Steps, ledges and kinks on the surfaces of platinum nanoparticles of different shapes (original) (raw)
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Nanotechnology, 2010
In this paper, Pt nanoparticles with good shapes of nanocubes and nano-octahedra and wellcontrolled sizes in the range 5-7 and 8-12nm, respectively, have been successfully synthesized. The modified polyol method by adding silver nitrate and varying the molar ratio of the solutions of silver nitrate and H2PtCl6 has been used to produce Pt nanoparticles of the size and shape to be controlled. The size and morphology of Pt nanoparticles have been studied by transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The results have shown that their very sharp and good shapes exist in the main forms of cubic, cuboctahedral, octahedral and tetrahedral shapes directly related to the crystal nucleation along various directions of the {100} cubic, {111} octahedral and {111} tetrahedral facets during synthesis. In particular, various irregular and new shapes of Pt nanoparticles have been found. Here, it is concluded that the role of silver ions has to be considered as an important factor for promoting and controlling the development of Pt nanoparticles of {100} cubic, {111} octahedral and {111} tetrahedral facets, and also directly orienting the growth and formation of Pt nanoparticles. © IOP Publishing Ltd.
Morphology mapping of platinum catalysts over the entire nanoscale
Catalysis Science & Technology, 2011
Platinum nanoparticles are exceptional heterogeneous catalysts that play an important part in our existing and future energy economy. Understanding the size, shape and morphological transformations that may occur under different temperature conditions is vital to ensuring the long term stability of platinum-based technologies, or for planning ideal operating and storage conditions for platinum nanoparticles. In this paper we present a combination of experimental and theoretical results exploring the relationship between as-grown and thermodynamically preferred morphologies of platinum catalysts over the entire nanoscale. A shape-dependent thermodynamic model has been used to predict the stable morphology as a function of the size and temperature, and the first nanoscale phase diagram of platinum is constructed, by considering 15 different ideal and imperfect structures and shapes. This phase diagram is then discussed in relation to the experiments, to establish the relative stability of different shapes and the sizes at which they may be expected.
Expansion of interatomic distances in platinum catalyst nanoparticles
Acta Materialia, 2010
We study the atomistic structure of Pt catalyst nanoparticles using HRTEM (high-resolution transmission electron microscopy). The particles exhibit a faceted, cubo-octahedral shape, extended planar defects, and mono-atomic surface steps. HRTEM imaging with negative spherical aberration yielded atomic-resolution images with a minimum of artifacts. Combining digital image processing, quantitative image analysis, and HRTEM image simulations to determine local variations of the spacing between neighboring Pt atom columns, we have found an expansion of the lattice parameter in the particle core and even larger, locally varying expansion of Pt-Pt next-neighbor distances at the particle surface. The latter likely originates from an amorphous oxide on the nanoparticle surface and/or dissolution of oxygen on subsurface sites. These structural features may significantly impact the catalytic activity of Pt nanoparticles.
Journal of physics. Condensed matter : an Institute of Physics journal, 2018
Platinum nanoparticles find significant use as catalysts in industrial applications such as fuel cells. Research into their design has focussed heavily on nanoparticle size and shape as they greatly influence activity. Using high throughput, high precision electron microscopy, the structures of commercially available Pt catalysts have been determined, and we have used classical and quantum atomistic simulations to examine and compare them with geometric cuboctahedral and truncated octahedral structures. A simulated annealing procedure was used both to explore the potential energy surface at different temperatures, and also to assess the effect on catalytic activity that annealing would have on nanoparticles with different geometries and sizes. The differences in response to annealing between the real and geometric nanoparticles are discussed in terms of thermal stability, coordination number and the proportion of optimal binding sites on the surface of the nanoparticles. We find tha...
Electrochimica Acta, 2010
We present a rigorous approach for the shape design of supported metal nanoparticle catalysts, morphologically identical to each other and epitaxially grown on strontium titanate substrates using electron beam lithography. We predict the particle shapes using Wulff construction based on density functional theory calculations of surface energies. Then, according to the theoretical predictions, we are able to tweak morphologies of the already produced nanocrystals by changing annealing conditions. The ability to design, produce and characterize the catalyst nanoparticles allows us to relate microscopic morphologies with macroscopic oxygen-reduction activities in perchloric acid [Komanicky et al., J. Am. Chem. Soc. 131 (2009) 5732]. The unexpectedly high oxygen-reduction activities proportional to inactive (1 0 0) facets led us to suggest a model where the reaction intermediates can cross over to neighboring facets in nanoscale proximity.
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Nanoscale
This work reports on the morphology of individual platinum nanocrystals with sizes of about 5 nm. By using the electron tomography technique that gives 3D spatial selectivity, access to quantitative information in the real space was obtained. The morphology of individual nanoparticles was characterized using HAADF-STEM tomography and it was shown to be close to a truncated octahedron. Using molecular dynamics simulations, this geometrical shape was found to be the one minimizing the nanocrystal energy. Starting from the tomographic reconstruction, 3D crystallographic representations of the studied Pt nanocrystals were obtained at the nanometer scale, allowing the quantification of the relative amount of the crystallographic facets present on the particle surface.
Kinetically Controlled Growth and Shape Formation Mechanism of Platinum Nanoparticles
The Journal of Physical Chemistry B, 1998
Recently, we have been able to synthesize platinum colloidal nanoparticles of different shapes (Science, 1996(Science, , 272, 1924. In this report, we present transmission electron microscopic (TEM) results on the time-dependent shape distribution of platinum nanoparticles during the growth period and its dependence on the concentration of the capping polymer as well as the pH of the solution. The results suggest a shape-controlled growth mechanism in which the difference between the rate of the catalytic reduction process of Pt 2+ on the {111} and {100} faces, the competition between the Pt 2+ reduction and the capping process on the different nanoparticle surfaces, and the concentration-dependent buffer action of the polymer itself all control the final distribution of the different shapes observed.
Crystal size and shape analysis of Pt nanoparticles in two and three dimensions
2006
Abstract. The majority of industrial catalysts are high-surface-area solids, onto which an active component is dispersed in the form of nanoparticles that have sizes of between 1 and 20 nm. In an industrial environment, the crystal size distributions of such particles are conventionally measured by using either bright-field transmission electron microscope (TEM) images or X-ray diffraction.