title: Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts.
abstract: The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Varnell
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Edmund C M
authors.initials: EC
authors.lastname: Tse
authors.affiliation: Department of Physics, Knox College, Galesburg, Illinois 61401, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Schulz
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Tim T
authors.initials: TT
authors.lastname: Fister
authors.affiliation: Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Richard T
authors.initials: RT
authors.lastname: Haasch
authors.affiliation: Department of Physics, Yeshiva University, New York, New York 10016, USA.
authors.forename: Janis
authors.initials: J
authors.lastname: Timoshenko
authors.affiliation: Department of Physics, Yeshiva University, New York, New York 10016, USA.
authors.forename: Anatoly I
authors.initials: AI
authors.lastname: Frenkel
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.|International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Gewirth