Platinum Nanostructures Research Articles

Stable platinum nanostructures on nitrogen-doped carbon obtained by high-temperature synthesis for use in PEMFC

We propose a novel, facile synthesis route to produce stable platinum-based polymer electrolyte membrane fuel cell catalysts supported on nitrogen-doped carbon. Platinum nanoparticles were decorated on polyaniline (PANI), a nitrogen-containing polymer, before its subsequent carbonization at 750 °C under nitrogen atmosphere. Thus, nitrogen-doped carbon-supported platinum catalysts were produced with homogeneously distributed small metal particles, which are otherwise difficult to obtain. Most remarkably the platinum nanoparticles did not grow significantly during the carbonization step. In contrast, commercially available standard catalysts on carbon materials subjected to the same heat treatment showed severe particle growth. In accordance with the high thermal stability, the PANI-derived catalyst shows good long-term stability in accelerated stress test and a promising performance as cathode material in 5 × 5 cm2 single cells. The synthesis is carried out without the need for special laboratory equipment, so it will be easy to scale up for industrial catalyst production.

Nanoporous Platinum Electrodes as Substrates for Metal Oxide-Supported Noble Metal Electrocatalytic Nanoparticles: Synergistic Effects During Electrooxidation of Ethanol

Electrocatalytic oxidation of ethanol in acid medium (0.5 mol dm–3 H2SO4) was significantly enhanced by not only supporting bimetallic PtRu nanoparticles on nanostructured metal oxides (TiO2 or WO3), but also by depositing such catalytic systems on planar nanoporous platinized electrode substrates. Incorporation of TiO2 or WO3 into the electrocatalytic interface was likely to improve proton mobility and to provide –OH groups capable of inducing the removal of poisoning species, such as CO, from the Pt sites in the bimetallic PtRu catalyst. Synergistic interactions between ruthenium and titania were also possible. Regularly porous nanostructured platinum substrate also permitted development of submicro ‘reactors’ where reactant molecules, electrolyte ions, and all active components (TiO2 or WO3, Pt substrate, PtRu catalytic sites) could co-exist and become easily accessible. While WO3 was able to undergo fast reversible redox transitions to non-stoichiometric oxides, efficient utilization of inert (non-electroactive) TiO2 required admixing with carbon nanotubes to ensure easy charge distribution and good conductivity at the electrocatalytic interface.

Electrochemical characteristics of nanostructured platinum electrodes – a cyclic voltammetry study

Platinum surfaces play a decisive role in catalysis in sensors, fuel cells, solar cells and other applications like neuronal stimulation and recording. Technical advances in nanotechnology contributed tremendously to the progress in these fields. A fundamental understanding of the chemical and physical interactions between the nanostructured surfaces and electrolytes is essential, but was barely investigated up to now. In this article, we present a wet-chemical process for the deposition of nanostructures on polycrystalline platinum surfaces. The electrochemically active surface area was increased by a factor of over 1000 times with respect to the geometrical surface. The influence of the nanostructures was examined in different acidic, alkaline, and neutral electrolytes. Comparing cyclic voltammograms of nanostructured and planar polycrystalline platinum revealed new insights into the microenvironment at the electrode-electrolyte interface. The characteristic features of the cyclic voltammograms were altered in their shape and strongly shifted with respect to the applied potential. In neutral buffered and unbuffered electrolytes the water window was expanded from 1.4 V to more than 2 V. The shifts were interpreted as local pH-changes and exhausted buffer capacity in direct proximity of the electrode surface due to the strong release and binding of protons, respectively. These polarized electrodes induce significant changes in the electrochemical potential of the electrolyte due to the high roughness of their surface. The electrochemical phenomena and the observed voltage shifts are crucial for the understanding of the basic mechanism at nanostructured electrodes and mandatory for designing fuel cells, sensors and many other devices.

Pure Platinum Nanostructures Grown by Electron Beam Induced Deposition

Platinum has numerous applications in catalysis, nanoelectronics, and sensing devices. Here we report a method for localized, mask-free deposition of high-purity platinum that employs a combination of room-temperature, direct-write electron beam induced deposition (EBID) using the precursor Pt(PF3)4, and low temperature (≤400 °C) postgrowth annealing in H2O. The annealing treatment removes phosphorus contaminants through a thermally activated pathway involving dissociation of H2O and the subsequent formation of volatile phosphorus oxides and hydrides that desorb during annealing. The resulting Pt is indistinguishable from pure Pt films by wavelength dispersive X-ray spectroscopy (WDS).

