Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 16, Issue 27, Pages 13800-13806Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4cp01634c
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Funding
- DOE-EPSCoR Implementation Program: Materials for Energy Conversion
- DOE-EERE Fuel Cell Technology Program
- National Science Foundation [DMR TG-110093]
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First-principles density functional theory (DFT) calculations were performed to explain the stability of catalytically active sites in Fe-N-x-C electrocatalysts, their ORR activity and ORR mechanism. The results show that the formation of graphitic in-plane Fe-N-4 sites in a carbon matrix is energetically favorable over the formation of Fe-N-2 sites. Chemisorption of ORR species O-2, O, OH, OOH, and H2O and O-O bond breaking in peroxide occur on both Fe-N-2 and Fe-N-4 sites. In addition to the favorable interaction of ORR species, the computed free energy diagrams show that elementary ORR reaction steps on Fe-N-x sites are downhill. Thus, a complete ORR is predicted to occur via a single site 4e(-) mechanism on graphitic Fe-N-x (x = 2, 4) sites. Because of their higher stability and working potential for ORR, Fe-N-4 sites are predicted to be prime candidate sites for ORR in pyrolyzed Fe-N-x-C electrocatalysts.
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