AgPt Nanoparticles Research Articles

Single Phase PtAg Bimetallic Alloy Nanoparticles Highly Dispersed on Reduced Graphene Oxide for Electrocatalytic Application of Methanol Oxidation Reaction

As renewable materials having high specific energy and environmentally safe characteristics, direct methanol fuel cells (DMFCs) have attracted huge interest to develop promising power devices with different strategies. Herein, single phase PtAg bimetallic alloy highly dispersed electrocatalyst on reduced graphene oxide (rGO) by a facile wet chemical co-reduction method. Different kinds of catalysts have been prepared with varying atomic ratios of Pt and Ag. Structural and morphological characterizations of as-synthesized catalysts are performed by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) and X-ray photoelectron diffraction (XPS) analysis. It is found that single phase PtAg bimetallic nanoparticles are successfully synthesized that are uniformly dispersed and attached on rGO sheets. High-angle annular dark-field scaning TEM (HAADF-STEM) and energy dispersive X-ray spectroscopic (EDX) analysis have also been performed, which confirm the single phase synthesis of uniformly dispersed PtAg bimetallic catalyst. MOR activity and durability has significantly increased by mutual coordination of both the metals in bimetallic nanocatalyst in comparison with the monometallic commercial Pt/C catalyst. The results can be attributed to the collective effects of the PtAg nanoparticles and the enhanced electron transfer characteristics of rGO sheets.

Effect of ionic liquid on the synthesis and electrocatalytic property of platinum-based bimetallic nanoparticles

Because of their many distinct advantages, the application of ionic liquids (ILs) for the synthesis and tailoring of nanoscale metal catalysts represents a burgeoning direction in materials chemistry. We herein depict the using of ammonium dibutyl phosphate ([AD]PO4), an organic soluble ionic liquid as an additive for the synthesis of Pt-based nanoparticles at elevated temperature in oleylamine. The experimental results reveal that not only the size/morphology, but also the electrocatalytic property of the platinum (Pt)-based bimetallic nanoparticles could be significantly tuned by a small amount of ionic liquid added in the reaction systems. For the silver (Ag)-Pt bimetallic system, core-shell Ag-Pt nanoparticles with dense or dendritic Pt shells are obtained at IL/oleylamine volume ratio of 0.25/10 and 0.5/10, while for gold (Au)-Pt bimetalic system, although the tuning of IL on the size/morphology of the particles are not apparent, the core-shell Au-Pt nanoparticles synthesized at IL/oleylamine volume ratio of 0.5/20 exhibit superior catalytic activity and durability for methanol oxidation reaction (MOR), compared to those prepared at other volume ratios. (C) 2015 Elsevier B.V. All rights reserved.

Rapid, Simple and Selective Determination of 2,4,6-dinitrophenol Based on PtAg /Mesoporous SiO<sub>2</sub> Nanocomposite Sensor with Electrochemical Detection

5-10nmPt-Ag nanoparticles were synthesized by Water thermal reduction, pluronic F127 and tetraethyl Orthosilicate (TEOS) have been used to synthesized mesoporous SiO2template. Pt-Ag nanoparticles have been absorbed onto the surface of mesoporous SiO2. Finally, PtAg/mesoporous SiO2nanocomposites have been modified on the surface of glass carbon electrode to prepared electrochemcial sensor which used to detect 2,4,6-dinitrophenol. In order to optimize experimental conditions, the synergistic reaction, buffer solution has been studied. The result show, when the potential at-0.404V, 2,4,6-dinitrophenol could be determined with a detection limit of 0.163μmol/L and linearity between 0.49-1667μmol/L . This sensor has high sensitivity, good reproducibility and stability.

