Platinum Nanostructures Research Articles

Co‐adsorption of O and H2O on Nanostructured Platinum Surfaces: Does OH Form at Steps?

An gestuften Platinoberflächen wird adsorbiertes OHad weniger bereitwillig gebildet als auf einer ebenen Pt(111)-Oberfläche. Entsprechend verbleiben Oad-Spezies auf Stufen, wenn H2O und Oad dort coadsorbiert werden. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Co-adsorption of O and H2O on Nanostructured Platinum Surfaces: Does OH Form at Steps?

Co-adsorption of O and H2O on Nanostructured Platinum Surfaces: Does OH Form at Steps?

Contribution of the Double Layer to Transient Faradaic Processes: Implications for Hydrodynamic Modulated Voltammetry of Nanostructures

The electrochemistry of Pt nanostructured electrodes is investigated using hydrodynamic modulated voltammetry (HMV). Here a liquid crystal templating process is used to produce platinum-modified electrodes with a range of surface areas (roughness factor 42.4-280.8). The electroreduction of molecular oxygen at these nanostructured platinum surfaces is used to demonstrate the ability of HMV to discriminate between faradaic and nonfaradaic electrode reactions. The HMV approach shows that the reduction of molecular oxygen experiences considerable signal loss within the high pseudocapacitive region of the voltammetry. Evidence for the contribution of the double layer to transient mass transfer events is presented. In addition, a model circuit and appropriate theoretical analysis are used to illustrate the transient responses of a time variant faradaic component. This in conjunction with the experimental evidence shows that, far from being a passive component in this system, the double layer can contribute to HMV faradaic reactions under certain conditions.

On the Role of Ascorbic Acid in the Synthesis of Single-Crystal Hyperbranched Platinum Nanostructures

In this paper, a very simple and efficient wet chemical route is proposed to directly produce single-crystal hyperbranched platinum nanostructures (HPNSs), in high yield, within 10 min simply by sonication treatment of an aqueous solution containing K2PtCl4 and ascorbic acid (AA) only. The results in this report demonstrate that even in the absence of any purposely added structure-directing agent and seed mediator, reaction kinetics of AA and the released byproduct derived from AA oxidation, that is, 2,3-diketo-l-gulonic acid (DGA), are capable of producing single-crystal HPNSs in aqueous medium. In addition to being a commonplace reducing agent (electron donor), AA plays a more important role relied on its byproduct, DGA, which serves as a shape-directing agent to direct the branched growth. The new insight into the role of AA in the synthesis of single-crystal HPNSs reported here provides a new viewpoint for further understanding the formation mechanism of anisotropic platinum nanostructures.

Local deposition of high-purity Pt nanostructures by combining electron beam induced deposition and atomic layer deposition

An approach for direct-write fabrication of high-purity platinum nanostructures has been developed by combining nanoscale lateral patterning by electron beam induced deposition (EBID) with area-selective deposition of high quality material by atomic layer deposition (ALD). Because virtually pure, polycrystalline Pt nanostructures are obtained, the method extends the application possibilities of EBID, whereas compared to other area-selective ALD approaches, a much higher resolution is attainable; potentially down to sub-10 nm lateral dimensions.

Influence of morphology in the catalytic activity of bioconjugated platinum nanostructures

Platinum nanoparticles stabilized by a protein, bovine serum albumin, have been synthesized successfully with two different morphologies such as cuboctahedra and nanorods. They have been characterized by the use of different techniques such as XPS, PCS, TEM, and STEM-HAADF. These nanoparticles have been applied as catalysts for the hydrogenation of allyl alcohol in an aqueous solution. A key finding of this article is the superior catalytic activity of the nanorods compared to the cuboctahedral particles. This difference in the catalytic activity was justified because of the variation in the amount of protein to stabilize the nanorods. A model for the nanorods and equations that describe the proportion of atoms in the different sites of the particle (face, vertex, edge, or interior) is used to calculate the percentage of atoms that are located on the nanorod surface. The stability of these particles as catalysts was also studied. The results showed that Pt nanorods and Pt cuboctahedra particles were degraded after 24 h of reaction.

