Abstract
Nitrogen-coordinated single atom iron sites (FeN4) embedded in carbon (Fe–N–C) are the most active platinum group metal-free oxygen reduction catalysts for proton-exchange membrane fuel cells. However, current Fe–N–C catalysts lack sufficient long-term durability and are not yet viable for practical applications. Here we report a highly durable and active Fe–N–C catalyst synthesized using heat treatment with ammonia chloride followed by high-temperature deposition of a thin layer of nitrogen-doped carbon on the catalyst surface. We propose that catalyst stability is improved by converting defect-rich pyrrolic N-coordinated FeN4 sites into highly stable pyridinic N-coordinated FeN4 sites. The stability enhancement is demonstrated in membrane electrode assemblies using accelerated stress testing and a long-term steady-state test (>300 h at 0.67 V), approaching a typical Pt/C cathode (0.1 mgPt cm−2). The encouraging stability improvement represents a critical step in developing viable Fe–N–C catalysts to overcome the cost barriers of hydrogen fuel cells for numerous applications.
Original language | English |
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Pages (from-to) | 652-663 |
Number of pages | 12 |
Journal | Nature Energy |
Volume | 7 |
Issue number | 7 |
DOIs | |
State | Published - Jul 2022 |
Funding
We acknowledge the support from the US DOE Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (DE-EE0008076 and DE-EE0008417). 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. The Talos F200X S/TEM tool was provided by US DOE, Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science user facilities. XAS measurements were performed at MRCAT at the Advanced Photon Source, a US DOE Office of Science user facility operated for the US DOE by Argonne National Laboratory. The operation of MRCAT is supported both by DOE and the MRCAT member institutions. 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 number DE-AC02-06CH11357. G. Wu also acknowledges support from the National Science Foundation (CBET-1604392, 1804326). Z. Feng acknowledges the support from the National Science Foundation (CBET-1949870, 2016192). G. Wang gratefully acknowledges the computational resources provided by the Center for Research Computing at the University of Pittsburgh. We also thank B. Lavina of the Advanced Photon Source for help with the acquisition of Mössbauer spectroscopy data. We acknowledge the support from the US DOE Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (DE-EE0008076 and DE-EE0008417). 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. The Talos F200X S/TEM tool was provided by US DOE, Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science user facilities. XAS measurements were performed at MRCAT at the Advanced Photon Source, a US DOE Office of Science user facility operated for the US DOE by Argonne National Laboratory. The operation of MRCAT is supported both by DOE and the MRCAT member institutions. 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 number DE-AC02-06CH11357. G. Wu also acknowledges support from the National Science Foundation (CBET-1604392, 1804326). Z. Feng acknowledges the support from the National Science Foundation (CBET-1949870, 2016192). G. Wang gratefully acknowledges the computational resources provided by the Center for Research Computing at the University of Pittsburgh. We also thank B. Lavina of the Advanced Photon Source for help with the acquisition of Mössbauer spectroscopy data.