential with a correlated ORR onset potential within 150 mV of Fe-N-C. Unlike the pyrrolic macrocycles, (phen2N2)Fe displays excellent selectivity for four-electron ORR, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data demonstrate that (phen2N2)Fe is a more effective model of Fe-N-C active sites relative to the pyrrolic iron macrocycles, thereby establishing a new molecular platform that can aid understanding of this important class of catalytic materials.

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

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-N<sub>4</sub> pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N<sub>4</sub> catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen<sub>2</sub>N<sub>2</sub>)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 (phen<sub>2</sub>N<sub>2</sub>)Fe are positively shifted relative to (Pc)Fe and (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen<sub>2</sub>N<sub>2</sub>)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 (phen<sub>2</sub>N<sub>2</sub>)Fe that are close to the average 1.94 Å length in Fe-N-C. Electrochemical studies establish that both (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)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 (phen<sub>2</sub>N<sub>2</sub>)Fe relative to (OEP)Fe. Consequently, the ORR onset for (phen<sub>2</sub>N<sub>2</sub>)Fe and (Pc)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe and (Pc)Fe, (phen<sub>2</sub>N<sub>2</sub>)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H<sub>2</sub>O<sub>2</sub> production, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data establish (phen<sub>2</sub>N<sub>2</sub>)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.<p><b></b></p>

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

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-N<sub>4</sub> pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N<sub>4</sub> catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen<sub>2</sub>N<sub>2</sub>)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 (phen<sub>2</sub>N<sub>2</sub>)Fe are positively shifted relative to (Pc)Fe and (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen<sub>2</sub>N<sub>2</sub>)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 (phen<sub>2</sub>N<sub>2</sub>)Fe that are close to the average 1.94 Å length in Fe-N-C. Electrochemical studies establish that both (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)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 (phen<sub>2</sub>N<sub>2</sub>)Fe relative to (OEP)Fe. Consequently, the ORR onset for (phen<sub>2</sub>N<sub>2</sub>)Fe and (Pc)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe and (Pc)Fe, (phen<sub>2</sub>N<sub>2</sub>)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H<sub>2</sub>O<sub>2</sub> production, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data establish (phen<sub>2</sub>N<sub>2</sub>)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.<p><b></b></p>

Probing the Oxygen Reduction Reaction Active Sites over Nitrogen-Doped Carbon Nanostructures (CNx) in Acidic Media Using Phosphate Anion

ACS Catalysis ◽  
2016 ◽  
Vol 6 (10) ◽  
pp. 7249-7259 ◽  
Author(s):  
Kuldeep Mamtani ◽  
Deeksha Jain ◽  
Dmitry Zemlyanov ◽  
Gokhan Celik ◽  
Jennifer Luthman ◽  
...  
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Carbon Nanostructures ◽  
Active Sites ◽  
Reduction Reaction ◽  
Phosphate Anion ◽  
Acidic Media ◽  
Nitrogen Doped ◽  
Nitrogen Doped Carbon

Identifying Active Sites of Nitrogen-Doped Carbon Materials for the CO2 Reduction Reaction

2018 ◽  
Vol 28 (21) ◽  
pp. 1800499 ◽  
Author(s):  
Song Liu ◽  
Hongbin Yang ◽  
Xiang Huang ◽  
Linghui Liu ◽  
Weizheng Cai ◽  
...  
Keyword(s):  
Active Sites ◽  
Carbon Materials ◽  
Co2 Reduction ◽  
Reduction Reaction ◽  
Nitrogen Doped ◽  
Nitrogen Doped Carbon ◽  
Co2 Reduction Reaction

Preparation of monodisperse ferrous nanoparticles embedded in carbon aerogels via in situ solid phase polymerization for electrocatalytic oxygen reduction