Short peptide-directed synthesis of one-dimensional platinum nanostructures with controllable morphologies.

Although one dimensional (1D) Pt nanostructures with well-defined sizes and shapes have fascinating physiochemical properties, their preparation remains a great challenge. Here we report an easy and novel synthesis of 1D Pt nanostructures with controllable morphologies, through the combination of designer self-assembling I3K and phage-displayed P7A peptides. The nanofibrils formed via I3K self-assembly acted as template. Pt precursors ((PtCl4)2− and (PtCl6)2−) were immobilized by electrostatic interaction on the positively charged template surface and subsequent reduction led to the formation of 1D Pt nanostructures. P7A was applied to tune the continuity of the Pt nanostructures. Here, the electrostatic repulsion between the deprotonated C-terminal carboxyl groups of P7A molecules was demonstrated to play a key role. We finally showed that continuous and ordered 1D Pt morphology had a significantly improved electrochemical performance for the hydrogen and methanol electro-oxidation in comparison with either 1D discrete Pt nanoparticle assemblies or isolated Pt nanoparticles.

Investigation into the Catalytic Activity of Porous Platinum Nanostructures

The catalytic activity of porous platinum nanostructures, viz. platinum nanonets (PtNNs) and platinum nanoballs (PtNBs), synthesized by radiolysis were studied using two model reactions (i) electron transfer reaction between hexacyanoferrate (III) and sodium thiosulfate and (ii) the reduction of p-nitrophenol by sodium borohydride to p-aminophenol. The kinetic investigations were carried out for the platinum nanostructure-catalyzed reactions at different temperatures. The pseudofirst-order rate constant for the electron transfer reaction between hexacyanoferrate (III) and sodium thiosulfate catalyzed by PtNNs and PtNBs at 293 K are (9.1 ± 0.7) × 10(-3) min(-1) and (16.9 ± 0.6) × 10(-3) min(-1), respectively. For the PtNN- and PtNB-catalyzed reduction of p-nitrophenol to p-aminophenol by sodium borohydride, the pseudofirst-order rate constant was (8.4 ± 0.3) × 10(-2) min(-1) and (12.6 ± 2.5) × 10(-2) min(-1), respectively. The accessible surface area of the PtNNs and PtNBs determined before the reaction are 99 and 110 m(2)/g, respectively. These nanostructures exhibit significantly higher catalytic activity, consistent with the largest accessible surface area reported so far for the solid platinum nanoparticles. The equilibrium of the reactants on the surface of the platinum nanostructures played an important role in the induction time (t0) observed in the reaction. A possible role of structural modifications of PtNBs catalyzed the reaction leading to change in the accessible surface area of PtNBs is being explored to explain the nonlinear behavior in the kinetic curve. The activation energy of the PtNN- and PtNB-catalyzed reduction of p-nitrophenol are 26 and 6.4 kJ/mol, respectively. These observations open up new challenges in the field of material science to design and synthesize platinum nanostructures which could withstand such reaction conditions.

Electrochemical synthesis of a novel platinum nanostructure on a glassy carbon electrode, and its application to the electrooxidation of methanol

We show that the addition of white dextrin during the electrochemical deposition of platinum nanostructures (nano-Pt) on a glassy carbon electrode (GCE) results in an electrochemically active surface that is much larger than that of platinum microparticles prepared by the same procedure but in the absence of dextrin. The nano-Pt deposits are characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy, and electrochemical methods. The SEM images reveal deposits composed of mainly nanoparticles and short nanorods. The GCE was applied as a novel and cost-effective catalyst for methanol oxidation. The use of nano-Pt improves the electrocatalytic activity and the stability of the electrodes.

