Structure Of Pt Nanoparticles Research Articles

Au@PtAg core/shell nanorods: tailoring enzyme-like activities via alloying

Pt nanoparticles (NPs) have been reported to demonstrate four kinds of enzyme-like activity including superoxide dismutase (SOD), catalase, oxidase and peroxidase. Some of these activities interfere with each other. For instance, as antioxidant enzyme mimics, their SOD and catalase activities are very helpful in scavenging related reactive oxygen species (ROSs). However, their oxidase-like and/or peroxidase-like activities may simultaneously oxidize some natural antioxidants, thus compromising the final anti-oxidation efficacy. Fine tuning different enzyme-like activities is therefore very important to realize the optimization of their functions. In this paper, our effort is focused in this direction by tailoring the electronic structure of Pt NPs via alloying with Ag. All four enzyme-like activities are found to be weakened by an increased Ag percentage in the alloy, as witnessed by decreased values of Kcat. The variation in the electronic structure also changes the substrate affinity. Introducing silver into Pt weakens the affinity for H2O2, which affects the limit of detection (LOD) for H2O2 and products with H2O2 involved. In contrast to Fe3O4 MNPs, for peroxidase-like activity, hydroxyl radicals are not involved in the oxidation of chromogenic substrates for the alloy nanostructures.

In situ TEM study of platinum electrode catalysts with 80kV-1MV accelerating voltage

We perform transmission electron microscopy (TEM) at different accelerating voltages for analysis of complex nano-structures of platinum (Pt) nanoparticle catalysts synthesized on titanium dioxide. TEM images obtained at 80, 200, 300, and 1000kV are carefully compared. The particle size, density and volume of the Pt nanoparticles deposited under different conditions are evaluated using electron tomography. The atomic structures of Pt nanoparticles on the TiO2 and amorphous carbon a surfaces are also investigated using spherical aberration corrected TEM in order to study the diffusion of these Pt nanoparticles and atoms.

Structure and morphology of platinum nanoparticles with critical new issues of low- and high-index facets

In this paper, Pt nanoparticles were successfully prepared by modified polyol method using silver nitrate as an effective structure-modifying agent. The characterization of Pt nanoparticles was investigated by using UV-Vis-NIR spectroscopy, transmission electron microscopy (TEM) and high resolution (HR) TEM, and x-ray diffraction (XRD). The method of selected area electron diffraction (SEAD) was used to study the structure of Pt nanoparticles. The results showed that the as-prepared Pt nanoparticles exhibiting the complexity of surface structure and morphology could be used as efficient catalysts for polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs).

Novel issues of morphology, size, and structure of Pt nanoparticles in chemical engineering: surface attachment, aggregation or agglomeration, assembly, and structural changes

In this paper, the polyhedral Pt nanoparticles were prepared by a modified polyol method using AgNO3 as a nanostructure-shaping agent. TEM and HRTEM images of Pt nanoparticles show the particle size in the 10 nm range for the well-controlled case. In contrast, Pt nanoparticles have the particle size in the 50 nm range for the uncontrolled case. To understand the important issues of morphology, size, surface and structure, the as-prepared Pt nanoparticles were investigated through UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution (HR)TEM measurements. In the two cases, the as-prepared Pt nanoparticles with and without the control procedures exhibit surface attachment, aggregation or agglomeration and assembly. The mechanisms can lead to the formation of the ultra-porous mesostructure of the as-prepared Pt nanoparticles by using various sophisticated control methods. Therefore, the experimental findings and observations showed the formations of the porous Pt nanostructures as the new Pt textures from self-aggregation or self-agglomeration and self-assembly of extreme importance in designing great superlattices under experimentally chemical and physical methods. This also proved the important role of PVP polymer in the protection of the as-prepared nanoparticles. In particular, a new phenomenon was found in the randomly natural collapse and self-breaking in the Pt nanostructures originating from the naked Pt nanoparticles without protective polymer agents. As a result, a porous meso-nanostructure was formed by the structural changes of Pt nanoparticles without stabilization of the PVP polymer. Finally, the discoveries of surface structure changes of polyhedral Pt shapes and morphologies in future are very important in further catalysis investigation.

