PtRu Alloy Research Articles

Nanoporous PtRu Alloys for Electrocatalysis

We describe a facile route to the straightforward fabrication of nanoporous (NP) PtRu alloys with predetermined bimetallic compositions. Electron microscopy and X-ray diffraction characterizations demonstrate that selective etching of Al from ternary PtRuAl source alloys generates three-dimensional bicontinuous NP-PtRu alloy nanostructures with a single-phase face-centered-cubic crystalline structure. X-ray photoelectron spectroscopy shows a slight electronic structure modification of Pt by alloying with Ru as well as uniform surface and bulk bimetallic ratio. With characteristic structural dimensions less than 5 nm, these high surface area bimetallic nanostructures show distinct electrocatalytic performance as the Ru content varies within the structure. Among all samples, NP-Pt(70)Ru(30) shows the highest specific activity as well as the most negative onset potential toward methanol oxidation reaction. NP-Pt(50)Ru(50) was found to possess a similar specific activity to the commercial E-TEK Pt(50)Ru(50)/C catalyst, but its onset and peak potentials are about 70 mV more negative. CO stripping experiments demonstrate that the adsorption of CO is the weakest on NP-Pt(70)Ru(30), and further increasing the Ru content actually shifts the CO stripping peak to a more positive potential. Thus, the overall sequence for CO-tolerance is NP-Pt(70)Ru(30) > NP-Pt(50)Ru(50) approximately = Pt(50)Ru(50)/C > NP-Pt(30)Ru(70) > Pt/C.

Electrodeposition of Arrays of Ru, Pt, and PtRu Alloy 1D Metallic Nanostructures

Arrays of Ru, Pt, and PtRu one dimensional (1D) nanowires (NWs) and nanotubes (NTs) were prepared by electrodeposition through the porous structure of an anodic aluminum oxide (AAO) membrane. In each case, micrometer-long NW and NT were formed with an outer diameter of ca. , close to the interior diameter of the porous AAO membrane. Arrays of NW and NT can be formed by varying the metallic salt concentration, the applied potential, and the conductivity of the electrolyte. The Ru and Pt deposition rates were measured in the various deposition conditions, using an electrochemical quartz crystal microbalance. The mechanisms responsible for the formation of Ru and Pt NW and NT are discussed based on the observed deposition rates and models found in the literature. Finally, it is shown that arrays of PtRu alloy NT and NW can be readily prepared and their compositions can be varied over the whole compositional range by changing the metallic salt concentration of the electrodeposition bath.

Preparation, characterization, and kinetic evaluation of dendrimer-derived bimetallic Pt–Ru/SiO 2 catalysts

A series of silica-supported Pt, Ru, and Pt–Ru catalysts has been synthesized using dendrimer–metal nanocomposite (DMN) precursors prepared by both co- and sequential complexation with metal salts. The catalysts have been characterized by several techniques, including electron microscopy, temperature-programmed titration of adsorbed oxygen, and X-ray diffraction. Liquid-phase selective hydrogenation of 3,4-epoxy-1-butene (EpB) was used as a probe reaction to evaluate their catalytic performance. The bimetallic catalyst prepared by the co-complexation method exhibits a superior catalytic activity compared to the sequential one, and is much more active than a conventional catalyst prepared by incipient wetness. The activity enhancement is attributed to a bifunctional performance of the PtRu alloy sites created, based on a strong correlation between turnover frequencies, and both the alloy compositions and metal surface site distributions. In addition, the co-complexation catalyst is selective toward crotonaldehyde, suggesting that this reaction pathway is favored on the PtRu sites.

