Platinum-cobalt Nanoparticles Research Articles

Magnetic aerogels from FePt and CoPt3 directly from organic solution.

Here the synthesis of magnetic aerogels from iron platinum and cobalt platinum nanoparticles is presented. The use of hydrazine monohydrate as destabilizing agent triggers the gelation directly from organic solution, and therefore a phase transfer to aqueous media prior to the gelation is not necessary. The aerogels were characterized through Transmission Electron Microscopy, Scanning Electron Microscopy, Powder X-Ray Diffraction Analysis and Argon Physisorption measurements to prove the formation of a porous network and define their compositions. Additionally, magnetization measurements in terms of hysteresis cycles at 5 K and 300 K (M-H-curves) as well as zero field cooled-field cooled measurements (ZFC-FC measurements) of the dried colloids and the respective xero- and aerogels were performed, in order to analyze the influence of the gelation process and the network structure on the magnetic properties.

Effect of heat treatment temperature on the Pt3Co binary metal catalysts for oxygen reduced reaction and DFT calculations

Synthesis of low-cost, high-activity and high-stability Pt-based catalysts is of great importance to the large commercialization of proton exchange membrane fuel cell (PEMFC). Doping non-precious metals such as cobalt (Co) with Pt is attractive due to the reduced depletion of Pt and, more importantly, the enhanced activity on the oxygen reduction reaction (ORR) compared with pure Pt. In this work, carbon-supported platinum-cobalt nanoparticles(NPs) were prepared by the impregnation reduction method for the ORR catalyst. By changing the heat treatment temperature, the structure, the crystal phase and the size of the Pt3Co nanoparticles could be controlled. TEM and XRD characterizations show that larger size NPs with higher alloying degree are obtained at higher temperature. The electrochemical results demonstrate that the Pt3Co NPs at 800 °C have the highest mass activity (0.41A/mgPt) and the best stability among all the samples due to their lower particle size and higher alloying degree. Further Density functional theory(DFT) calculation shows that the surface of the Pt3Co structure with high alloying degree can reduce the rate-determining step barrier and improve the ORR activity.

Magnetic Force-Induced Alignment of Microtubules by Encapsulation of CoPt Nanoparticles Using a Tau-Derived Peptide.

Construction of magnetotactic materials is a significant challenge in nanotechnology applications such as nanodevices and nanotransportation. Artificial magnetotactic materials can be designed from magnetotactic bacteria because these bacteria use magnetic nanoparticles for aligning with and moving within magnetic fields. Microtubules are attractive scaffolds to construct magnetotactic materials because of their intrinsic motility. Nonetheless, it is challenging to magnetically control their orientation while retaining their motility by conjugating magnetic nanoparticles on their outer surface. Here we solve the issue by encapsulating magnetic cobalt-platinum nanoparticles inside microtubules using our developed Tau-derived peptide that binds to their internal pockets. The in situ growth of cobalt-platinum nanoparticles resulted in the formation of a linear-chain assembly of nanoparticles inside the microtubules. The magnetic microtubules significantly aligned with a high order parameter (0.71) along the weak magnetic field (0.37 T) and showed increased motility. This work provides a new concept for designing magnetotactic materials.

Monodisperse Pt-Co/GO anodes with varying Pt: Co ratios as highly active and stable electrocatalysts for methanol electrooxidation reaction

The intense demand for alternative energy has led to efforts to find highly efficient and stable electrocatalysts for the methanol oxidation reaction. For this purpose, herein, graphene oxide-based platinum-cobalt nanoparticles (Pt100−xCox@GO NPs) were synthesized in different ratios and the synthesized nanoparticles were used directly as an efficient electrocatalyst for methanol oxidation reaction (MOR). The characterizations for the determination of particle size and surface composition of nanoparticles were performed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The structure of the catalysts was detected as face-centered cubic and the dispersion of them on graphene oxide was homogenous (distributed narrowly (4.01 ± 0.51 nm)). Cyclic voltammetry (CV) and chronoamperometry (CA) was utilized for testing electrocatalytic activities of all prepared NPs for the methanol oxidation reaction. It was detected that the newly produced NPs were more active and stable than commercially existing Pt(0)/Co nanomaterial in methanol electro-oxidation in acidic media.

