- Nano Express
- Open Access
Kinetic study of Pt nanocrystal deposition on Ag nanowires with clean surfaces via galvanic replacement
© Shen et al.; licensee Springer. 2012
Received: 7 February 2012
Accepted: 6 May 2012
Published: 6 May 2012
Without using any templates or surfactants, this study develops a high-yield process to prepare vertical Ag-Pt core-shell nanowires (NWs) by thermally assisted photoreduction of Ag NWs and successive galvanic replacement between Ag and Pt ions. The clean surface of Ag nanowires allows Pt ions to reduce and deposit on it and forms a compact sheath comprising Pt nanocrystals. The core-shell structural feature of the NWs thus produced has been demonstrated via transmission electron microscopy observation and Auger electron spectroscopy elemental analysis. Kinetic analysis suggests that the deposition of Pt is an interface-controlled reaction and is dominated by the oxidative dissolution of Ag atoms. The boundaries in between Pt nanocrystals may act as microchannels for the transport of Ag ions during galvanic replacement reactions.
One-dimensional nanostructures have attracted much interest because of their fascinating properties and extensive use in electronics, sensing, catalysis, and electrochemical applications [1–4]. For example, changing the morphology of Pt nanostructure from nanoparticle to nanowire (NW) has been regarded as an important strategy to improve the performance of Pt-based catalysts, which have been widely used as the anode of direct methanol fuel cells for catalyzing the dehydrogenation of methanol [5–7]. By doing so, an enhancement in electrocatalytic activity can be obtained due to the large side surface, which is able to provide additional catalytic active facets. A great deal of effort has been devoted to the synthesis of Pt nanowires; however, it still remains a huge challenge to synthesize long and oriented single-crystalline Pt NWs [8–11]. Using template- and surfactant-free processes, the Pt NWs produced are extremely fine (mostly less than 10 nm in diameter) but exhibit a limit in length of about 200 nm.
A recently developed process, thermally assisted photoreduction, [16, 17] has been successfully applied to prepare Ag nanowires with the length up to 10 μm on TiO2-coated substrates in large quantities without using templates and surfactants. The substrate could be rigid like Si wafers or flexible like carbon cloths. Ag nanowires thus produced are single-crystalline with a preferred <110> growth direction. The approach of this work is to use these clean-surface Ag NWs as sacrificial templates for the galvanic exchange with Pt ions to synthesize ultra-long Ag-Pt core-shell nanowires in large yield. In addition to the optical properties and microstructural characteristics, the mechanisms and reaction kinetics are also discussed.
Synthesis of Ag NWs on TiO2
Galvanic exchange between Ag and Pt salts
Ag NWs thus prepared were removed from the TiO2 substrate by ultrasonic oscillation and then immersed in 0.05 M aqueous Na2Pt(OH)6 solution for the exchange of Pt (step 4 in Figure 1). Instead of commonly used precursor, H2PtCl6, Na2Pt(OH)6 was adapted in this study because Pt ions can be reduced more easily mainly due to the smaller electronegativity of the OH group (3.02) [18, 19] compared with Cl (3.16). The solution was then isothermally heated to reflux at 100°C, 170°C, and 200°C. After a certain reaction period, the samples were rinsed with deionized water and dried under N2 before analysis.
Characterizations of core-shell NWs
The structure and phase of the NWs were characterized by transmission electron microscopy (TEM) (G2, Philips Tecnai, Amsterdam, The Netherlands) with an accelerating voltage of 200 kV and also a grazing incidence X-ray diffraction meter (D/MAX2500, Rigaku Corporation, Tokyo, Japan) (incidence angle of 0.5°) with graphite monochromatic CuKα radiation (λ = 0.15418 nm) at a scanning rate of 2° per min from 30° to 80°. The morphology and size distribution were obtained by scanning electron microscopy (SEM) (JSM-6700, JEOL Ltd., Akishima, Tokyo, Japan) with an accelerating voltage of 20 kV. The measurements of the UV-visible (vis) absorption spectra were carried out at room temperature using a Hitachi-4001 spectrophotometer (Hitachi High-Tech, Minato-ku, Tokyo, Japan). Auger electron spectroscopy (AES) (MICROLAB 350, Thermo VG Scientific, West Sussex, England) equipped with an Ar ion gun was used to investigate the elemental distribution of the cross-sectioned nanowires.
