Au-Pt Alloy Research Articles

Debye temperature for binary alloys and its relationship with cohesive energy

Abstract The cohesive energy, formation enthalpies, and elastic constants of AgAl, AuAg, AuPd, AuPt, CuNi, CuPt, NiPb, NiPd, NiPt, and PtPd alloys are calculated by molecular dynamics simulation and first-principle calculation. It is found that the calculated formation enthalpies generally agree with the availible experimental data. The Debye temperatures of these alloys with different compositions are computed from the obtained elastic constants. An empirical relationship between Debye temperature and cohesive energy is developed, which is confirmed by both the simulation and calculation.

Peptide templated AuPt alloyed nanoparticles as highly efficient bi-functional electrocatalysts for both oxygen reduction reaction and hydrogen evolution reaction

Peptide driven metallic nanomaterials fabrication under mild conditions has become a significant research thrust recently, thanks to its capability to generate multifunctional materials with tunable electronic and catalytic properties. Herein, peptide Z1 is employed to fabricate a series of AuPt alloyed nanoparticles with different Au-to-Pt ratios. The morphology is examined by electron microscopic techniques, and well-defined peanut-shape is observed for Au33Pt67 while spherical particles are obtained for the other samples. The AuPt alloys demonstrate effective electrocatalytic activity toward both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) and Au33Pt67 exhibits the best bifunctional electrocatalytic performance. Its ORR activity is superior than commercial Pt/C in alkaline media, verified by the positive onset potential (+1.02 V vs. RHE) and large diffusion-limited current density, while its HER activity is comparable with Pt/C, evidenced by the small overpotential at 10 mA cm−2 (−171 mV vs. RHE) and low Tafel slope. Moreover, Au33Pt67 exhibits markedly higher long-term durability than Pt/C for both ORR and HER. The excellent activity and stability for ORR and HER are ascribed to Au alloying Pt induced synergistic effects. The results highlight the advantages of using peptide to fabricate bi-functional or multiple functional electrocatalysts with desirable activity and robust stability.

Electrochemical reduction of CO2 on compositionally variant Au-Pt bimetallic thin films

The electrocatalytic reduction of CO2 on Au-Pt bimetallic catalysts with different compositions was evaluated, offering a platform for uncovering the correlation between the catalytic activity and the surface composition of bimetallic electrocatalysts. The Au-Pt alloy films were synthesized by a magnetron sputtering co-deposition technique with tunable composition. It was found that the syngas ratio (CO:H2) on the Au-Pt films is able to be tuned by systematically controlling the binary composition. This tunable catalytic selectivity is attributed to the variation of binding strength of COOH and CO intermediates, influenced by the surface electronic structure (d-band center energy) which is linked to the surface composition of the bimetallic films. Notably, a gradual shift of the d-band center away from the Fermi level was observed with increasing Au content, which correspondingly reduces the binding strength of the COOH and CO intermediates, leading to the distinct catalytic activity for the reduction of CO2 on the compositionally variant Au-Pt bimetallic films. In addition, the formation of formic acid in the bimetallic systems at reduced overpotentials and higher yield indicates that synergistic effects can facilitate reaction pathways for products that are not accessible with the individual components.

M13 Virus-Incorporated Biotemplates on Electrode Surfaces To Nucleate Metal Nanostructures by Electrodeposition.

We report a virus-incorporated biological template (biotemplate) on electrode surfaces and its use in electrochemical nucleation of metal nanocomposites as an electrocatalytic material for energy applications. The biotemplate was developed with M13 virus (M13) incorporated in a silicate sol-gel matrix as a scaffold to nucleate Au-Pt alloy nanostructures by electrodeposition, together with reduced graphene oxide (rGO). The phage when engineered with Y3E peptides could nucleate Au-Pt alloy nanostructures, which ensured adequate packing density, simultaneous stabilization of rGO, and a significantly increased electrochemically active surface area. Investigation of the electrocatalytic activity of the resulting sol-gel composite catalyst toward methanol oxidation in an alkaline medium showed that this catalyst had mass activity greater than that of the biotemplate containing wild-type M13 and that of monometallic Pt and other Au-Pt nanostructures with different compositions and supports. M13 in the nanocomposite materials provided a close contact between the Au-Pt alloy nanostructures and rGO. In addition, it facilitated the availability of an OH--rich environment to the catalyst. As a result, efficient electron transfer and a synergistic catalytic effect of the Au and Pt in the alloy nanostructures toward methanol oxidation were observed. Our nanocomposite synthesis on the novel biotemplate and its application might be useful for developing novel clean and green energy-generating and energy-storage materials.