Atomic Structure of Bimetallic Nanoparticles in PtAg/C Catalysts: Determination of Components Distribution in the Range from Disordered Alloys to “Core–Shell” Structures

Nanocatalysts PtAg/C with different distributions of components in bimetallic PtAg nanoparticles were synthesized by the methods of simultaneous and sequential reduction of Ag+ and Pt(IV) in carbon suspension, prepared on the basis of ethylene glycol–water solvent. The characterization of atomic structure of as prepared PtAg nanoparticles and PtAg nanoparticles obtained after acid treatment at 90 °C was performed by Pt L3-edge extended X-ray absorption fine structure (EXAFS) using the technique for determining local structure parameters of the absorbing Pt atoms, which have the nearest surrounding consisting of Pt and Ag atoms. This technique enabled stable and unambiguous values of parameters for the local structure of Pt atoms in PtAg nanoparticles to be obtained under severe correlations between some of these parameters. The effects of averaging over the sizes and compositions of PtAg nanoparticles on the obtained values of structural parameters were studied by the method of cluster simulations. Analys...

Enhancing the electrocatalytic property of hollow structured platinum nanoparticles for methanol oxidation through a hybrid construction.

The integration of different components into a hybrid nanosystem for the utilization of the synergistic effects is an effective way to design the electrocatalysts. Herein, we demonstrate a hybrid strategy to enhance the electrocatalytic property of hollow structured Pt nanoparticles for methanol oxidation reaction. This strategy begins with the preparation of bimetallic Ag-Pt nanoparticles with a core-shell construction. Element sulfur is then added to transform the core-shell Ag-Pt nanostructures into hybrid nanodimers consisting of Ag2S nanocrystals and remaining Pt domains with intact hollow interiors (Ag2S-hPt). Finally, Au is deposited at the surface of the Ag2S domain in each hetero-dimer, resulting in the formation of ternary Ag2S-Au-hPt nanocomposites with solid-state interfaces. The ternary nanocomposites exhibit enhanced electrocatalytic property toward methanol oxidation due to the strong electronic coupling between Pt and other domains in the hybrid particles. The concept might be used toward the design and synthesis of other hetero-nanostructures with technological importance.

Determination of the local atomic structure of material from X-ray absorption spectroscopy data without fourier analysis of experimental spectra

A technique for analyzing the extended X-ray absorption fine structure spectra of an atom in different structural states in a material under study is proposed. This technique makes it possible to determine the parameters of the nearest environment of absorbing atoms without applying Fourier filtering and related techniques. The proposed approach is tested by an example of the L3 absorption spectra of platinum, obtained by direct calculation for models of one-component platinum nanoparticles and bimetallic Pt-Ag nanoparticles with different core and shell structures. The error in determining the structural parameters is analyzed, and the range of applicability of the technique proposed is discussed.

PtM/C (M = Ni, Cu, or Ag) electrocatalysts: effects of alloying components on morphology and electrochemically active surface areas

The microstructures of Pt/C and PtM/C (M = Ni, Cu, or Ag) electrocatalysts were studied using X-ray diffraction and transmission electron microscopy (TEM). The electrochemically active surface areas of the prepared materials were estimated by cyclic voltammetry in 1 M H2SO4. The materials, with metal contents ranging from 30 to 35 wt.%, were synthesized by chemically reducing the metal precursors in water–ethylene glycol solutions. The actual composition of the bimetallic nanoparticles corresponds to a theoretical (1:1) composition for the PtAg/C catalysts, whereas in the PtNi/C and PtCu/C materials, a portion of the alloying component exists in an oxide form. Decreasing the average metallic crystallite sizes from 3.5 to 1.6 nm does not increase the electrochemically active surface area. This apparent contradiction is because a majority of the PtNi and PtCu nanoparticles consist of 2–4 disordered crystallites. In addition, a portion of the PtNi or PtCu nanoparticle surface is covered by nickel or copper oxides, respectively. PtAg nanoparticles, which have a smaller size relative to other bimetallic particles according to the TEM data, are characterized by an intense platinum surface segregation. The agglomeration processes are lowest for the PtAg nanoparticles.

