Platinum-gold Alloys Research Articles

Electrocatalytic Oxidation of HCOOH on an Electrodeposited AuPt Electrode: its Possible Application in Fuel Cells

ABSTRACT: Controlled electrodeposition of dendritic nano-structured gold-platinum (AuPt) alloy onto an elec-trochemically pretreated carbon paper substrate was conducted in an attempt to improve catalystutilization and to secure an electronic percolation network toward formic acid (FA) fuel cell appli-cation. The AuPt catalysts were obtained by potentiostatic deposition. AuPt catalysts synthesizedas bimetallic alloys with 60% Au content exhibited the highest catalytic activity towards formicacid electro-oxidation. The origin of this high activity and the role of Au were evaluated, in par-ticular, by XPS analysis. Polarization and stability measurements with 1 mg cm −2 AuPt catalyst(only 0.4 mg cm −2 Pt) showed 52 mW cm −2 and sustainable performance using 3 M formic acid anddry air at 40 o C.Keywords : electrodeposition, AuPt alloy, dendritic nanostructure, formic acid fuel cells. Received August 23, 2010 : Accepted September 7, 2010 1. Introduction Small organic molecules (SOM) such as methanol,formic acid, formate, and ethanol have great potentialas possible fuels in direct small organic fuel cells.

A signal-on electrochemical probe-label-free aptasensor using gold–platinum alloy and stearic acid as enhancers

In the present study, a new electrochemical probe-label-free aptasensor for thrombin (TB) based on the amplification of gold–platinum alloy nanoparticles (Au–PtNPs) and stearic acid was reported. Nafion@multiwalled carbon nanotubes (MWCNTs) coated electrode was firstly modified with electrochemical probe of methylene blue (MB). Then, Au–PtNPs were electrodeposited onto the electrode surface for the immobilization of aptamer and further hybridization of stearic acid labeled thrombin aptamer (TBA). In the presence of TB, the TBA bound with TB and released from the self-assembled duplex on the electrode into solution, decreasing the steric hindrance of the aptasensor and facilitating catalytic efficiency of Au–PtNPs in the presence of MB toward H 2O 2 with an enhanced electrochemical signal. With the enhanced effect of Au–PtNPs/MB modified electrode and stearic acid, a detection limit as low as 3 pM for TB was achieved. The aptasensor also exhibited good selectivity and reproducibility.

Intense pulsed light induced platinum–gold alloy formation on carbon nanotubes for non-enzymatic glucose detection

We demonstrated a novel method for the formation of alloy nano-islands on carbon nanotube (CNT). The two metal layers (Pt, Au) were sputtered on CNTs and the intense pulsed light (IPL) was irradiated on the metal layers. The absorbed light provides enough energy for the diffusion mixing between Pt and Au, forming Pt–Au alloy phase. While the alloy is being formed by the IPL irradiation, the metal layers are broken into nano-islands on CNT due to the surface energy minimization between the metal layers and CNT. The surface characterizations of the Pt–Au/CNT were performed with X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy. Different compositions of alloy nanoparticles were obtained by adjusting the deposition thicknesses of Pt and Au on CNT. Pt 50Au 50/CNT electrode showed the highest glucose oxidation current peak among Pt, Pt 70Au 30, Pt 50Au 50, Pt 30Au 70, and Au/CNT electrodes while the electroactive surface areas of them are kept to be similar (average surface area = 7.00 cm 2, coefficient of variation = 0.06). The amperometric response of Pt 50Au 50/CNT electrode to the glucose concentrations showed a wide linear range up to 24.44 mM with a high detection sensitivity of 10.71 μA mM −1 cm −2. Reproducibility and long-term stability of the Pt–Au/CNT electrode were also proven in the experiments.