Electrochemical Detection of Hydroxylamine via Au-Pt Alloy Nanoparticle-modified Single-walled Carbon Nanotube Electrodes.

In the present study, we developed an electrochemical sensor for highly sensitive detection of hydroxylamine using Au-Pt alloy nanoparticles. Au-Pt alloy nanoparticles were electrochemically deposited on a working electrode made of single-walled carbon nanotubes. The framework composition in the Au-Pt alloy nanoparticle was easily controlled by adjusting the Au3+:Pt4+ composition ratio in the precursor solution. Morphological and chemical characterizations of the resulting Au-Pt alloy nanoparticles were performed using field emission scanning electron microscopy, X-ray diffraction, and energy dispersion X-ray spectroscopy. When the Au3+:Pt4+ ratio in the precursor solution was 1:5, the ratio of Au:Pt atom in alloy nanoparticle was about 6:4. Au60Pt40 alloy nanoparticles were found to have the optimum synthetic ratio for hydroxylamine detection. The electrocatalytic performance of Au-Pt alloy nanoparticles in the presence of hydroxylamine was also characterized using cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In the chronoamperometric detection of hydroxylamine, the sensor exhibited a detection limit of 0.80 μM (S/N = 3) and a high sensitivity of 184 μA mM-1 cm-2. Moreover, the amperometric response of the sensor in 1 mM hydroxylamine was stable for a long time (450 s). Long-term stability tests showed that the current responses to hydroxylamine were 96, 91 and 85% of the initial signal value after storage for 5, 10, and 20 days, respectively.

Preparation of an Au-Pt alloy free from artifacts in magnetic resonance imaging

PurposeWhen magnetic resonance imaging (MRI) is performed on patients carrying metallic implants, artifacts can disturb the images around the implants, often making it difficult to interpret them appropriately. However, metallic materials are and will be indispensable as raw materials for medical devices because of their electric conductivity, visibility under X-ray fluoroscopy, and other favorable features. What is now desired is to develop a metallic material which causes no artifacts during MRI. Materials and methodsIn the present study, we prepared a single-phase and homogeneous Au-Pt alloys (Au; diamagnetic metal, and Pt; paramagnetic metal) by the processing of thermal treatment. Volume magnetic susceptibility was measured with a SQUID Flux Meter and MRI artifact was evaluated using a 1.5-T scanner. ResultsAfter final thermal treatment, an entirely recrystallized homogeneous organization was noted. The Au-35Pt alloy was shown to have a volume magnetic susceptibility of −8.8ppm, causing almost free from artifacts during MRI. ConclusionsWe thus prepared an Au-35Pt alloy which had a magnetic susceptibility very close to that of living tissue and caused much fewer artifacts during MRI. It is promising as a material for spinal cages, intracranial electrodes, cerebral aneurysm embolization coils, markers for MRI and so on.

Selective deposition of Au-Pt alloy nanoparticles on ellipsoidal zirconium titanium oxides for reduction of 4-nitrophenol

Au-Pt alloy nanoparticles that are selectively anchored on TiO2 surface of the ellipsoidal zirconium titanium composite oxides were successfully prepared by a facile two-step method: prefabricated binary composite oxides on the ellipsoidal Fe2O3@SiO2 by a versatile cooperative template-directed coating method, and then in situ formation of Au-Pt alloy NPs with Sn2+ as the reduction agent. The alloy catalysts were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The result suggested that highly dispersive and ultrafine Au-Pt alloy nanoparticles were deposited onto TiO2 surface of the binary oxides solely. The particle size of nanoalloys was closely related to the ratio of Zr: Ti in the composite oxides shell. Increasing the content of Zr element led to a growth in the size of alloy nanoparticles. When used as catalysts for the reduction of 4-nitrophenol, the prepared supported alloyed catalysts exhibited high catalytic activity, and the sample could be easily recycled without a significant decrease of the catalytic activity.