Oxidation and Corrosion of Platinum–Nickel and Platinum–Cobalt Nanoparticles in an Aqueous Acidic Medium

We report on the synthesis, characterization, and corrosion behavior of randomly oriented platinum–nickel and platinum–cobalt nanoparticles (PtNi-NPs, PtCo-NPs). Unsupported and carbon-supported nanocatalysts were synthesized using the “water-in-oil” microemulsion method. X-ray diffraction (XRD) was used to examine their average crystallite size, which was 2.3 nm in both cases. The shape, size, and size distribution of the nanoparticles were evaluated using transmission electron microscopy (TEM); they were determined to be spherelike with an average size of 3.3 and 3.2 nm for PtNi-NPs and PtCo-NPs, respectively, and a narrow size distribution. Comparison of the XRD and TEM data indicated that the nanocatalysts were polycrystalline in nature. Thermogravimetric analysis (TGA) measurements were carried out to evaluate the metal loadings of the carbon-supported nanocatalysts, which were 38.1 wt % for PtNi-NPs and 40.8 wt % for PtCo-NPs. Static Density Functional Theory (DFT) calculations were performed to ana...

In situ atomic-scale observation of oxygen-driven core-shell formation in Pt3Co nanoparticles

The catalytic performance of core-shell platinum alloy nanoparticles is typically superior to that of pure platinum nanoparticles for the oxygen reduction reaction in fuel cell cathodes. Thorough understanding of core-shell formation is critical for atomic-scale design and control of the platinum shell, which is known to be the structural feature responsible for the enhancement. Here we reveal details of a counter-intuitive core-shell formation process in platinum-cobalt nanoparticles at elevated temperature under oxygen at atmospheric pressure, by using advanced in situ electron microscopy. Initial segregation of a thin platinum, rather than cobalt oxide, surface layer occurs concurrently with ordering of the intermetallic core, followed by the layer-by-layer growth of a platinum shell via Ostwald ripening during the oxygen annealing treatment. Calculations based on density functional theory demonstrate that this process follows an energetically favourable path. These findings are expected to be useful for the future design of structured platinum alloy nanocatalysts.

Direct observations of dynamic PtCo interactions in fuel cell catalyst precursors at the atomic level using E(S)TEM.

Reduction reactions in practical bimetallic platinum-cobalt electrode catalyst precursors containing platinum, cobalt and cobalt oxides in hydrogen at 200, 450 and 700 °C for 6 h have been studied in situ using an aberration corrected environmental (scanning) transmission electron microscope (AC E(S)TEM). Little difference was observed in reduction at 200 °C but during and after reduction at 450 °C, small nanoparticles less than 3 nm in diameter with tetragonal PtCo structures were observed and limited Pt3 Co ordering could be seen on the surfaces of larger nanoparticles. During and after reduction at 700 °C, fully ordered Pt3 Co and PtCo nanoparticles larger than 4 nm were produced and the average nanoparticle size almost trebled relative to the fresh precursor. After reduction at 450 and 700 °C, most nanoparticles were disordered platinum/cobalt alloys with fcc structure. After reduction at 700 °C many of the smallest nanoparticles disappeared suggesting Ostwald ripening had occurred. Mechanisms concerning the thermal transformation of mixed cobalt and platinum species are discussed, offering new insights into the creation of bimetallic platinum-cobalt nanoparticles in fuel cell catalysts.

Aqueous phase reforming of ethylene glycol over bimetallic platinum-cobalt on ceria–zirconia mixed oxide

The roles of cobalt promoter on the bimetallic platinum-cobalt supported on the CeO2-ZrO2 mixed oxide were investigated for aqueous phase reforming reaction of ethylene glycol (EG) to verify the effects of cobalt to an enhanced activity and stability of PtCo/CeO2-ZrO2, where the CeO2-ZrO2 mixed oxide was prepared by sol–gel method at a fixed Ce/(Ce + Zr) molar ratio of 0.4. The enhanced catalytic activity for an aqueous-phase reforming (APR) as well as water gas shift (WGS) reaction of EG was observed on the PtCo/CeO2-ZrO2 at a Co/Pt molar ratio of 0.5. The higher activity and stability on the PtCo/CeO2-ZrO2 at an optimal Co/Pt ratio were mainly attributed to an enhanced WGS activity and less aggregation of active metals due to a high dispersion of platinum nanoparticles with a proper interaction between platinum and oxophilic cobalt nanoparticles. A facile reduction behavior of the supported bimetallic platinum-cobalt nanoparticles through an enhanced hydrogen spillover on the platinum nanoparticles also increased CC cleavage reaction of EG with the suppressed deposition of inactive coke precursors on the partially reduced active nanoparticles. These synergy effects of platinum-cobalt nanoparticles with a close interaction and a less aggregation of active metals were responsible for an enhanced APR and WGS activity on the PtCo/CeO2-ZrO2 at an optimal Ce/(Ce + Zr) ratio as well.

