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Performance enhancement and degradation mechanism identification of a single-atom Co–N–C catalyst for proton exchange membrane fuel cells

Abstract

The development of catalysts free of platinum-group metals and with both a high activity and durability for the oxygen reduction reaction in proton exchange membrane fuel cells is a grand challenge. Here we report an atomically dispersed Co and N co-doped carbon (Co–N–C) catalyst with a high catalytic oxygen reduction reaction activity comparable to that of a similarly synthesized Fe–N–C catalyst but with a four-time enhanced durability. The Co–N–C catalyst achieved a current density of 0.022 A cm−2 at 0.9 ViR-free (internal resistance-compensated voltage) and peak power density of 0.64 W cm−2 in 1.0 bar H2/O2 fuel cells, higher than that of non-iron platinum-group-metal-free catalysts reported in the literature. Importantly, we identified two main degradation mechanisms for metal (M)–N–C catalysts: catalyst oxidation by radicals and active-site demetallation. The enhanced durability of Co–N–C relative to Fe–N–C is attributed to the lower activity of Co ions for Fenton reactions that produce radicals from the main oxygen reduction reaction by-product, H2O2, and the significantly enhanced resistance to demetallation of Co–N–C.

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Fig. 1: Synthesis and characterization of the atomically dispersed Co–N–C catalyst.
Fig. 2: Structural characterization of the Co–N–C catalysts.
Fig. 3: RRDE and PEM fuel cell performance measurements.
Fig. 4: Catalysts durability studied on RRDE and MEA.
Fig. 5: Fundamental understanding of degradation mechanisms.

Data availability

The data that support the findings of this study are available within the paper and its Supplementary Information or from the corresponding author upon reasonable request.

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Acknowledgements

The authors acknowledge support from the US Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (DOE-EERE-HFTO) through the Electrocatalysis consortium (ElectroCat) and the DOE programme managers, D. Papageorgopoulos, S. Thompson, D. Peterson and G. Kleen. The XPS measurement was performed using EMSL(grid.436923.9), a DOE Office of Science user facility sponsored by the Biological and Environmental Research programme. PNNL is operated by Battelle for the US DOE under contract DE-AC05-76RLO1830. X-ray spectroscopy experiments were performed at MRCAT at the Advanced Photon Source (APS), a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. The operation of MRCAT is supported both by DOE and the MRCAT member institutions. Argonne National Laboratory is operated for the US DOE by the University of Chicago Argonne LLC under contract no. DE-AC02-06CH11357. Electron microscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. The DFT calculations were performed on the computers of the University of Pittsburgh Center for Research Computing as well as the Extreme Science and Engineering Discovery Environment (XSEDE), which is funded by National Science Foundation grant no. ACI-1053575.

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Contributions

X.X. and Y.S. formulated the concept. X.X. performed the synthesis and electrochemical tests. C.H. and V.R. performed the PEM fuel cell tests and analysed the data. Y.H. and X.S.L. conducted the Brunauer–Emmett–Teller and non-local DFT analyses, J.L. the thermogravimetric analysis, Z.N. and M.E.B. the PXRD analysis and T.L. the ICP-OES analysis. D.A.C. and M.S. performed the electron microscopy characterization. M.H.E. performed the XPS tests. E.C.W., A.J.K. and D.J.M. acquired and analysed the XAS data. G. Wang and B.L. performed the DFT calculations and analysed the results. Y.C. performed the Mössbauer measurements and analysed the data. U.M. and P.Z. performed the in situ CO2 emission tests and analysed the data. G. Wu provided guidance on catalyst design, synthesis and characterization. Y.S. supervised the research. X.X., Y.S., G. Wu, G. Wang, D.J.M. and P.Z. co-wrote the paper. All the authors discussed and commented on the manuscript. The views and opinions of the authors expressed here do not necessarily state or reflect those of the US government or any agency thereof. Neither the US government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.

Corresponding authors

Correspondence to Gang Wu, Vijay Ramani or Yuyan Shao.

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Competing interests

Battelle Memorial Institute has filed a USPTO provisional patent application (no. 62/985,713) on the Co–N–C catalyst and its synthesis reported in this paper; the inventors are Y.S. and X.X.; the status is provisional; and the title is ‘A High-Performing and Stable Platinum Group Metal (PGM) Catalyst for Fuel Cells’.

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Peer review information Nature Catalysis thanks Anatoly Frenkel and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–25, Tables 1–7, Discussions 1–4 and references.

Supplementary Data 1

Atomic coordinates of the optimized computational models.

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Xie, X., He, C., Li, B. 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). https://doi.org/10.1038/s41929-020-00546-1

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