Au-Pt alloy nanoparticles obtained by nanosecond laser irradiation of gold and platinum bulk targets in an ethylene glycol solution

Au-Pt alloy nanoparticles (NPs) of different compositions ( Au0Pt100 , Au30Pt70 , Au50Pt50 , Au70Pt30 , and Au100Pt0 were obtained using the nanosecond laser ablation of gold and platinum bulk targets in ethylene glycol, followed by mixing highly monodisperse Au and Pt nanocolloids, for the first time. UV-vis absorption spectra of NPs showed that by increasing the Au content in the Au-Pt NPs, the surface plasmon resonance (SPR) peak red-shifted, from 260 to 573nm in a nonlinear way. In addition, the mean crystalline size, crystal structure, d-spacing, and lattice parameters of NPs were estimated from the XRD spectra. Microscopy studies revealed the most NPs have a spherical or near-spherical shape, and the average sizes of Au0Pt100 , Au30Pt70 , Au50Pt50 , Au70Pt30 , and Au100Pt0 NPs were calculated to be 12.50, 14.15, 18.53, 19.29, and 26.38nm, respectively. Also, the chemical identity of the molecules adhering to the NPs surface was considered by Raman and FT-IR spectroscopy techniques. Among different synthesis methods, the demonstrated technique allows easy synthesis of alloy NPs in aqueous media at room temperature with no formation of by-products.

Pt catalysts supported on ion exchange resins for selective glycerol oxidation. Effect of Au incorporation

In this paper, bimetallic Pt-Au catalysts were studied for the selective liquid phase oxidation of glycerol. The support used was a macroporous weak anion exchange resin. Two different preparation methods were employed: simultaneous exchange of both metals, and a sequential exchange using the controlled surface reaction technique. PtAu catalysts with a total metal content of 0.4wt% were prepared, with different Pt:Au molar ratios: 1:1; 2:1 and 1:2. The monometallic Au catalyst resulted inactive for the reaction. Nevertheless, it was found that the addition of Au improved the monometallic Pt catalyst activity. XPS results suggest the formation of a Pt-Au alloy, which could be related with conversion improvement. Not only the presence of Pt-Au alloyed particles, but also the Pt/Au ratio on the catalyst surface influences the activity. When the Au particles reduced on top of Pt (controlled surface reaction method), the Pt amount exposed at the catalyst surface was considerably reduced. For this reason, this Pt-Au sample did not show a significant improvement of conversion with respect to the monometallic platinum.

Facile Aqueous-Phase Synthesis of the PtAu/Bi2O3 Hybrid Catalyst for Efficient Electro-Oxidation of Ethanol.

In this work, we present a facile aqueous-phase synthesis of a hybrid catalyst consisting of PtAu alloy supported on Bi2O3 microspheres. Multistep reduction of HAuCl4 and K2PtCl4 salts on Bi2O3 and subsequent annealing lead to the formation of this hybrid catalyst. To the best of our knowledge, this is the first report of using Bi2O3 as a catalyst support in fuel cell applications. The material was characterized by powder X-ray diffraction and various microscopic techniques. This composite showed remarkable activity as well as stability toward the electro-oxidation of ethanol in comparison to commercially available Pt/C. The order of the reactivity was found to be commercial Pt/C (50.4 mA/m2mgPt-1) < Pt/Bi2O3(10) (108 mA/m2mgPt-1) < PtAu/Bi2O3(10) (459 mA/m2mgPt-1). The enhancement in the activity can be explained through cooperative effects, namely, ligand effects of gold and Bi2O3 support, which helps in removing carbon monoxide molecules to avoid the poisoning of the Pt active sites.