Understanding Electrocatalytic Activity Enhancement of Bimetallic Particles to Ethanol Electro-oxidation. 1. Water Adsorption and Decomposition on PtnM (n = 2, 3, and 9; M = Pt, Ru, and Sn)

The fundamental assumption of the bi-functional mechanism for PtSn alloy to catalyze ethanol electro-oxidation reaction (EER) is that Sn facilitates water dissociation and EER occurs over Pt site of the PtSn alloy. To clarify this assumption and achieve a good understanding about the EER, H(2)O adsorption and dissociation over bimetallic clusters PtM (M=Pt, Sn, Ru, Rh, Pd, Cu and Re) are systematically investigated in the present work. To discuss a variety of effects, Pt(n)M (n=2, and 3; M=Pt, Sn and Ru), one-layer Pt(6)M (M=Pt, Sn and Ru), and two-layer (Pt(6)M)Pt(3) (M=Pt, Sn, Ru, Rh, Pd, Cu and Re) clusters are used to model the PtM bimetallic catalysts. Water exhibits atop adsorption on Pt and Ru sites of the optimized clusters Pt(n)M (n=2, and 3; M=Pt and Ru), yet bridge adsorption on Sn sites of Pt(2)Sn as well as distorted tetrahedral Pt(3)Sn. However, in the cases of one-layer Pt(6)M and two-layer Pt(9)M cluster models water preferentially binds to all of investigated central atom M of surface layer in atop configuration with the dipole moment of water almost parallel to the cluster surface. Water adsorption on the Sn site of Pt(n)Sn (n=2 and 3) is weaker than those on the Pt site of Pt(n) (n=3 and 4) and the Ru site of Pt(n)Ru (n=2 and 3), while water adsorptions on the central Sn atom of Pt(6)Sn and Pt(9)Sn are enhanced so significantly that they are even stronger than those on the central Pt and Ru atoms of PtnM (n=6 and 9; M=Pt and Ru). For all of the three cluster models, energy barrier (E(a)) for the dissociation of adsorbed water over Sn is lower than over Ru and Pt atoms (e.g., E(a): 0.78 vs 0.96 and 1.07 eV for Pt(9)M), which also remains as external electric fields were added. It is interesting to note that the dissociation energy on Sn site is also the lowest (E(diss): 0.44 vs 0.61 and 0.67eV). The results show that from both kinetic and thermodynamic viewpoints Sn is more active to water decomposition than pure Pt and the PtRu alloy, which well supports the assumption of the bi-functional mechanism that Sn site accelerates the dissociation of H(2)O. The extended investigation for water behavior on the (Pt(6)M)Pt(3) (M=Pt, Sn, Ru, Rh, Pd, Cu and Re) clusters indicate that the kinetic activity for water dissociation increases in the sequence of Cu < Pd < Rh < Pt < Ru < Sn < Re.

Ultrathin Pt-Based Alloy Nanowire Networks: Synthesized by CTAB Assistant Two-Phase Water−Chloroform Micelles

Ultrathin Pt-based PtM (M = Pd, Ru, Au, Fe) alloy nanowire networks could be facilely synthesized using a soft template formed by cetyltrimethylammonium bromide in a two-phase water−chloroform system. The as-synthesized Pt-based alloyed nanowires show the fcc crystal phase. They have an average diameter of ∼2.3 nm and form porous nanonetworks, which can be potentially used for a number of catalytic applications. It was found that PtRu alloy nanonetworks showed more efficient catalytic activity for the hydrogenation of azo bonds in methyl orange than that of PtPd, PtAu, and pure Pt.

Nano-architectured Pt-Mo Anode Electrocatalyst for High CO-tolerance in PEM Fuel Cells

PEM fuel cell MEAs with Nafion electrolytes and common cathodes were tested with Pt0.8Mo0.2 alloy and MoOx@Pt core-shell anode electrocatalysts for anode CO tolerance and short-term stability to corroborate earlier thin-film RDE results. Polarization curves at 70 {degree sign}C for the Pt0.8Mo0.2 alloy in H2 with 25 to 1000 ppm CO showed a significant increase in CO tolerance in comparison to PtRu electrocatalysts. MoOx@Pt core-shell electrocatalysts, which showed extremely high activity for H2 in 1000 ppm CO during RDE studies, performed poorly in MEA testing, in comparison to the PtMo and PtRu alloys on a current per total catalyst loading basis. The discrepancy is attributed to residual stabilizer from the core-shell synthesis impacting catalyst-ionomer interfaces. Nonetheless, the MoOx@Pt electrochemical performance, with its reduced Pt content, is comparable or superior to the highly active Pt0.8Mo0.2 electrocatalyst for CO concentrations of 250 ppm or lower on a per gram of precious metal basis.

