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

2021 ◽  
Author(s):  
Giorgia Daniel ◽  
Tomasz Kosmala ◽  
Federico Brombin ◽  
Marco Mazzucato ◽  
Alessandro Facchin ◽  
...  
Keyword(s):  
Active Sites ◽  
Chemical Properties ◽  
Platinum Group Metal ◽  
Reduction Reaction ◽  
Point Of View ◽  
Thermochemical Conversion ◽  
Chitosan Hydrogel ◽  
Acidic Aqueous Solution ◽  
Before And After ◽  
Nitrogen Doped Carbon

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.

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

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 390
Author(s):  
Giorgia Daniel ◽  
Tomasz Kosmala ◽  
Federico Brombin ◽  
Marco Mazzucato ◽  
Alessandro Facchin ◽  
...  
Keyword(s):  
Active Sites ◽  
Chemical Properties ◽  
Platinum Group Metal ◽  
Reduction Reaction ◽  
Point Of View ◽  
Thermochemical Conversion ◽  
Chitosan Hydrogel ◽  
Acidic Aqueous Solution ◽  
Before And After ◽  
Nitrogen Doped Carbon

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 terms 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 due to 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.

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

scholarly journals The Challenge of Achieving a High Density of Fe-Based Active Sites in a Highly Graphitic Carbon Matrix

Catalysts ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 144 ◽  
Author(s):  
Jingkun Li ◽  
Qingying Jia ◽  
Sanjeev Mukerjee ◽  
Moulay-Tahar Sougrati ◽  
Goran Drazic ◽  
...  
Keyword(s):  
Porous Structure ◽  
Active Sites ◽  
Carbon Matrix ◽  
Platinum Group Metal ◽  
Reduction Reaction ◽  
High Specific Surface Area ◽  
High Density ◽  
Graphitic Carbon ◽  
High Degree ◽  
Degree Of Graphitization

As one of the most promising platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR), Fe–N–C catalysts with a high density of FeNx moieties integrated in a highly graphitic carbon matrix with a proper porous structure have attracted extensive attention to combine the high activity, high stability and high accessibility of active sites. Herein, we investigated a ZnCl2/NaCl eutectic salts-assisted ionothermal carbonization method (ICM) to synthesize Fe–N–C catalysts with tailored porous structure, high specific surface area and a high degree of graphitization. However, it was found to be challenging to anchor a high density of FeNx sites onto highly graphitized carbon. Iron precursors with preexisting Fe–N coordination were required to form FeNx sites in the nitrogen-doped carbon with a high degree of graphitization, while individual Fe and N precursors led to a Fe–N–C catalyst with poor-ORR activity. This provides valuable insights into the synthesis-structure relationship. Moreover, the FeNx moieties were identified as the major active sites in acidic conditions, while both FeNx sites and Fe2O3 were found to be active in alkaline medium.

scholarly journals High-performance fuel cell cathodes exclusively containing atomically dispersed iron active sites

2019 ◽  
Vol 12 (8) ◽  
pp. 2548-2558 ◽  
Author(s):  
Hanguang Zhang ◽  
Hoon T. Chung ◽  
David A. Cullen ◽  
Stephan Wagner ◽  
Ulrike I. Kramm ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Active Sites ◽  
High Performance ◽  
Platinum Group Metal ◽  
Reduction Reaction ◽  
Polymer Electrolyte Fuel Cells ◽  
Metal Free ◽  
Fuel Cell Cathodes ◽  
Iron Active Sites ◽  
Cell Cathodes

Platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) with atomically dispersed FeN4 sites have emerged as a potential replacement for low-PGM catalysts in acidic polymer electrolyte fuel cells (PEFCs).

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.

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