(Invited) Alkaline Fuel Cells (AFCs) and Alkaline Membrane Fuel Cells ( AMFCs)

I was fortunate to have many technical discussions with Russ Kunz over the years and learnt a lot from him. Russ was a rarely encountered combination of scientist and technologist , a combination which is prerequisite for being a leader, as he was, in the field of fuel cell development. I chose the subject of this talk having been a common theme in our technical discussions, as Russ was the house expert at UTC for the alkaline fuel cells (AFCs) used in space applications, whereas I got intrigued in recent years by the potential of alkaline membrane fuel cells ( AMFCs) which share key features with the AFC while aiming to operate with no liquid electrolyte. The talk will accordingly review first some interesrting key features of materials and processes in AFCs about which I learnt to large degree from discussions with Russ. The first subject is the ORR in highly alkaline electrolytes and why gold is actually the active catalyst component in AFCs , being used as a AuPt alloy with the Pt serving basically just to harden the metal catalyst particles. The high activity of gold as ORR catalyst in alkaline media, does not fit the extensively taught volcano shaped relationship between M-O bond strength and ORR rate at a metal M. Gold is way down on the descending branch of the volcano plot in acid electrolyte, but is more active than Pt in alkaline media. This has been explained by the stabilization of a peroxide anion intermediate formed in alkaline electrolytes (HO2- or O2=) on the electrolyte side of the metal electrolyte interface, thereby removing the need of significant M-O interaction to stabilize the HOOads intermediate formed in acid. This opens the door for metals of very low affinity to oxygen to become very active ORR electrocatalysts thanks to the low overpotential they require to generate oxide free metal sites. In the case of the AMFCs, this high activty of coinage metals in alkaline environment is the basis for the possible choice of silver as ORR electrocatalyst, having activity in alkaline electrolyte comparable to Pt, at a market price which is about 1% that of Pt. One central aspect which is quite different in AFCs and AMFCs, is water managment. The AMFC presents a significant challenge of combined tendencies for cathode dry-out and anode flooding, originating form the cell water product forming in the anode ( fuel side) and consumed by the electrode process in the cathode ( air side). The resulting demands of water diffusivity through the cell membrane as well as electrode structures required to achieve passive control of the water profile in the AMFCs , staisfying the ORR consumption and ionomer hydration demands, will be described. Finally, the HOR in alkaline media in general and in the AMFC in particular has received significant attention recently. The rate of the HOR at Pt in 0.1-1MKOH solutions is significantly lower vs. the rate in acid. However, AMFC polarization curves to be presented show a performance that is not much below that of PEMFC in operation on hydrogen and air. This is achieved with HOR catalyzed by very low loadings of Pt in the form of alloy ( or other combination ) with an oxophilic metal component which facilitates completion of the HOR process and, securing optimized cell hydration under current.

Tunability of the Adsorbate Binding on Bimetallic Alloy Nanoparticles for the Optimization of Catalytic Hydrogenation.

In this paper, we show that PtAu and PdAu random alloy dendrimer-encapsulated nanoparticles with an average size of ∼1.6 nm have different catalytic activity trends for allyl alcohol hydrogenation. Specifically, PtAu nanoparticles exhibit a linear increase in activity with increasing Pt content, whereas PdAu dendrimer-encapsulated nanoparticles show a maximum activity at a Pd content of ∼60%. Both experimental and theoretical results suggest that this contrasting behavior is caused by differences in the strength of H binding on the PtAu and PdAu alloy surfaces. The results have significant implications for predicting the catalytic performance of bimetallic nanoparticles on the basis of density functional theory calculations.

Epitaxial growth of zigzag PtAu alloy surface on Au nano-pentagrams with enhanced Pt utilization and electrocatalytic performance toward ethanol oxidation reaction

Improving Pt utilization is of fundamental importance for many significant processes in energy conversion, which is strongly dependent on the surface structure of used catalysts. Based on the traditional Pt-on-Au system which has been proved to be an ideal nanostructure for improving the catalytic activity and stability of Pt, and the recent follow-up studies on this system, we introduce here a new strategy for fabricating Pt surface with high-index facets over the Pt-on-Au system. To achieve this goal, we elaborately designed and fabricated a unique zigzag PtAu alloy nanosurface on Au nano-pentagrams (PtAu/Au NPs) through epitaxial growth of Pt along the high-index facets on the pre-synthesized Au nano-pentagrams. Owing to the surface electronic interaction between Au and Pt and the exposed high-index facets from the unique morphology of zigzag PtAu alloy nanosurface, the as-prepared PtAu/Au NPs exhibited excellent electrocatalytic performance toward ethanol oxidation reaction (EOR) in alkaline condition. The specific activity (8.3mAcm−2) and mass activity (4.4Amg−1) obtained from PtAu/Au NPs are about 5.2 and 5.5 times, respectively, higher than those from commercial Pt/C for EOR.