Polyaniline Coated Active Carbon as Binary Catalysts Support for Direct Methanol Fuel Cell

Conducting polymer coated graphitized active carbon as fuel cell catalysts support improves both the catalytic performance and stability. The PANi coating prevent aggregation and the loss of particles and shows improved long-term stability. X-ray diffraction indicated the Pt/Ru alloy is homogeneous and lacks Pt-core Ru-shell structure. The superior fuel cell performance and better electrocatalytic stability observed for Pt-Ru/P1ACg are attributed from its high degree of Pt-Ru alloy, and high active surface area. This study unveils a new design of durable catalysts by coating a layer of conducting polymer on carbon support which improves catalytical activity, CO tolerance and stability over other catalysts based on the current art.

Facile synthesis of bimodal porous silica and multimodal porous carbon as an anode catalyst support in proton exchange membrane fuel cell

A simple and easy sol–gel approach has been developed to directly synthesize in situ three-dimensionally interconnected uniform ordered bimodal porous silica (BPS) incorporating both the macroporosity and mesoporosity in the lattice without extra synthesis process performed in previous work. Multimodal porous carbon (MPC) was fabricated through the inverse replication of the BPS. The unique structural characteristics such as well-developed 3-D interconnected ordered macropore framework with open mesopores embedded in the macropore walls, large surface area (1120 m 2 g −1) and mesopore volume (1.95 cm 3 g −1) make MPC very attractive as an anode catalyst support in polymer exchange membrane fuel cell. The MPC-supported Pt-Ru alloy catalyst has demonstrated much higher power density toward hydrogen oxidation than the commercial carbon black Vulcan XC-72-supported ones.

Preparation of Well-Alloyed PtRu/C Catalyst by Sequential Mixing of the Precursors in a Polyol Method

A well-alloyed and highly CO-tolerant 45 wt % PtRu/C catalyst was prepared by sequential mixing of the precursors in a polyol method. The alloying degree of the PtRu/C catalyst was much higher than that of the conventional PtRu/C catalyst prepared by simultaneous mixing of the precursors in the polyol method. In the sequential mixing approach, Pt and Ru compounds were reduced at the same time because was partly reduced to before the addition of , which promoted PtRu alloy formation, and subsequent reduction treatment by ethylene glycol at a high temperature further improved the alloying degree. Greater CO tolerance of the well-alloyed PtRu/C catalyst was verified by a negative shift in peak potential of electro-oxidation in CO stripping voltammetry. The well-alloyed PtRu/C catalyst showed a better single-cell performance than the conventional and commercial PtRu/C catalysts when the anode was fed with CO-contaminated .

Methanol Electro-Oxidation on Pt-Ru Alloy Nanoparticles Supported on Carbon Nanotubes

Carbon nanotubes (CNTs) have been investigated in recent years as a catalyst support for proton exchange membrane fuel cells. Improved catalyst activities were observed and attributed to metal-support interactions. We report a study on the kinetics of methanol electro-oxidation on CNT supported Pt-Ru alloy nanoparticles. Alloy catalysts with different compositions, Pt53Ru47/CNT, Pt69Ru31/CNT and Pt77Ru23/CNT, were prepared and investigated in detail. Experiments were conducted at various temperatures, electrode potentials, and methanol concentrations. It was found that the reaction order of methanol electro-oxidation on the PtRu/CNT catalysts was consistent with what has been reported for PtRu alloys with a value of 0.5 in methanol concentrations. However, the electro-oxidation reaction on the PtRu/CNT catalysts displayed much lower activation energies than that on the Pt-Ru alloy catalysts unsupported or supported on carbon black (PtRu/CB). This study provides an overall kinetic evaluation of the PtRu/CNT catalysts and further demonstrates the beneficial role of CNTs.

