Pure Platinum Research Articles

Metal Alloy ICF Capsules Created by Electrodeposition

Electrochemical deposition is an attractive alternative to physical vapor deposition and micromachining to produce metal capsules for inertial confinement fusion (ICF). Electrochemical deposition (also referred to as electrodeposition or plating) is expected to produce full-density metal capsules without seams or inclusions of unwanted atomic constituents, the current shortcomings of micromachine and physical vapor deposition, respectively.Here, we discuss new cathode designs that allow for the rapid electrodeposition of gold and copper alloys on spherical mandrels by making transient contact with the constantly moving spheres. Electrodeposition of pure gold, copper, platinum, and alloys of gold-copper and gold-silver are demonstrated, with nonporous coatings of >40 µm achieved in only a few hours of plating. The surface roughness of the spheres after electrodeposition is comparable to the starting mandrel, and the coatings appear to be fully dense with no inclusions.A detailed understanding of the electrodeposition conditions that result in different alloy compositions and plating rates will allow for the electrodeposition of graded alloys on spheres in the near future. This report on the electrodeposition of metals on spherical mandrels is an important first step toward the fabrication of graded-density metal capsules for ICF experiments at the National Ignition Facility.

Nature of Highly Active Electrocatalytic Sites for the Hydrogen Evolution Reaction at Pt Electrodes in Acidic Media.

The hydrogen evolution reaction (HER) is one of the two processes in electrolytic water splitting. Known for more than two centuries, the HER still receives great attention in fundamental and applied science in view of its apparent simplicity (only two electrons are transferred), fast kinetics in acidic media, and promising technological applications in electrolyzers. However, the exact nature of active catalytic sites for this reaction is often uncertain, especially at nonuniform metal electrodes. Identification of such centers is important, as the HER will probably be central in future energy provision schemes, and it is simultaneously a convenient model reaction to study structure–composition–activity relations in catalysis. In this work, using simple coordination–activity considerations, we outline the location and geometric configuration of the active sites at various model Pt single-crystal electrodes. We show that when the coordination of such surface sites is optimized and their density at the surface is maximized, the experimental-specific HER activities are among the highest reported in the literature for pure platinum with a well-defined surface structure under similar conditions.

(Invited) Catalyst Design for Oxygen Reduction Reaction: Platinum Monometallic, Binary and Ternary Nanocatalyst

Improving design and/or reducing noble metal content in electrocatalysts for fuel cell electrodes while maintaining and/or increasing proton exchange membrane fuel cell (PEMFC) performance in terms of durability and power density are crucial challenges for PEMFC mass market applications. The formation of platinum alloys with transition metals represents a promising way for improving the activity of Pt-based catalysts [1-3]. Pt based alloys have indeed often demonstrated higher electrocatalytic activity towards ORR than pure platinum. On the other hand, the structure and morphology of the catalyst [4] also play very important roles in the electrocatalytic efficiency for ORR. In this context, the present study aims at systematically comparing the catalytic activity and the selectivity towards the ORR of binary and ternary catalysts based on Pt, and Au in order to determine the effects of alloyed metals, in terms of kinetics and selectivity. For this purpose, monometallic Pt/C, binary PtxM1-x/C and ternary PtxAuyMz/C (with M a transition metal) nanocatalysts supported on carbon have been first synthesized by a wet chemical method allowing the synthesis of the whole range of alloys and comprehensively characterized. The morphologies, compositions and structures of the particles were characterized by physical methods (thermogravimetric analysis, transmission electron microscopy, X-ray diffraction, atomic absorption, X-ray photoelectron spectroscopy). Electrochemical active surface areas and surface compositions were estimated by cyclic voltammetry. Electrocatalytic activity and selectivity of catalysts were studied by rotating disc and rotating ring disc electrodes. Acknowledgement: The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement #325327 (SMARTCat project) and from the ADEME (French Environment and Energy Management Agency) for its financial support through the EXALAME project. [1] M.T. Paffet, J.G. Beery, S. Gottesfeld, J. Electrochem. Soc. 135 (1988) 1431–1436. [2] C. Wang, M. Chi, D. Li, D. van der Vliet, G. Wang, Q. Lin, J. F. Mitchell, K. L. More, N. M. Markovic, V. R. Stamenkovic, ACS Catal. 1 (2011) 1355–1359. [3] T. Toda, H. Igarashi, H. Uchida, M. Watanabe, J. Electrochem. Soc. 146 (1999) 3750–3756. [4] D. Alloyeau, C. Mottet, C. Ricolleau, Nanoalloys, London: Springer-Verlag; 2012.