Simple synthesis of hierarchical AuPt alloy nanochains for construction of highly sensitive hydrazine and nitrite sensors

Herein, a single-step co-reduction aqueous route was designed for preparation of hierarchical AuPt alloy nanochains, firstly using amprolium hydrochloride as a new stabilizing agent and structure-director. The morphology, structure, composition, and size of the products were characterized by a series of technique. The growth mechanism of AuPt nanochains was discussed in details. The AuPt nanochains modified glassy carbon electrode showed the improved analytical performances for determination of nitrite and hydrazine. The linear ranges of nitrite are 0.5–366.4μM and 466.4–2666.4μM for the two segments, and the detection limit is 0.03μM (S/N=3). The linear ranges of hydrazine are 5.0–116.4μM and 166.4–2666.4μM for the two segments, along with the low detection limit of 0.26μM (S/N=3). The performances of AuPt nanochains were superior to those of individual Pt and Au nanoparticles. It is ascribed to the specific hierarchical structures and synergistic effects of the bimetals.

High-temperature oxidation behaviors and surface oxide color of Pd-free, Au-Pt-based metal-ceramic alloys for dental applications

The effects of small additions of oxide-forming elements (In, Fe, Sn, or Zn) on high-temperature oxidation behaviors and surface oxide colors in experimental Pd-free, Au-Pt-based metal-ceramic alloys for dental applications were investigated by means of spectrophotometric colorimetry, thin-film X-ray diffraction, and field-emission electron probe microanalysis. Three mirror-polished plate samples sized 10 × 10 × 0.5 mm3 from each alloy were subjected to the oxide-forming heat treatments at 950 °C for 10 min in air and then submitted to the above-mentioned investigations. The sole addition of Fe or Sn to the parent Au-10 at.% Pt alloy (AP10) formed very thin external oxide layers of Fe2O3 or SnO2, respectively. Chromaticity indices for these oxidized surfaces largely varied with concentrations of Fe or Sn due to light interference phenomena. On the other hand, the sole addition of In to the parent AP10 alloy developed In2O3 precipitates by the internal oxidation mechanism. Their surface colors did not change significantly regardless of In concentrations. It was highlighted that the combinative addition of 2 at.% In and Fe or Sn to the AP10 alloy well developed In2O3 precipitates in the Au-Pt alloy substrate by the internal oxidation mechanism. Owing to this significant effect of In inclusion, all of the oxidized ternary AP10-In and quaternary (AP10-In2)-Fe/Sn alloys showed similar surface oxide colors with a* coordinates (red-green direction) of nearly +4 and b* coordinates (yellow-blue direction) of nearly +11, which were pale yellow-brown subjectively. Results of this study are expected to be useful in designing esthetic and novel Pd-free, Au-Pt-based metal-ceramic alloys for dental applications.

Self-Supported PtAuP Alloy Nanotube Arrays with Enhanced Activity and Stability for Methanol Electro-Oxidation.

Inhibiting CO formation can more directly address the problem of CO poisoning during methanol electro-oxidation. In this study, 1D self-supported porous PtAuP alloy nanotube arrays (ANTAs) are synthesized via a facile electro-codeposition approach and present enhanced activity and improved resistance to CO poisoning through inhibiting CO formation (non-CO pathway) during the methanol oxidation reaction in acidic medium. This well-controlled Pt-/transition metal-/nonmetal ternary nanostructure exhibits a specific electroactivity twice as great as that of PtAu alloy nanotube arrays and Pt/C. At the same time, PtAuP ANTAs show a higher ratio of forward peak current density (If ) to backward peak current density (Ib ) (2.34) than PtAu ANTAs (1.27) and Pt/C (0.78). The prominent If /Ib value of PtAuP ANTAs indicates that most of the intermediate species are electro-oxidized to carbon dioxide in the forward scan, which highlights the high electroactivity for methanol electro-oxidation.

Laser-Irradiation-Induced Melting and Reduction Reaction for the Formation of Pt-Based Bimetallic Alloy Particles in Liquids.