Enhanced catalytic activity of solid and hollow platinum-cobalt nanoparticles towards reduction of 4-nitrophenol

Previous investigations of hollow platinum nanoparticles have shown that such nanostructures are more active catalysts than their solid counterparts towards the following electrochemical reactions: reduction of oxygen, evolution of hydrogen, and oxidation of borohydride, methanol and formic acid. In this work we show that synthesised using standard galvanic replacement reaction (with Co templates) hollow platinum nanoparticles exhibit enhanced catalytic activity also towards reduction of 4-nitrophenol by sodium borohydride in water. Unlike in the case of procedures involving hollow platinum catalysts employed so far to carry out this reaction it is not necessary to couple analysed platinum nanoparticles to the surface of an electrode. Simplification of the analyzed reaction may eliminate same experimental errors. We found that the enhanced catalytic activity of hollow Pt nanoparticles is not only connected with generally observed larger surface area of hollow nanostructures, but is also due to the contamination of formed hollow nanostructures with cobalt, from which sacrificial templates used in the synthesis of hollow Pt nanostrustures have been formed. Because using sacrificial templates is a typical method of synthesis of hollow metal nanostructures, formed hollow nanoparticles are probably often contaminated, which may significantly influence their catalytic activity.

Chloride Ion Mediated Synthesis of Metal/Semiconductor Hybrid Nanocrystals.

A synthetic route to prepare metal-semiconductor hybrid nanoparticles is presented, along with the possibility to tune the ratio of primary to secondary nucleation and the morphology of the semiconductor material grown on the metal nanoparticle seeds. Gold and cobalt-platinum nanoparticles are employed as metal seeds, on which CdS or CdSe is grown. Using transmission electron microscopy, absorption spectroscopy (UV-vis), and powder X-ray diffraction as characterization techniques, a significant influence of chloride ions on the type of nucleation (that is, secondary or primary nucleation) as well as on the shape of the resulting heterostructures is observed. Partially replacing the commonly used cadmium precursor CdO by varying amounts of CdCl2 opens access to rod-like, multiarmed, flower-like, and bullet-like structures. The results suggest that neither pure CdO nor pure CdCl2 as precursors but only a mixture of both make these structures obtainable. In this article, the influence of the chloride ion concentration during semiconductor growth on metal seeds is investigated in depth. The morphology of the resulting heterostructures is characterized carefully, and a growth mechanism is suggested. Furthermore, it is shown that this synthetic approach can be transferred to seeds of various metals such as platinum, gold, and cobalt platinum.

One-pot synthesis of graphene supported platinum–cobalt nanoparticles as electrocatalysts for methanol oxidation

In the present study the graphene supported platinum–cobalt nanoparticles were prepared via microwave synthesis. The composition of prepared catalysts was examined by Inductively Coupled Plasma Optical Emission Spectroscopy. The shape and size of catalyst particles were determined by Transmission Electron Microscopy. The electrocatalytic activity of the graphene supported platinum–cobalt nanoparticles was investigated towards the electro-oxidation of methanol in an alkaline medium. It has been found that the graphene supported platinum–cobalt nanoparticles having the Pt:Co molar ratio 1:7 show the highest activity towards the electro-oxidation of methanol among the catalysts with the Pt:Co molar ratios equal to 1:1 and 1:44, graphene supported bare Co and Pt/C catalysts.

Electrophoretic Deposition of Cobalt Ferrite and Platinum Cobalt Nanoparticles as Electrocatalysts

Cobalt ferrite and platinum cobalt nanoparticles were deposited using electrophoretic deposition (EPD) from two different bath chemistries. The first bath contained 2 g/L particles suspended in 90 vol.% water and 10 vol.% isopropanol with 0.4 g/L hexadecyltrimethlyammonium bromide. The second bath contained 2 g/L particles suspended in 100 % ethanol. The deposits were tested for electrocatalytic properties for the oxidation of ammonium sulfite to ammonium sulfate. Linear sweep voltammetry showed that both EPD deposits of cobalt ferrite and platinum cobalt nanoparticles had electrocatalytic activity.

Electrophoretic Deposition of Cobalt Ferrite and Platinum Cobalt Nanoparticles As Electrocatalysts

not Available.

Preparation and properties of nanoparticles by chemical reactions with assistance of physics factors

Versatile chemical reactions with the help of physical factors such as microwaves, sonic radiations, laser, elevated temperature and pressure have successfully been used to prepared silicon (high surface area), iron oxide (in amorphous and crystalline state), silver, gold, iron-platinum, cobalt-platinum nanoparticles. The microwaves fostered the chemical reactions via homogeneous and fast heating processes; the sonic radiations from an ultrasonicator created ultra-fast cooling rates at high power or just played a role of mechanical waves at low power; laser provided energy nanoparticles from bulk plates; elevated temperature and pressure produced good environments for unique reactions. All those preparation methods are simple and inexpensive but they could produce nanoparticles with interesting properties.