Electrochemical deposition of gold–platinum alloy nanoparticles on an indium tin oxide electrode and their electrocatalytic applications

Gold–platinum (Au–Pt) hybrid nanoparticles (Au–PtNPs) were successfully deposited on an indium tin oxide (ITO) surface using a direct electrochemical method. The resulting nanoparticles were characterized by scanning electron microscopy (SEM), UV–vis spectroscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and electrochemical methods. It was found that the size of the Au–PtNPs depends on the number of electrodeposition cycles. Au–PtNPs obtained by 20 electrodeposition cycles had a cauliflower-shaped structure with an average diameter of about 60 nm. These Au–PtNPs exhibited alloy properties. Electrochemical measurements showed that the charge transfer resistivity was significantly decreased for the Au–PtNPs/ITO electrode. Additionally, the Au–PtNPs displayed an electrocatalytic activity for nitrite oxidation and oxygen reduction. The Au–PtNPs/ITO electrodes reported herein could possibly be used as electrocatalysts and sensors.

Ultrasonic-electrodeposition of gold–platinum alloy nanoparticles on multi-walled carbon nanotubes – ionic liquid composite film and their electrocatalysis towards the oxidation of nitrite

We report here for the first time on the electrochemical co-deposition of gold–platinum (AuPt) nanoparticles on multi-walled carbon nanotubes (MWNT) – ionic liquid (i.e. trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, [P 6,6,6,14][NTf 2]) composite surface in ultrasonic field. The obtained AuPt nanoparticles were characterized by scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. It was found that they were well-dispersed on the composite surface, with particle size about 10 nm. Furthermore, they exhibited alloy features. Electrochemical impedance spectroscopy and voltammetric experiments showed that the resulted AuPt-MWNT-[P 6,6,6,14][NTf 2] modified electrode possessed rather small electron transfer resistance and good catalytic activity towards nitrite oxidation. Under the optimized conditions, the oxidation current of nitrite was linear to its concentration in the range of 5–200 nM and the detection limit was down to 1.0 nM (S/N = 3).

Temperature-programmed reduction study on carbon-supported platinum–gold alloy catalysts

Alloy catalysts of Pt–Au/C with different Pt/Au ratios were prepared by the precipitation–deposition of metal chlorides and reduced by H 2 at 470 K. The surface composition of alloy crystallites deposited on the prepared catalysts was characterized by a technique of temperature-programmed reduction (TPR). In the characterization, O 2 was chemisorbed on the reduced catalysts and the chemisorbed O 2 was reduced by TPR. A low-temperature routine (LT) in the temperature range between 120 and 430 K was used for the TPR characterization. Monometallic catalysts of Au/C and Pt/C showed a reduction peak in the LT-TPR at reduction temperature ( T r ) = 145 and 240 K, respectively. T r from alloyed catalysts fell in the range and increased monotonously with their Pt/Au ratios. Interior Pt atoms in deposited alloy particles tended to segregate toward their surface during oxidation treatment at elevated temperatures.

A novel glucose biosensor based on immobilization of glucose oxidase in chitosan on a glassy carbon electrode modified with gold–platinum alloy nanoparticles/multiwall carbon nanotubes

A novel glucose biosensor was constructed, based on the immobilization of glucose oxidase (GOx) with cross-linking in the matrix of biopolymer chitosan (CS) on a glassy carbon electrode (GCE), which was modified with gold–platinum alloy nanoparticles (Au–PtNPs) by electrodeposition on multiwall carbon nanotubes (CNTs) in CS film (CNTs/CS). The properties of Au–PtNPs/CNTs/CS were characterized by scan electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectra (EIS). Primary study indicated that Au–PtNPs/CNTs had a better synergistic electrocatalytic effect on the reduction of hydrogen peroxide than did AuNPs/CNTs or PtNPs/CNTs at a low applied potential window. With GOx as a model enzyme, a new glucose biosensor was fabricated. The biosensor exhibited excellent performances for glucose at a low applied potential (0.1 V) with a high sensitivity (8.53 μA mM −1), a low detection limit (0.2 μM), a wide linear range (0.001–7.0 mM), a fast response time (<5 s), and good reproducibility, stability, and selectivity. In addition, the biosensor was applied in the determination of glucose in human blood and urine samples, and satisfied results were obtained.