An optimum morphology of platinum nanoparticles with excellent electrocatalytic activity for a highly efficient dye-sensitized solar cell

Remarkable morphology of platinum (Pt) nanostructures from submicron clusters, by way of nanoclusters, to nanoparticles (NPs) was obtained through controlling the heating rate of thermo-decomposition of Pt precursor molecules. Uniform and dense distribution of Pt-NPs was obtained on FTO glass substrate prepared at the heating rate lower than 1.2°Cmin−1. The highest electrocatalytic performance, which corresponded to the lowest charge transfer resistance of 0.86Ω cm2, was achieved with the counter electrode prepared at the heating rate of 1.2°Cmin−1 during sintering. The heating rate during sintering proved to be a sensitive parameter for determining the morphology of Pt-NPs formed on the surface of FTO glass substrate, which subsequently influenced the catalytic activity of the Pt-NPs and subsequently the photovoltaic performance of a dye-sensitized solar cell (DSC). The highest conversion efficiency of the DSC prepared with the heating rate of 1.2°Cmin−1 was 9.30% with fill factor of 67.21%, Jsc of 18.14mAcm−2, and Voc of 762.5mV.

Platinum nanostructures via self-assembly of an amyloid-like peptide: a novel electrocatalyst for the oxygen reduction

An aniline-GGAAKLVFF peptide (AFP) was prepared by solid-phase synthesis. The peptide can readily self-assemble into fibrils. Platinum nanoparticles (Pt NPs) were directly immobilized on the surface of the AFP fibrils via electrostatic interaction. Compared to other currently available techniques for the fabrication of metal-peptide fibrils, the noncovalent functionalization strategy is able to deposit nanoparticles on peptide fibrils with different morphologies and high metal loading, which is important for applications in catalysis, electronic materials and other corresponding fields. The Pt-AFP fibrils were employed to modify the electrode, which exhibits high electrocatalytic activities towards oxygen reduction. Thus, the Pt-AFP fibrils hold great potential for polymer electrolyte fuel cells and other electrochemical applications.

3-Dimensionally self-assembled single crystalline platinum nanostructures on few-layer graphene as an efficient oxygen reduction electrocatalyst

Here, we report for the first time the synthesis of a 3-D self-assembled single crystalline platinum nanostructure directly on the graphene surface (PtNAGE) without using any harmful structural directing agents. A slow reduction method is used to prepare the desired platinum morphology. Initial formation of platinum nanoparticles and their homogenous dispersion on the surface of graphene have been observed 10 h after the commencement of the reduction using formic acid as the reducing agent. From these initially deposited seed particles, the growth starts on the {111} facets along the direction and the nanostructure formation is completed within 72 h of the commencement of the reaction. The individual assembly has a diameter of ∼80 nm. PtNAGE shows superior electrocatalytic activity towards oxygen reduction compared to graphene supported platinum (PtGE) and commercial carbon supported platinum (PtC) catalysts. PtNAGE is less vulnerable to strong hydroxyl adsorption compared to PtC and PtGE. Specific activity and mass activity of the catalyst are high compared to PtC by a factor of 6.50 and 1.80, respectively, and 4.00 and 3.05, respectively, compared to PtGE. The limiting current density of PtNAGE is 1.28 and 1.20 times higher than PtGE and PtC, respectively. Kinetic analysis of PtNAGE shows that the oxygen reduction reaction follows first order kinetics involving a four electron transfer mechanism with the direct formation of water. In addition to this, it has been observed that PtNAGE also prevents surface area degradation better than the commercial platinised carbon under potential induced conditions.

Electrochemical Characterization of Platinum Nanotubules Made via Template Wetting Nanofabrication

Standard oxidation-reduction reactions such as those of ferrocyanide and ferrocene have long been employed in evaluating and comparing new electrode structures with more traditional configurations. A variety of nanostructured carbon electrodes developed in recent years have been reported to exhibit faster electron transfer kinetics than more traditional carbon structures when studied with these redox reactions. This type of comparison has not been widely explored for nanostructured platinum electrodes that have become increasingly common. In this work, a platinum nanotubule array electrode was fabricated via a simple template-based process and evaluated using the standard ferrocyanide redox reaction. The nanotubule array electrodes were observed to more closely approach ideal reversible behavior than a typical Pt black/Nafion fuel cell electrode or a standard polished Pt disc electrode. The apparent heterogeneous electron transfer coefficient was determined using the Nicholson method and found to be one to two orders of magnitude greater for the nanotubule array electrodes, depending on the diameter of the nanotubules, in comparison with these same two more traditional electrode structures.

