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Title: Chemical Kinetic Method for Active-Site Quantification in Fe-N-C Catalysts and Correlation with Molecular Probe and Spectroscopic Site-Counting Methods

Journal Article · · Journal of the American Chemical Society
ORCiD logo [1];  [1]; ORCiD logo [1];  [1]; ORCiD logo [2];  [3]; ORCiD logo [4]; ORCiD logo [4];  [5]; ORCiD logo [6]; ORCiD logo [6];  [5]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [7]; ORCiD logo [6]; ORCiD logo [1]; ORCiD logo [1]
  1. University of Wisconsin - Madison, WI (United States)
  2. University of California, Irvine, CA (United States)
  3. University at Buffalo, The State University of New York, NY (United States)
  4. Technical University Berlin (Germany)
  5. Technische Universität München (TUM), Garching (Germany)
  6. Univ. Montpellier (France)
  7. Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin (Germany)

Mononuclear Fe ions ligated by nitrogen (FeNx) dispersed on nitrogen-doped carbon (Fe-N-C) serve as active centers for electrocatalytic O2 reduction and thermocatalytic aerobic oxidations. Despite their promise as replacements for precious metals in a variety of practical applications, such as fuel cells, the discovery of new Fe-N-C catalysts has relied primarily on empirical approaches. In this context, the development of quantitative structure–reactivity relationships and benchmarking of catalysts prepared by different synthetic routes and by different laboratories would be facilitated by the broader adoption of methods to quantify atomically dispersed FeNx active centers. In the present study, we develop a kinetic probe reaction method that uses the aerobic oxidation of a model hydroquinone substrate to quantify the density of FeNx centers in Fe- N-C catalysts. The kinetic method is compared with low-temperature Mössbauer spectroscopy, CO pulse chemisorption, and electrochemical reductive stripping of NO derived from NO2 on a suite of Fe-N-C catalysts prepared by diverse routes and featuring either the exclusive presence of Fe as FeNx sites or the coexistence of aggregated Fe species in addition to FeNx. The FeNx site densities derived from the kinetic method correlate well with those obtained from CO pulse chemisorption and Mössbauer spectroscopy. The broad survey of Fe-N-C materials also reveals the presence of outliers and challenges associated with each site quantification approach. Furthermore, the kinetic method developed here does not require pretreatments that may alter active-site distributions nor specialized equipment beyond reaction vessels and analytical instrumentation (e.g., NMR).

Research Organization:
University of Wisconsin - Madison, WI (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Advanced Materials & Manufacturing Technologies Office (AMMTO)
Grant/Contract Number:
FG02-05ER15690
OSTI ID:
2274937
Journal Information:
Journal of the American Chemical Society, Vol. 145, Issue 48; ISSN 0002-7863
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

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