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In a seed-mediated synthesis, nanocrystal growth is often described by assuming the absence of homogeneous nucleation in the solution. Here we provide new insights into the nucleation and growth mechanisms underlying the formation of bimetallic nanodendrites that are characterized by a dense array of Pt branches anchored to a Pd nanocrystal core. These nanostructures can be easily prepared by a one-step, seeded growth method that involves the reduction of K2PtCl4 by L-ascorbic acid in the presence of 9-nm truncated octahedral Pd seeds in an aqueous solution. Transmission electron microscopy (TEM) and high-resolution TEM analyses revealed that both homogeneous and heterogeneous nucleation of Pt occurred at the very early stages of the synthesis and the Pt branches grew through oriented attachment of small Pt particles that had been formed via homogeneous nucleation. These new findings contradict the generally accepted mechanism for seeded growth that only involves heterogeneous nucleation and simple growth via atomic addition. We have also investigated the electrocatalytic properties of the Pd–Pt nanodendrites for the oxygen reduction and formic acid oxidation reactions by conducting a comparative study with foam-like Pt nanostructures prepared in the absence of Pd seeds under otherwise identical conditions.


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Nucleation and Growth Mechanisms for Pd–Pt Bimetallic Nanodendrites and Their Electrocatalytic Properties

Show Author's information Byungkwon Lim1Majiong Jiang2Taekyung Yu1Pedro H. C. Camargo1Younan Xia1( )
Department of Biomedical Engineering, Washington UniversitySt. Louis, Missouri 63130 USA
Department of Chemistry, Washington UniversitySt. Louis, Missouri 63130 USA

Abstract

In a seed-mediated synthesis, nanocrystal growth is often described by assuming the absence of homogeneous nucleation in the solution. Here we provide new insights into the nucleation and growth mechanisms underlying the formation of bimetallic nanodendrites that are characterized by a dense array of Pt branches anchored to a Pd nanocrystal core. These nanostructures can be easily prepared by a one-step, seeded growth method that involves the reduction of K2PtCl4 by L-ascorbic acid in the presence of 9-nm truncated octahedral Pd seeds in an aqueous solution. Transmission electron microscopy (TEM) and high-resolution TEM analyses revealed that both homogeneous and heterogeneous nucleation of Pt occurred at the very early stages of the synthesis and the Pt branches grew through oriented attachment of small Pt particles that had been formed via homogeneous nucleation. These new findings contradict the generally accepted mechanism for seeded growth that only involves heterogeneous nucleation and simple growth via atomic addition. We have also investigated the electrocatalytic properties of the Pd–Pt nanodendrites for the oxygen reduction and formic acid oxidation reactions by conducting a comparative study with foam-like Pt nanostructures prepared in the absence of Pd seeds under otherwise identical conditions.

Keywords: Palladium, oxygen reduction, formic acid oxidation, platinum, seeded growth

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Received: 14 November 2009
Revised: 25 November 2009
Accepted: 27 November 2009
Published: 27 March 2010
Issue date: February 2010

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© The Author(s) 2010

Acknowledgements

Acknowledgements

This work was supported in part by the National Science Foundation (NSF) (No. DMR-0804088) and startup funds from Washington University in St. Louis. T.Y. was also partially supported by the National Research Foundation of Korea Grant funded by the Korean Government (No. NRF-2009-352-D00160). Pedro Henrique Cury Camargo (P.H.C.C.) was also partially supported by the Fulbright Program and the Brazilian Ministry of Education (CAPES). Part of the work was performed at the Nano Research Facility (NRF), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under award No. ECS-0335765. NRF is part of the School of Engineering and Applied Science at Washington University in St. Louis.

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