Nanoscale ◽  
2020 ◽  
Vol 12 (28) ◽  
pp. 15318-15324
Author(s):  
Wei Hong ◽  
Xin Feng ◽  
Lianqiao Tan ◽  
Aiming Guo ◽  
Bing Lu ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Active Sites ◽  
Solid Phase ◽  
Reduction Reaction ◽  
Carbon Aerogels ◽  
Structured Materials ◽  
Nitrogen Doped ◽  
Electrocatalytic Oxygen Reduction ◽  
Nitrogen Doped Carbon

Core–shell structured materials constructed by using Fe/Fe3C cores and nitrogen doped carbon shells represent a type of promising non-precious oxygen reduction reaction (ORR) catalyst due to well-established active sites at the interface positions.

scholarly journals Recent Advances in Non-Precious Transition Metal/Nitrogen-doped Carbon for Oxygen Reduction Electrocatalysts in PEMFCs

Catalysts ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 141 ◽  
Author(s):  
Meixiu Song ◽  
Yanhui Song ◽  
Wenbo Sha ◽  
Bingshe Xu ◽  
Junjie Guo ◽  
...  
Keyword(s):  
Transition Metal ◽  
Oxygen Reduction ◽  
Active Sites ◽  
Proton Exchange Membrane ◽  
High Efficiency ◽  
Catalytic Performance ◽  
Reduction Reaction ◽  
Proton Exchange ◽  
Nitrogen Doped ◽  
Nitrogen Doped Carbon

The proton exchange membrane fuel cells (PEMFCs) have been considered as promising future energy conversion devices, and have attracted immense scientific attention due to their high efficiency and environmental friendliness. Nevertheless, the practical application of PEMFCs has been seriously restricted by high cost, low earth abundance and the poor poisoning tolerance of the precious Pt-based oxygen reduction reaction (ORR) catalysts. Noble-metal-free transition metal/nitrogen-doped carbon (M–NxC) catalysts have been proven as one of the most promising substitutes for precious metal catalysts, due to their low costs and high catalytic performance. In this review, we summarize the development of M–NxC catalysts, including the previous non-pyrolyzed and pyrolyzed transition metal macrocyclic compounds, and recent developed M–NxC catalysts, among which the Fe–NxC and Co–NxC catalysts have gained our special attention. The possible catalytic active sites of M–NxC catalysts towards the ORR are also analyzed here. This review aims to provide some guidelines towards the design and structural regulation of non-precious M–NxC catalysts via identifying real active sites, and thus, enhancing their ORR electrocatalytic performance.

Solution Plasma Synthesis of Nitrogen-Doped Carbon Nanoballs as Effective Metal-Free Electrocatalysts for Oxygen Reduction Reaction

2014 ◽  
Vol 1641 ◽  
Author(s):  
Gasidit Panomsuwan ◽  
Satoshi Chiba ◽  
Nagahiro Saito ◽  
Takahiro Ishizaki
Keyword(s):  
Thermal Annealing ◽  
Organic Liquid ◽  
Reduction Reaction ◽  
Limiting Current ◽  
Plasma Synthesis ◽  
Plasma Process ◽  
Onset Potential ◽  
Nitrogen Doped ◽  
Before And After ◽  
Nitrogen Doped Carbon

ABSTRACTNitrogen-doped carbons nanoballs were synthesized from an organic liquid precursor (a mixture of benzene and pyrazine) by solution plasma process. After synthesis, they were further annealed at 700 and 900 °C under N2 atmosphere. The nitrogen-doped carbon nanoballs before and after thermal annealing process exhibit a similar morphological feature, and their diameters are in the range between 20 and 40 nm. With higher annealing temperature, the graphitization of the nitrogen-doped carbon nanoballs increases. For the electrocatalytic activity in an alkaline solution, the limiting current density and onset potential for the ORR activity can be significantly improved for the samples after thermal annealing at 900 °C. We anticipate that solution plasma process will be a viable alternative way for synthesizing heteroatom-doped carbon electrocatalysts for broad application in the field of fuel cells, metal-air batteries, and supercapacitors.

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