Performance Improvements in High-Temperature PEM Fuel Cells

The work presented here focuses on recent results obtained on degradation of PBI membranes used in membrane electrode assemblies (MEAs) for high temperature polymer electrolyte fuel cells (HTPEM) that operates in the temperature range 140-180 °C. The testing is done at 160 °C using either pure hydrogen or reformate of different compositions. Pure platinum versus PtCo alloys have been studied. The latest developments show that it is possible to reduce the Pt loading, increase the platinum utilization and achieve a long lifetime. We have shown that cells based on a thermally cured membrane proved a degradation rate of as little as 0.5 μV/h over an extended period of time. This is, to the authors’ knowledge, lower than what is ever reported for HTPEM. The degradation mechanisms over time have been studied using SEM and TEM characterization tools. It has been shown that the Pt nanocatalyst particles grow from approx. 3 to 9 nm over 17,000 hours on the cathode side, while the anode is far less affected. The durability of HTPEM can now be considered similar to low temperature PEM as shown in Fig. 1. Here, more than 15,000 hours is demonstrated in single cells at 300 mA/cm2. The degradation rate is around 4 μV/h for approx. 13,000 hours. The high operating temperature makes it possible to make commercial fuel cell systems using methanol (methanol-water mixtures) as fuel. The HTPEM cells can tolerate CO impurities up to more than 3 vol-% without significant losses. Several demonstration projects have been made, including a Fiat 500 equipped with a 5 kW methanol based fuel cell system. This car is in every day operation at a catering company in Denmark. Another project is a street sweeper with the same type and size of system as shown in Fig. 2. Figure 1

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.

Estimate of the applicability of Pd–Pt nanoalloy for data recording by the method of phase change

Based on the computer simulation, the applicability of using individual nanoclusters of Pt, Pd, and particles of the Pd–Pt nanoalloy as unites of storage of data bits in nonvolatile memory devices, store capability of which is based on the principle of the phase change of the state of the carrier of information, has been estimated. To this end, the temperature and size limits of stability of different internal structures of nanoparticles in the course of the heating (to melting) and subsequent solidification (crystallization) with different rates of heat removal have been established. The results of the computer simulation of the nanoparticles of chemically pure platinum, palladium, and their alloy with different content of Pt atoms have been compared. It has been concluded that the best material for the memory cells the store capability of which is based on the occurrence of phase transitions is the nanoclusters of the Pd–Pt alloy with 10% platinum with a diameter D ≥ 3.5 nm.

Synthesis of NiPt alloy nanoparticles by galvanic replacement method for direct ethanol fuel cell

The alloy of NiPt nanoparticles was successfully synthesized by galvanic replacement method in which Ni nanoparticles used as the templates and H2PtCl6 solution as additional reagent. The preparation conditions of Ni nanoparticle were optimized. The effect of platinum contents on the structure, morphology, magnetic and electrocatalyst of NiPt was investigated. The phase analysis by XRD showed the presence of Ni and Pt crystalline phases on the alloy. The TEM images indicated that the NiPt nanoparticles had porous crystalline structure with grain size in the range of 25 nm–30 nm. Besides, composition analysis by EDX showed that the ratios of Ni and Pt were changed with a change of the amount of H2PtCl6 using for the galvanic reaction. The magnetic properties of NiPt nanoparticles change significantly with a change of Pt composition. The NiPt nanoparticles exhibit ferromagnetic behavior depending on the amount of Pt composition. In particular, saturation magnetization decreases from 6.5 emu/g to 4.0 emu/g with the decrease of Ni:Pt ratio from 57.0:3.6 to 57.0:8.1 respectively. With lower Ni:Pt ratio (57.0:18.0), the NiPt nanoparticles exhibits superparamagnetic properties. The magnetic properties were attributed to the formation of NiPt alloy in which the electrons transfer from Pt atoms to d band of Ni. The cyclic voltammetry measurement showed that NiPt nanoparticles exhibit better ethanol oxidation in alkali medium comparing with pure Platinum.

