title: Atomic Structure of Pt3Ni Nanoframe Electrocatalysts by in Situ X-ray Absorption Spectroscopy.
abstract: Understanding the atomic structure of a catalyst is crucial to exposing the source of its performance characteristics. It is highly unlikely that a catalyst remains the same under reaction conditions when compared to as-synthesized. Hence, the ideal experiment to study the catalyst structure should be performed in situ. Here, we use X-ray absorption spectroscopy (XAS) as an in situ technique to study Pt3Ni nanoframe particles which have been proven to be an excellent electrocatalyst for the oxygen reduction reaction (ORR). The surface characteristics of the nanoframes were probed through electrochemical hydrogen underpotential deposition and carbon monoxide electrooxidation, which showed that nanoframe surfaces with different structure exhibit varying levels of binding strength to adsorbate molecules. It is well-known that Pt-skin formation on Pt-Ni catalysts will enhance ORR activity by weakening the binding energy between the surface and adsorbates. Ex situ and in situ XAS results reveal that nanoframes which bind adsorbates more strongly have a rougher Pt surface caused by insufficient segregation of Pt to the surface and consequent Ni dissolution. In contrast, nanoframes which exhibit extremely high ORR activity simultaneously demonstrate more significant segregation of Pt over Ni-rich subsurface layers, allowing better formation of the critical Pt-skin. This work demonstrates that the high ORR activity of the Pt3Ni hollow nanoframes depends on successful formation of the Pt-skin surface structure.
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Nigel
authors.initials: N
authors.lastname: Becknell
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Yijin
authors.initials: Y
authors.lastname: Kang
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Chen
authors.initials: C
authors.lastname: Chen
authors.affiliation: Department of Chemical Engineering, University of California , Berkeley, California 94720, United States.
authors.forename: Joaquin
authors.initials: J
authors.lastname: Resasco
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Nikolay
authors.initials: N
authors.lastname: Kornienko
authors.affiliation: The Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Jinghua
authors.initials: J
authors.lastname: Guo
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Nenad M
authors.initials: NM
authors.lastname: Markovic
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Gabor A
authors.initials: GA
authors.lastname: Somorjai
authors.affiliation: Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Vojislav R
authors.initials: VR
authors.lastname: Stamenkovic
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Kavli Energy Nanoscience Institute , Berkeley, California 94720, United States.
authors.forename: Peidong
authors.initials: P
authors.lastname: Yang