Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

High loading of single atomic iron sites in Fe–NC oxygen reduction catalysts for proton exchange membrane fuel cells

Nature Catalysis volume 5, pages 311–323 (2022)Cite this article

Subjects

Abstract

Non-precious iron-based catalysts (Fe–NCs) require high active site density to meet the performance targets as cathode catalysts in proton exchange membrane fuel cells. Site density is generally limited to that achieved at a 1–3 wt%(Fe) loading due to the undesired formation of iron-containing nanoparticles at higher loadings. Here we show that by preforming a carbon–nitrogen matrix using a sacrificial metal (Zn) in the initial synthesis step and then exchanging iron into this preformed matrix we achieve 7 wt% iron coordinated solely as single-atom Fe–N4 sites, as identified by 57Fe cryogenic Mössbauer spectroscopy and X-ray absorption spectroscopy. Site density values measured by in situ nitrite stripping and ex situ CO chemisorption methods are 4.7 × 1019 and 7.8 × 1019 sites g−1, with a turnover frequency of 5.4 electrons sites−1 s−1 at 0.80 V in a 0.5 M H2SO4 electrolyte. The catalyst delivers an excellent proton exchange membrane fuel cell performance with current densities of 41.3 mA cm−2 at 0.90 ViR-free using H2–O2 and 145 mA cm−2 at 0.80 V (199 mA cm−2 at 0.80 ViR-free) using H2–air.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Learn more

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Calculation of the Fe–NC SD and effect on performance.
Fig. 2: Structural analysis of Fe–NC catalysts.
Fig. 3: Analysis of Fe coordination environments before and after activation.
Fig. 4: SD and TOF measurements of Fe–NCs in a pH 5.2 electrolyte.
Fig. 5: ORR activity and correlation with SD and kinetic activity in a pH 0.3 electrolyte.
Fig. 6: Performance tests with Fe–NCΔ-DCDA as the cathode catalyst in a single-cell PEMFC.

Data availability

The data used in the production of the figures in this paper are available for download at https://doi.org/10.5281/zenodo.6411262. Additional data can be available from the authors upon reasonable request.

References

  1. Hydrogen Roadmap Europe (Fuel Cells and Hydrogen 2 Joint Undertaking, 2019); https://www.fch.europa.eu/sites/default/files/Hydrogen%20Roadmap%20Europe_Report.pdf

  2. Multi-Year Research Development, and Demonstration Plan: Section 3.4 Fuel Cells, Office of Energy Efficiency and Renewable Energy (Fuel Cell Technologies Office, 2016); https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf

  3. Wilson, A., Kleen, G. & Papageorgopoulos, D. Fuel Cell System Cost–2017 (DOE Hydrogen and Fuel Cells Program, 2017).

  4. Jaouen, F. et al. Recent advances in non-precious metal catalysis for oxygen-reduction reaction in polymer electrolyte fuel cells. Energy Environ. Sci. 4, 114–130 (2011).

    Article  CAS  Google Scholar 

  5. Jaouen, F. et al. Toward platinum group metal-free catalysts for hydrogen/air proton-exchange membrane fuel cells. Johns. Matthey Technol. Rev. 62, 231–255 (2018).

    Article  CAS  Google Scholar 

  6. Chung, H. T. et al. Direct atomic-level insight into the active sites of a high-performance PGM-free ORR catalyst. Science 357, 479–484 (2017).

    Article  CAS  PubMed  Google Scholar 

  7. Lefèvre, M., Proietti, E., Jaouen, F. & Dodelet, J.-P. Iron-based catalysts with improved oxygen reduction activity in polymer electrolyte fuel cells. Science 324, 71–74 (2009).

    Article  PubMed  CAS  Google Scholar 

  8. Wu, G., More, K. L., Johnston, C. M. & Zelenay, P. High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science 332, 443–447 (2011).

    Article  CAS  PubMed  Google Scholar 

  9. Tylus, U. et al. Elucidating oxygen reduction active sites in pyrolyzed metal–nitrogen coordinated non-precious-metal electrocatalyst systems. J. Phys. Chem. C 118, 8999–9008 (2014).