Precision Plating of Electrogenic Cells on Microelectrodes Enhanced with Nano-Porous Platinum for Cell-Based Biosensing Applications

Microelectrode Array (MEA) devices are well established platforms for biosensing applications, however, limitations in electrode materials and cell coupling to electrodes still exist. Signal-to-noise ratio (SNR), a fabrication limitation, can be improved by reducing the impedance of the microelectrodes without increasing their physical size using conductive nanomaterials. Platinum is a well-studied conductive material that has been determined to be compatible with MEA devices, contains high electronic conductivity, is non-toxic to cells and has excellent catalytic activity. Nano-porous platinum, as compared to pure platinum, has larger surface area enabled by nano-scale definition, and as a result can lower the impedance of microelectrodes. Therefore, in this study nano-porous platinum was electroplated onto thin film gold electrodes to increase SNR in a single-well MEA device. Numerous commercial and research grade MEAs are available and have been subject to for various applications such as disease modeling and pharmaceutical screening. Although high densities of cells can increase the probability of cell-electrode coupling, only signals near electrodes will be detected. Our approach introduces a method of precise patterning of cells on electrodes to increase the probability of cell-electrode coupling and reducing inaccuracies and expenses associated with cell plating. The single-well MEA glass die was designed and fabricated to contain 64 microelectrodes (30 µm diameter with a pitch of 200 µm) and 4 internal on-chip reference electrodes. The MEA glass die fabrication was performed on a 4-inch, 500 µm thick glass wafer. First, metal traces composed of titanium and gold were deposited using lift-off lithography. Subsequently, 5 µm of SU-8 was spin coated and defined as an insulation layer. A separate printed circuit board (PCB) was designed and fabricated to contain 72 contact pads and routing traces. The biocompatible epoxy 353ND was used to package the glass die and PCB in specific orientations determined by alignment markers. Ball bonding with 20 µm diameter gold wire was used to wirebond the glass die to the PCB. A packaging technique was developed that would allow the characterization of key properties of the MEA. This technique involved using copper wire, 100 µm in diameter, and attaching it to the contact pads on the backside of PCBs using a conductive epoxy. Finally, a polystyrene culture well and lid were attached to the MEA using the epoxy, 353ND. Nano-Porous platinum electroplating solution was prepared with a combination of chloroplantinic acid, HCl and lead acetate, all diluted in DI water. Fully packaged devices containing approximately 3 mL of electrolyte were placed within the Axion BioSystems Muse for nano-porous platinum electrodeposition, utilizing the custom Application Specific Integrated Circuit (ASIC) in the system at room temperature. The nano-porous platinum electroplated devices were subsequently characterized using electrical impedance spectroscopy and cyclic voltammetry against the control devices, which contained gold electrodes. The impedance of each device was measured across a scanned frequency range of 10 Hz-100 kHz between the microelectrode, the internal reference electrode and cellular conductive media. The impedance of the nano-porous platinum devices is an order of magnitude lower than the devices with gold electrodes. Cyclic voltammograms were obtained at a scan rate of 20 mV/s in the range from -0.28 to 1.2 V vs. Ag/AgCl. RMS noise comparison between nano-porous platinum electroplated devices and control devices (gold electrodes) was determined using the Muse system and Axion’s Integrated Studio (AxIS) software. Biosensing applications for the devices were explored using electrogenic cells in combination with a precise plating technique. As depicted in Figure 1, cells were positioned in a pattern on and around electrodes to increase the probability of cell-electrode coupling. The electrical response was obtained and analyzed using the Muse system and AxIS software. SNR of action potentials recorded from cells growing on devices enhanced with nano-porous platinum electrodeposition and cells on control devices with gold electrodes were compared. Activity within neuronal networks / beat frequencies of cell patches on electrodes were monitored over the course of 2-3 weeks. The methods explored in this study not only decreases impedance of microelectrodes to increase SNR but also increases cell-electrode coupling by warranting the placement of cells next or on the electrodes by precision patterning. Future studies will aim to optimize electrode sensitivity using novel electrode materials, the porosity of different materials, and characterization using emerging analytical methods. Eventually these devices will provide in vitro systems to monitor both acute and chronic effects of drugs and toxins as well as to perform functional studies under physiological or induced pathophysiological conditions that mimic in vivo damages. Figure 1: Electrogenic cells patterned near nano-porous platinum electrode Figure 1