Synergistic activity of gold-platinum alloy nanoparticle catalysts

The understanding of the composition–activity relationship is essential for the exploitation of the synergistic properties of multimetallic nanoparticles in catalytic reactions. This paper focuses on the discussion of findings from the investigation of bimetallic gold-platinum (AuPt) nanoparticles of different compositions. Infrared spectroscopic data for CO adsorption on silica-supported AuPt nanoparticles reveal that the surface binding sites are dependent on the bimetallic composition. The analysis of this dependence further led to the conclusion that the relative Au-atop and Pt-atop sites for the linear CO adsorption on the nanoparticle surface are not only correlated with the bimetallic composition, but also with the electronic effect as a result of the d-band shift of Pt in the bimetallic nanocrystals, which is the first demonstration of the nanoscale core–surface property correlation for the bimetallic nanoparticles over a wide range of bimetallic composition. A further examination of the electrocatalysis data for methanol oxidation reaction on carbon-supported AuPt nanoparticle catalysts reveal important insights into the participation of CO or OH adsorption on Au sites and the catalytic activity of Pt in the AuPt alloys with relatively high Au concentration. Implications of these findings to synergistic correlation of the bifunctional activity of the bimetallic nanoparticle catalysts with the bimetallic composition are also discussed.

Electrocatalytic Oxidation of Glucose at Carbon Electrodes Modified with Gold and Gold–Platinum Alloy Nanoparticles in an Alkaline Solution

Abstract The electrocatalytic oxidation of glucose in an alkaline solution was examined using gold and gold–platinum alloy nanoparticles as catalysts. In electrolysis, the catalytic activity for oxidation of glucose could be kept much longer time at gold nanoparticle-modified electrode than at a gold plate electrode. Preliminary electrolysis results at 0.3 V indicated that current efficiency for oxalate as 18-electron oxidation product at gold nanoparticle-modified electrode was approximately twice higher than that at gold–platinum alloy nanoparticle-modified electrode.

Reversible Strain in Porous Metals Charged in Electrolytes

AbstractNanoporous metal samples with millimetre size were prepared either by compacting nanocrystalline powders or by dealloying, the dissolution of the less noble metal(s) of an alloy. The samples were immersed in an electrolyte, and their length was measured as a function of the applied potential in-situ in a dilatometer. The results obtained for nanocrystalline platinum, nanoporous gold and for gold platinum alloys show that the length varies in dependence of the surface charge. The strain amplitude of nanocrystalline platinum was 0.15%, and even larger strains have been measured using an Au-Pt alloy. This strain is comparable to commercial piezoceramics, but it is achieved using smaller voltages.The strain measured for nanoporous gold prepared by dealloying was smaller than that mainly due to the larger structure size (20 nm structure size compared to 6 nm Pt crystallite size), but in the case of gold, it was possible to prepare stable composite structures of a metal foil and of the nanoporous gold. If such a bimetallic foil is charged, it is found to bend. Due to the mechanical amplification of the contraction or expansion of the nanoporous part of the foil, it was possible to observe the effect of electric charges on the surface stress of metals directly with the naked eye for the first time.These results demonstrate that nanoporous metals might be useful for actuator applications and for the study of surface strain effects. Furthermore, they are the first realization of a general concept that suggests that most of the properties of conducting nanomaterials can be tuned by controlling the surface charge.

The electrochemistry of gold–platinum alloys

The electrochemical properties of gold, platinum and gold–platinum alloy electrodes under different heat treatment conditions have been studied in 0.5 M H 2SO 4 and 0.5 M NaOH. The electro-oxidation of 0.1 M ethylene glycol in 0.5 M NaOH at these electrodes has also been studied. It was found that all the gold–platinum electrodes are more active for ethylene glycol electro-oxidation than both pure gold and platinum, and that the gold–platinum electrodes in the solid solution condition are more active than the two-phase electrodes. Poisoning of all the electrodes occurs during electrolysis of ethylene glycol at a fixed potential. Potential pulsing is successful in removing the poisoning species formed at the pure gold and pure platinum electrodes. High apparent current densities are found during the first few cycles at the Au–Pt alloy electrodes. These high current densities are also associated with more severe poisoning – than at both pure gold and platinum – and longer cleaning cycles are needed to remove the poisons at these electrodes.