Morphology controlled 1D Pt nanostructures synthesized by galvanic displacement of Cu nanowires in chloroplatinic acid

One-dimensional platinum (Pt) nanostructures with different shape, size, and morphology were synthesized by galvanic displacement of sacrificial Cu nanowires in chloroplatinic acid baths. By increasing the concentration of H2PtCl6, the morphology of Pt nanostructures greatly altered from Pt nanoparticles decorated Cu nanowires, Pt coated Cu core–shell nanowires, dense Pt nanotubes to porous Pt nanotubes. At low concentration of H2PtCl6 (<1 mM), the Pt content monotonically increased with an increase in [H2PtCl6] (upto approx. 80 at.%). The Pt content became independent of [H2PtCl6] at higher concentration. The average external diameter and wall thickness of Pt nanotubes decreased with increasing [H2PtCl6] suggesting that the dissolution of copper is strongly dependent on [Cl−], which led to changes in the morphology of Pt nanostructures.

Microstructure-Electrocatalytic Relationships Towards Proper Design of Free-Standing Nanostructured Platinum Electrodes for Fuel Cells

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Liquid-precursor electron-beam-induced deposition of Pt nanostructures: dose, proximity,resolution

While electron-beam-induced deposition (EBID) from various gaseous precursorshas been known and studied for decades, EBID from bulk liquid precursorsis very much in its infancy and the following is only the second report onthis technique. Here we present liquid-precursor (LP-)EBID of platinum(Pt) nanostructures from a dilute aqueous solution of chloroplatinic acid (H2PtCl6). We investigate how the lateral size of Pt nanoparticles (NPs) varies with charge dose,and how already deposited Pt NPs are affected by the subsequent deposition of theirneighbors (proximity effect). We also demonstrate LP-EBID of dense arrays of small Ptdots (60 nm pitch, 30 nm diameter) and thin Pt lines (60 nm pitch, 25 nm width), whichcompare favorably with the typical resolution of resist-based electron-beam lithography.

Synthesis of platinum nanostructures in zeolite mordenite using a solid-state reduction method

Platinum nanoparticles and nanowires have been synthesized inside zeolite mordenite using a solid-state reduction method. Tetrammine platinum nitrate was introduced into the pores via incipient wetness impregnation and it was reduced using powder sodium borohydride. With this method it was possible to obtain single crystal nanowires along the edges of the zeolite particle. The molar ratio of the reducing agent to platinum atoms was a critical parameter for the formation of either uniform nanoparticles or nanowires. Using a regular aqueous sodium borohydride solution reduction it was not possible to obtain nanowires in this zeolite. To the best of the author's knowledge this is the first time sodium borohydride in its solid form is used as a reducing agent to form nanostructures and this is also the first time a solid-state method is used to form nanostructures in a zeolite.

Nanostructured Heterogeneous Catalysts: Well Defined Platinum Nanoparticles Supported on Alumina. Preparation, Characterization and Application to the Selective Hydrogenation of Buta-1,3-diene

Platinum nanoparticles with specific morphologies were prepared in aqueous solution. Key parameters, such as cationic surfactant (cetyltrimethylammonium bromide CTAB) and platinum precursor (H2 PtCl6 ) ratio, temperature, atmosphere (argon or hydrogen), were required to control the formation of nanostructured platinum particles, with well defined morphologies, and even to control their morphology. Platinum nanoparticles with mainly cubic morphologies, with a mix of morphologies (rods, cubes, tetrahedra) or with mainly polyhedric morphologies, were thus obtained depending on CTAB/Pt ratio, atmosphere and temperature. A mechanism of formation of theses platinum nanoparticles was proposed using a time resolved transmission electron microscopy study. After deposition onto Al2 O3 , the well crystallized nanostructured platinum particles were evaluated in the selective hydrogenation of buta-1,3-diene. Catalysts prepared with platinum nanoparticles exposing mainly the (111) crystallographic plane (polyhedric morphologies) were the most selective for the selective hydrogenation of buta-1,3-diene into butenes with a drastic decreasing of further hydrogenation into n-butane.