Facile Production of Ordered 3D Platinum Nanowire Networks with “Single Diamond” Bicontinuous Cubic Morphology

Direct electrochemical templating is carried out using a thin layer of a self-assembled diamond phase (QIID) of phytantriol to create a platinum film with a novel nanostructure. Small-angle X-ray scattering shows that the nanostructured platinum films are asymmetrically templated and exhibit “single diamond” morphology with Fd3m symmetry.

Platinum nanostructures formed by femtosecond laser irradiation in water

Platinum nanostructures with various morphologies, such as spike-like, ripple-like and array-like structures, have been fabricated by 400 nm and 800 nm femtosecond laser irradiation in water. Different structures can be formed on the surfaces as a function of the laser wavelength, the fluence and scan methods. The reflectance measurements of these structures show much larger absorption on the irradiated surfaces than untreated platinum surfaces.

In Situ Gel‐to‐Crystal Transition and Synthesis of Metal Nanoparticles Obtained by Fluorination of a Cyclic β‐Aminoalcohol Gelator

A new fluorinated version of a cyclic β-aminoalcohol gelator derived from 1,2,3,4-tetrahydroisoquinoline is presented. The gelator is able to gel various nonprotic solvents through OH⋅⋅⋅N hydrogen bonds and additional CH⋅⋅⋅F interactions due to the introduction of fluorine. A bimolecular lamellar structure is formed in the gel phase, which partly preserves the pattern of molecular organization in the single crystal. The racemate of the chiral gelator shows lower gelation ability than its enantiomer because of a higher tendency to form microcrystals, as shown by X-ray diffraction analysis. The influence of fluorination on the self-assembly of the gelator and the properties of the gel was investigated in comparison to the original fluorine-free gel system. The introduction of fluorine brings two new features. The first is good recognition of o-xylene by the gelator, which induces an in situ transition from gels of o-xylene and of an o-xylene/toluene mixture to identical single crystals with unique tubular architecture. The second is the enhanced stability of the toluene gel towards ions, including quaternary ammonium salts, which enables the preparation of a stable toluene gel in the presence of chloroaurate or chloroplatinate. The gel system can be used as a template for the synthesis of spherical gold nanoparticles with a diameter of 5 to 9 nm and wormlike platinum nanostructures with a diameter of 2 to 3 nm and a length of 5 to 12 nm. This is the first example of a synthesis of platinum nanoparticles in an organogel medium. Therefore, the appropriate introduction of a fluorine atom and corresponding nonbonding interactions into a known gelator to tune the properties and functions of a gel is a simple and effective tactic for design of a gel system with specific targets.

Platinum nanoparticles deposited on substrates by solventless chemical reduction of a platinum precursor with ethylene glycol vapor and its application as highly effective electrocatalyst in dye-sensitized solar cells

To deposit nanostructured platinum (Pt) on substrates has fundamental and practical significance as Pt is a noble metal and an effective electrocatalyst. In this paper, we report a facile and scalable method to deposit Pt nanoparticles on substrates through the solventless chemical reduction of H2PtCl6 with vapor of ethylene glycol (EG) below 200°C. The Pt nanoparticles have a size below 6nm, and they homogeneously distribute on the substrates. They have good adhesion to the substrates. They are highly catalytic for the reduction of triiodide that is the chemical reduction at the counter electrode of dye-sensitized solar cells (DSCs). Though DSCs with Pt deposited by the EG vapor reduction and pyrolysis exhibit comparable high photovoltaic efficiency of more than 8% at high Pt loading, the photovoltaic efficiency of DSCs with Pt by the EG vapor reduction is much higher than that by pyrolysis when the Pt loading is quite low. DSCs with a Pt loading of 0.19μgcm−2 deposited by this method can have a power conversion efficiency of 6.61%, which is even higher than that (6.19%) of DSCs with a Pt loading of 0.78μgcm−2 deposited by pyrolysis. Thus, this method can significantly reduce the Pt loading to ¼ or even lower in comparison with Pt by pyrolysis which has been regarded as the method to deposit Pt with the highest electrocatalytic activity as the counter electrode of DSCs. The excellent electrocatalytic activity of Pt is attributed to the small Pt particle size.