Surface-Enhanced Raman Scattering of 4-Aminobenzenethiol in Nanogaps between a Planar Ag Substrate and Pt Nanoparticles

To determine how effectively transition metal nanoparticles can couple with a noble metal substrate to induce higher electromagnetic fields, we examined the surface-enhanced Raman scattering (SERS) characteristics of 4-aminobenzenethiol (4-ABT) positioned in the gaps formed by a flat Ag substrate and 20–150 nm Pt nanoparticles. Initially, no Raman peaks of 4-ABT could be identified when 4-ABT was self-assembled on a polished flat Ag substrate; however, Raman peaks could be seen by attaching Pt nanoparticles onto the pendent amine groups. Conversely, a higher Raman signal was observed when larger Pt nanoparticles were attached onto 4-ABT, regardless of the excitation wavelength. Moreover, a higher Raman signal was measured in response to excitation at 488 nm, followed by excitation at 514.5, 568, and 632.8 nm. Very similar size and excitation wavelength dependences were found from the 3-dimensional finite-difference time-domain simulation. Accordingly, the highest enhancement was achieved using ∼150 nm Pt particles at 488 nm excitation with an enhancement factor (EF) of 3.5 × 104 per Pt particle. However, the electromagnetic field enhancement observed was not in conformity with the UV/vis absorbance of ∼150 nm Pt nanoparticles, which suggested that higher EFs would be measured in the order of excitations at 632.8 > 568 > 514.5 > 488 nm. This discrepancy was attributed to the structure of Pt nanoparticles in that the 150 nm Pt particles were actually composed of 7 nm seed particles; thus, the electromagnetic interactions of individual Pt seed particles with the underlying Ag substrate occurred collectively, being more effective at shorter excitation wavelengths.

Decoration of single-walled carbon nanotubes with Pt nanoparticles from an organometallic precursor

Carbon nanotubes (CNTs) are nanomaterials of high interest due to their unique structural, electrical, and mechanical properties. Carbon materials have been widely employed to support metallic nanoparticles for catalysis and electrochemical applications. In this work, we investigated the synthesis of platinum nanoparticles generated from the complex Pt2(dba)3 (tris(dibenzylideneacetone) diplatinum) and stabilized with a long alkyl chain amine, hexadecylamine (HDA) and supported on functionalized single-walled carbon nanotubes (SWCNTs). High resolution transmission electron microscopy (HRTEM) studies revealed isolated Pt nanoparticles (2–3 nm) on SWCNTs. Powder X-ray diffraction (XRD) was used to assess the structure of Pt nanoparticles dispersed on SWCNTs assigned to Pt face-centered cubic (fcc). Additionally, infrared Fourier transform spectroscopy confirmed the presence of the stabilizer at the surface of the Pt nanoparticles even after the purification step and functional groups at the surface of pre-treated SWCNTs. This synthetic method may be an alternative route to prepare small size Pt nanoparticles supported on functionalized SWCNTs.

Size Influence on the Oxygen Reduction Reaction Activity and Instability of Supported Pt Nanoparticles

Size-dependent oxygen reduction reaction activity (ORR) and instability of Pt nanoparticles is of great importance in proton exchange membrane fuel cell applications. In this study, the size-dependence of ORR activity on Pt nanoparticles (NPs) was investigated on high-surface-area carbon supported Pt NPs below 5 nm in acidic electrolytes using rotating disk electrode method. The ORR activity was correlated to the estimated surface coverage by OH anion from cyclic voltammogram measurements and the surface composition and electronic structure of Pt NPs, which was studied using X-ray photoemission spectroscopy, and ultraviolet photoemission spectroscopy. The results revealed a size-independent ORR activity on Pt NPs below 5 nm, which was attributed to similar surface compositions and surface electronic structures of Pt NPs below 5 nm as well as comparable OH anion coverage at the potential where ORR was evaluated. In contrast, the instability of Pt NPs under accelerated potential cycling was found to be strongly dependent on the particle size.

Analysis of 3D structures of platinum nanoparticles by high energy X-ray diffraction and reverse Monte Carlo simulations

In this paper, the atomic-scale three-dimensional structure of Pt nanoparticles were determined using high energy X-ray diffraction techniques and reverse Monte Carlo simulations. It was found that dendrimer encapsulated Pt nanoparticles are more ordered than those stabilized by long-chain alkanes. Furthermore, Pt nanoparticles measured in ambient dry conditions exhibit higher local atomic order compared to Pt nanoparticles measured in aqueous solutions. The atomic-scale structural information presented here can offer a more comprehensive understanding of the structure–property relationship for Pt nanoparticles and can be further used in the design of nanoparticles with improved properties.