Exploring the applications of a pulsating jet hydrodynamic modulated voltammetric (HMV) system – Electrochemistry of nanostructured Pt electrodes and trace analysis

The electrochemistry of nanostructured electrodes is investigated using hydrodynamic modulated voltammetry (HMV). Here a liquid crystal templating process is used to produce a platinum modified electrode with a relatively high surface area (Roughness factor, Rf = 42.4). The electroreduction of molecular oxygen at a nanostructured platinum surface is used to demonstrate the ability of HMV to discriminate between Faradaic and non-Faradaic electrode reactions. The HMV approach shows that the reduction of molecular oxygen shows considerable hysteresis correlating with the formation and stripping of oxide species at the platinum surface. Without the HMV analysis it is difficult to discern the same detail under the conditions employed. In addition the detection limit of the apparatus is explored and shown, under ideal conditions, to be of the order of 45 nmol dm −3 employing [Fe(CN) 6] 4− as a test species.

Some properties of electrochemical nanostructures

The physical and electronic properties of several platinum nanostructures have been investigated by density functional calculations. Particular attention has been paid to the structure of the d-band. Our results predict, that nanowires and small platinum clusters supported on Au(111) should be excellent catalysts for the hydrogen evolution reaction; a monolayer of platinum on Au(111) should also be better than pure platinum.

Responses of fibroblasts and glial cells to nanostructured platinum surfaces

The chronic performance of implantable neural prostheses is affected by the growth ofencapsulation tissue onto the stimulation electrodes. Encapsulation is associated withactivation of connective tissue cells at the electrode’s metallic contacts, usually made ofplatinum. Since surface nanotopography can modulate the cellular responses to materials,the aim of the present work was to evaluate the ‘in vitro’ responses of connective tissuecells to platinum strictly by modulating its surface nanoroughness. Using molecular beamepitaxy combined with sputtering, we produced platinum nanostructured substratesconsisting of irregularly distributed nanopyramids and investigated their effect on theproliferation, cytoskeletal organization and cellular morphology of primary fibroblasts andtransformed glial cells. Cells were cultured on these substrates and their responses tosurface roughness were studied. After one day in culture, the fibroblasts were moreelongated and their cytoskeleton less mature when cultured on rough substrates. This effectincreased as the roughness of the surface increased and was associated with reduced cellproliferation throughout the observation period (4 days). Morphological changesalso occurred in glial cells, but they were triggered by a different roughness scaleand did not affect cellular proliferation. In conclusion, surface nanotopographymodulates the responses of fibroblasts and glial cells to platinum, which may be animportant factor in optimizing the tissue response to implanted neural electrodes.

Facile Synthesis of Three-Dimensional Dendritic Platinum Nanoelectrocatalyst

Design and synthesis of three-dimensional (3D) dendritic platinum nanostructures (DPNs), with its advantages of high surface area, low density, and reduced materials costs represent a highly interesting class of materials. In this paper, a very simple and efficient wet chemical route to straightforward synthesis of well-dispersed 3D DPNs at high yield was proposed, which was carried out by simply mixing K2PtCl4 aqueous solution and poly(vinyl pyrrolidone) (PVP) at a constant 30 °C for 1 h in the presence of ascorbic acid (AA). As-prepared 3D DPNs were highly porous, self-supporting nanostructures that possessed high surface area and supply enough absorption sites for reactant molecules and were shown to be active as nanoelectrocatalyst for the reduction of dioxygen and oxidation of methanol.