Metal-enhanced intrinsic fluorescence of nucleic acids using platinum nanostructured substrates

We investigated the feasibility of using platinum nanostructures to accomplish the metal-enhanced fluorescence (MEF) in the UV spectral region. We examine the possibility for detection of the intrinsic fluorescence from nucleotides and G-quadruplex DNA on platinum nanoparticles. Guanosine monophosphate (GMP) showed significant increases (∼20-fold) in fluorescence intensities in the presence of platinum nanostructures when compared to quartz controls. G-quadruplex DNA demonstrated ∼5-fold increase in fluorescence intensity and higher photostability in the presence of Pt nanostructures. We performed Finite Element Method simulations to explore how Pt nanoparticles interact with plane waves and conformed that the Pt nanostructures are promising for enhancing the fluorescence emission in the UV region.

Atomic layer deposition of platinum thin films on anodic aluminium oxide templates as surface-enhanced Raman scattering substrates

Platinum thin films are deposited on anodic aluminium oxide (AAO) templates by atomic layer deposition (ALD). The highly ordered island-like platinum nanostructures formed on the AAO template produce a high Raman scattering signal because of the periodical hexagonal arrangement. As an illustration, dramatic enhancement is achieved using Rhodamine 6G (R6G) as a molecular probe.Field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) show that the gap between the island-like structures is below 10 nm. Owing to activation by the incident laser beam, the localized electromagnetic field on the platinum island surface can be dramatically enhanced by the sub-10 nm regime subsequently amplifying the Raman signal. Finite-difference time-domain (FDTD) calculation matches the experimental phenomena suggesting that the excellent surface-enhanced Raman scattering (SERS) characteristics of the platinum structure arise from the high density and abundance of hot spots. Because the platinum film is inert in air, the SERS enhancing substrate can be used reliably in many trace chemical and biological detection applications.

Selective Etching Induces Selective Growth and Controlled Formation of Various Platinum Nanostructures by Modifying Seed Surface Free Energy

We present a strategy to achieve heterogeneous seeded growth on nanoparticle (NP) surfaces and construct various Pt nanostructures (cage- and ring-like) by using selective etching as surface-free-energy-distribution modifier. Preprepared Au polyhedron NPs (octahedron, decahedron, nanorod, and nanoplate) are mixed with KI, H(2)PtCl(6), and surfactant. Under heating, KI is first oxidized to I(2), which then selectively etches the edges of Au polyhedrons. Consequently, the partial removal of surface Au atoms creates highly active sites (exposed high-index facets, atom steps, and kinks) on the etched edges. Then the reduced Pt(0) atoms deposit on the etched edges preferentially and grow further, generating bimetallic nanostructures, Au octahedrons, or decahedrons with edges coated by Pt. The Pt layer protects the Au on the etched edges against further etching, changing the etching route and causing the Au on {111} facets without a Pt layer to be etched. After the Au is removed completely from the bimetallic nanostructures, ring-like, frame-like, and octahedral cage-like Pt nanostructures form. The evolution from Au polyhedrons to Pt ring or octahedron cage is investigated systematically by high-resolution transmission electron microscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray, scanning transmission electron microscopy, and high-angle annular dark field.

Facile electrochemical approach for the effective detection of guanine

An electrochemical sensor for the sensitive determination of guanine has been developed, which is based on the electrodeposition of a nanostructured platinum thin film on a glassy carbon electrode. The effects of the electrodeposition time of the platinum thin film, pH, square-wave frequency and electroactive interferents on the voltammetric response of the sensor were evaluated. The optimized sensor exhibited excellent performance for the detection of guanine with a high sensitivity (157.8nAμM−1), a low detection limit (3.1×10−8M), a wide linear range (0.1–500μM), as well as good reproducibility, stability, and selectivity.

Investigation of nanostructured platinum–nickel supported on the titanium surface as electrocatalysts for alkaline fuel cells

This study involves the formation of nanostructured platinum–nickel supported on the titanium surface catalysts using the galvanic displacement technique and investigation of their electrocatalytic activity toward the oxidation of borohydride, methanol and ethanol in an alkaline media by cyclic voltammetry and chronoamperometry. Scanning electron microscopy, Energy Dispersive X-ray Spectroscopy and X-ray diffraction were used to characterize the surface structure, composition and morphology. The nanoPt(Ni)/Ti and nanoPt/Ti catalysts exhibited a higher catalytic efficiency to the oxidation of borohydride, ethanol and methanol as compared with that of pure Pt.