Title

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

Authors

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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