Nanocomposite based on depositing platinum nanostructure onto carbon nanotubes through a one-pot, facile synthesis method for amperometric sensing

Platinum nanoparticles (Pt NPs) were deposited onto multi-walled carbon nanotubes (MWNTs) through direct chemical reduction without any other stabilizing agents. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry were employed to characterize the morphology of the as-prepared nanocomposite (noted as Pt NPs–MWNTs) and further identify the Pt NPs on the surface of MWNTs. The nanocomposite demonstrated the ability to electrocatalyze the oxidation of hydrogen peroxide and substantially raises the response current. A sensitivity of 591.33 μA mM −1 cm −2 was obtained at Pt NPs–MWNTs modified electrode. Thus, we immobilized glucose oxidase (GOD) as a model enzyme on the nanocomposite-based electrode with a thin layer of Nafion to fabricate a glucose biosensor, which showed sensitive and fast response to glucose. The influence of the GOD loading was investigated and the biosensor with an enzyme loading concentration of 10 mg/mL shows optimal performance for glucose detection, that is, a detection limit of 3 μM and a response time of 3 s, respectively.

Use of the Carbothermal Route to Prepare Anisotropic Single-Crystal Platinum Nanostructures with Low Resistivity

We have used a carbothermal process in the absence of a catalyst or template to prepare two-dimensional (2D) platinum (Pt) nanoplatelets and one-dimensional (1D) Pt nanobelts on sapphire surfaces. This paper describes the first examples of the growth of Pt nanobelts and mesobelts. It appears that the presence of adequate quantities of diamond and Y2O3 powder at a molar ratio was a critical factor controlling the Pt gas species to form nanobelts at a relative low level of supersaturation. When the growth time was 15 h, we obtained ultralong (0.5 mm) mesobelts and microsheets. Electrical measurements indicated that the single-crystal Pt nanobelt had an extremely low resistivity of 16.8 μΩ cm and a failure current density of greater than 1 × 107 A cm−2. These unique Pt nanobelts are potentially attractive nanoscale building blocks for use as interconnects in nanoelectronic devices.

Evolution of Dendritic Platinum Nanosheets into Ripening-Resistant Holey Sheets

Under electron-beam irradiation, dendritic platinum nanosheets structurally evolve into metastable "holey" nanosheets. Monte Carlo simulations of this structural transformation agree well with electron microscope images detailing the ripening process. The experiments and simulations show that nanoscale holes of a critical size are persistent and give holey sheets their morphological stability and sustained high surface area. Platinum nanostructures composed of these holey nanosheets exhibit improved durability in electrocatalytic reactions due to their remarkable ripening resistance.

Electrochemical preparation and structural characterization of platinum thin film on a polypyrrole film modified ITO electrode

Platinum nanostructures have been fabricated by electrochemical deposition of platinum onto indium tin oxide (ITO) glass substrate modified with thin polypyrrole film. The crystal size and the number density of the platinum nanoparticles have been examined by varying several deposition parameters, including the thickness of the PPy film and the current densities for platinum deposition. Optimal conditions for uniform growth of nanoparticles well-dispersed on the ITO have been determined, along with insight into the mechanism of crystal growth. The PPy film thickness principally affect the size and number density of the nanoparticles, while the platinum deposition current densities could be used to regulate the shape of the nanoparticles. In addition, the flower-like platinum nanoparticles showed high catalytic activity on electrochemical oxidation of methanol, and its activity was measured to be approximately 1.9 times that of bare platinum.

Preparation of nanosized metal (oxides) by gas phase hydrolysis using mesoporous materials as nanoreactors

Immobilized nanosized metal (oxides) on carbonaceous carriers were prepared by hydrolysis under mild conditions by using the carrier pores as a kind of nanoreactor. Metal alkoxide vapor was adsorbed on the carrier and then formed the product upon exposure to water vapor. With this facile method, Titania, Vanadia, Rhodium (oxide), and Platinum (oxide) nanostructures were prepared at high yields, high loadings, and good dispersion in the carrier material. High number concentrations of spheroidal nanoparticles of uniform size (diameter ca. 5 nm) were obtained from less reactive precursors, whereas with highly reactive precursors, such nanoparticles occurred only after subsequent calcination. Nanoparticles appeared to be the thermodynamically stable form of the metal (oxide) produced in the pores. Highly reactive precursors formed metastable seeds, which nucleated and restructured into nanoparticles upon subsequent exposure to heat. The presented method allows for preparation of metal (oxide) nanostructures and effective control of their size and shape.