title: In Situ Probing of the Active Site Geometry of Ultrathin Nanowires for the Oxygen Reduction Reaction.
abstract: To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (∼2 nm) core-shell Pt∼Pd9Au nanowires, which have been previously shown to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu∼Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Hence, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general.
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook , Stony Brook, New York 11794-3400, United States.
authors.forename: Haiqing
authors.initials: H
authors.lastname: Liu
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Building 555, Upton, New York 11973, United States.
authors.forename: Wei
authors.initials: W
authors.lastname: An
authors.affiliation: Department of Physics, Yeshiva University , New York, New York 10016, United States.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Physics, Yeshiva University , New York, New York 10016, United States.
authors.forename: Anatoly I
authors.initials: AI
authors.lastname: Frenkel
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Building 555, Upton, New York 11973, United States.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Sasaki
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook , Stony Brook, New York 11794-3400, United States.
authors.forename: Christopher
authors.initials: C
authors.lastname: Koenigsmann
authors.affiliation: Center for Functional Nanomaterials, Brookhaven National Laboratory , Building 735, Upton, New York 11973, United States.
authors.forename: Dong
authors.initials: D
authors.lastname: Su
authors.affiliation: Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712-1224, United States.
authors.forename: Rachel M
authors.initials: RM
authors.lastname: Anderson
authors.affiliation: Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712-1224, United States.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Crooks
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Building 555, Upton, New York 11973, United States.
authors.forename: Radoslav R
authors.initials: RR
authors.lastname: Adzic
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Building 555, Upton, New York 11973, United States.
authors.forename: Ping
authors.initials: P
authors.lastname: Liu
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook , Stony Brook, New York 11794-3400, United States.|Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory , Building 480, Upton, New York 11973, United States.
authors.forename: Stanislaus S
authors.initials: SS
authors.lastname: Wong