Roles of Surface Steps on Pt Nanoparticles in Electro-oxidation of Carbon Monoxide and Methanol

Design of highly active nanoscale catalysts for electro-oxidation of small organic molecules is of great importance to the development of efficient fuel cells. Increasing steps on single-crystal Pt surfaces is shown to enhance the activity of CO and methanol electro-oxidation up to several orders of magnitude. However, little is known about the surface atomic structure of nanoparticles with sizes of practical relevance, which limits the application of fundamental understanding in the reaction mechanisms established on single-crystal surfaces to the development of active, nanoscale catalysts. In this study, we reveal the surface atomic structure of Pt nanoparticles supported on multiwall carbon nanotubes, from which the amount of high-index surface facets on Pt nanoparticles is quantified. Correlating the surface steps on Pt nanoparticles with the electrochemical activity and stability clearly shows the significant role of surface steps in enhancing intrinsic activity for CO and methanol electro-oxidation. Here, we show that increasing surface steps on Pt nanoparticles of approximately 2 nm can lead to enhanced intrinsic activity up to approximately 200% (current normalized to Pt surface area) for electro-oxidation of methanol.

Application of high-energy X-rays and Pair-Distribution-Function analysis to nano-scale structural studies in catalysis

We investigate the structure of supported Pt catalysts using high-energy X-ray scattering coupled with Pair-Distribution-Function (PDF) analysis. Recently, experimental approaches that enable the collection of PDF data in situ have been developed with time-resolution sufficient to study the structure of Pt nano-particles as they form. The differential PDF approach is utilized which allows the atom–atom correlations involving only Pt to be selectively recovered, enabling structural investigation of the supported particles and the mechanism of their formation. In parallel to the in situ analysis, we have examined samples prepared ex situ. Data collected on the ex situ samples show that the initial deposition of Pt 4+ occurs as the PtCl 6 2− species which are retained even when annealed in an oxygen atmosphere. The Pt differential PDFs of the samples reduced in hydrogen at 200 and 500 °C indicated nano-crystalline face-centered-cubic (fcc) metallic Pt particles. The ex situ reduced samples also contain a weak correlations at 2.1 Å, which we assign to Pt–O interactions between the particles and the support surface. The in situ experiments, following the reduction of Pt 4+ from 0 to 227 °C, indicate that the initial Pt nano-particles formed are ca. 1 nm in size, and become larger and more crystalline by 200 °C. The data suggest a particle growth mechanism where the initial particles that form are small (<1 nm), then agglomerate into ensembles of many small particles and lastly anneal to form larger well-ordered particles. Lastly, we discus potential future developments in operando PDF studies, and identify opportunities for synchronous application of complementary methods.

Structure and electrocatalytic performance of carbon-supported platinum nanoparticles

The structure of Pt nanoparticles and the composition of the catalyst-Nafion films strongly determine the performance of proton exchange membrane fuel cells. The effect of Nafion content in the catalyst ink, prepared with a commercially available carbon-supported Pt, in the kinetics of the hydrogen oxidation reaction (HOR), has been studied by the thin layer rotating disk electrode technique. The kinetic parameters have been related to the catalyst nanoparticles structure, characterized by X-ray diffraction and high-resolution transmission electron microscopy. The size-shape analysis is consistent with the presence of 3D cubo-octahedral Pt nanoparticles with average size of 2.5 nm. The electrochemically active surface area, determined by CO stripping, appears to depend on the composition of the deposited Pt/C-Nafion film, with a maximum value of 73 m 2 g Pt −1 for 30 wt.% Nafion. The results of CO stripping indicate that the external Pt faces are mainly (1 0 0) and (1 1 1) terraces, thus confirming the cubo-octahedral structure of nanoparticles. Cyclic voltammetry combined with the RDE technique has been applied to study the kinetic parameters of HOR besides the ionomer resistance effect on the anode kinetic current at different ionomer contents. The kinetic parameters show that H 2 oxidation behaves reversibly with an estimated exchange current density of 0.27 mA cm −2.

Preparation Ru, Bi monolayer modified Pt nanoparticles as the anode catalyst for methanol oxidation

Platinum nanoparticles were successfully electrodeposited on indium tin oxide (ITO) surface in the solution with hexachloroplatinic acid and copper ion by cyclic voltammogram method. The micrographs and structure of Pt nanoparticles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The electrocatalytic properties of Pt nanoparticles/ITO or modified by Ru, Bi underpotential deposition (UPD) for methanol oxidation have been investigated by cyclic voltammetry (CV) and chronoamperometry (CA). High electroactivity and good long-term stability can be observed. These results indicate that Pt nanoparticles modified by UPD may have potential applications in designing noble metal catalysts of fuel cells with low loading and high activity at the atomic level.