Staircase and pulse potential electrochemical techniques for the facile and rapid synthesis of Pt and PtAg materials

Electrochemical synthesis is an attractive option for the synthesis of materials because electrocrystallization is faster (microseconds), easier (fewer variables influence structure) and more cost-effective (only requiring an ion source and electrolyte) than traditional chemical methods. Pt and PtAg materials were synthesised using electrochemical techniques, including staircase cyclic voltammetry (CV). Differential pulse amperometry (DPA), square wave voltammetry (SWV) and second harmonic AC voltammetry (2nd H AC V) were employed as pulse potential techniques. Characterisation was conducted using X-ray diffraction, field emission scanning electron microscopy, X-ray fluorescence, cyclic voltammetry in acidic and basic media and by assessing the behaviour of the synthesised materials in oxygen reduction reaction (ORR). For the cyclic voltammetry and DPA techniques, a decrease in the interfacial electrode/solution concentration resulted in the formation of semi-spherical nanoparticles with dendritic nanosheet growth. Semi-spherical Pt nanoparticles with small crystal sizes were obtained using SWV and 2nd H AC V due to the enhancement of the Pt seed growth by the low-time pulse potential period. Silver incorporation allowed the formation of well-defined cubic-shaped and flower-like PtAg nanoparticles without the need for surfactants and/or reductants. Silver acted both as a silver ion source and an additive, due to its passivation of the particle surfaces.

Nano Brazing of Pt-Ag Nanoparticles under Femtosecond Laser Irradiation

Abstract Nano brazing of Pt-Ag nanoparticles with nano Ag filler metal is reported in this letter, which presents an effective way to join nanoobjects by femtosecond laser irradiation. The nano brazed interface between Pt-Ag and Ag showed good lattice matching along (111)Ag//(111)Ag-Pt. Lattice mismatch can hardly be observed at the interface between the filler metal and Pt-Ag nanoparticle, which is important for the joint strength and normally does not occur during joining. The very low mismatch also suggested that melting and solidification occurred during nano brazing by femtosecond laser. The role of Brownian motion on the nano joining process is also discussed in this paper.

Titania-supported silver-based bimetallic nanoparticles as photocatalysts

Photocatalytic process has shown recently a great potential as an environmental friendly and clean remediation technology for organic pollutants in wastewater. This work described the synthesis of silver-based bimetallic nanoparticles using colloid chemistry and the subsequent immobilization onto titania to form composite photocatalytic materials (titania-supported Ag-Pt nanoparticles). The photocatalysts were characterized by X-ray diffraction, electron microscopy, and nitrogen physisorption. The catalytic activity of the photocatalysts was evaluated by photocatalytic degradation of phenol and 2-chlorophenol (2-CP) in synthetic wastewater solutions. The photocatalytic processes were conducted in a batch photoreactor containing appropriate solutions of phenol and 2-CP with UV irradiation of 450 W. UV-visible spectrophotometer was used for analyzing the concentration of phenol and 2-CP in solutions. Parameters affecting the photocatalytic process such as the solution pH, phenol and 2-CP concentrations, and catalyst concentration were investigated. The results obtained revealed that TiO(2)-supported Ag/Pt nanoparticles showed a higher activity for UV-photocatalytic degradation of both phenol and 2-CP pollutants in the solution (as compared to the plain rutile TiO(2)). The photodegradation processes were optimized by the 0.5-g/L catalyst with a pollutant concentration of 50 mg/L for all the samples. Complete degradation for both phenol and 2-CP was achieved after 120 min.

Extraordinary mechanical flexibility in composite thin films composed of bimetallic AgPt nanoparticle-decorated multi-walled carbon nanotubes

Flexible, transparent, and conducting composite thin films, constructed from multi-walled carbon-nanotube-supported silver–platinum alloy nanoparticles (AgPt–MWCNT) on a flexible polyethylene terephthalate (PET) substrate through the combination of a two-step polyol process for synthesizing composites of carbon nanotubes (CNTs) and metallic nanoparticles (NPs) with an ultrasonic atomization-spin coating method for preparing thin films, have been fabricated. AgPt NPs with an average size of approximately 26nm were uniformly attached to the sidewalls of MWCNTs to form an effective and strongly mechanical conductive network. These composites were then exposed to microwave plasma irradiation, which can lower the contact resistance between the metallic NPs and CNTs and reinforce the network bridges. The resulting AgPt–MWCNT–PET thin films exhibit improved optoelectronic and mechanical properties, and they possess a sheet resistance of 154Ω/sq with a transmittance of 80% at 550nm. These values are competitive with those of most other CNT-based films. Most importantly, the corresponding sheet conductivity does not decrease even after 500 bending cycles. Therefore, the as-produced AgPt–MWCNT–PET films may be direct alternatives to indium tin oxide and other transparent conducting oxide films.