    Article  CAS  Google Scholar 

  10. Sahraie, N. R. et al. Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts. Nat. Commun. 6, 8618 (2015).

  11. Jasinski, R. A new fuel cell cathode catalyst. Nature 201, 1212–1213 (1964).

    Article  CAS  Google Scholar 

  12. Jasinski, R. Cobalt phthalocyanine as a fuel cell cathode. J. Electrochem. Soc. 112, 526 (1965).

    Article  CAS  Google Scholar 

  13. Gupta, S., Tryk, D., Bae, I., Aldred, W. & Yeager, E. Heat-treated polyacrylonitrile-based catalysts for oxygen electroreduction. J. Appl. Electrochem. 19, 19–27 (1989).

    Article  CAS  Google Scholar 

  14. Martinez, U., Babu, S. K., Holby, E. F. & Zelenay, P. Durability challenges and perspective in the development of PGM-free electrocatalysts for the oxygen reduction reaction. Curr. Opin. Electrochem. 9, 224–232 (2018).

    Article  CAS  Google Scholar 

  15. Malko, D., Lopes, T., Symianakis, E. & Kucernak, A. The intriguing poison tolerance of non-precious metal oxygen reduction reaction (ORR) catalysts. J. Mater. Chem. A 4, 142–152 (2016).

    Article  CAS  Google Scholar 

  16. Kramm, U. I. et al. On an easy way to prepare metal–nitrogen doped carbon with exclusive presence of MeN4-type sites active for the ORR. J. Am. Chem. Soc. 138, 635–640 (2016).

    Article  CAS  PubMed  Google Scholar 

  17. Ranjbar Sahraie, N., Paraknowitsch, J. P., Göbel, C., Thomas, A. & Strasser, P. Noble-metal-free electrocatalysts with enhanced ORR performance by task-specific functionalization of carbon using ionic liquid precursor systems. J. Am. Chem. Soc. 136, 14486–14497 (2014).

    Article  CAS  PubMed  Google Scholar 

  18. Serov, A., Artyushkova, K. & Atanassov, P. Fe–N–C oxygen reduction fuel cell catalyst derived from carbendazim: synthesis, structure, and reactivity. Adv. Energy Mater. 4, 1301735 (2014).

    Article  CAS  Google Scholar 

  19. Zhang, H. et al. Single atomic iron catalysts for oxygen reduction in acidic media: particle size control and thermal activation. J. Am. Chem. Soc. 139, 14143–14149 (2017).

    Article  CAS  PubMed  Google Scholar 

  20. Zhang, H. et al. High-performance fuel cell cathodes exclusively containing atomically dispersed iron active sites. Energy Environ. Sci. 12, 2548–2558 (2019).

    Article  CAS  Google Scholar 

  21. Ferrandon, M. et al. Multitechnique characterization of a polyaniline–iron–carbon oxygen reduction catalyst. J. Phys. Chem. C 116, 16001–16013 (2012).

    Article  CAS  Google Scholar 

  22. Wan, X. et al. Fe–N–C electrocatalyst with dense active sites and efficient mass transport for high-performance proton exchange membrane fuel cells. Nat. Catal. 2, 259–268 (2019).

    Article  CAS  Google Scholar 

  23. Liu, M., Liu, J., Li, Z., Song, Y. & Wang, F. A silica-confined strategy for completely atomic level Fe(II)–NC catalysts with a non-planar structure toward oxygen reduction reaction. J. Catal. 370, 21–29 (2019).

    Article  CAS  Google Scholar 

  24. He, Y. et al. Highly active atomically dispersed CoN4 fuel cell cathode catalysts derived from surfactant-assisted MOFs: carbon-shell confinement strategy. Energy Environ. Sci. 12, 250–260 (2019).

    Article  CAS  Google Scholar 

  25. Hu, B.-C. et al. SiO2-protected shell mediated templating synthesis of Fe–N-doped carbon nanofibers and their enhanced oxygen reduction reaction performance. Energy Environ. Sci. 11, 2208–2215 (2018).

    Article  CAS  Google Scholar 

  26. He, Y., Liu, S., Priest, C., Shi, Q. & Wu, G. Atomically dispersed metal–nitrogen–carbon catalysts for fuel cells: advances in catalyst design, electrode performance, and durability improvement. Chem. Soc. Rev. 49, 3484–3524 (2020).