Preparation of carbon nanotubes supported platinum nanoparticles by an organic colloidal process for nonenzymatic glucose sensing

Multi-walled carbon nanotubes (MWNTs) supported platinum nanoparticles with narrow size distribution were prepared by an organic colloidal process with sodium citrate as the coordination reagent and stabilizer, and ethylene glycol as the reduction reagent. A nonenzymatic glucose sensor with high sensitivity based on the Pt/MWNTs electrode was demonstrated. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to investigate the size distributions and the crystal structure of Pt nanoparticles on the MWNTs. The TEM images show that the Pt nanoparticles with about 2–4 nm in diameter are well dispersed on the MWNTs. The Pt/MWNTs shows high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution. At +0.5 V, the Pt/MWNTs nanocomposite electrode exhibits linearity in the range of 1 mM to 23 mM (R > 0.998) glucose with a response time of 11.6 s. The detection limit is 50 μM (S/N = 3). It was demonstrated that the Pt/MWNTs electrode with high electrocatalytic activity to glucose oxidation could find application in nonenzymatic detection of glucose.

Hydrogenation of α, β unsaturated aldehydes over polycrystalline, (111) and (100) preferentially oriented Pt nanoparticles supported on carbon

The influence of the shape/surface structure of Pt nanoparticles on the selective hydrogenation of crotonaldehyde and cinnamaldehyde has been studied. (111) and (100) preferentially oriented Pt nanoparticles (10 nm) as well as polyoriented Pt nanoparticles (3 nm) were synthesized, characterized (by TEM, cyclic voltammetry and adsorption microcalorimetry) and their catalytic properties evaluated. TEM analysis provided information about the size and shape of the Pt nanoparticles, whereas cyclic voltammetry allowed gaining qualitative and quantitative information about their surface structure. Thus, small Pt nanoparticles ( ≈ 3 nm ) were revealed to have a polyoriented surface, containing high ratio of corner and edges atoms to terrace atoms, whereas large Pt nanoparticles ( ≈ 10 nm ) were shown to have larger Pt domains with (100) and (111) surface structures. Microcalorimetric results for CO adsorption showed higher values of initial heat for polyoriented Pt/C compared to preferentially oriented samples, thus accounting for a higher amount of highly unsaturated surface platinum atoms for Pt/C, in agreement with cyclic voltammetry. The catalytic performances of the samples showed a strong structure-sensitive character for both reactions, with TOF values following the trend Pt(100)/C > Pt(111)/C > Pt/C. Moreover, Pt(111)/C showed higher selectivities to unsaturated alcohol than Pt(100)/C and Pt/C samples.

Structural characterization of Pt nanoclusters deposited on graphite: Effects of substrate and surrounding medium

The structure of Pt6, Pt13, Pt20, Pt40, Pt60, Pt100, and Pt150 nanoparticles deposited on graphite surfaces, and the changes on such structures induced by the interactions with OH-terminated polyamidoamine dendrimers of the lowest generations G0OH and G1OH are examined using classical molecular dynamics simulations. It is shown that the particle/substrate interaction depends strongly on the particle size, with variations following an oscillatory pattern according to the degree of completeness of the particle's outer atomic shell. The results for the bare clusters suggest the existence of ordered structures with mixed fcc and hcp structures. Less ordered structures show a tendency of the nanoparticle to adopt a spherical shell. Details of the morphology and interactions of Pt6, Pt13, and Pt20 with the substrate in the presence of the dendrimers are compared with those for the bare nanoparticles deposited on graphite. Simulation results reveal a strong attachment of the dendrimer branches to the metal particle. The binding, which is driven by the oxygen and nitrogen amide atoms, the tertiary amines, and the dendrimer terminal groups, has significant effects on the structure of Pt nanoparticles on graphite surfaces, manifested by atomic rearrangements in the metal clusters causing modifications to their initial structure and the appearance of new layers.

Small-angle X-ray scattering of carbon-supported Pt nanoparticles for fuel cell

Small-angle X-ray scattering is applied to investigate the structure of Pt nanoparticles for fuel cells with high Pt mass loading at various hot pressures. The two-dimension-like and monolayer aggregates with fractal structure formed from primary (or elementary) Pt particles are found. The SAXS analysis of size, shape, specific surface and structure of both the aggregates and the primary Pt particles is reported here, using model-independent and model-fitting methods. The analysis yields self-consistent results. This quantitative characterization is used to evaluate the role of Pt catalysts regarding different process parameters, and provides useful information for improving fuel cell performance.