A surface-science-based model for the selectivity of platinum–gold alloy electrodes in zirconia-based NO x sensors

Recent surface chemistry experiments help explain the operation of an exhaust gas NO x sensor that uses a platinum–gold alloy electrode to selectively remove oxygen but not NO from an interior chamber. The electrode surface must dissociate O 2 for removal by electrochemical pumping, but must be at least 100 times less active for dissociating NO. In ultrahigh vacuum studies on stepped platinum single crystals, NO dissociation is strongly suppressed by surface gold coverages as low as 0.4 monolayer (ML), as well as by co-adsorbed oxygen and NO, probably because the dissociation process requires a special ensemble of several unoccupied Pt atoms. Oxygen dissociation is much less affected by surface modifications. In general, the surface composition of an alloy is very different from its bulk composition and depends on gas composition. By considering the energetics of the Pt–Au system we argue that under all conditions of interest for sensor operation the ensembles of free Pt atoms required for NO dissociation are strongly disfavored. A surface chemistry-based explanation is also suggested for the ammonia interference reported for this NO x sensor.

Characterization of the surface of protein-adsorbed dental materials by wetting and streaming potential measurements

In this study we have elucidated the water-wettability and the electrokinetic surface potential of protein-covered dental materials. The proteins used here as typical proteins were human serum albumin and lysozyme from hen's egg. The wettability (hydrophobicity/hydrophilicity) and the surface potential may dominate bacterial adhesion on the tooth materials and hence influence their biological activity. The artificial tooth materials we investigated were platinum–gold alloy, porcelain and dental resin. Hydroxyapatite was chosen as a reference reflecting natural tooth surface. The wetting was measured by the dropping time method of a thin liquid film along the surface of a protein-covered solid plate sample. The zeta potential was derived from the streaming potential invoked by flowing an electrolyte solution between two parallel sample plates. A variety of surface properties have been found for different combinations of protein and dental material.

Volume magnetic susceptibility of gold–platinum alloys: possible materials to make mass standards for the watt balance experiment

In 2000, the Bureau National de Métrologie (BNM, France) decided to develop a new watt balance experiment. Among numerous design studies, the choice of the transfer mass is particularly important. Because of the proximity to a source of high magnetic intensity, this mass must have a magnetic susceptibility as weak as possible. Gold–platinum alloy seems to meet this requirement, as well as additional requirements for density and hardness values, making it a possible candidate for mass standard realization. Five different gold–platinum alloys were studied, their volume magnetic susceptibility ranging from −2.8×10−5 to −2.1×10−5 for two of them and from +1.1×10−5 to +8.8×10−5 for the other three.

Flight experience on CHAMP and GRACE with ultra-sensitive accelerometers and return for LISA

The challenging drag-free sensor of the Laser Interferometer Space Antenna (LISA) mission is derived from electrostatic accelerometers developed for a long time in ONERA. The LISA sensor includes a gold platinum alloy inertial mass free-floating in space and used as reflectors for the laser interferometer. This test mass should not undergo more than 3 × 10−15 m s−2 Hz−1/2 acceleration at 0.1 mHz. This tremendous performance is not close to what has been reached so far, but should be approached within one order of magnitude with the projected SMART-2 ESA mission by 2006. Meanwhile, ONERA has participated in several space missions with the flight of increasingly sensitive accelerometers. The German CHAMP mission aims at mapping the Earth's magnetic and gravity fields. More than two years data have been accumulated showing a resolution better than 3 × 10−9 m s−2 Hz−1/2 for the accelerometer. With the JPL/NASA GRACE mission launched in March 2002, even more sensitive measurements have been obtained. From these two flight experiments with electrostatic sensors very similar in concept to that of LISA, the accelerometric environment on board a satellite is discussed at nanogravity levels. It is also shown that these first analyses are compatible with the expected LISA performance when the results are extrapolated to the LISA environment, needing femto-gravity levels.