    Article  CAS  PubMed  Google Scholar 

  27. Das, R., Pachfule, P., Banerjee, R. & Poddar, P. Metal and metal oxide nanoparticle synthesis from metal organic frameworks (MOFs): finding the border of metal and metal oxides. Nanoscale 4, 591–599 (2012).

    Article  CAS  PubMed  Google Scholar 

  28. Morozan, A., Goellner, V., Nedellec, Y., Hannauer, J. & Jaouen, F. Effect of the transition metal on metal–nitrogen–carbon catalysts for the hydrogen evolution reaction. J. Electrochem. Soc. 162, H719 (2015).

    Article  CAS  Google Scholar 

  29. Ellingham, H. J. T. Reducibility of oxides and sulfides in metallurgical processes. J. Soc. Chem. Ind. 63, 125–133 (1944).

    Article  CAS  Google Scholar 

  30. Mehmood, A. et al. Facile metal coordination of active site imprinted nitrogen doped carbons for the conservative preparation of non‐noble metal oxygen reduction electrocatalysts. Adv. Energy Mater. 8, 1701771 (2018).

    Article  CAS  Google Scholar 

  31. Menga, D. et al. Active‐site imprinting: preparation of Fe–N–C catalysts from zinc ion–templated ionothermal nitrogen‐doped carbons. Adv. Energy Mater. 9, 1902412 (2019).

    Article  CAS  Google Scholar 

  32. Li, J. et al. Evolution pathway from iron compounds to Fe1(II)–N4 sites through gas-phase iron during pyrolysis. J. Am. Chem. Soc. 142, 1417–1423 (2019).

    Article  CAS  Google Scholar 

  33. Jiao, L. et al. Chemical vapour deposition of Fe–N–C oxygen reduction catalysts with full utilization of dense Fe–N4 sites. Nat. Mater. 20, 1385–1391 (2021).

    Article  CAS  PubMed  Google Scholar 

  34. Malko, D., Kucernak, A. & Lopes, T. In situ electrochemical quantification of active sites in Fe–N/C non-precious metal catalysts. Nat. Commun. 7, 13285 (2016).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  35. Luo, F. et al. Accurate evaluation of active-site density (SD) and turnover frequency (TOF) of PGM-free metal–nitrogen-doped carbon (MNC) electrocatalysts using CO cryo adsorption. ACS Catal. 9, 4841–4852 (2019).

    Article  CAS  Google Scholar 

  36. Malko, D., Kucernak, A. & Lopes, T. Performance of Fe–N/C oxygen reduction electrocatalysts toward NO2–, NO, and NH2OH electroreduction: from fundamental insights into the active center to a new method for environmental nitrite destruction. J. Am. Chem. Soc. 138, 16056–16068 (2016).

    Article  CAS  PubMed  Google Scholar 

  37. Leonard, N. D. et al. Deconvolution of utilization, site density, and turnover frequency of Fe–nitrogen–carbon oxygen reduction reaction catalysts prepared with secondary N-precursors. ACS Catal. 8, 1640–1647 (2018).

    Article  CAS  Google Scholar 

  38. Primbs, M. et al. Establishing reactivity descriptors for platinum group metal (PGM)-free Fe–N–C catalysts for PEM fuel cells. Energy Environ. Sci. 13, 2480–2500 (2020).

    Article  CAS  Google Scholar 

  39. Osmieri, L. et al. Status and challenges for the application of platinum group metal-free catalysts in proton exchange membrane fuel cells. Curr. Opin. Electrochem. 25, 100627 (2021).

    Article  CAS  Google Scholar 

  40. Uddin, A. et al. High power density platinum group metal-free cathodes for polymer electrolyte fuel cells. ACS Appl. Mater. Interfaces 12, 2216–2224 (2019).

    Article  CAS  Google Scholar 

  41. Gupta, S. et al. Engineering favorable morphology and structure of Fe–N–C oxygen‐reduction catalysts through tuning of nitrogen/carbon precursors. ChemSusChem 10, 774–785 (2017).

    Article  CAS  PubMed  Google Scholar 

  42. Terrell, E. & Garcia-Perez, M. Application of nitrogen-based blowing agents as an additive in pyrolysis of cellulose. J. Anal. Appl. Pyrol. 137, 203–211 (2019).

    Article  CAS  Google Scholar 

  43. Li, J. et al. Volcano trend in electrocatalytic CO2 reduction activity over atomically dispersed metal sites on nitrogen-doped carbon. ACS Catal. 9, 10426–10439 (2019).

