title: Experimental Observation of Redox-Induced Fe-N Switching Behavior as a Determinant Role for Oxygen Reduction Activity.
abstract: The commercialization of electrochemical energy conversion and storage devices relies largely upon the development of highly active catalysts based on abundant and inexpensive materials. Despite recent achievements in this respect, further progress is hindered by the poor understanding of the nature of active sites and reaction mechanisms. Herein, by characterizing representative iron-based catalysts under reactive conditions, we identify three Fe-N4-like catalytic centers with distinctly different Fe-N switching behaviors (Fe moving toward or away from the N4-plane) during the oxygen reduction reaction (ORR), and show that their ORR activities are essentially governed by the dynamic structure associated with the Fe(2+/3+) redox transition, rather than the static structure of the bare sites. Our findings reveal the structural origin of the enhanced catalytic activity of pyrolyzed Fe-based catalysts compared to nonpyrolyzed Fe-macrocycle compounds. More generally, the fundamental insights into the dynamic nature of transition-metal compounds during electron-transfer reactions will potentially guide rational design of these materials for broad applications.
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Qingying
authors.initials: Q
authors.lastname: Jia
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Nagappan
authors.initials: N
authors.lastname: Ramaswamy
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Hasnain
authors.initials: H
authors.lastname: Hafiz
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Urszula
authors.initials: U
authors.lastname: Tylus
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Kara
authors.initials: K
authors.lastname: Strickland
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Gang
authors.initials: G
authors.lastname: Wu
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Barbiellini
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Arun
authors.initials: A
authors.lastname: Bansil
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Edward F
authors.initials: EF
authors.lastname: Holby
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Piotr
authors.initials: P
authors.lastname: Zelenay
authors.affiliation: Department of Chemistry and Chemical Biology, and ‡Department of Physics, Northeastern University , Boston, Massachusetts 02115, United States.|Materials Science and Technology Division, and ∥Materials Physics and Applications Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Mukerjee
mesh_terms: D002384:Catalysis; D007501:Iron / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D007501:Iron; D009584:Nitrogen; D010100:Oxygen
keywords: active sites; dynamic structure; non-PGM catalysts; oxygen reduction reaction; redox transition