Computer Analysis of the Field Ion Images of Platinum Irradiated with Ar+ (E = 30 keV) Ions

The work presents the field ion microscopy images of the surface atomic layers of irradiated platinum (layer-by-layer from 1st to 5th and more distant). A specially developed algorithm and software were used for image analysis to study the effect of Ar+ ions (E = 30 keV) on the subsurface atomic structure of pure platinum. The coordinates of atoms, the brightness of their images, and their sizes were determined. The curves of the distribution of the brightness and atomic radii were built. It is shown that the width of the distributions significantly decreases when moving from the damaged surface deep into the platinum bulk, whereas the number of atoms in the field ion microscopy images increases. Field ion microscopy images with only those atoms whose brightness (or radius) is in certain range were synthesized (these atoms can be highlighted in the ionic field microscopy images). It has been established that damaged zones include the images of atoms with both abnormally low and abnormally high radii. The principal possibility of reconstruction of the 3D-picture of the irradiated metal at a temperature of liquid nitrogen (T ∼ 77 K) is shown.

Facile processes for producing robust, transparent, conductive platinum nanofiber mats.

Mechanically robust freestanding platinum (Pt) nanofiber (NF) meshes are of great interest in applications where the corrosion resistance, malleability, and stability of a pure platinum structure must be combined with high surface area for catalysis. For photoelectrochemical applications, transparent electrodes are desirable. Several 1-dimensional (1D) Pt-based materials have been developed, but energy-intensive fabrication techniques and unsatisfactory performance have limited their practical implementation in next-generation photoelectrochemical applications. Here, we introduce relatively simple yet commercially-viable methods for creating robust, free-standing PtNF mats through combined electrospinning/solution blowing and electroplating steps. The PtNFs obtained by these processes exhibited outstanding low sheet resistance (Rs) values with reasonable transparency. In addition, the PtNFs were highly bendable and stretchable. Thus, the new methods and materials presented here hold great promise for creating mechanically robust and catalytically active transparent conducting films for diverse photoelectrochemical applications.

Drift as a Function of Temperature in Platinum–Rhodium-Alloyed Thermoelements

Platinum–rhodium-alloyed thermocouples are the most commonly used high-temperature reference thermometer in national measurement institutes, second tier laboratories and industry. Despite the common use of these thermocouples, there is still a great deal that is not known about the drift processes that occur in them. Drift processes in these alloys are known to be made up of three main components: crystallographic changes, rhodium oxidation and migration, and contamination. Through careful use, contamination can be largely avoided; however, the other two processes often cannot. Research on drift in the different platinum–rhodium alloys is important because the largest uncertainty component during calibration of these thermocouple types is due to inhomogeneity, and the same mechanisms responsible for inhomogeneity are responsible for the drift. This study investigates the drift processes as a function of temperature and time for the 5 %, 13 %, 17 %, 20 %, 30 % and 40 % Rh alloys when paired with pure platinum. The use of a linear gradient furnace and high-resolution homogeneity scanner has enabled identification of drift characteristics in the temperature range $$100 \,^{\circ }$$ C to $$950 \,^{\circ }$$ C, where the bulk of reversible drift occurs. The experiments have quantified the drift rates and magnitude for thermoelements given two commonly used annealing procedures: the high-temperature quench anneal and the low-temperature vacancy anneal. Consequently, this study provides users of platinum–rhodium thermoelements with guidance on what levels of drift they should expect and exposure times before re-annealing is required. It also shows that a Pt–Rh alloy of 20 % Rh is by far the most stable and has properties comparable to the Pt–Pd thermocouple.

A Computational and Experimental Study on the Binding of Dithio Ligands to Sperrylite, Pentlandite, and Platinum

This benchmark study documents a combined computational and experimental investigation into the binding of three commercial dithio collector ligands used in industrial froth flotation processes to separate high-value minerals from lower-value materials. First-principles condensed-matter simulations showed that ethyl xanthate, N,N-diethyl dithiocarbamate, and diisobutyl dithiophospinate anions all bind least strongly to the [100] Miller index plane of the platinum-containing mineral sperrylite, followed by the [111] MI surface of the mixed nickel/iron sulfide mineral pentlandite, whereas all ligands showed the strongest binding affinity to the [111] MI surface model of pure platinum. Calculations also support experimental observations that neutral ethyl xanthogen disulfide formed upon oxidation of ethyl xanthate binds much more weakly than the monomer. A monolayer of water molecules would easily be displaced from all surfaces by any of the collector ligands. The hydroxide anion was found to have binding en...

