高指数晶面金属纳米结构的可控合成及电催化性能研究

英文题名：Controlled Synthesis and Electrocatalytic Properties of Metal Nanostructures with High-Index Facets
作者：王成名
论文级别：博士
学科专业名称：纳米化学
中文关键词：铂 ; 钯 ; 纳米晶 ; 高指数晶面 ; 复合结构 ; 甲酸氧化 ; 氧还原反应 ; 电催化性能 ; 活性和稳定性
英文关键词：platinum ; palladium ; nanocrystals ; high-index facets ; hybrid structure ; formic acid oxidation ; oxygen reduction reaction ; electrocatalytic performance ; activity and durability
学位年度：2013
导师：熊宇杰
学科代码：0703
学位授予单位：中国科学技术大学
论文提交日期：2013-10-01

摘要

人类正在面临着日益严重的能源危机和环境问题。低温燃料电池,是解决以上两个问题的最重要的一种技术手段,应用前景广阔。如何提高催化性能和节约应用成本,也就是如何优化催化剂的组成、尺寸、结构、形貌和晶面等,是技术应用的瓶颈和关键所在。铂Pt和钯Pd等贵金属纳米晶催化剂,是最常用的高效、稳定、耐久的燃料电池催化剂。实验测量和理论模拟都证实,发生在催化剂上的反应能量和反应速率相当敏感地依赖于裸露的表面晶面。高指数晶面,相对于其低指数的基础晶面,存有台阶和缺陷,有相对大量的低配位原子,具有更好的活性。本文重点通过选择不同表面修饰剂、控制反应动力学、设计电化置换反应、活化与外延生长、调控氧化刻蚀过程等,可控合成出具有高指数晶面的贵金属纳米晶(主要是Pt、Pd及其有关合金),优化并提升质子交换膜燃料电池反应(如甲酸氧化和氧还原反应等)性能。已经开展的研究内容如下：
     1.铂纳米晶枝状结构的可控合成及其电催化应用。枝状纳米晶的结构调控,可以调节对其催化活性有重要影响的两大参数——比表面积,原子在表面的台阶steps、突起ledges和缺陷kinks的数目。本工作中,我们发展出了一种简单的合成体系,通过调节体系中添加的盐酸的浓度能够调控铂纳米晶的枝状数目。在这个合成方法中,HCl通过氧化刻蚀在调节枝状数目中起到了3重调控作用：(i)晶种和纳米晶的结晶度；(ii)提供给生长位点的{111}或{100}晶面的数目：(iii)溶液中新生的铂原子的供给动力学。因此,可调的铂的枝状结构——相同化学环境下的三足、四足、六足、八足结构——可以在单一体系中简单地调节刻蚀强度而被理性合成出来。铂的枝状结构的可控性揭示,它们的电催化性能可以通过构建复杂结构来最优化。在不同的枝状结构中,与其他多足结构及商业Pt/C催化剂在甲酸氧化反应中的性能相比,铂八足结构表现出特别高的活性。本工作可以预期将为设计更为复杂的纳米结构以及在各种应用中实现独特功能作用提供新的视角。
     2.氧还原反应中具有高活性和高稳定性的铂-石墨烯复合结构。获得在燃料电池氧还原反应中铂电催化剂的高活性和高稳定性仍然是个重大挑战。我们开发出了一类具有高度凹面立方体(HCC)结构的铂纳米晶催化剂,具有{311}等高指数晶面和高氧还原活性。HCC纳米晶的稳定性可通过和石墨烯的组装得到显著提高。该独特的复合结构表现出进一步增强的电化学活性,比商用的Pt/C催化剂活性高出七倍。这种复合结构也在半波电位(E1/2)方面表现出了突出的高性能。在较低Pt担载量为46μb/cm2时,这种催化剂的半波电位高达0.967V,比商用Pt/C催化剂高出63mV,而且还稍高于文献中活性最高的多孔Pt-Ni催化剂的记录。本工作为通过调节负载基质的表面和界面来设计高性能电催化剂铺平了道路。
     3.动力学控制下各向异性生长的钯孪晶纳米结构及其在电化置换反应中的应用。五重孪晶结构是具有面心立方结构的金属纳米晶体中的重要种类,当它们的{100}面被保护起来的时候,它们可以各向异性生长成纳米线。我们开发了一种温和的方法去获得富有{311}和{611}高指数晶面的Pd瓜子状纳米晶。研究表明反应动力学是调控晶体生长模式的关键,同时选择性的包覆作用也对晶面控制具有重要作用。此孪晶结构的各向异性生长,提供了无需通过使用长链包覆剂/保护剂便可构建高指数晶面的一种新途径。这些高指数晶面的纳米晶体相比于低指数晶面纳米晶体,表现出卓越的化学活性,为与HAuCl4溶液发生的电化置换反应所证实。这个工作将为高指数晶面金属纳米晶体新合成方法的发展和催化等多领域应用等打开一扇大门。
     4.{730}高指数晶面Pd-Pt凹面纳米立方体的外延生长合成及电催化应用。我们开发了一种方法,通过刻蚀法对纳米立方体的表面进行选择性活化,进而很好控制其外延生长。通过在Pd立方体纳米晶晶种的角和边上进行生长,实现了Pd凹面纳米立方体的合成,在纳米晶表面形成了{730}高指数晶面和高活性位点,有利于催化应用。这种方法相较以往方法,可以防止原子生长在其他位点上并保证了纳米晶颗粒尺寸在晶种生长过程中基本维持不变。由于颗粒大小基本保持不变,活性位点和高指数晶面的出现使得纳米晶产物在甲酸氧化反应中有着更优越的电催化活性。另一方面,这种方法使得具有高催化活性的贵金属能外延生长在其他类型的较便宜的金属上,降低了昂贵材料的使用成本而又同时维持高的催化活性。在本章里,我们证实在Pd纳米晶上沉积非常有限量的Pt(Pt的质量分数只占3.3%),得到的Pd-Pt凹面纳米立方体在氧还原反应中表现了优良的催化活性。初步的研究表明,通过简单地改变表面化学状态,该合成方法同样适用于将不同材料选择性地沉积在纳米晶体表面上。
     5.钯纳米晶体在电催化甲酸氧化反应中的形貌效应。本章选用适当的金属前驱物、还原剂、稳定剂和保护剂,通过调控氧化刻蚀和反应动力学等,成功合成了形貌和尺寸均不相同的Pd纳米晶。经过认真的纳米粒子清洗和电极修饰组装,考察了它们在电催化甲酸氧化反应中的形貌与性能的关系。研究结果表明,Pd纳米晶样品的最大电流密度以纳米八面体(anooctahedra)<纳米线(nanowires)<纳米立方体(nanocubes)<纳米瓜子(nanotapers)<凹面纳米立方体(concave nanocubes)的顺序递增,催化甲酸氧化反应的起始氧化电位均小于0.2V。研究结果印证了Pd纳米晶催化甲酸氧化反应的催化性能在尺寸效应上主要受活性表面积的影响,扣除表面积效应后的催化性能与其尺寸没有明确关系。该系列Pd纳米晶的催化性能主要取决于其表面结构,得出Pd纳米晶催化甲酸氧化反应遵循{111}.晶面<{100}晶面<高指数晶面的性能活性顺序。综合最大电流密度和最小操作电位因素发现,Pd凹面纳米立方体和纳米瓜子具有相对较好的商用价值。
Human beings are now facing the increasingly serious energy crisis and environmental problems. Low-temperature fuel cell, which is one of the most important technical means to address these two issues, has a broad application prospect. It has been the key and bottleneck of technology applications how to improve catalytic performance and save application cost by optimizing the composition, size, structure and shape of a nanocatalyst. Noble metal nanocatalysts including platinum and palladium nanocrystals, as the most efficient, stable and durable catalysts for fuel cells, are commonly used. It has been confirmed by experimental measurements and theoretical simulations that the reaction rate and energy on a nanocatalyst quite sensitively depends on the crystal facets exposed on its surface. High-index facets of a nanocrystal with more steps, defects and low coordination atoms, have a higher catalytic activity than low-index facets. This research is focused on the controllable synthesis of noble metal nanocrystals with high index facets (mainly Pt, Pd and related alloys) by selecting different capping agents, controlling reaction kinetics, designing galvanic displacement reaction, modulating activation and epitaxial growth, employing oxidation etching process, and further optimizes the catalytic performance of some important reaction such as formic acid oxidation and oxygen reduction reaction in the proton exchange membrane fuel cells. Related research works are summarized as follows:
     1. Control over the branched structures of platinum nanocrystals for electrocatalytic applications. Structural control of branched nanocrystals allows tuning two parameters that are critical to their catalytic activity:the surface-to-volume ratio, and the number of atomic steps, ledges, and kinks on surface. In this work, we have developed a simple synthetic system that allows tailoring the numbers of branches in Pt nanocrystals by tuning the concentration of additional HC1. In the synthesis, HC1plays triple functions in tuning branched structures via oxidative etching:(i) the crystallinity of seeds and nanocrystals;(ⅱ) the number of{111} or {100} faces provided for growth sites;(ⅲ) the supply kinetics of freshly formed Pt atoms in solution. As a result, tunable Pt branched structures-tripods, tetrapods, hexapods, and octopods with identical chemical environment-can be rationally synthesized in a single system by simply altering the etching strength. The controllability in branched structures enables to reveal that their electrocatalytic performance can be optimized by constructing complex structures. Among various branched structures, Pt octopods exhibit particularly high activity in formic acid oxidation as compared with their counterparts and commercial Pt/C catalysts. It is anticipated that this work will open a door to design more complex nanostructures and to achieve specific functions for various applications.
