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Title: Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation

Abstract

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). We report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunable through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. In using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change ofmore » chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe3+ to Fe2+) likely bonded with pyridinic N (FeN4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe–N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H2SO4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μgPt/cm2). Finally, enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6–1.0 V) in O2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.« less

Authors:
 [1];  [2];  [3]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5];  [1];  [5]; ORCiD logo [5]; ORCiD logo [2];  [5]; ORCiD logo [1]
  1. State Univ. of New York (SUNY), Buffalo, NY (United States). Dept. of Chemical and Biological Engineering
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials
  3. Oregon State Univ., Corvallis, OR (United States). School of Chemical and Biological and Environmental Engineering
  4. Univ. of South Carolina, Columbia, SC (United States). Dept. of Chemical Engineering
  5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Fuel Cell Technologies Office
OSTI Identifier:
1394763
Report Number(s):
BNL-114340-2017-JA
Journal ID: ISSN 0002-7863; R&D Project: 16060; 16060; KC0403020; TRN: US1702386
Grant/Contract Number:  
SC0012704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 40; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
29 ENERGY PLANNING, POLICY, AND ECONOMY; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Atomic iron catalysts; electrocatalysis; oxygen reduction; metal-organic frameworks; size control; Center for Functional Nanomaterials

Citation Formats

Zhang, Hanguang, Hwang, Sooyeon, Wang, Maoyu, Feng, Zhenxing, Karakalos, Stavros, Luo, Langli, Qiao, Zhi, Xie, Xiaohong, Wang, Chongmin, Su, Dong, Shao, Yuyan, and Wu, Gang. Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation. United States: N. p., 2017. Web. doi:10.1021/jacs.7b06514.
Zhang, Hanguang, Hwang, Sooyeon, Wang, Maoyu, Feng, Zhenxing, Karakalos, Stavros, Luo, Langli, Qiao, Zhi, Xie, Xiaohong, Wang, Chongmin, Su, Dong, Shao, Yuyan, & Wu, Gang. Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation. United States. https://doi.org/10.1021/jacs.7b06514
Zhang, Hanguang, Hwang, Sooyeon, Wang, Maoyu, Feng, Zhenxing, Karakalos, Stavros, Luo, Langli, Qiao, Zhi, Xie, Xiaohong, Wang, Chongmin, Su, Dong, Shao, Yuyan, and Wu, Gang. 2017. "Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation". United States. https://doi.org/10.1021/jacs.7b06514. https://www.osti.gov/servlets/purl/1394763.
@article{osti_1394763,
title = {Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation},
author = {Zhang, Hanguang and Hwang, Sooyeon and Wang, Maoyu and Feng, Zhenxing and Karakalos, Stavros and Luo, Langli and Qiao, Zhi and Xie, Xiaohong and Wang, Chongmin and Su, Dong and Shao, Yuyan and Wu, Gang},
abstractNote = {It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). We report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunable through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. In using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe3+ to Fe2+) likely bonded with pyridinic N (FeN4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe–N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H2SO4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μgPt/cm2). Finally, enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6–1.0 V) in O2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.},
doi = {10.1021/jacs.7b06514},
url = {https://www.osti.gov/biblio/1394763}, journal = {Journal of the American Chemical Society},
issn = {0002-7863},
number = 40,
volume = 139,
place = {United States},
year = {2017},
month = {9}
}

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