Laser melting in liquids (LML) is one of the most effective methods to prepare bimetallic alloys; however, despite being an ongoing focus of research, the process involved in the formation of such species remains ambiguous. In this paper, we prepared two types of Pt-based bimetallic alloys by LML, including Pt-Au alloys and Pt-iron group metal (iM=Fe/Co/Ni) alloys, and investigated the corresponding mechanisms of alloying process. Detailed component and structural characterizations indicate that laser irradiation induced a quite rapid formation process (not exceeding 10 s) of Pt-Au alloy nanospheres, and the crystalline structures of Pt-Au alloys is determined by the monometallic constituents with higher content. For Pt-iM alloys, we provide direct evidence to support the conclusion that FeOx /CoOx /NiOx colloids can be reduced to elementary Fe/Co/Ni particles by ethanol molecules during laser irradiation, which then react with Pt colloids to form Pt-iM sub-microspheres. These results demonstrate that LML provides an optional route to prepare Pt-based bimetallic alloy particles with tunable size, components, and crystalline phase, which should have promising applications in biological and catalysis studies.

Characterisation and radiolysis of modified lithium orthosilicate pebbles with noble metal impurities

Modified lithium orthosilicate (Li4SiO4) pebbles with additions of titanium dioxide (TiO2) are suggested as an alternative tritium breeding ceramic for the European solid breeder test blanket module. The noble metals – platinum (Pt), gold (Au) and rhodium (Rh), can be introduced into the modified Li4SiO4 pebbles during the melt-based process, due to the corrosion of Pt-Rh and Pt-Au alloy crucible components. In this study, the surface microstructure, chemical and phase composition of the modified Li4SiO4 pebbles with different contents of the noble metals was analysed. The influence of the noble metals on the radiolysis was evaluated after irradiation with accelerated electrons (E=5MeV), up to 12MGy absorbed dose at 300–345K in a dry argon atmosphere. Using electron spin resonance (ESR) spectroscopy, it was determined that the noble metals (up to 300ppm) do not significantly influence the formation and accumulation of radiation-induced defects (RD) in the modified Li4SiO4 pebbles.

AuPt Alloy Nanostructures with Tunable Composition and Enzyme-like Activities for Colorimetric Detection of Bisulfide

Tuning the enzyme-like activity and studying the interaction between biologically relevant species and nano-enzymes may facilitate the applications of nanostructures in mimicking natural enzymes. In this work, AuPt alloy nanoparticles (NPs) with varying compositions were prepared through a facile method by co-reduction of Au3+ and Pt2+ in aqueous solutions. The composition could be tuned easily by adjusting the molar ratios of added Pt2+ to Au3+. It was found that both peroxidase-like and oxidase-like activity of AuPt alloy NPs were highly dependent on the alloy compositions, which thus suggesting an effective way to tailor their catalytic properties. By investigating the inhibitory effects of HS− on the enzyme-like activity of AuPt alloy NPs and natural enzyme, we have developed a method for colorimetric detection of HS− and evaluation of the inhibiting effects of inhibitors on natural and artificial enzymes. In addition, the responsive ability of this method was influenced largely by the composition: AuPt alloy NPs show much lower limit of detection for HS− than Pt NPs while Pt NPs show wider linear range than AuPt alloy NPs. This study suggests the facile way not only for synthesis of alloy nanostructures, but also for tuning their catalytic activities and for use in bioanalysis.

Cell death affected by dental alloys: Modes and mechanisms.

Previous reports have demonstrated that ions released from dental alloys might cause cytotoxicity. However, how dental alloys influence the organism has not been extensively studied. In order to make it clear, the cytotoxic effect of four dental alloys on L929 cells was evaluated by flow cytometry (FCM) and Real-time quantitative PCR assay (Real-time qPCR) to identify the cell death mode and its biological mechanism. The cells were treated with the leach liquors of cobalt-chromium (Co-Cr), commercially pure titanium (CP-Ti), palladium-based (Pd-based) and gold-platinum (Au-Pt) alloys for 48 and 72 h. FCM results indicated, apart from Au-Pt alloy, the major cell death of dental alloys was time-dependent early apoptosis rather than necrosis/late apoptosis. Caspase 3 and Caspase 9 mRNA expression were determined by Real-time qPCR, and shared the same trend in each group over time. Hence, except for Au-Pt alloy, dental alloys might cause time-dependent early apoptosis via the intrinsic pathway.