Results and discussion
Morphology and structure of Ag NWs
Optical and structural characteristics of Ag-Pt core-shell NWs
Reaction kinetics and mechanisms
Activation energies of the reactions in galvanic replacement
Decrease in Ag
Gain of Pt
where SHE is the standard hydrogen electrode.
In this study, surfactant-free single crystalline Ag NWs prepared by thermally assisted photoreduction were used as sacrificial templates for the galvanic deposition of Pt. Through this simple route, large quantities of vertical Ag-Pt core-shell NWs could be prepared. Due to the great reduction potential, Pt ions could be reduced by the electrons generated from the oxidative dissolution of Ag. A compact shell comprising Pt nanocrystals can thus be formed on the surface of Ag NWs. TEM observation and AES elemental mapping both verify the core-shell structural feature of these NWs. According to the kinetic analysis and estimated activation energy, the galvanic exchange of Ag by Pt ions was an interface-controlled process, which was dominated by the dissociation of Ag atoms.
Y-LS is a Ph.D. student at the Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan. S-YC is an associate professor of the Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan. J-MS is an associate professor of the Department of Materials Science and Engineering, National Chung Hsing University, Taichung, Taiwan. I-GC is a distinguished professor at the Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan.
The authors thank the National Science Council of Taiwan for funding, NSC 100-2120-M-006-006, to support this work.
- Melinda M, Peter P, Akos K, Zoltan K: Low-temperature large-scale synthesis and electrical testing of ultralong copper nanowires. Langmuir 2010, 26: 16496. 10.1021/la101385eView ArticleGoogle Scholar
- Xia Y, Yang P, Sun Y, Wu Y, Mayers B, Gates B, Yin Y, Kim F, Yan H: One-dimensional nanostructures: synthesis, characterization, and applications. Adv Mater 2003, 15: 353. 10.1002/adma.200390087View ArticleGoogle Scholar
- Choi WC, Woo SI: Bimetallic Pt–Ru nanowire network for anode material in a direct-methanol fuel cell. J. Power Sources 2003, 124: 420. 10.1016/S0378-7753(03)00812-7View ArticleGoogle Scholar
- Mikhail L, Manoj KR, Garrett M, Ashok K: Structure and opto-electrochemical poperties of ZnO nanowires grown on n-Si substrate. Langmuir 2011, 27: 9012. 10.1021/la200584jView ArticleGoogle Scholar
- Lee EP, Peng Z, Chen W, Chen S, Yang H, Xia Y: Electrocatalytic properties of Pt nanowires supported on Pt and W gauzes. Acs Nano 2008, 2: 2167. 10.1021/nn800458pView ArticleGoogle Scholar
- Liu L, Pippel E, Scholz R, Gösele U: Nanoporous Pt-Co alloy nanowires: fabrication, characterization, and electrocatalytic properties. Nano Lett 2009, 9: 4352. 10.1021/nl902619qView ArticleGoogle Scholar
- Formo E, Peng Z, Lee E, Lu X, Yang H, Xia Y: Direct oxidation of methanol on Pt nanostructures supported on electrospun nanofibers of anatase. J Phys Chem C 2008, 112: 9970.View ArticleGoogle Scholar
- Lee EP, Peng Z, Cate DM, Yang H, Campbell CT, Xia Y: Growing Pt nanowires as a densely packed array on metal gauze. J Am Chem Soc 2007, 129: 10634. 10.1021/ja074312eView ArticleGoogle Scholar
- Lee EP, Chen J, Yin Y, Campbell CT, Xia Y: Pd-catalyzed growth of Pt nanoparticles or nanowires as dense coatings on polymeric and ceramic particulate supports. Adv Mater 2006, 18: 3271. 10.1002/adma.200601070View ArticleGoogle Scholar
- Song Y, Garcia RM, Dorin RM, Wang H, Qiu Y, Coker EN, Steen WA, Miller JE, Shelnutt JA: Synthesis of platinum nanowire networks using a soft template. Nano Lett 2007, 7: 3650. 10.1021/nl0719123View ArticleGoogle Scholar
- Sun S, Jaouen F, Dodelet JP: Controlled growth of Pt nanowires on carbon nanospheres and their enhanced performance as electrocatalysts in PEM fuel cells. Adv Mater 2008, 20: 3900. 10.1002/adma.200800491View ArticleGoogle Scholar
- Wang H, Xu C, Cheng F, Zhang M, Wang S, Jiang SP: Pd/Pt core–shell nanowire arrays as highly effective electrocatalysts for methanol electrooxidation in direct methanol fuel cells. Electrochem Commun 2008, 10: 1575. 10.1016/j.elecom.2008.08.011View ArticleGoogle Scholar
- Slawiński GW, Zamborini FP: Synthesis and alignment of silver nanorods and nanowires and the formation of Pt, Pd, and core/shell structures by galvanic exchange directly on surfaces. Langmuir 2007, 23: 10357. 10.1021/la701606pView ArticleGoogle Scholar
- Wang S, Kristian N, Jiang S, Wang X: Controlled synthesis of dendritic Au@Pt core–shell nanomaterials for use as an effective fuel cell electrocatalyst. Nanotechnology 2009, 20: 1.Google Scholar
- Park DY, Jung HS, Rheem Y, Hangarter CM, Lee YI, Ko JM, Choa YH, Myung NV: Morphology controlled 1D Pt nanostructures synthesized by galvanic displacement of Cu nanowires in chloroplatinic acid. Electrochim Acta 2010, 55: 4212. 10.1016/j.electacta.2010.02.054View ArticleGoogle Scholar
- Tung HT, Chen IG, Song JM, Yen CW: Thermally assisted photoreduction of vertical silver nanowires. J Mater Chem 2009, 19: 2386. 10.1039/b817482bView ArticleGoogle Scholar
- Tung HT, Song JM, Feng SW, Kuo C, Chen IG: Dependence of surface atomic arrangement of titanium dioxide on metallic nanowire nucleation by thermally assisted photoreduction. Phys Chem Chem Phys 2010, 12: 740.View ArticleGoogle Scholar
- Shen YL, Chen SY, Song JM, Chin TK, Lin CH, Chen IG: Direct growth of ultra-long platinum nanolawns on a semiconductor photocatalyst. Nanoscale Res Lett 2011, 6: 380. 10.1186/1556-276X-6-380View ArticleGoogle Scholar
- Huheey JE: The electronegativities of groups. J Phys Chem 1965, 69: 3284. 10.1021/j100894a011View ArticleGoogle Scholar
- Kato M: Simple criteria for epitaxial relationships between f.c.c. and b.c.c. crystals. Mater Sci Eng, A 1991, 146: 205. 10.1016/0921-5093(91)90278-UView ArticleGoogle Scholar
- Barbic M, Mock JJ, Smith DR, Schultz SJ: Single crystal silver nanowires prepared by the metal amplification method. Appl Phys 2002, 91: 9341.View ArticleGoogle Scholar
- Zhang D, Qi L, Yang J, Ma J, Cheng H, Huang L: Wet chemical synthesis of silver nanowire thin films at ambient temperature. Chem Mater 2004, 16: 872. 10.1021/cm0350737View ArticleGoogle Scholar
- Zhao D, Wang YH, Yan B, Xu BQ: Manipulation of Pt∧Ag nanostructures for advanced electrocatalyst. J Phys Chem C 2009, 113: 1242. 10.1021/jp806190wView ArticleGoogle Scholar
- Lopez T, Villa M, Gomez R: UV–vis diffuse reflectance spectroscopic study of Pt, Pd, and Ru catalysts supported on silica. J Phys Chem 1991, 95: 1690. 10.1021/j100157a038View ArticleGoogle Scholar
- Inaba M, Honma Y, Hatanaka T, Otake Y: Effects of the annealing conditions on the oxidation behavior of Fe-36Ni alloys. Appl Surf Sci 1986, 27: 164. 10.1016/0169-4332(86)90105-4View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.