Ultra-low platinum coverage at gold electrode surfaces: A different approach to the reversible hydrogen reaction

The hydrogen reversible reaction (HRR) with ultra-low concentrations of platinum sites supported on a gold substrate is studied with decreasing amounts of active sites (estimate coverage range from 0.006 to 10−5) at a rotating electrode in a 0.5M H2SO4 solution. These particular experimental conditions allow the voltammetric study of the HRR without diffusion limitation in the whole range of potential. In the absence of a more precise determination of the amount of platinum surface sites, a method is given to compare results obtained from distinct experimental runs. Once eliminated the contribution of gold to the current recorded, it becomes possible to normalize the currents in the entire range of platinum coverage. It shows that below 0.2V, the normalized HER and the HOR currents are linearly connected to the amount of active sites. At higher potentials the normalized currents indicate a systematic decrease of the efficiency of the active sites for HOR that deviates from linearity when their surface concentration decreases. Around the reversible potential, the voltammetric profiles obey to the Butler-Volmer formalism. The conditions of its applicability are discussed. The simulation of the experimental current allows the determination of the partial oxidation and reduction currents. The simulated reduction current is then compared to the HER current recorded in a solution without dissolved hydrogen and saturated with argon. The close fit of the two responses gives evidence for the possibility to have access to HER kinetic data free of diffusion. Finally a comparison is made between results obtained at ultra-low content of platinum active sites with pure platinum as well as for an intermediate coverage of gold with platinum.

Mechanisms for oxygen reduction reactions on Pt-rich and Pt-poor PtFe alloys as the fuel cell cathode

The mechanism of Pt-M (3d-metal)-enhanced performance compared to that of pure platinum as the cathode catalyst in fuel cells is not entirely clear. In this paper, a DFT calculation is applied to study the electronic structures of Pt-Fe alloys and ORR (Oxygen Reduced Reaction) on Pt(111), Pt-skinned Pt3Fe(111) and Pt-skinned PtFe3(111) surfaces. With the charge transfer between Pt and Fe, the electronic structure thoroughly differs from that of pure Pt. Consequently, a further change in interaction between the surface and adsorbates, which are produced during the ORR process, primarily causes the improvement in ORR performance. When used as a catalyst, the Pt-skinned Pt-Fe alloy surface is superior to the Pt surface and has three main advantages: (i) a more appropriate potential for each electron step (closer to the stand reversible potential), (ii) a smaller O2 adsorption energy, and (iii) a smaller H2O desorption energy. The theoretical results also show that the Pt-skinned PtFe3(111) surface has obviously higher activity than the Pt-skinned Pt3Fe(111), which implies that activity is improved with the increase in Fe content. This work provides a new approach to understand the excellent ORR performance of Pt-M alloys and design other non-noble metal catalysts.

Oxygen Reduction Reaction at Binary and Ternary Nanocatalysts Based on Pt, Ni and Au

