Long-Range Segregation Phenomena in Shape-Selected Bimetallic Nanoparticles: Chemical State Effects

    Authors

    M. Ahmadi; F. Behafarid; C. H. Cui; P. Strasser;B. R. Cuenya

    Comments

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    Abbreviated Journal Title

    ACS Nano

    Keywords

    PtNi; octahedral; nanoparticle; segregation; diffusion; PtNi alloy; AFM; XPS; OXYGEN REDUCTION REACTION; RAY PHOTOELECTRON-SPECTROSCOPY; FUEL-CELL; ELECTROCATALYSTS; METAL-SUPPORT INTERACTIONS; ALLOY NANOPARTICLES; CO; OXIDATION; IN-SITU; PLATINUM NANOPARTICLES; HYDROGENATION ACTIVITY; SURFACE-COMPOSITION; Chemistry, Multidisciplinary; Chemistry, Physical; Nanoscience &; Nanotechnology; Materials Science, Multidisciplinary

    Abstract

    A study of the morphological and chemical stability of shape-selected octahedral Pt0.5Ni0.5 nanoparticles (NPs) supported on highly oriented pyrolytic graphite (HOPG) is presented. Ex situ atomic force microscopy (AFM) and in situ X-ray photoelectron spectroscopy (XPS) measurements were used to monitor the mobility of Pt0.5Ni0.5 NPs and to study long-range atomic segregation and alloy formation phenomena under vacuum, H-2, and O-2 environments. The chemical state of the NPs was found to play a pivotal role in their surface composition after different thermal treatments. In particular, for these ex situ synthesized NPs, Ni segregation to the NP surface was observed in all environments as long as PtOx species were present. In the presence of oxygen, an enhanced Ni surface segregation was observed at all temperatures. In contrast, in hydrogen and vacuum, the Ni outward segregation occurs only at low temperature ( < 200-270 degrees C), while PtOx species are still present. At higher temperatures, the reduction of the Pt oxide species results in Pt diffusion toward the NP surface and the formation of a Ni-Pt alloy. A consistent correlation between the NP surface composition and its electrocatalytic CO oxidation activity was established.

    Journal Title

    Acs Nano

    Volume

    7

    Issue/Number

    10

    Publication Date

    1-1-2013

    Document Type

    Article

    Language

    English

    First Page

    9195

    Last Page

    9204

    WOS Identifier

    WOS:000326209100093

    ISSN

    1936-0851

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