Facile Synthesis of Bimetallic Nanoplates Consisting of Pd Cores and Pt Shells through Seeded Epitaxial Growth

Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130, USA.
Nano Letters (Impact Factor: 13.59). 08/2008; 8(8):2535-40. DOI: 10.1021/nl8016434
Source: PubMed


Pd-Pt core-shell nanoplates with hexagonal and triangular shapes were synthesized through the heterogeneous, epitaxial growth of Pt on Pd nanoplates. The Pd nanoplates were synthesized by reducing Na2PdCl4 precursor with PVP as a reducing agent, which then served as seeds for the nucleation of Pt atoms formed by reducing H2PtCl6 with citric acid. Characterization of the as-prepared Pd-Pt nanoplates by scanning transmission electron microscopy and high-resolution transmission electron microscopy reveals that a thin, uniform Pt shell was formed around the Pd nanoplate, demonstrating the layer-by-layer epitaxial growth of Pt on Pd surface in this approach. The close lattice match between Pd and Pt (lattice mismatch of only 0.77%) and the slow reduction rate associated with the mild reducing power of citric acid play key roles in achieving the epitaxial growth of Pt shells on Pd nanoplates.

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    • "For these reasons electrochemically controlled design of uniform Pt nano-structures is very attractive, yet challenging task that has been pursued over decades. Examples among the electroless methods for Pt developed so far are spontaneous deposition [1] [2] [3] based on the reduction of spontaneously pre-adsorbed Pt-complex using the potential or reducing agents in the solution; galvanic displacement of a less noble metal core [4] [5] [6] [7] often called " transmetalation " and chemical reduction in a hydrogen atmosphere or in presence of reducing agents in the solution [8] [9]. Besides these approaches there has been a steady interest in understanding and optimization of the conventional electrodeposition approaches (potential/current controlled) for growth of Pt thin films and nanostructures [10] [11] [12] [13] [14] [15] [16] [17]. "
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    ABSTRACT: A surface limited redox replacement (SLRR) protocol for the growth of Pt thin films using adsorbed H or also called underpotentially deposited H (H-UPD) is developed in this work. In contrast to the previously reported studies on SLRR deposition, this work presents the first application of the SLRR protocol in a single-cell configuration using a nonmetal UPD system. Utilizing H-UPD to mediate Pt growth is of significance for “green” Pt deposition that minimizes the use of environmentally hazardous chemicals by precluding possible mediator metal incorporation reported in standard Pt SLRR protocols. Open circuit chronopotentiometry and quartz-crystal microbalance experiments demonstrate steady displacement kinetics and a yield that is equal to the expected stoichiometric Pt(II)–H exchange ratio (1:2). Cyclic voltammetry characterization of Pt films shows that the growth via SLRR of H-UPD results in increase of the surface roughness with the number of replacement steps. The morphology of as-deposited films has been analyzed by Scanning Tunneling Microscopy. Moreover, the roughness of SLRR deposited Pt films has been compared with films grown in the same solution at two different overpotentials: without adsorbed H (bulk deposition) and with H-UPD floating on the surface i.e. H-surfactant mediated growth (SMG). The results show clear advantages of using the SLRR approach which generates films with nearly two times lower roughness than the ones grown by bulk deposition and SMG. The generality of the proposed approach is validated by growth of Pt films on two types of Pd surfaces: Pd ultrathin films on Au (Pd/Au) and Pd nanocubes. The Pt overlayers grown by 30 replacements on Pd structures have been characterized by H-UPD and their catalytic activity examined by formic acid oxidation reaction.
    Full-text · Article · Dec 2013 · Electrochimica Acta
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    • ", which is also consistent with our observation; that is, the formation of Pt bumps at multiple sites on the Pd seed. In a previous study, we observed the conformal growth of thin Pt layers on the surface of Pd nanoplates in the presence of citric acid as both the reducing and capping agent [5]. Citric acid seems to play a significant role in stabilizing the {111} facets of the deposited Pt layers and lowering their surface energy, thus promoting the layered growth. "
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    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. KeywordsPalladium-platinum-seeded growth-oxygen reduction-formic acid oxidation
    Full-text · Article · Feb 2010 · Nano Research
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    ABSTRACT: Zinc nanoplates were grown using thermal evaporation without catalyst or template involved. Tunneling electron microscopy and selected area electron diffraction analyses showed that the plates were single crystals with either {0001} or {11–20} as basal surfaces. The morphological characteristics were explained in terms of the intrinsic growth anisotropy of zinc, the surface energy of the nano-crystals, the size of the critical nucleus and the migration of the adatoms. Our results suggested a promising low-cost route for synthesis of pure zinc nanoplates which could be used as precursor for further preparing core-shell nanoplate structures.
    No preview · Article · Sep 2012 · Science China Technological Sciences
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