Improving design and/or reducing noble metal content in electrocatalysts for fuel cell electrodes while maintaining and/or increasing proton exchange membrane fuel cell (PEMFC) performance in terms of durability and power density are crucial challenges for PEMFC mass market applications. A possible way consists in combining noble metals (Pt, Pd, Au ...) and non-noble metals for preparing binary and ternary nanocatalysts. The formation of platinum alloys with transition metals such as Ni, Co, Fe, Cr represents a promising way for improving the activity of Pt-based catalysts [1-3]. Pt based alloys have indeed often demonstrated higher electrocatalytic activity towards ORR than pure platinum. However, while non-noble metals are interesting from a cost reduction point of view, their presence may involve lower stability of the catalyst than that of pure platinum due to their dissolution [4.5], which leads to a loss of performances in PEMFC. Au addition was proposed to improve durability of the nanocatalysts [6-9]. On the other hand, the atomic structure and morphology [10] also play very important roles in the electrocatalytic efficiency for ORR. In this context, the present study aims at systematically comparing the catalytic activity and the selectivity towards the ORR of binary and ternary catalysts based on Pt, Ni, Co and Au in order to determine the best atomic ratio for this reaction, in terms of kinetics current density and of number of exchanged electrons per oxygen molecule reduced. For this purpose, monometallic (Pt/C), binary (PtxNi10-x/C and PtxCo10-x/C) and ternary (PtxAuyNiz/C and PtxAuyCoz/C) nanocatalysts supported on carbon Vulcan XC-72 have been first synthesized by a wet chemical method and comprehensively characterized. The morphologies, compositions and structures of the particles were characterized by physical methods (transmission electron microscopy, X-ray diffraction and atomic absorption), whereas metal loadings on the carbon support was determined by thermogravimetric analysis. Electrochemical active surface areas and surface compositions were estimated by cyclic voltammetry. Electrocatalytic activity, selectivity and durability of catalysts were studied by the rotating disc (Figure 1) and rotating ring disc electrodes. After having determined the best atomic ratios for the different metals, i. e. Pt7Ni3, Pt6Ni2Au2/C and Pt5Ni1.7Au3.3/C, plasma sputtering method was use to prepare alloyed PtxAuyNiz/C and Auy@PtxNiz core-shell electrodes with ultra-low metal loadings (10 µgmetal cm-2). This method is indeed very convenient for controlling the materials loading, composition and structure by controlling the physical parameters of deposition. The electrocatalytic behavior of these different electrode structures was evaluated and compared to that of chemical catalysts. Acknowledgement: The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement #325327 (SMARTCat project). Reference [1] M.T. Paffet, J.G. Beery, S. Gottesfeld, J. Electrochem. Soc. 135 (1988) 1431–1436. [2] C. Wang, M. Chi, D. Li, D. van der Vliet, G. Wang, Q. Lin, J. F. Mitchell, K. L. More, N. M. Markovic, V. R. Stamenkovic, ACS Catal. 1 (2011) 1355–1359. [3] T. Toda, H. Igarashi, H. Uchida, M. Watanabe, J. Electrochem. Soc. 146 (1999) 3750–3756. [4] M. Watanabe, K. Tsurumi, T. Mizukami, T. Nakamura, P. Stonehart, J. Electrochem. Soc. 141 (1994) 2659–2668. [5] C.F. Yu, S. Koh, J.E. Leisch, M.F. Toney, P. Strasser, Faraday Discuss. 140 (2009) 283–296. [6] D.F. Yancey, E.V. Carino, R.M. Crooks, J. Am. Chem. Soc. 132 (2010) 10988–10989. [7] J. Zhang, K. Sasaki, E. Sutter, R.R. Adzic, Science 315 (2007) 220–222. [8] K. Sasaki, H. Naohara, Y. Cai, Y.M. Choi, P. Liu, M.B. Vukmirovic, J.X. Wang, R.R. Adzic, Angew. Chem. Int. Ed. 49 (2010) 8602–8607. [9] V. Tripkovic, H.A. Hansen, J. Rossmeisl, Tejs Vegge, Phys. Chem. Chem. Phys. 17 (2015) 11647–11657. [10] D. Alloyeau, C. Mottet, C. Ricolleau, Nanoalloys, London: Springer-Verlag; 2012. Figure 1

Ir@Pt bimetallic overlayer catalysts for aqueous phase glycerol hydrodeoxygenation

Silica-alumina supported bimetallic overlayer catalysts of platinum on Ir (Ir@Pt) were synthesized using the directed deposition technique to investigate the modification of the Pt catalytic properties. Weakened hydrogen adsorption strength was obtained for Ir@Pt overlayer catalysts compared to pure platinum using hydrogen chemisorption and an ethylene hydrogenation descriptor reaction, consistent with literature computational studies. This reduced adsorption strength is expected to increase the Pt overlayer reactivity compared to pure Pt by releasing Pt active sites from strongly adsorbed H2 or CO. The effect of multiple Pt overlayer depositions is also studied, and it is postulated that overlayer catalysts with double and triple platinum overlayer deposition would form Pt multilayer structures. Multiple overlayers displayed a smaller degree of modification in H2 adsorption strength from pure Pt, compared to Ir@Pt single deposition sample. In aqueous phase glycerol hydrodeoxygenation, Ir@Pt single deposition sample showed higher turnover frequencies of glycerol conversion and C3 hydrocarbon production than pure Pt and the bimetallic alloy sample. The activity enhancement of Ir@Pt compared to pure Pt is ascribed to the weakened hydrogen adsorption of Ir@Pt, as fewer Pt active sites were blocked by strong H2 or CO adsorption. The improved selectivity toward C3 hydrocarbons of Ir@Pt compared to pure Pt suggested a feasible approach of using overlayer catalysts to manipulate the selectivity of Pt overlayer without sacrificing the Pt overlayer reactivity.

