Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 118, Issue 17, Pages 8999-9008Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp500781v
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Funding
- U. S. Department of Energy, EERE [DE-EE-0000459]
- U.S. Department of Energy, Office of Basic Energy Sciences
- Center for Synchrotron Biosciences from the National Institute of Biomedical Imaging and Bioengineering (NBIB) [P30-EB-009998]
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Detailed understanding of the nature of the active centers in non-precious-metal-based electrocatalyst, and their role in oxygen reduction reaction (ORR) mechanistic pathways will have a profound effect on successful commercialization of emission-free energy devices such as fuel cells. Recently, using pyrolyzed model structures of iron porphyrins, we have demonstrated that a covalent integration of the Fe-N-x sites into pi-conjugated carbon basal plane modifies electron donating/withdrawing capability of the carbonaceous ligand, consequently improving ORR activity. Here, we employ a combination of in situ X-ray spectroscopy and electrochemical methods to identify the various structural and functional forms of the active centers in non-heme Fe/N/C catalysts. Both methods corroboratively confirm the single site 2e(-) x 2e(-) mechanism in alkaline media on the primary Fe2+-N-4 centers and the dual-site 2e(-) x 2e(-) mechanism in acid media with the significant role of the surface bound coexisting Fe/FexOy nanoparticles (NPs) as the secondary active sites.
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