    Article  CAS  Google Scholar 

  44. Wyckoff, R. W. G. Crystal Structures (John Wiley, 1963).

  45. Zitolo, A. et al. Identification of catalytic sites for oxygen reduction in iron- and nitrogen-doped graphene materials. Nat. Mater. 14, 937–942 (2015).

    Article  CAS  PubMed  Google Scholar 

  46. Li, J. et al. Identification of durable and non-durable FeNx sites in Fe–N–C materials for proton exchange membrane fuel cells. Nat. Catal. 4, 10–19 (2021).

    Article  CAS  Google Scholar 

  47. Kramm, U. I., Lefèvre, M., Larouche, N., Schmeisser, D. & Dodelet, J.-P. Correlations between mass activity and physicochemical properties of Fe/N/C catalysts for the ORR in PEM fuel cell via 57Fe Mössbauer spectroscopy and other techniques. J. Am. Chem. Soc. 136, 978–985 (2014).

    Article  CAS  PubMed  Google Scholar 

  48. Kneebone, J. L. et al. A combined probe-molecule, Mössbauer, nuclear resonance vibrational spectroscopy, and density functional theory approach for evaluation of potential iron active sites in an oxygen reduction reaction catalyst. J. Phys. Chem. C 121, 16283–16290 (2017).

    Article  CAS  Google Scholar 

  49. Mineva, T. et al. Understanding active sites in pyrolyzed Fe–N–C catalysts for fuel cell cathodes by bridging density functional theory calculations and 57Fe Mössbauer spectroscopy. ACS Catal. 9, 9359–9371 (2019).

    Article  CAS  Google Scholar 

  50. Jing, M. et al. A feasible strategy to enhance mass transfer property of carbon nanofibers electrode in vanadium redox flow battery. Electrochim. Acta https://doi.org/10.1016/j.electacta.2021.138879 (2021).

  51. Birchall, T. An investigation of some iron halide complexes by Mössbauer spectroscopy. Can. J. Chem. 47, 1351–1354 (1969).

    Article  CAS  Google Scholar 

  52. Wang, Z. & Inagaki, M. Mössbauer study of iron chloride–graphite intercalation compounds synthesized in molten salt. Carbon 29, 423–427 (1991).

    Article  CAS  Google Scholar 

  53. Li, J. et al. Thermally driven structure and performance evolution of atomically dispersed FeN4 sites for oxygen reduction. Angew. Chem. Int. Ed. 58, 18971–18980 (2019).

    Article  CAS  Google Scholar 

  54. Boldrin, P. et al. Deactivation, reactivation and super-activation of Fe–N/C oxygen reduction electrocatalysts: gas sorption, physical and electrochemical investigation using NO and O2. Appl. Catal. B 292, 120169 (2021).

    Article  CAS  Google Scholar 

  55. Zalitis, C. M., Kucernak, A. R. J., Lin, X. & Sharman, J. D. B. Electrochemical measurement of intrinsic oxygen reduction reaction activity at high current densities as a function of particle size for Pt4–xCox /C (x = 0,1,3) catalysts. ACS Catal. 10, 4361–4376 (2020).

    Article  CAS  Google Scholar 

  56. Al-Zoubi, T. et al. Preparation of nonprecious metal electrocatalysts for the reduction of oxygen using a low-temperature sacrificial metal. J. Am. Chem. Soc. 142, 5477–5481 (2020).

    Article  CAS  PubMed  Google Scholar 

  57. Li, J. et al. Structural and mechanistic basis for the high activity of Fe–N–C catalysts toward oxygen reduction. Energy Environ. Sci. 9, 2418–2432 (2016).

    Article  CAS  Google Scholar 

  58. Xie, X. et al. Performance enhancement and degradation mechanism identification of a single-atom Co–N–C catalyst for proton exchange membrane fuel cells. Nat. Catal. 3, 1044–1054 (2020).

    Article  CAS  Google Scholar 

  59. Banham, D. et al. Critical advancements in achieving high power and stable nonprecious metal catalyst-based MEAs for real-world proton exchange membrane fuel cell applications. Sci. Adv. 4, eaar7180 (2018).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  60. Chenitz, R. et al. A specific demetalation of Fe–N4 catalytic sites in the micropores of NC_Ar + NH3 is at the origin of the initial activity loss of the highly active Fe/N/C catalyst used for the reduction of oxygen in PEM fuel cells. Energy Environ. Sci. 11, 365–382 (2018).