Size-controlled synthesis and characterization of CoPt nanoparticles using protein shells.

Nanostructured magnetic materials such as iron oxide and bimetallic nanoparticles can be potentially applied to a variety of fields, including electronics and nanomedicine. To develop these applications, it is important to control their particle size which affects their magnetic properties. In particular, it is a major challenge to synthesize small-sized nanoparticles with high reproducibility. In this study, we synthesized cobalt-platinum nanoparticles (CoPt NPs) in an ambient solution phase using PepA, a bacterial aminopeptidase, as a protein shell, and investigated the physicochemical and magnetic properties of NPs with and without encapsulating proteins. The size of CoPt NPs encapsulated by PepA was stringently controlled from 1.1 to 2.8 nm, and their magnetic property was related to the size. The CoPt NPs with the diameter of 1.1 nm showed a superparamagnetic behavior only at low temperatures, while 2.1 and 2.8 nm CoPt NPs were ferromagnetic below the blocking temperature. PepA had no deleterious effects on the coercivity of CoPt NPs, as evidenced by the marginal effect of PepA on the coercivity of CoPt NPs. This study demonstrated that the particle size and magnetic property of CoPt NPs can be controlled by using PepA as a protein shell. Encapsulation by PepA will aid the development of multifunctional magnetic materials, since the biocompatibility and modification capability of PepA can be synergistically combined with the advanced functionalities of CoPt NPs.

The next big things are tiny

The next big things are tiny

Magnetization reversal in isolated and interacting single-domain nanoparticles

Computational and experimental results of thermally induced magnetization reversal in single-domain magnetic nanoparticles are reported. The simulations are based on direct integration of the Fokker-Planck equation that governs the dynamics of the magnetic moment associated with the nanoparticles. A mean-field approximation is used to account for the influence of the dipolar interaction between nanoparticles. It is shown that the interactions can either speed up or slow down the reversal process, depending on the angle between the external magnetic field and the axis of easy magnetization. The numerical results are in good agreement with experimental measurements of cobalt-platinum nanoparticles.

The effect of electrochemical CO annealing on platinum–cobalt nanoparticles in acid medium and their correlation to the oxygen reduction reaction

This paper describes a modification of the surface properties of a carbon-supported Pt 3Co catalyst resulting from an electrochemical cycling treatment in a 0.1 M HClO 4 and in a CO-saturated 0.1 M HClO 4 solution (electrochemical CO-annealing). The procedure generated a Pt-rich surface with electrochemical properties different from that presented by the as-received (untreated) sample. This was evidenced by a shift in the CO stripping peak to more positive potentials in the CO stripping voltammetry, and by an increased charge of H upd region and a modification of the oxide reduction peak observed in the base cyclic voltammogram. In situ X-ray absorption spectroscopy experiments conducted in the dispersive mode revealed differences in the electronic 5d band occupancy after the CO annealing, whereas the behavior of the intensity of the white-line as function of the potential for this material approached that found for pure Pt/C nanoparticles, in contrast to the small potential dependence profile exhibited by the as-received Pt 3Co nanoparticles. Mass activities towards the oxygen reduction reaction measured by rotating disk experiments carried out at 1600 rpm in a O 2-saturated solution at 25 °C increased from 0.10 A/mg of Pt to 0.19 A/mg of Pt, evidencing the higher Pt utilization in the CO-annealed Pt 3Co/C electrocatalyst. The origin of the different electrochemical behavior is discussed.

On the Changes of the Electronic Structure of Platinum-Cobalt Nanoparticles by Surface Segregation and Their Correlation to the Oxygen Reduction Reaction

not Available.

Tunable Electrical Transport through Annealed Monolayers of Monodisperse Cobalt−Platinum Nanoparticles

We synthesized monodisperse cobalt-platinum nanoparticles Co(0.14-0.22)Pt(0.86-0.78) of 9 nm in diameter by colloidal chemistry methods and deposited them by the Langmuir-Blodgett technique as highly ordered monolayers onto substrates with e-beam defined gold electrodes. Upon annealing we observe an increase of conductivity over more than 4 orders of magnitude. A first attempt of explanation of this unanticipated effect, a nanoparticle displacement, could not be confirmed for annealing temperatures below 400 °C. A second approach, a carbonization of the ligands, however, could be confirmed by Raman spectroscopy. The simple thermal treatment allows tuning essential properties of electronic devices based on nanoparticles by the manipulation of the interparticle coupling, namely the electrical conductivity, the Coulomb blockade characteristic, and the activation energy of the system.