     2. A unique platinum-graphene hybrid structure for high activity and durability in oxygen reduction reaction. It remains a grand challenge to achieve both high activity and durability in Pt electrocatalysts for oxygen reduction reaction (ORR) in fuel cells. Here we develop a class of Pt highly concave cubic (HCC) nanocrystals, which are enriched with high-index facets and exhibit high ORR activity. The durability of HCC nanocrystals can be significantly improved via assembly with graphene. The unique hybrid structure displays further enhanced specific activity, which is7-fold greater than the state-of-the-art Pt/C catalysts. Strikingly, it exhibits impressive performance in terms of half-wave potential (E1/2). The E1/2of0.967V at the Pt loading as low as46μg cm-2, which stands as63mV higher than that of the Pt/C catalysts, is slightly superior to the record observed for the most active porous Pt-Ni catalyst in literature. This work paves the way to designing high-performance electrocatalysts by modulating their surface and interface with loading substrates.
     3. Anisotropic growth of palladium twinned nanostructures controlled by kinetics and their unusual activities in galvanic replacement. Five-fold twinned structures are a class of important members in the family of metallic nanocrystals with face-centered cubic (fCC) structures, which can anisotropically grow into nanowires when their{100} facets are protected. In this work, a facile synthetic approach has been firstly developed to synthesize a new structure of palladium nanocrystals, which are palladium nanotapers potentially enclosed by high-index facets. We have revealed that the reaction kinetics holds the key to tuning the growth mode of the nanocrystals while the selective capping effect makes a contribution to facet control. The anisotropic growth of twinned structures here provides a new approach for constructing a high-index surface without the need to use long-chain capping agents. These palladium nanotapers exhibit superior chemical activities compared to their low-index counterparts, as proven in the galvanic replacement. It is anticipated that this work opens a door for the development of new synthetic methods for metallic nanocrystals with high-index facets for various applications such as catalysis.
     4. Synthesis and eletrocatalytic applications of Pd-Pt concave nanocubes with {730} high-index facets by epitaxial growth methods. A method has been developed for controlled epitaxial growth on cubic nanocrystals by selectively activating their surface via etching. Pd concave nanocubes were produced via seeding growth on their corners and edges, formulating high-index facets and highly active sites for catalysis. This method offers a better capability of preventing atomic addition on undesired locations and maintaining particle size in the seeding process, as compared with the previous technique. With the particle size well maintained, the products fully exhibit superior electrocatalytic performance enabled by active sites and high-index facets in formic acid oxidation. Another contribution of this work is to enable the growth of a noble metal with high catalytic activities on another type of cheaper metal, which greatly reduces the usage of expensive materials while retaining high catalytic activity. In this work, we have demonstrated the deposition of a very limited amount of Pt (only3.3wt%.) on Pd nanocrystals towards high electrocatalytic activities in oxygen reduction reaction. Preliminary studies demonstrate that the synthetic strategy can be also applied to the controllable deposition of a different material on the faces of a nanocrystal by simply altering surface conditions.
     5. Structural effects of palladium nanocrystal electrodes on electrocatalytic oxidation reaction of formic acid. Palladium nanocrystals with various shapes and sizes were controllably synthesized by altering oxidative etching and reaction kinetics in the presence of appropriate metal precursors, reducing agents, stabilizers and capping agents, based on our previous works. Upon cleaning nanoparticles and assembling them onto electrodes, we systematically investigated the relationship between nanocrystal structures and catalytic performance in the oxidation of formic acid. It demonstrates that the maximum current densities of Pd nanocrystals increase in the order of nanoctahedra

引文

1. Fahlman BD. In Materials Chemistry, Springer:Mount pleasant,2007,1, 282-283.
    2. Halperin WP. Quantum size effects in metal particles. Rev. Mod. Phys.1986,58, 533-606.
    3. Alivisatos AP. Semiconductor clusters, nanocrystals, and quantum dots. Science 1996,271,933-937.
    4. Likharev KK. Correlated discrete transfer of single electrons in ultrasmall tunnel-junctions. Ibm J.Res. Dev.1988,32,144-158.
    5. Mott NF. Metal-insulator transition. Rev. Mod. Phys.1968,40,677-683.
    6. Jeong U, Teng X, Wang Y, Yang H, Xia YN. Superparamagnetic colloids: Controlled synthesis and niche applications. Adv. Mater.2007,19:33-60.
    7. Xia YN, Xiong YJ, Lim B, Skrabalak SE. Shape-controlled synthesis of metal nanocrystals:Simple chemistry meets complex physics? Angew. Chem. Int. Ed. 2009,48,60-103.
    8. Somorjai GA. Modern surface science and surface technologies:An introduction. Chem. Rev.1996,96,1223-1235.
    9. Jeong S, Woo K, Kim D, Lim S, Kim JS, Shin H, Xia YN, Moon J. Controlling the thickness of the surface oxide layer on Cu nanoparticles for the fabrication of conductive structures by ink-jet printing. Adv. Funct. Mater.2008,18,679-686.
    10. Tani T. Physics of the photographic latent image. Phys. Today,1989,42,36-41.
    11. Murray CB, Sun SH, Doyle H, Betley T. Monodisperse 3d transition-metal (Co, Ni, Fe) nanoparticles and their assembly into nanoparticle superlattices. Mrs Bulletin,2001,26,985-991.
    12. Sanders AW, Routenberg DA, Wiley BJ, Xia YN, Dufresne ER, Reed MA. Observation of plasmon propagation, redirection, and fan-out in silver nanowires. Nano Lett.2006,6,1822-1826.
    13. Taton TA, Mirkin CA, Letsinger RL. Scanometric DNA array detection with nanoparticle probes. Science 2000,289,1757-1760.
    14. Chen J, Saeki F, Wiley BJ, Cang H, Cobb MJ, Li ZY, Au L, Zhang H, Kimmey MB, Li XD, Xia YN. Gold nanocages:Bioconjugation and their potential use as optical imaging contrast agents. Nano Lett.2005,5,473-477.
    15. Skrabalak SE, Chen J, Au L, Lu X, Li X, Xia YN. Gold nanocages for biomedical applications.Adv. Mater.2007,19,3177-3184.
    16. Nicewarner-Pena SR, Freeman RG, Reiss BD, He L, Pena DJ, Walton ID, Cromer R, Keating CD, Natan MJ. Submicrometer metallic barcodes. Science 2001,294,137-141.
    17. Polshettiwar V, Varma RS. Green chemistry by nano-catalysis. Green Chem. 2010,12,743-754.
    18. Tian N, Zhou ZY, Sun SG, Ding Y, Wang ZL. Synthesis of tetrahexahedral platinum nanocrystals with high-index facets and high electro-oxidation activity. Science 2007,316,732-735.
    19. Guo S, Dong S, Wang E. Pt-on-Pd bimetallic nanodendrites supported on graphene nanosheet:facile synthesis and used as an advanced nanoelectrocatalyst for methanol oxidation. ACS Nano,2010,4,547-555.
    20. Kowal A, et al. Ternary Pt/Rh/SnO2 electrocatalysts for oxidizing ethanol to CO2. Nat. Mater.2009,8,325-330.
    21. Bashyam R, Zelenay P. A class of non-precious metal composite catalysts for fuel cells. Nature 2006,443,63-66.
    22. Huang X, et al. Solution-phase epitaxial growth of noble metal nanostructures on dispersible single-layer molybdenum disulfide nanosheets. Nat.Commun.20134, 1444 doi:10.1038/ncomms2472.
    23. Lu YC, et al. Platinum-Gold Nanoparticles:A highly active bifunctional electrocatalyst for rechargeable lithium-air batteries. J. Am. Chem. Soc.2010,132, 12170-12171.
    24. Mallouk TE. Fuel-cells-miniaturized electrochemistry. Nature 1990,343, 515-516.
    25. Steele BCH, Heinzel A. Materials for fuel-cell technologies. Nature 2001,414, 345-352.
    26. Yang H, Teng XW, Maksimuk S. Metal Nanoclusters in Catalysis and Materials Science:The Issue of Size Control. Part II:Morphologies [M]. Amsterdam Netherlands,2008,17,307-320.
    27. Wang ZL. Transmission electron microscopy of shape-controlled nanocrystals and their assemblies. J. Phys. Chem. B,2000,104,1153-1175.
    28. Niu W, Zhang L, Xu G. Shape-controlled synthesis of singlecrystalline palladium nanocrystals. ACS Nano 2010,4,1987-1996.
    29. Yu Y, Zhang Q, Liu B, Lee JY Synthesis of nanocrystals with variable high-index Pd facets through the controlled heteroepitaxial growth of trisoctahedral Au templates. JAm. Chem. Soc.2010,132:18258-18265.
    30. Zhang J, Langille MR, Personick ML, Zhang K, Li S, Mirkin CA. Concave cubic gold nanocrystals with high-index facets. J Am. Chem. Soc.2010,132, 14012-14014.
    31. Xia X, Zeng J, Mcdearmon B, Zheng Y, Li Q, Xia YN. Silver nanocrystals with concave surfaces and their optical and surface-enhanced Raman scattering properties. Angew. Chem. Int. Ed. 2011,50,12542-12546.
    32. Xie S, Choi SI, Xia X, Xia YN. Catalysis on faceted noble-metal nanocrystals: both shape and size matter. Current Opinion in Chemical Engineering 2013,2, 142-150.
    33. Zhou ZY, Tian N, Li JT, Broadwell I, Sun SG. Nanomaterials of high surface energy with exceptional properties in catalysis and energy storage. Chem. Soc. Rev.2011,40,4167-4185.
    34. Tian N, Zhou ZY, Sun SG. Platinum metal catalysts of high-index surfaces:From single-crystal planes to electrochemically shape-controlled nanoparticles. J. Phys. Chem. C 2008,112,19801-19817.
    35. Larny C, Leget JM. Electrocatalytic oxidation of small organic molecules at Platinum single crystals. J. Chim. Phys.1991,88,1649-1671.
    36. Markovic NM, Ross PN. Surface science studies of model fuel cell electrocatalysts. Surface Science Reports 2002,45,117-229.
    37. Adzic RR, Tripkovic AV, O'grady WE. Structural effects in electrocatalysis. Nature 1982,296,137-138.
    38. Falicov LM, Somorjai GA. Correlation between catalytic activity and bonding and coordination number of atoms and molecules on transition metal surfaces: Theory and experimental evidence. Proc. Natl. Acad. Sci. USA 1985,82, 2207-2211.
    39. Somorjai GA, Blakely DW. Mechanism of catalysis of hydrocarbon reactions by platinum surfaces. Nature 1975,258,580-583.
    40. Sun SG, Chen AC, Huang TS, Li JB, Tian ZW. Electrocatalytic properties of Pt (111), Pt (332), Pt (331) and Pt (110) single crystal electrodes towards ethylene glycol oxidation in sulphuric acid solutions. J. Electroanal. Chem.1992,340, 213-226.
    41. LaMer VK, Dinegar RH. Theory, production and mechanism of formation of monodispersed hydrosols.J. Am. Chem. Soc.1950,72,4847-4854.
    42. Iijima S, Ichihashi T. Structural instability of ultrafine particles of metals. Phys. Rev. Lett.1986,56,616-619.
    43. Smith DJ, Petfordlong AK, Wallenberg LR, Bovin JO. Dynamic atomic-level rearrangements in small gold particles. Science 1986,233,872-875.
    44. Baletto F, Ferrando R. Structural properties of nanoclusters:Energetic, thermodynamic, and kinetic effects. Rev. Mod. Phys.2005,77,371-423.
    45. Baletto F, Ferrando R, Fortunelli A, Montalenti F, Mottet C. Crossover among structural motifs in transition and noble-metal clusters. J. Chem. Phys.2002,116, 3856-3863
    46. Xiong YJ, Xia YN. Shape-controlled synthesis of metal nanostructures:The case of palladium. Adv. Mater.2007,19,3385-3391.
    47. Teng X, Yang H. Synthesis of platinum multipods:An induced anisotropic growth. Nano Lett.2005,5,885-891.
    48. Lim SI, Ojea-Jimenez I, Varon M, Casals E, Arbiol J, Puntes, V. Synthesis of platinum cubes, polypods, cuboctahedrons, and raspberries assisted by cobalt nanocrystals. Nano Lett.2010,10,964-973.
    49. Yin Y, Alivisatos AP. Colloidal nanocrystal synthesis and the organic-inorganic interface. Nature 2005,437,664-670.
    50. Wang Y, Ren J, Deng K, Gui L, Tang Y. Preparation of tractable platinum, rhodium, and ruthenium nanoclusters with small particle size in organic media. Chem. Mater.2000,12(6),1622-1627.
    51. Zhao SY, Chen SH, Wang SY, Li DG, Ma HY. Preparation, phase transfer, and self-assembled monolayers of cubic Pt nanoparticles. Langmuir,2002,18, 3315-3318.
    52. Sun Y, Gates B, Mayers B, Xia YN. Crystalline silver nano wires by soft solution processing. Nano Lett.2002,2,165-168.
    53. Wu YE, Cai SF3 Wang DS, He W. and Li YD. Syntheses of water-soluble octahedral, truncated octahedral, and cubic Pt-Ni nanocrystals and their structure-activity study in model hydrogenation reactions J. Am. Chem. Soc.2012, 134,8975-8981.
    54. Henglein A, Giersig M. Reduction of Pt (Ⅱ) by H2:Effects of citrate and NaOH and reaction mechanism. J. Phys. Chem.B 2000,104,6767-6772.
    55. Yu YT, Xu BQ. Impact of protector molecules on the shape of Pt nanocrystals synthesized with K2PtCl6 as the precursor. Chemical Research In Chinese Universities.2004,25,2384-2386.
    56. Fu X, Wang Y, Wu N, Gui L, Tang Y. Shape-selective preparation and properties of oxalate-stabilized Pt colloid. Langmuir 2002,18,4619-4624.
    57. Chen JY, Xiong YJ, Yin YD, Xia YN. Pt Nanoparticles surfactant-directed assembled into colloidal spheres and used as substrates in forming Pt nanorods and nanowires. Small 2006,2,1340-1343.
    58. Lee H, Habas SE, Kweskin S, Butcher D, Somorjai GA, Yang PD. Morphological control of catalytically active platinum nanocrystals. Angew. Chem. Int. Ed.2006, 45,7824-7828.
    59. Ren J, Tilley RD. Preparation, self-assembly, and mechanistic study of highly monodispersed nanocubes. J. Am. Chem. Soc.2007,129,3287-3291.
    60. Miyazaki A, Nakano Y. Morphology of platinum nanoparticles protected by poly(N-isopropylacrylamide). Langmuir,2000,16,7109-7111.
    61. Esumi K, Shiratori M, Ishizuka H, Tano T, Torigoe K, Meguro K. Preparation of bimetallic palladium-platinum colloids in organic solvent by solvent extraction-reduction. Langmuir 1991,7,457-459.
    62. Tran TT, Lu XM. Synergistic Effect of Ag and Pd Ions on Shape-Selective Growth of Polyhedral Au Nanocrystals with High-index Facets. J. Phys. Chem. C, 2011,115,3638-3645.
    63. Zhang H, et al. Synthesis of Pd-Pt bimetallic nanocrystals with a concave structure through a bromide-induced galvanic replacement reaction. J. Am. Chem. Soc.2011,133,6078-6089.
    64. Chen J, Wiley B, McLellan J, Xiong YJ, Li ZY, Xia YN. Optical properties of Pd-Ag and Pt-Ag nanoboxes synthesized via galvanic replacement reactions. Nano Lett.2005,5,2058-2062.
    65. Sun Y, Xia YN. Alloying and dealloying processes involved in the preparation of metal nanoshells through a galvanic replacement reaction. Nano Lett.2003,3, 1569-1572.
    66. Lu X, Chen J, Skrabalak SE, Xia YN. Galvanic replacement reaction:a simple and powerful route to hollow and porous metal nanostructures. Proc. IMechE, Part N:J. Nanoengineering and Nanosystems.2007,221,1-16.
    67. Bansal V, et al. Galvanic Replacement Reaction on Metal Films:A one-step approach to create nanoporous surfaces for catalysis. Adv. Mater.2008,20, 717-723.
    68. Chen HM, et al. Hollow platinum spheres with nano-channels:synthesis and enhanced catalysis for oxygen reduction. J. Phys. Chem. C 2008,112, 7522-7526.
    69. Sun YG, Xia YN. Multiple-walled Nanotubes Made of Metals. Adv. Mater.2004, 16,264-268.
    70. Teng X, et al. Formation of Pd/Au nanostructures from Pd nanowires via galvanic replacement reaction. J. Am. Chem. Soc.2008,130,1093-1101.
    71. Pearson A, et al. Galvanic replacement mediated transformation of Ag nanospheres into dendritic Au-Ag nanostructures in the ionic liquid [BMIM][BF4]. Chem. Commun.,2010,46,731-733.
    72. Xiong YJ, Chen JY, Wiley B, Xia YN, Aloni S, Yin YD. Understanding the role of oxidative etching in the polyol synthesis of Pd nanoparticles with uniform shape and size. J. Am. Chem. Soc.2005,127,7332-7333.
    73. Wiley BJ, Herricks T, Sun YG, Xia YN. Polyol synthesis of silver nanoparticles: Use of chloride and oxygen to promote the formation of single-crystal, truncated cubes and tetrahedrons. Nano Lett.2004,4,1733-1739.
    74. Wiley BJ, Xiong YJ, Li ZY, Yin YD, Xia YN. Right bipyramids of silver:A new shape derived from single twinned seeds. Nano Lett.2006,6,765-768.
    75. Wiley BJ, Chen Y, McLellan JM, Xiong YJ, Li ZY, Ginger D, Xia YN. Synthesis and optical properties of silver nanobars and nanorice. Nano Lett.2007, 7,1032-1036.
    76. Xiong YJ, Cai H, Wiley BJ, Wang J, Kim MJ, Xia YN. Synthesis and mechanistic study of palladium nanobars and nanorods. J. Am. Chem. Soc.2007,129, 3665-3675.
    77. Xiong YJ, Wiley BJ, Xia YN. Nanocrystals with unconventional shapes-a class of promising catalysts. Angew. Chem. Int. Ed. 2007,46,7157-7159.
    78. Xiong YJ, Siekkinen AR, Wang J, Yin Y, Kim MJ, Xia YN. Synthesis of silver nanoplates at high yields by slowing down the polyol reduction of silver nitrate with polyacrylamide. J. Mater. Chem.2007,17,2600-2602.
    79. Zettsu N, McLellan JM, Wiley B, Yin YD, Li ZY, Xia YN. Synthesis, stability, and surface plasmonic properties of rhodium multipods, and their use as substrates for surface-enhanced Raman scattering. Angew. Chem. Int. Ed.2006, 45,1288-1292.
    80. Wiley B, Sun Y, Xia YN. Synthesis of silver nanostructures with controlled shapes and properties. Acc. Chem. Res.2007,40,1067-1076.
    81. Xiong YJ, McLellan JM, Yin Y, Xia YN. Synthesis of palladium icosahedra with twinned structure by blocking oxidative etching with citric acid or citrate ions. Angew. Chem. Int. Ed 2007,46,790-794.
    82. Wiley B, Sun YG,Xia YN. Polyol synthesis of silver nanostructures:Control of product morphology with Fe(Ⅱ) or Fe(Ⅲ) species. Langmuir,2005,21, 8077-8080.
    83. Tao A, Sinsermsuksakul P, Yang P. Polyhedral silver nanocrystals with distinct scattering signatures. Angew. Chem. Int. Ed.2006,45,4597-4601.
    84. Korte KE, Skrabalak SE, Xia YN. Rapid synthesis of silver nanowires through a CuCl-or CuCl2-mediated polyol process. J. Mater. Chem.2008,18,437-441.
    85. Xiong YJ, McLellan JM, Chen JY, Yin YD, Li ZY, Xia YN. Kinetically controlled synthesis of triangular and hexagonal nanoplates of palladium and their SPR/SERS properties. J. Am. Chem. Soc.2005,127,17118-17127.
    86. Xiong YJ, Chen JY, Wiley B, Xia YN, Yin YD, Li ZY. Size-dependence of surface plasmon resonance and oxidation for Pd nanocubes synthesized via a seed etching process. Nano Lett.2005,5,1237-1242.
    87. Li B, Long R, Zhong XL, Bai Y, Zhu ZJ, Zhang X, Zhi M, He JW, Wang CM, Li ZY, Xiong YJ. Investigation of size-dependent plasmonic and catalytic properties of metallic nanocrystals enabled by size control with HC1 oxidative etching. Small,2012,8,1710-1716.
    88. Xiong YJ, Wiley BJ, Chen JY, Li ZY, Yin YD, Xia YN. Corrosion-based synthesis of single-crystal Pd nanoboxes and nanocages and their surface plasmon properties. Angew. Chem. Int. Ed.2005,44,7913-7917.
    89. Sun YG, Xia YN. Shape-controlled synthesis of gold and silver nanoparticles. Science,2002,298:2176-2179.
    90. Chen JY, Herricks T, Geissler M, Xia YN. Single-crystal nanowires of platinum can be synthesized by controlling the reaction rate of a polyol process. J. Am. Chem. Soc.2004,126:10854-10855.
    91. Xiong YJ, Washio I, Chen J, Cai H, Li ZY, Xia YN. Poly(vinyl pyrrolidone):A dual functional reductant and stabilizer for the facile synthesis of noble metal nanoplates in aqueous solutions. Langmuir,2006,22,8563-8570.
    92. Xia YN, Kim E, Whitesides GM. Microcontact printing of alkanethiols on silver and its application in microfabrication. J. Electrochem. Soc.1996,143, 1070-1079.
    93. Ahmadi TS, Wang ZL, GreenTC, Henglein A, El-Sayed MA. Shape-controlled synthesis of colloidal platinum nanoparticles. Science 1996,272,1924-1926.
    94. Chiu CY, Li Y, Ruan L, Ye XC, Murray CB, Huang Y. Platinum nanocrystals selectively shaped using facet-specific peptide sequences. Nat. Chem.2011,3, 393-399.
    95. Chen J, Lim B, Lee EP, Xia YN. Shape-controlled synthesis of platinum nanocrystals for catalytic and electrocatalytic applications. Nano Today.2009,4, 81-95.
    96. Yu T, Kim DY, Zhang H, Xia YN. Platinum concave nanocubes with high-index facets and their enhanced activity for oxygen reduction reaction. Angew. Chem. Int. Ed.2011,50,2773-2777.
    97. Zhang H, Jin MS, Xia YN. Noble-metal nanocrystals with concave surfaces: synthesis and applications. Angew. Chem. Int. Ed.2012,51,7656-7673.
    98. Huang XQ, Zhao ZP, Fan JM, Tan YM, Zheng NF. Amine-assisted synthesis of concave polyhedral platinum nanocrystals having{411} high-index facets. J. Am. Chem. Soc.2011,133,4718-4721.
    99. Tian N, Zhou ZY, S Sun G. Electrochemical preparation of Pd nanorods with high-index facets. Chem. Commun.2009,1502-1504.
    100Jin MS, Zhang H, Xie ZX, Xia YN. Palladium concave nanocubes with high-index facets and their enhanced catalytic properties. Angew. Chem. Int. Ed.. 2011,50:7850-7854.
    101.Zhang H, Jin MS and Xia YN. Noble-Metal Nanocrystals with concave surfaces: Synthesis and applications. Angew. Chem. Int. Ed.2012,51,7656-7673.
    102.Liu X.G. Wu NQ, Wunsch BH, Barsotti Jr RJ and Stellacci F. Shape-controlled growth of micrometer sized gold crystals by a slow reduction method. Small 2006,2,1046-1050.
    103.Chen Y, Gu X, Nie CG, Jiang ZY, Xie ZX, Lin CJ. Shape controlled growth of gold nanoparticles by a solution synthesis. Chem. commun.2005,33:4181-4183.
    104.Seo D, Park JC, Song H. Polyhedral gold nanocrystals with Oh symmetry:From octahedral to cubes. J. Am. Chem. Soc.2006,128,14863-14870.
    105.Ma YY, Kuang Q, Jiang ZY, Xie ZX, Huang RB, Zheng LS. Synthesis of trisoctahedral gold nanocrystals with exposed high-index Facets by a Facile Chemical Method. Angew. Chem. Int. Ed.2008,47,8901-8904.
    106.Kim F, Connor S, Song H, Kuykendall T, Yang P. Platonic gold nanocrystals. Angew. Chem. Int. Ed.2004,43,3673-3677.
    107.Wiley BJ, Im SH, Li ZY, McLellan JM, Siekkinen A, Xia YN. Maneuvering the surface plasmon resonance of silver nano structures through shape-controlled synthesis. J. Phys. Chem. B 2006,110:15666-15675.
    108.Lee YT, Im SH, Wiley B, Xia YN. Quick formation of single-crystal nanocubes of silver through dual functions of hydrogen gas in polyol synthesis, Chem. Phys. Lett.2005,411,479-483.
    109.McLellan JM, Siekkinen A, Chen JY, Xia YN. Comparison of the surface-enhanced Raman scattering on sharp and truncated silver nanocubes, Chem. Phys. Lett.2006,427,122-126.
    110.Park KH, Jang K, Kim HJ, Son SU. Near-monodisperse tetrahedral rhodium nanoparticles on charcoal:The shape-dependent catalytic hydrogenation of arenes. Angew. Chem. Int. Ed. 2007,46,1152-1155.
    111.Zhang H, Li WY, Jin MS, Zeng J, Yu TK, Yang DR, Xia YN. Controlling the morphology of rhodium nanocrystals by manipulating the growth kinetics with a syringe pump. Nano Lett.2011,11,898-903.
    112.Ferrando R, Jellinek J, Johnston RL. Nanoalloys:From theory to applications of alloy clusters and nanoparticles. Chem. Rev.2008,108,845-910.
    113.Lim B, Wang J, Camargo P, Cobley C, Kim M, Xia YN. Twin-induced growth of palladium-platinum alloy nanocrystals. Angew. Chem. Int. Ed.2009,48, 6304-6308.
    114.Zhang H, Jin MS, and Xia YN. Enhancing the catalytic and electrocatalytic properties of Pt-based catalysts by forming bimetallic nanocrystals with Pd. Chem. Soc. Rev.2012,41,8035-8049.
    115.Zhang H, Jin MS, Wang J, Kim M, Yang D, Xia YN. Nanocrystals composed of alternating shells of Pd and Pt can be obtained by sequentially adding different precursors. J. Am.Chem. Soc.2011,133,10422-10425.
    116.O'Hayre R, Cha S, Colella W, Prinz FB. Fuel Cell Fundamentals. John Wiley and Sons, New York,2006.
    117.Litster S, McLean G. PEM fuel cell electrodes. Journal Power Sources,2004,130, 61-76.
    118.Capon A, Parsons R. The oxidation of formic acid on noble metal electrodes:II. A comparison of the behaviour of pure electrodes. J Electroanal Chem Interfa Electrochem,1973,44:239-254.
    119.Tarnowski DJ, Korzeniewski C. Effects of surface step density on the electrochemical oxidation of ethanol to acetic acid. J. Phys. Chem. B 1997,101, 253-258.
    120.Baldauf M, Kolb DM. Formic acid oxidation on ultrathin Pd films on Au (hkl) and Pt (hkl) electrodes. J. Phys. Chem.1996,100,11375-11381.
    121.Vesselli E, et al. Carbon dioxide hydrogenation on Ni (110). J. Am. Chem. Soc. 2008,130,11417-11422.
    122.Reilly JP, O'Connel D, Barnes CJ. Modification of formate stability by alloying: the Cu (100)-c (2x 2)-Pt system. J. Phys. Condens. Matter 1999,11,8417-8430.
    123.Li Y, Boone E, El-Sayed MA. Size effects of PVP-Pd nanoparticles on the catalytic Suzuki reactions in aqueous solution. Langmuir 2002,18,4921-4925.
    1. Rouxoux A, Schulz J, Patin H. Reduced transition metal colloids:A novel family of reusable catalysts? Chem. Rev.2002,102,3757-3778.
    2. William KR, Burstein GT. Low temperature fuel cells:Interactions between catalysts and engineering design. Catal. Today 1997,38,401-410.
    3. Tsung CK, Kuhn JN, Huang W, Aliaga C, Huang LI, Somorjai GA, Yang P. Sub-10 nm platinum nanocrystals with size and shape control:Catalytic study for ethylene and pyrrole hydrogenation. J. Am. Chem. Soc.2009,131,5816-5822.
    4. Huang X, Zhao Z, Fan J, Tan Y, Zheng N. Amine-assisted synthesis of concave polyhedral platinum nanocrystals having{411} high-index facets. J. Am. Chem. Soc.2011,133,4718-4721.
    5. Tian N, Zhou ZY, Sun SG, Ding Y, Wang ZL. Synthesis of tetrahexahedral platinum nanocrystals with high-index facets and high electro-oxidation activity. Science 2007,316,732-735.
    6. Grozovski V, Solla-Gullon J, Climent V, Herrero E, Feliu JM. Formic acid oxidation on shape-controlled Pt nanoparticles studied by pulsed voltammetry. J. Phys. Chem. C 2010,114,13802-13812.
    7. Iwasita T, Xia XH, Herrero E, Liess HD. Early stages during the oxidation of HCOOH on single-crystal Pt electrodes as characterized by infrared spectroscopy. Langmuir 1996,12,4260-4265.
    8. Hoshi N, Kida K, Nakamura M, Nakada M, Osada K. Structural effects of electrochemical oxidation of formic acid on single crystal electrodes of palladium. J. Phys. Chem. B 2006,110,12480-12484.
    9. Arenz M, Stamenkovic V, Schmidt TJ, Wandelt K, Ross PN, Markovic NM. The electro-oxidation of formic acid on Pt-Pd single crystal bimetallic surfaces. Phys. Chem. Chem. Phys.2003,5,4242-4251.
    10. Rodriguez P, Herrero E, Solla-Gullon J, Vidal-Iglesias FJ, Aldaz A, Feliu JM. Specific surface reactions for identification of platinum surface domains:Surface characterization and electrocatalytic tests. Electrochim. Acta 2005,50, 4308-4317.
    11. Vidal-Iglesias FJ, Solla-Gullon J, RodriguezP, Herrero E, Montiel V, Feliu JM, Aldaz A. Shape-dependent electrocatalysis:Ammonia oxidation on platinum nanoparticles with preferential (100) surfaces. Electrochem. Commun.2004,6, 1080-1084.
    12. Olofsson, G, Wallenberg, L. R, Andersson, A. Selective catalytic oxidation of ammonia to nitrogen at low temperature on Pt/CuO/Al2O3. J. Catal.2005,230, 1-13.
    13. Van der Vliet D, Wang C, Debe M, Atanasoski R, Markovic NM, Stamenkovic VR. Platinum-alloy nanostructured thin film catalysts for the oxygen reduction reaction. Electrochim. Acta 2011,56,8695-8699.
    14. Bonakdarpour A, Dahn TR, Atanasoski RT, Debe MK, Dahn JR. H2O2 release during oxygen reduction reaction on Pt nanoparticles. Electrochem. Solid State Lett.2008,11, B208-B211.
    15. Mazumder V, Chi MF, More KL, Sun SH. Core/shell Pd/FePt nanoparticles as an active and durable catalyst for the oxygen reduction reaction. J. Am. Chem. Soc. 2010,132,7848-7849.
    16. Gutierrez de Dios FJ, Gomez R, Feliu JM. Preparation and elecrocatalytic activity of Rh adlayers on Pt(100) electrodes:Reduction of nitrous oxide. Electrochem. Commun.2001,3,659-664.
    17. Duca M, Cucarella MO, Rodriguez P, Koper MTM. Direct reduction of nitrite to N2 on a Pt(100) electrode in alkaline media. J. Am. Chem. Soc.2010,132, 18042-18044.
    18. Duca M, Figueiredo MC, Climent V, Rodriguez P, Feliu JM, Koper MTM. Selective catalytic reduction at quasi-perfect Pt(100) domains:A universal low-temperature pathway from nitrite to N2. J. Am. Chem. Soc.2011,133, 10928-10939.
    19. Davis SM, Zaera F, Somorjai GA. Surface structure and temperature dependence of N-hexane skeletal rearrangement reactions catalyzed over platinum single crystal surfaces:Marked structure sensitivity of aromatization. J. Catal. 1984,85, 206-223.
    20. Lee H, Habas SE, Kweskin S, Butcher D, Somorjai GA, Yang P. Morphological control of catalytically active platinum nanocrystals. Angew. Chem. Int. Ed. 2006, 45,7824-7828.
    21. Bratlie KM, Lee H, Komvopoulos K, Yang P Somorjai GA. Platinum nanoparticle shape effects on benzene hydrogenation selectivity. Nano Lett.2007, 7,3097-3101.
    22. Xia YN, Xiong YJ, Lim B, Skrabalak SE. Shape-controlled synthesis of metal nanocrystals:Simple chemistry meets complex physics? Angew. Chem. Int. Ed. 2009,48,60-103.
    23. Tao A, Habas S, Yang P. Shape control of colloidal metal nanocrystals. Small 2008,4,310-325.
    24. Chen J, Lim BK, Lee EP, Xia YN. Shape-controlled synthesis of platinum nanocrystals for catalytic and electrocatalytic applications. Nano Today 2009,4, 81-95.
    25. Lim B, Xia YN. Metal nanocrystals with highly branched morphologies. Angew. Chem. Int. Ed.2011,50,76-85.
    26. Maksimuk S, Teng X, Yang H. Roles of twin defects in the formation of platinum multipod nanocrystals. J. Phys. Chem. C 2007,111,14312-14319.
    27. Manna L, Milliron DJ, Meisel A, Scher EC, Alivisatos A P. Controlled growth of tetrapod-branched inorganic nanocrystals. Nat. Mater.2003,2,382-385.
    28. Chen M, Xie Y, Lu J, Xiong YJ, Zhang S, Qian Y, Liu X. Synthesis of rod-, twinrod-, and tetrapod-shaped CdS nanocrystals using a highly oriented solvothermal recrystallization technique. J. Mater. Chem.2002,12,748-753.
    29. Milliron DJ, Hughes SM, Cui Y, Manna L, Li J, Wang LW, Alivisatos AP. Colloidal nanocrystal heterostructures with linear and branched topology. Nature 2004,430,190-195.
    30. Mahmoud MA, Tabor CE, El-Sayed MA, Ding Y, Wang ZL. A new catalytically active colloidal platinum nanocatalyst:The multiarmed nanostar single crystal.J. Am. Chem. Soc.2008,130,4590-4591.
    31. Lim B, Jiang M, Camargo PHC, Cho EC, Tao J, Lu X, Zhu Y, Xia YN. Pd-Pt bimetallic nanodendrites with high activity for oxygen reduction. Science 2009, 324,1302-1305.
    32. Teng X, Yang H. Synthesis of platinum multipods:An induced anisotropic growth. Nano Lett.2005,5,885-891.
    33. Lim SI, Ojea-Jimenez I, Varon M, Casals E, Arbiol J, Puntes V. Synthesis of platinum cubes, polypods, cuboctahedrons, and raspberries assisted by cobalt nanocrystals. Nano Lett.2010,10,964-973.
    34. Chen J, Herricks T, Xia YN. Poly synthesis of platinum nanostructures:Control of morphology through the manipulation of reduction kinetics. Angew. Chem. Int. Ed.2005,44,2589-2592.
    35. Kirkland AI, Jefferson DA, Duff DG, Edwards PP, Gameson I, Johnson BFG, Smith DJ. Structural studies of trigonal lamellar particles of gold and silver. Proc. R. Soc. London, A 1993,440,589-609.
    36. Xiong YJ, McLellan JM, Chen J, Tin Y, Li ZY, Xia YN. Kinetically controlled synthesis of triangular and hexagonal nanoplates of palladium and their SPR/SERS Properties. J. Am. Chem. Soc.2005,127,17118-17127.
    37. Xiong YJ, Washio I, Chen J, Cai H, Li ZY, Xia YN. Poly(vinyl pyrrolidone):A dual functional reductant and stabilizer for the facile synthesis of noble metal nanoplates in aqueous solutions. Langmuir 2006,22,8563-8570.
    38. XiongYJ, Siekkinen AR, Wang J, Yin Y, Kim MJ, Xia YN. Synthesis of silver nanoplates at high yields by slowing down the polyol reduction of silver nitrate with polyacrylamide. J. Mater. Chem.2007,17,2600-2602.
    39. Xiong YJ, Chen J, Wiley B, Xia YN, Aloni S, Yin Y. Understanding the role of oxidative etching in the polyol synthesis of Pd nanoparticles with uniform shape and size. J. Am. Chem. Soc.2005,127,7332-7333.
    40. Xiong YJ, Chen J, Wiley B, Xia YN, Yin Y, Li ZY. Size-dependence of surface plasmon resonance and oxidation for Pd nanocubes synthesized via a seed etching process. Nano Lett.2005,5,1237-1242.
    41. Xiong YJ, Cai H, Wiley BJ, Wang J, Kim M, Xia YN. Synthesis and mechanistic study of palladium nanobars and nanorods. J. Am. Chem. Soc.2007,129, 3665-3675.
    42. Chernov AA. Theory of the stability of face forms of crystals. Sov. Phys. Cryst. 1972,16,734-753.
    43. Carrasquillo A, Jeng JJ, Barriga RJ, Temesghen WF, Soriaga MP. Electrode-surface coordination chemistry:Ligand substitution and competitive coordination of halides at well-defined Pd(100) and Pd(111) single crystals. Inorg. Chim. Acta 1997,255,249-254.
    44. Wanger CD, Riggs WM, Davis LE, Moulder JF, Muilenberg GE. Handbook of X-Ray Photoelectron Spectroscopy, Perkin:Elmer Corp. Eden Prairie,1978
    45. Bard AJ, Faulkner LR. Electrochemical Methods:Fundamentals and Applications,2nd Ed, JohnWiley & Sons:New York,2001,543-579.
    46. Rice C, Ha S, Masel RI, Waszczuk P, Wieckowski A, Barnard, T. Direct formic acid fuel cells. J. Power Source 2002,111,83-89.
    47. Kang Y, Qi L, Li M, Diaz RE, Su D, Adzic RR, Stach E, Li J, Murray CB. Highly active Pt3Pb and core-shell Pt3Pb-Pt electrocatalysts for formic acid oxidation. ACS Nano 2012,6,2818-2825.
    1. Mallouk TE. Fuel-cells-miniaturized electrochemistry. Nature 1990,343, 515-516.
    2. Steele BCH, Heinzel A. Materials for fuel-cell technologies. Nature 2001, 414,345-352.
    3. Greeley J, et al. Alloys of platinum and early transition metals as oxygen reduction electrocatalysts. Nat. Chem.2009,1,552-556.
    4. Stamenkovic VR, et al. Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces. Nat. Mater.2007,6,241-247.
    5. Min MK, Cho JH, Cho KW, Kim H. Particle size and alloying effects of Pt-based alloy catalysts for fuel cell applications. Electrochim. Acta.2000,45, 4211-4217.
    6. Van der Vliet D, et al. Platinum-alloy nanostructured thin film catalysts for the oxygen reduction reaction. Electrochim. Acta.2011,56,8695-8699.
    7. Mazumder V, Chi MF, More KL, Sun SH. Core/shell Pd/FePt nanoparticles as an active and durable catalyst for the oxygen reduction reaction. J. Am. Chem. Soc. 2010,132,7848-7849.
    8. Stamenkovic V, Schmidt TJ, Ross PN, Markovic NM. Surface segregation effects in electrocatalysis:kinetics of oxygen reduction reaction on polycrystalline Pt3Ni alloy surfaces. J. Electroanal. Chem.2003,554,191-199.
    9. Anderson AB, et al. Activation energies for oxygen reduction on platinum alloys: Theory and experiment. J. Phys. Chem. B.2005,109,1198-1203.
    10. Wang C, et al. Monodisperse Pt3Co nanoparticles as a catalyst for the oxygen reduction reaction:Size-dependent activity. J. Phys. Chem. C 2009,113, 19365-19368.
    11. Lim B, et al. Pd-Pt bimetallic nanodendrites with high activity for oxygen reduction. Science 2009,324,1302-1305.
    12. Stamenkovic VR, et al. Improved oxygen reduction activity on Pt3Ni(111) via increased surface site availability. Science 2007,315,493-497.
    13. Sasaki K, et al. Recent advances in platinum monolayer electrocatalysts for oxygen reduction reaction:Scale-up synthesis, structure and activity of Pt shells on Pd cores. Electrochim. Acta.2010,55,2645-2652.
    14. Gong KP, Su D, Adzic RR. Platinum-monolayer shell on AuNi0.5Fe nanoparticle core electrocatalyst with high activity and stability for the oxygen reduction reaction. J. Am. Chem. Soc.2010,132,14364-14366.
    15. Koenigsmann C, et al. Enhanced electrocatalytic performance of processed, ultrathin, supported Pd-Pt core-shell nanowire catalysts for the oxygen reduction reaction. J. Am. Chem. Soc,2011,133,9783-9795.
    16. Xing YC, et al. Enhancing oxygen reduction reaction activity via Pd-Au alloy sublayer mediation of Pt monolayer electrocatalysts.J. Electroanal. Chem.2010, 1,3238-3242.
    17. Zhou WP, et al. Gram-scale-synthesized Pd2Co-supported Pt monolayer electrocatalysts for oxygen reduction reaction. J. Phys. Chem. C.2010,114, 8950-8957.
    18. Snyder J, Fujita T, Chen MW, Erlebacher J. Oxygen reduction in nanoporous metal-ionic liquid composite electrocatalysts. Nat. Mater.2010,9,904-907.
    19. Liang YY, et al. Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction. Nat. Mater.2011,10,780-786.
    20. Gong KP, Du F, Xia ZH, Durstock M, Dai LM. Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction. Science 2009,323, 760-764.
    21. Lefevre M, Proietti E, Jaouen F, Dodelet JP. Iron-based catalysts with improved oxygen reduction activity in polymer electrolyte fuel cells. Science 2009,324, 71-74.
    22. Wu G, More KL, Johnston CM, Zelenay P. High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science 2011,332, 443-447.
    23. Kuzume A, Herrero E, Feliu JM. Oxygen reduction on stepped platinum surfaces in acidic media. J. Electroanal. Chem.2007,599,333-343.
    24. Macia MD, Campina JM, Herrero E, Feliu JM. On the kinetics of oxygen reduction on platinum stepped surfaces in acidic media. J. Electroanal. Chem. 2004,564,141-150.
    25. Komanicky V, Menzel A, You H. Investigation of oxygen reduction reaction kinetics at (111)-(100) nanofaceted platinum surfaces in acidic media. J. Phys. Chem. B.2005,109,23550-23557.
    26. Lim B, Xia YN. Metal nanocrystals with highly branched morphologies. Angew. Chem. Int. Ed.2011,50,76-85.
    27. Xia YN, Xiong YJ, Lim B, Skrabalak SE. Shape-controlled synthesis of metal nanocrystals:Simple chemistry meets complex physics? Angew. Chem. Int. Ed. 2009,48,60-103.
    28. Yu T, Kim DY, Zhang H, Xia YN. Platinum concave nanocubes with high-index facets and their enhanced activity for oxygen reduction reaction. Angew. Chem. Int. Ed.2011,50,2773-2777.
    29. Mahmoud MA, Tabor CE, El-Sayed MA, Ding Y, Wang ZL. A new catalytically active colloidal platinum nanocatalyst:the multiarmed nanostar single crystal. J. Am. Chem. Soc.2008,130,4590-4591.
    30. Meyer JC, et al. The structure of suspended graphene sheets. Nature 2007,446, 60-63.
    31. Novoselov KS, et al. Two-dimensional gas of massless Dirac fermions in graphene. Nature 2005,438,197-200.
    32. Zhang YB, Tan YW, Stormer HL, Kim P. Experimental observation of the quantum Hall effect and Berry's phase in graphene. Nature 2005,438,201-204.
    33. Yang J, Zang CL, Sun L, Zhao N, Cheng XN. Synthesis of graphene/Ag nanocomposite with good dispersibility and electroconductibility via solvothermal method. Mater. Chem. Phys.2011,129,270-274.
    34. Eda G, Fanchini G, Chhowalla M. Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material. Nat. Nanotechnol.2008,3, 270-274.
    35. Lee C, Wei X, Kysar JW, Hone J. Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 2008,321,385-388.
    36. Guo SJ, Sun SH. FePt nanoparticles assembled on graphene as enhanced catalyst for oxygen reduction reaction. J. Am. Chem. Soc..2012,134,2492-2495.
    37. Zhou M, Zhang AH, Dai ZX, Feng YP, Zhang C. Strain-enhanced stabilization and catalytic activity of metal nanoclusters on graphene. J. Phys. Chem. C 2010, 114,16541-16546.
    38. Hummers WS, Offeman RE. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958,80,1339-1339.
    39. Ma L, et al. Control over the branched structures of platinum nanocrystals for electrocatalytic applications. ACS Nano.2012,6,9797-9806.
    40. Wanger CD, Riggs WM, Davis LE, Moulder JF, Muilenberg GE. Handbook of X-Ray Photoelectron Spectroscopy, Perkin-Elmer Corp. Eden Prairie,1978.
    41. Lindstrom RW, et al. Active area determination of porous Pt electrodes used in polymer electrolyte fuel cells:Temperature and humidity effects. J Electrochem Soc.2010,157, B1795-B1801.
    42. Lee SJ, et al. Effects of nafion impregnation on performances of PEMFC electrodes. Electrochim. Acta.1998,43,3693-3701.
    43. Markus Nesselberger et al. The particle size effect on the oxygen reduction reaction activity of Pt catalysts:Influence of electrolyte and relation to single crystal models. J. Am. Chem. Soc.2011,133,17428-17433.
    44. Peng ZM, Yang H. Synthesis and oxygen reduction electrocatalytic property of Pt-on-Pd bimetallic heteronanostructures. J. Am. Chem. Soc.2009,131, 7542-7543.
    45. Peng ZM, Yang H. Designer platinum nanoparticles:Control of shape, composition in alloy, nanostructure and electrocatalytic property. Nano Today 2009,4,143-164.
    46. Clouser SJ, Huang JC, Yeager E. Temperature dependence of the Tafel slope for oxygen reduction on platinum in concentrated phosphoric acid. J. Appl. Electrochem.1993,23,597-605.
    47. Ghoneim MM, Clouser S, Yeager E. Oxygen reduction kinetics in deuterated phosphoric acid. J. Electrochem. Soc.1985,132,1160-1162.
    48. Hsueh KL, Gonzalez ER, Srinivasan S. Electrolyte effects on oxygen reduction kinetics at platinum:A rotating-ring disk electrode analysis. Electrochim Acta. 1983,28,691-697.
    49. Kamat PV. Graphene-based nanoarchitectures. Anchoring semiconductor and metal nanoparticles on a two-dimensional carbon support. J. Phys. Chem. Lett. 2010,1,520-527.
    50. Park S, Ruoff RS. Chemical methods for the production of graphenes. Nat. Nanotechnol.2009,4,217-224.
    51. Li D, Muller MB, Gilje S, Kaner RB, Wallace GG Processable aqueous dispersions of graphene nanosheets. Nat. Nanotechnol.2008,3,101-105.
    52. Raman RKS, et al. Protecting copper from electrochemical degradation by graphene coating. Carbon 2012,50,4040-4045.
    53. Tuinstra F, Koenig JL. Raman spectrum of graphite. J. Chem. Phys.1970,53, 1126-1130.
    54. Tung VC, Allen MJ, Yang Y, Kaner RB. High-throughput solution processing of large-scale graphene. Nat. Nanotechnol.2009,4,25-29.
    55. Stankovich S, et al. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007,45,1558-1565.
    56. Zhu CZ, Guo SJ, Fang YX, Dong SJ. Reducing sugar:new functional molecules for the green synthesis of graphene nanosheets. ACS Nano 2010,4,2429-2437.
    57. Markovic NM, Gasteiger HA, Grgur BN, Ross PN. Oxygen reduction reaction on Pt (111):effects of bromide. J. Electroanal. Chem.1999,467,157-163.
    58. Zhang J, Sasaki K, Sutter E, Adzic RR. Stabilization of platinum oxygen-reduction electrocatalysts using gold clusters. Science 2007,315, 220-222.
    59. Li YJ, et al. Stabilization of high-performance oxygen reduction reaction Pt electrocatalyst supported on reduced graphene oxide/carbon black composite. J. Am. Chem. Soc.2012,134,12326-12329.
    60. Kim KS, et al. Large-scale pattern growth of graphene films for stretchable transparent electrodes. Nature 2009,457,706-710.
    61. Geim AK. Graphene:Status and prospects. Science 2009,324,1530-1534.
    1. Xia YN, Xiong YJ, Lim B, Skrabalak SE. Shape-controlled synthesis of metal nanocrystals:Simple chemistry meets complex physics? Angew. Chem. Int. Ed. 2009,48,60-103.
    2. Somorjai GA. Surface science and catalysis. Science,1985,227,902-908.
    3. Xiong YJ, Wiley B, Xia YN. Nanocrystals with unconventional shapes-A class of promising catalysts. Angew. Chem. Int. Ed.2007,46,7157-7159.
    4. Ming T, Feng W, Tang Q, Wang F, Sun L, Wang J, Yan C. Growth of tetrahexahedral gold nanocrystals with high-index facets. J. Am. Chem. Soc.2009, 131,16350-16351.
    5. Yu Y, Zhang Q, Lu X, Lee JY. Seed-mediated synthesis of monodisperse concave trisoctahedral gold nanocrystals with controllable sizes. J. Phys. Chem. C 2010, 114,11119-11126.
    6. Zheng Y, Tao J, Liu H, Zeng J, Yu T, Ma Y, Moran C, Wu L, Zhu Y, Liu J, Xia YN. Facile synthesis of gold nanorice enclosed by high-index facets and its application for CO oxidation. Small 2011,16,2307-2312.
    7. Lofton C, Sigmund W. Mechanisms controlling crystal habits of gold and silver colloids. Adv. Funct. Mater.2005,15,1197-1208.
    8. Li B, Long R, Zhong XL, Bai Y, Zhu ZJ, Zhang X, Zhi M, He JW, Wang CM, Li ZY, Xiong YJ. Investigation of size-dependent plasmonic and catalytic properties of metallic nanocrystals enabled by size control with HC1 oxidative etching. Small,2012,8,1710-1716.
    9. Xiong YJ, Washio I, Chen JY, Cai HG, Li ZY, Xia YN. Poly(vinyl pyrrolidone):A dual functional reductant and stabilizer for the Facile synthesis of metal nanoplates in aqueous solutions. Langmuir,2006,22,8563-8570.
    10. Handbook of Chemistry and Physics ed. R. C. Weast, CRC Press, Boca Raton, FL, 60th Edn.1980
    11. Xiong YJ, Cai H, Wiley BJ, Wang J, Kim MJ, Xia YN. Synthesis and mechanistic study of palladium nanobars and nanorods. J. Am. Chem. Soc.2007,129, 3665-3675.
    12. Huang X, Zheng N. One-pot, high-yield synthesis of 5-fold twinned Pd nanowires and nanorods. J. Am. Chem. Soc.2009,131,4602-4603.
    13. Xiong YJ. Cai HG, Yin YD, Xia YN. Synthesis and characterization of fivefold twinned nanorods and right bipyramids of palladium. Chem. Phys. Lett.2007, 440,273-278.
    14. Xiong YJ, McLellan JM, Chen JY, Yin YD, Li ZY, Xia YN. Kinetically controlled synthesis of triangular and hexagonal nanoplates of palladium and their SPR/SERS properties. J. Am. Chem. Soc.2005,127,17118-17127.
    15. Zhang H, et al. Synthesis of Pd-Pt bimetallic nanocrystals with a concave structure through a bromide-induced galvanic replacement reaction. J. Am. Chem. Soc.2011,133,6078-6089.
    16. Zhang H, Jin M, Liu H, Wang J, Kim MJ, Yang D, Xie Z, Liu J, Xia YN. Facile synthesis of Pd-Pt alloy nanocages and their enhanced performance for preferential oxidation of CO in excess hydrogen. ACSNano 2011,5,8212-8222.
    17. Chen J, McLellan JM, Siekkinen A, Xiong YJ, Li ZY. Xia YN. Facile synthesis of gold-silver nanocages with controllable pores on the surface. J. Am. Chem. Soc. 2006,128,14776-14777.
    18. Xia X, Zeng J, Mcdearmon B, Zheng Y, Li Q, Xia YN. Silver nanocrystals with concave surfaces and their optical and surface-enhanced Raman scattering properties. Angew. Chem. Int. Ed.2011.50,12542-12546.
    19. Jin MS, Zhang H, Xie ZX, Xia YN. Palladium concave nanocubes with high-index facets and their enhanced catalytic properties. Angew. Chem. Int. Ed. 2011,50,7850-7854.
    1. Fu Q, Li WX, Yao Y, Liu H, Su HY, Ma D, Gu XK, Chen L, Wang Z, Zhang H, Wang B, Bao X. Interface-confined ferrous centers for catalytic oxidation. Science 2010,328,1141-1144.
    2. Mu R, Fu Q, Xu H, Zhang H, Huang Y, Jiang Z, Zhang S, Tan D and Bao X. Synergetic effect of surface and subsurface Ni species at Pt-Ni bimetallic catalysts for CO oxidation. J. Am.Chem. Soc.2011,133,1978-1986.
    3. Narayanan R and El-Sayed MA. Shape-dependent catalytic activity of platinum nanoparticles in colloidal solution. Nano Lett.2004,4,1343-1348.
    4. Somorjai GA, Introduction to Surface Chemistry and Catalysis, Wiley Publishers, New York,1994.
    5. Tian N, Zhou ZY, Sun, SG, Ding Y, Wang ZL. Synthesis of tetrahexahedral platinum nanocrystals with high-index facets and high electro-oxidation activity. Science 2007,316,732-735.
    6. Jin MS, Zhang H, Xie ZX, Xia YN. Palladium concave nanocubes with high-index facets and their enhanced catalytic properties. Angew. Chem. Int. Ed. 2011,50,7850-7854
    7. Yu T, Kim DY, Zhang H, Xia YN. Platinum concave nanocubes with high-index facets and their enhanced activity for oxygen reduction reaction. Angew. Chem. Int. Ed.2011,50,2773-2777.
    8. Zhang H, Li WY, Jin MS, Zeng J, Yu TK, Yang DR, Xia YN. Controlling the morphology of rhodium nanocrystals by manipulating the growth kinetics with a syringe pump. Nano Lett.2011,11,898-903.
    9. Xie S, Lu N, Xie Z, Wang J, Kim MJ and Xia YN. Synthesis of Pd-Rh core-frame concave nanocubes and their conversion to Rh cubic nanoframes by selective etching of the Pd cores. Angew. Chem. Int. Ed.2012,51,10266-10270.
    10. Zhang H, Jin MS, Xia YN. Noble-metal nanocrystals with concave surfaces: Synthesis and applications. Angew. Chem. Int. Ed.2012,51:7656-7673.
    11. Zhang GR, Wu J, Xu BQ. Syntheses of sub-30 nm Au@Pd concave nanocubes and Pt-on-(Au@Pd) trimetallic nanostructures as highly efficient catalysts for ethanol oxidation. J. Phys. Chem. C 2012,116,20839-20847.
    12. Chernov AA. Theory of the stability of face forms of crystals. Sov. Phys. Cryst. 1972,16,734-753.
    13. Li Y, Hong XM, Collard DM, El-Sayed MA. Suzuki cross-coupling reactions catalyzed by palladium nanoparticles in aqueous solution. Org. Lett.2000,2, 2385-2388.
    14. Lee H, Habas SE, Kweskin S, Butcher D, Somorjai GA, Yang PD. Morphological control of catalytically active platinum nanocrystals. Angew. Chem. Int. Ed.2006, 45,7824-7828.
    15. Bratlie KM, Lee H, Komvopoulos K, Yang P, Somorjai GA. Platinum nanoparticle shape effects on benzene hydrogenation selectivity. Nano Lett.2007, 7,3097-3101.
    16. Hoshi N, Kida K, Nakamura M, Nakada M, Osada K. Structural effects of electrochemical oxidation of formic acid on single crystal electrodes of palladium. J Phys Chem B,2006,110:12480-12484.
    17. Huang X, Tang S, Zhang H, Zhou Z and Zheng N. Controlled formation of concave tetrahedral/trigonal bipyramidal palladium nanocrystals. J. Am. Chem. Soc.2009,131,13916-13917.
    18. Arenz M, Stamenkovic V, Schmidt TJ, Wandelt K, Ross PN and Markovic NM. The electro-oxidation of formic acid on Pt-Pd single crystal bimetallic surfaces Phys. Chem. Chem. Phys.2003,5,4242-4251.
    19. Olofsson G Wallenberg LR and Andersson A. Selective catalytic oxidation of ammonia to nitrogen at low temperature on Pt/CuO/Al2O3. J. Catal 2005,230, 1-13.
    20. Mazumder V, Chi MF, More KL, Sun SH. Core/shell Pd/FePt Nanoparticles as an active and durable catalyst for the oxygen reduction reaction. J. Am. Chem. Soc. 2010,132,7848-7849.
    21. Jin MS, Liu H, Zhang H, Xie Z, Liu J, Xia YN. Synthesis of Pd nanocrystals enclosed by{100} facets and with sizes< 10 nm for application in CO oxidation. Nano Res.2011,4,83-91.
    22. Xia YN, Xiong YJ, Lim B, Skrabalak SE. Shape-controlled synthesis of metal nanocrystals:Simple chemistry meets complex physics? Angew. Chem. Int. Ed. 2009,48,60-103.
    23. Xiong YJ, Cai H, Wiley BJ, Wang J, Kim M, Xia YN. Synthesis and mechanistic study of palladium nanobars and nanorods. J. Am. Chem. Soc.2007,129, 3665-3675.
    24. Xiong YJ. Morphological changes in Ag nanocrystals triggered by citrate photoreduction and governed by oxidative Etching. Chem. Commun.2011,47, 1580-1582.
    25. Handbook of Chemistry and Physics, ed. R. C. Weast, CRC Press, Boca Raton, FL,60th edn,1980.
    26. Zhang H, et al. Synthesis of Pd-Pt bimetallic nanocrystals with a concave structure through a bromide-induced galvanic replacement reaction. J. Am. Chem. Soc.2011,133,6078-6089.
    27. Zhang H, Jin MS, Liu H, Wang J, Kim MJ, Yang D, Xie Z, Liu J and Xia YN. Facile synthesis of Pd-Pt alloy nanocages and their enhanced performance for preferential oxidation of CO in excess hydrogen. ACS Nano 2011,5,8212-8222.
    28. Grozovski V, Solla-Gullon J, Climent V, Herrero E, Feliu JM. Formic acid oxidation on shape-controlled Pt nanoparticles studied by pulsed voltammetry. J. Phys. Chem. C2010,114,13802-13812.
    29. Tian N, Zhou ZY, Sun SG. Platinum metal catalysts of high-index surfaces:From single-crystal planes to electrochemically shape-controlled nanoparticles. J. Phys. Chem. C 2008,112,19801-19817.
    30. Wang CM, Wang LL, Long L, Ma L, Wang LM, Li Z, Xiong YJ. Anisotropic growth of palladium twinned nanostructures controlled by kinetics and their unusual activities in galvanic replacement. J. Mater. Chem.2012,22,8195-8198.
    31. Lu X, Tuan HY, Chen J, Li ZY, Korgel BA, Xia YN. Mechanistic studies on the galvanic replacement reaction between multiply twinned particles of Ag and HAuCl4 in an organic medium. J. Am. Chem. Soc.2007,129,1733-1742.
    1. Tian N, Zhou ZY, Sun SG, Ding Y, Wang ZL. Synthesis of tetrahexahedral platinum nanocrystals with high-index facets and high electro-oxidation activity. Science 2007,316,732-735.
    2. Llorca MJ, Feliu JM, Aldaz A, Clavilier J. Formic acid oxidation on Pdad+ Pt(100) and Pdad+Pt(111) electrodes. JElectroanal Chem.1994,376,151-160
    3. Baldauf M, Kolb DM. Formic acid oxidation on ultrathin Pd films on Au(hkl) and Pt(hkl) electrodes. J Phys Chem.1996,100,11375-11381.
    4. Kibler LA, El-Aziz AM, Hoyer R, Kolb DM. Tuning reaction rates by lateral strain in a palladium monolayer. Angew. Chem. Int. Ed.2005,44,2080-2084.
    5. Capon A, Parsons R. The oxidation of formic acid on noble metal electrodes:II. A comparison of the behaviour of pure electrodes. J Electroanal Chem Interfa Electrochem.1973,44,239-254.
    6. Meng H, Sun S, Masse JP, Dodelet JP. Electrosynthesis of Pd single-crystal nanothorns and their application in the oxidation of formic acid. Chem Mater. 2008,20,6998-7002.
    7. Jin MS, Zhang H, Xie ZX, Xia YN. Palladium nanocrystals enclosed by{100} and{111} facets in controlled proportions and their catalytic activities for formic acid oxidation. Energy Environ Sci.2012,5,6352-6357.
    8. Zhou WP, Lewera A, Larsen R, Masel RI, Bagus PS, Wieckowski A. Size effects in electronic and catalytic properties of unsupported palladium nanoparticles in electrooxidation of formic acid. JPhys Chem B 2006,110,13393-13398.
    9. Xiong YJ, Wiley B, Xia YN. Nanocrystals with unconventional shapes-A class of promising catalysts. Angew. Chem. Int. Ed. 2007,46,7157-7159.
    10. Baldauf M, Kolb DM. Formic acid oxidation on ultrathin Pd films on Au(hkl) and Pt(hkl) electrodes. JPhys Chem.1996,100,11375-11381.
    11. Hoshi N, Kida K, Nakamura M, Nakada M, Osada K. Structural effects of electrochemical oxidation of formic acid on single crystal electrodes of palladium. J Phys Chem B 2006,110,12480-12484.
    12. Xia YN, Xiong YJ, Lim B, Skrabalak SE. Shape-controlled synthesis of metal nanocrystals:Simple chemistry meets complex physics? Angew. Chem. Int. Ed. 2009,48,60-103.
    13. Lim B, Jiang MJ, Tao J, Camargo PHC, Zhu YM, Xia YN. Shape-controlled synthesis of Pd nanocrystals in Aqueous Solutions. Adv Funct Mater.2009,19, 189-200.
    14. Lu CL, Prasad KS, Wu HL, Ho JAA, Huang MH. Au nanocube-directed fabrication of Au-Pd core-shell nanocrystals with tetrahexahedral, concave octahedral, and octahedral structures and their electrocatalytic activity. J. Am. Chem, Soc.2010,132,14546-14553.
    15. Zhang H, Jin MS, Xia YN. Noble-metal nanocrystals with concave surfaces: Synthesis and applications. Angew. Chem. Int. Ed.2012,51,7656-7673.
    16. Tian N, Zhou ZY, Yu NF, Wang LY, Sun SG. Direct electrodeposition of tetrahexahedral Pd nanocrystals with high-index facets and high catalytic activity for ethanol electrooxidation. J. Am. Chem. Soc.2010,132,7580-7581.
    17. Wang F, Li CH, Sun LD, Wu HS, Ming TA, Wang JF, Yu JC, Yan CH. Heteroepitaxial growth of high-index-faceted Palladium nanoshells and their catalytic performance. J. Am. Chem. Soc.2011,133,1106-1111.
    18. Yu Y, Zhang QB, Liu B, Lee JY. Synthesis of nanocrystals with variable high-index Pd facets through the controlled heteroepitaxial growth of trisoctahedral Au templates. J.Am. Chem. Soc.2010,132,18258-18265.
    19. Li B, Long R, Zhong XL, Bai Y, Zhu ZJ, Zhang X, Zhi M, He JW, Wang CM, Li ZY, Xiong YJ. Investigation of size-dependent plasmonic and catalytic properties of metallic nanocrystals enabled by size control with HC1 oxidative etching. Small 2012,8,1710-1716.
    20. Wang CM, Wang LL, Long R, Ma L, Wang LM, Li ZQ, Xiong YJ. Anisotropic growth of palladium twinned nanostructures controlled by kinetics and their unusual activities in galvanic replacement. J. Mater. Chem.2012,22,8195-8198.
    21. Xiong YJ. Cai HQ Yin YD, Xia YN. Synthesis and characterization of fivefold twinned nanorods and right bipyramids of palladium. Chem. Phys. Lett.2007, 440,273-278.
    22. Sun YG, Mayers B, Herricks T, Xia YN. Polyol synthesis of uniform silver nanowires:A plausible mechanism and the supporting evidence. Nano Lett.2003, 3,955-960.
    23. Ma L, Wang CM, Gong M, Liao LW, Long R, Wang JG, Wu D, Zhong W, Kim MJ, Chen YX, Xie Y, Xiong YJ. Control over the branched structures of platinum nanocrystals for electrocatalytic applications. ACS Nano,2012,6,9797-9806.
    24. Jin MS, Zhang H, Xie ZX, Xia YN. Palladium concave nanocubes with high-index facets and their enhanced catalytic properties. Angew. Chem. Int. Ed. 2011,50,7850-7854.
    25. Xiong YJ, McLellan JM, Yin YD, Xia YN. Synthesis of palladium icosahedra with twinned structure by blocking oxidative etching with citric acid or citrate ions. Angew. Chem. Int. Ed.2007,46,790-794.
    26. Lim B, Xiong YJ, Xia YN. A water-based synthesis of octahedral, decahedral, and icosahedral Pd nanocrystals. Angew. Chem. Int. Ed.2007,46,9279-9282.
    27. Xiong YJ, Washio I, Chen JY, Cai HG, Li ZY, Xia YN. Poly(vinyl pyrrolidone):A dual functional reductant and stabilizer for the Facile synthesis of metal nanoplates in aqueous solutions. Langmuir,2006,22,8563-8570.
    28. Weast RC. Handbook of Chemistry and Physics. Boca Raton:CRC Press,1980.
    29. Xiong YJ, Cai HG, Wiley BJ, Wang JG, Kim MJ, Xia YN. Synthesis and mechanistic study of Palladium nanobars and nanorods.J. Am. Chem. Soc.2007, 127,3665-3675.
    30. Huang XQ, Zheng NF. One-pot, high-yield synthesis of 5-fold twinned Pd nanowires and nanorods. J. Am. Chem. Soc.2009,131,4602-4603.
    31. Stamenkovic VR, Fowler B, Mun BS, Wang GF, Ross PN, Lucas CA, Markovic NM. Improved oxygen reduction activity on Pt3Ni{111} via increased surface site availability. Science 2007,315,493-497.
    32. Narayanan R, El-Sayed MA. Shape-dependent catalytic activity of platinum nanoparticles in colloidal solution. Nano Lett.2004,4,1343-1348.
    33. Somorjai GA. Introduction to Surface Chemistry and Catalysis. New York:Wiley Publishers,1994.
    34. Rice C, Ha S, Masel RI,Waszczuk P, Wieckowski A, Barnard T. Direct formic acid fuel cells. J Power Source 2002,111,83-89.
    35. Rice C, Ha S. Masel RI, Wieckowski A. Catalysts for direct formic acid fuel cells. J Power Sources 2003,115,229-235.