    Article  CAS  Google Scholar 

  61. Gao, Y. et al. New insight into effect of potential on degradation of Fe-NC catalyst for ORR. Front. Energy 15, 421–430 (2021).

    Article  Google Scholar 

  62. Litster, S. Advanced PGM-free Cathode Engineering for High Power Density and Durability, DOE Annual Merit Review Presentation Database (DOE Hydrogen Program, 2021).

  63. Zelenay, P. & Meyers, D. ElectroCat 2.0 (Electrocatalysis Consortium), Annual Merit Review Presentation Database (DOE Hydrogen Program, 2021).

  64. Filipponi, A. & Di Cicco, A. X-ray-absorption spectroscopy and n-body distribution functions in condensed matter. II. Data analysis and applications. Phys. Rev. B 52, 15135–15149 (1995).

    Article  CAS  Google Scholar 

  65. Filipponi, A., Di Cicco, A. & Natoli, C. R. X-ray-absorption spectroscopy and n-body distribution functions in condensed matter. I. Theory. Phys. Rev. B 52, 15122–15134 (1995).

    Article  CAS  Google Scholar 

  66. Artyushkova, K. Misconceptions in interpretation of nitrogen chemistry from X-ray photoelectron spectra. J. Vac. Sci. Technol. A 38, 031002 (2020).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

This work was funded by the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement no. 779366. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe research. The work was supported by the UK Engineering and Physical Sciences Research Council under project EP/P024807/1.

Author information

Authors and Affiliations

  1. Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, London, UK

    Asad Mehmood, Mengjun Gong & Anthony Kucernak

  2. ICGM, Université de Montpellier, CNRS, ENSCM, Montpellier, France

    Frédéric Jaouen, Aaron Roy & Moulay-Tahar Sougrati

  3. Synchrotron SOLEIL, L’orme des Merisiers, BP 48 Saint Aubin, Gif-sur-Yvette, France

    Andrea Zitolo & Anastassiya Khan

  4. Department of Chemistry, Chemical Engineering Division, Technical University of Berlin, Berlin, Germany

    Mathias Primbs & Peter Strasser

  5. Johnson Matthey Technology Center, Reading, UK

    Alex Martinez Bonastre & Dash Fongalland

  6. Department of Materials Chemistry, National Institute of Chemistry, Ljubljana, Slovenia

    Goran Drazic

Authors
  1. Asad Mehmood
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Mengjun Gong
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Frédéric Jaouen
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Aaron Roy
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Andrea Zitolo
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Anastassiya Khan
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Moulay-Tahar Sougrati
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Mathias Primbs
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Alex Martinez Bonastre
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Dash Fongalland
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Goran Drazic
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Peter Strasser
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. Anthony Kucernak
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

A.M. and A.K. conceived the idea and designed the experiments. A.M. and M.G. synthesized the materials and carried out electrochemical tests and physical characterizations. A.K. developed the geometrical models of the catalyst. A.M. and M.G. carried out the small-size single-cell tests. F.J., A.R. and M.-T.S. performed the Mössbauer measurements and data analysis, A.Z. and A.K. performed the XAS measurements, data analysis and fitting, and interpretation of the XANES and EXAFS results, M.P. and P.S. conducted CO chemisorption measurements and data analysis, A.M.B. and D.F. carried out large-size single-cell tests, and G.D. performed energy-dispersive X-ray spectroscopy STEM and atomic-resolution STEM measurements and data analysis. A.M., F.J. and A.K. wrote and edited the manuscript with feedback from all the contributing authors. A.K. acted as the project supervisor.

Corresponding author

Correspondence to Anthony Kucernak.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Catalysis thanks the anonymous reviewers for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Method 1, Figs. 1–37, Tables 1–7 and Notes 1–10.

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Mehmood, A., Gong, M., Jaouen, F. et al. High loading of single atomic iron sites in Fe–NC oxygen reduction catalysts for proton exchange membrane fuel cells. Nat Catal 5, 311–323 (2022). https://doi.org/10.1038/s41929-022-00772-9

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41929-022-00772-9

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing