Abstract
Fe–N–C catalysts are the most promising platinum group metal-free oxygen-reduction catalysts, but they suffer from a low density of active metal sites and the so-called activity–stability trade-off. Here we report an Fe–N–C catalyst prepared by adding an optimal amount of H2 to the traditional inert atmosphere during the thermal activation. The presence of H2 significantly increases the total density of FeN4 sites, suppressing the unstable pyrrolic-N-coordinated S1 sites and favouring the stable pyridinic-N-coordinated S2 sites with shortened Fe–N bond lengths. We propose that the intrinsically stable S2 sites are probably arranged in well-graphitized carbon layers, and the S1 sites exist in less-graphitized carbon. H2 could remove unstable S1 sites and retain stable S2 sites during the pyrolysis to break the challenging activity–stability trade-off. The Fe–N–C catalyst in membrane electrode assemblies maintains a current density of 67 mA cm−2 at 0.8 V (H2–air) after 30,000 voltage cycles (0.60 to 0.95 V under H2–air), achieving encouraging durability and performance simultaneously.
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Acknowledgements
We acknowledge support from the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office. Scanning transmission electron microscopy research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. This work was in part authored by Argonne National Laboratory, which is operated for the US DOE by the University of Chicago Argonne LLC under contract no. DE-AC02-06CH11357. G. Wu also thanks the New York State’s Center of Excellence in Materials Informatics (CMI) at the University at Buffalo, as well as the National Science Foundation (CBET-1604392, 1804326 and 2223467), for partial support.
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G. Wu, J.-P.D. and Y.Z. were the primary writers of the paper. Y.Z., J.L., B.Z., S.K. and G. Wu designed the catalyst synthesis and performed the electrochemical experiments, characterized the catalyst and analysed the data. C.L. and J.X. carried out fuel cell tests and data analysis. D.A.C. and M.J.Z. together performed the electron microscopy imaging and further characterizations. B. Li and G. Wang designed and performed DFT calculations. M.L., M.W. and Z.F. designed and performed X-ray absorption spectroscopy and data analysis. R.P.H., E.E.A., B. Lavina and D.J.M. designed and performed Mössbauer spectroscopy experiments and data analysis. G. Wu supervised the execution of the overall project.
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Zeng, Y., Li, C., Li, B. et al. Tuning the thermal activation atmosphere breaks the activity–stability trade-off of Fe–N–C oxygen reduction fuel cell catalysts. Nat Catal 6, 1215–1227 (2023). https://doi.org/10.1038/s41929-023-01062-8
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DOI: https://doi.org/10.1038/s41929-023-01062-8
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