Activation/Inhibition Effects during the Coelectrodeposition of PtAg Nanoparticles: Application for ORR in Alkaline Media

PtAg bimetallic nanoparticles for oxygen reduction reaction (ORR) in alkaline media were prepared by pulse electrodeposition (PED). During PED the reduction of Ag(+) ions predominates, thus an increased Ag content in the co-deposit is accomplished. The mechanism for this anomalous co-deposition was elucidated by potential pulse experiments, which revealed that nuclei formation mainly occurs via the reduction of Pt(2+) ions. The growth of the particles is diffusion controlled leading to the formation of a Ag shell covering a PtAg alloyed region. However, the shell is not growing homogeneously on the PtAg alloy. Hence, regions of the PtAg alloy are exposed, which exhibit an enhanced ORR activity compared to a pure Ag surface.

Lattice contracted AgPt nanoparticles

Lattice distortion in AgPt nanoparticles was studied using X-ray diffraction and other techniques. These nanoparticles show high catalytic activity in the reduction of p-nitrophenol and had a turn over frequency of 5.4 × 10(2) s(-1).

Direct oxidation of sodium borohydride on Pt, Ag and alloyed Pt–Ag electrodes in basic media: Part II. Carbon-supported nanoparticles

We studied the borohydride oxidation reaction (BOR) by voltammetry in 0.1 M NaOH/10 −3 M BH 4 − on carbon-supported Pt, Ag and alloyed PtAg nanoparticles (here-after denoted as Pt/C, Ag/C and Pt–Ag/C). In order to compare the different electrocatalysts, we measured the BOR kinetic parameters and the number of electrons exchanged per BH 4 − anion (faradaic efficiency). The BOR kinetics is much faster for Pt/C than for Ag/C ( i Pt = 0.15 , i Ag = 3.1 × 1 0 − 4 A cm −2 at E = − 0.65 V vs. NHE at 25 ° C), but both materials present similar Tafel slope values. The n value involved in the BOR depends on the thickness of the active layer of electrocatalysts. For a “thick layer” (approximately 3 μ m), n is nearly 8 on Pt/C and ∼ 4 on Ag/C, whereas n decreases for thinner Pt/C active layers ( n ∼ 2 for thickness < 1 μ m). These results are in favour of the sequential BH 4 − hydrolysis (yielding H 2) followed by hydrogen oxidation reaction (HOR), or direct sequential BOR on Pt/C, whereas Ag/C promotes direct but incomplete BOR (Ag has no activity regarding hydrogen evolution reaction, HER). The n value close to 8 for the thick Pt/C layer displays the sufficient residence time of the molecules formed (H 2 by heterogeneous hydrolysis or BOR intermediates) within the active layer, which favours the complete HOR and/or BOR. Two PtAg/C nanoparticles alloys have been tested (noted APVES-4C and APVES-E1). They show different behavior; the borohydride oxidation reaction kinetics is faster on APVES-E1 than on APVES-4C ( b = 0.15 , i − 0.65 V = 0.09 and b = 0.31 V dec −1, i − 0.65 V = 6.3 × 1 0 − 3 A cm −2, respectively, at 25 ° C), but the n values are higher on APVES-4C than APVES-E1 (nearly 8 vs. 3, respectively, at 25 ° C). These discrepancies probably originate from the heterogeneity of such bimetallic materials, as observed from physicochemical characterizations.

A Phase-Transfer Identification of Core−Shell Structures in Ag−Pt Nanoparticles

Ag-Pt nanoparticles with a confirmed core-shell structure could only be formed by the successive reduction method using Ag nanoparticles as the seeds. The core-shell structure could be conveniently inferred from the transferability of the particles from water to toluene. Independent measurements by UV-vis spectroscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy were used to validate the experimental results. The reverse order of synthesis using Pt nanoparticles as the seeds did not result in any core-shell product. Instead a physical mixture of Ag nanoparticles and the original Pt seeds was obtained under the same experimental conditions.