Optical Properties of Au-Pt and Au-Pt-In Alloys

The effects of platinum addition to gold and indium addition to a gold-platinum alloy on their optical properties were investigated using a computer-controlled spectrophotometer. Spectral reflectance data from a polished sample for the incident CIE standard illuminant D65 was collected as a function of the wavelength at 10 nm intervals from 360 to 740 nm. Three coordinates,L* (lightness),a* (red-green),b* (yellow-blue), in the CIE 1976L*a*b* colour space, were determined to quantify the colour of experimental binary Au-Pt and ternary Au-Pt-In alloys. p ]The pronounced step near 520 nm (approximately 2.4 eV) in the spectral reflectance-wavelength curve for pure gold, which is responsible for the rich yellow colour of gold, became less pronounced with the addition of platinum. The decoloring effect of platinum was found to be due to this phenomenon. The addition of indium of up to ca 4 at% to a Au-10 at% Pt alloy increased both chromaticity indices, ie,a* andb* values, giving a gold tinge to the alloy: this effect was brought about by both the slight increase in reflectance in the long-wavelength range and the slight decrease in reflectance in the short-wavelength range of the visible spectrum.

Gold–platinum alloy nanoparticle assembly as catalyst for methanol electrooxidation

This paper describes preliminary findings of a thiolate-capped gold–platinum alloy nanoparticle assembly (metallic core and organic shell) as a novel catalyst for electrooxidation of methanol.

Finely divided platinum–gold alloy powders prepared in ethylene glycol

Abstract Particles of Pt–Au alloy (50:50 wt.% ratio) have been synthesized by chemical reduction of an ethylene glycol solution of AuCl 4 − and PtCl 6 2− by heating at a slow rate to 120°C. The effect of the synthesis procedure on the alloy characteristics of these particles was assessed from their X-ray diffractograms. True alloyed particles give diffractograms whose main peaks correspond neither to those of metallic gold nor to metallic platinum. Electron microscopy observation revealed that Pt–Au alloy particles are formed by aggregation of nanosized particles.

SPANISH COLONIAL AND INDIGENOUS PLATINUM: A HISTORICAL ACCOUNT OF TECHNOLOGY AND FABRICATION

The pre-Columbian Indians of Ecuador and Colombia were the first people to make use of native platinum. The dating of this metallurgy is difficult but it probably goes back to the early centuries Be and continues at least until ad 800. The Indians made use of sintering in the production of their platinum-gold alloys, some of which are plated with platinum over gold by the process of diffusion bonding of small platinum grains to the gold surface. This pre-Hispanic platinum metallurgy has no parallel in the Old World, where platinum remained unknown and unused in any quantity until the scientists of the seventeenth and eighteenth centuries began to investigate its properties. The Spanish platinum industry and the attempts of French and Spanish scientists to make use of the metal are briefly discussed.

Spanish colonial and indigenous platinum: a historical account of technology and fabrication

The pre-Columbian Indians of Ecuador and Colombia were the first people to make use of native platinum. The dating of this metallurgy is difficult but it probably goes back to the early centuries Be and continues at least until AD 800. The Indians made use of sintering in the production of their platinum-gold alloys, some of which are plated with platinum over gold by the process of diffusion bonding of small platinum grains to the gold surface. This pre-Hispanic platinum metallurgy has no parallel in the Old World, where platinum remained unknown and unused in any quantity until the scientists of the seventeenth and eighteenth centuries began to investigate its properties. The Spanish platinum industry and the attempts of French and Spanish scientists to make use of the metal are briefly discussed.