Electrochemical alcohol oxidation: a comparative study of the behavior of methanol, ethanol, propanol, and butanol on carbon-supported PtSn, PtCu, and Pt nanoparticles

Carbon-supported PtCu and PtSn (both with an atomic ratio of 3:1) nanoparticles were prepared by reducing Pt, Sn, and Cu precursors via refluxing in ethanol. They were characterized using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and transmission electron microscopy (TEM). X-ray diffraction indicated that the lattice parameter of Pt increases with the addition of Sn and decreases with the addition of Cu, indicating that both PtCu and PtSn are solid solutions. EDX analysis revealed that the compositions of these materials are close to their nominal compositions, while TEM showed that both materials presented a homogeneous particle distribution on the carbon support and low particle agglomeration. Electrochemical experiments indicated that all of the materials are electrochemically active with respect to methanol, ethanol, propanol, and butanol oxidation in H2SO4 solution. The electrochemical measurements also showed that PtSn is more active in ethanol oxidation, whereas PtCu is more active in methanol oxidation. Both materials showed similar electrooxidative activities towards propanol and butanol, and they presented higher electrochemical acidities than pure platinum for alcohol oxidation.

Tensile properties and microstructures of multilayer PtTiZr/Ti laminate composites prepared by hot pressing and rolling

The development of platinum/titanium bi-metal laminated composites is useful for improving the mechanical characteristics of platinum and for reducing platinum consumption. A multi-layered Pt0.5Ti0.2Zr/Ti laminate composite was prepared by hot pressing and rolling using foils of Pt0.5Ti0.2Zr micro-alloy and Ti. The effect of the pressing and rolling temperatures on the tensile properties and microstructures of the composite was studied. The results showed that the compaction temperature of the composite stack should not be very high, because at high temperatures, metal compounds are formed at the layer interfaces, which adversely affect the mechanical properties and structure of the composite. It was also observed that the micro-alloying method effectively improves the layer continuity and the straightness and uniformity of the laminated structures. The composites manufactured by hot pressing and large deformation rolling at 500°C exhibit excellent tensile properties and a good microstructure. The mechanical performance of the composites is significantly improved with respect to that of pure platinum.

Oxygen reduction on SILAR deposited iron oxide onto graphite felt electrode

The potential characteristics of graphite felt electrodes, modified by iron oxide, for oxygen reduction are evaluated. Modification is carried out by Successive Ion Layer Adsorption and Reaction (SILAR) method, using a solution of ferric nitrate in methanol for the adsorption of ions, and a solution of sodium hypochlorite for reaction. The reaction activity of the oxygen reduction from the air, in sodium sulfate based solution varying the number of SILAR cycles, as well as the influence of pH is investigated. By comparing the activity with pure platinum, similar activity is obtained at pH=9.2, as well as good electrode stability. Possible mechanism of the oxygen reduction on the graphite felt modified by iron oxide is discussed.

Enhanced Electrocatalytic Activity toward the Oxygen Reduction Reaction through Alloy Formation: Platinum–Silver Alloy Nanocages

Platinum–silver nanocage catalysts with a precisely defined shape and composition were synthesized using the galvanic replacement reaction (GRR) and utilized as electrocatalysts for the oxygen reduction reaction (ORR). The electrocatalytic activity of these platinum–silver nanocages was determined as a function of platinum content. The specific current density of all platinum–silver nanocages was found to be 2–3 times greater than the specific current densities previously reported for solid platinum catalysts under similar conditions. The highest specific current densities were observed for the platinum–silver nanocages with the lowest platinum content. After a thorough structural and electronic investigation by TEM, XRD, and XPS, it was determined that all platinum–silver nanocage catalysts exibit an expanded lattice compared to pure platinum materials. This resulted in a negative shift in the onset potential of the oxygen reduction reaction. However, despite this negative shift, the catalyst with a low ...