Structural and Architectural Evaluation of Bimetallic Nanoparticles: A Case Study of Pt−Ru Core−Shell and Alloy Nanoparticles

A comprehensive structural/architectural evaluation of the PtRu (1:1) alloy and Ru@Pt core-shell nanoparticles (NPs) provides spatially resolved structural information on sub-5 nm NPs. A combination of extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), pair distribution function (PDF) analyses, Debye function simulations of X-ray diffraction (XRD), and field emission transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS) analyses provides complementary information used to construct a detailed picture of the core/shell and alloy nanostructures. The 4.4 nm PtRu (1:1) alloys are crystalline homogeneous random alloys with little twinning in a typical face-centered cubic (fcc) cell. The Pt atoms are predominantly metallic, whereas the Ru atoms are partially oxidized and are presumably located on the NP surface. The 4.0 nm Ru@Pt NPs have highly distorted hcp Ru cores that are primarily in the metallic state but show little order beyond 8 A. In contrast, the 1-2 monolayer thick Pt shells are relatively crystalline but are slightly distorted (compressed) relative to bulk fcc Pt. The homo- and heterometallic coordination numbers and bond lengths are equal to those predicted by the model cluster structure, showing that the Ru and Pt metals remain phase-separated in the core and shell components and that the interface between the core and shell is quite normal.

The effects of ruthenium-oxidation states on Ru dissolution in PtRu thin-film electrodes

The effects of ruthenium (Ru)-oxidation states were investigated on Ru dissolution from PtRu thin-film electrodes, with the 200 cycles between 0.4 and 1.05 V (versus normal hydrogen electrode). The Ru-oxidation states of the PtRu thin films were systematically modified by an anodic (oxidation) treatment. The anodic-treated PtRu electrodes, whose methanol-oxidation activity was similar to untreated electrodes before the 200 cycles, showed a remarkable decrease in methanol oxidation after the cycles, because of the Ru dissolution from the PtRu surface. The results suggest that the Ru-oxide species are the origin of Ru dissolution in the PtRu alloy.

Electro-oxidation of ethanol and ethylene glycol on carbon-supported nano-Pt and -PtRu catalyst in acid solution

Present paper reports kinetics of electro-oxidation of ethanol (EtOH) and ethylene glycol (EG) onto Pt and PtRu nanocatalysts of different compositions in the temperature range of 298–318 K. These catalysts have been characterized by SEM, EDX, XRD, CV and amperometry. It has been observed that apparent activation energies for oxidation of EtOH and EG pass through a minimum at about 15–20 at.% of Ru in the PtRu alloy catalysts. Anodic peak current vs. composition curve also shows a maximum around this composition. The results have been explained by a geometric model, which proposes requirement of an ensemble of three Pt atoms with an adjacent Ru atom onto PtRu surface for an efficient electro-oxidation of EtOH or EG. This is further supported from statistical data analysis of probability of occurrence of such ensembles onto PtRu alloy surface. Present results also suggest that electro-oxidation of EG onto nano-PtRu catalyst surfaces follows a different path from that of EtOH at alloy composition less than 15 at.% of Ru.

Methanol Electrooxidation on PtRu Bulk Alloys and Carbon-Supported PtRu Nanoparticle Catalysts: A Quantitative DEMS Study

Methanol electrooxidation on smooth Pt and PtRu bulk alloys and carbon-supported Pt and PtRu nanoparticle catalysts has been studied using cyclic voltammetry and potential step chronoamperometry combined with differential electrochemical mass spectrometry (DEMS). The current efficiencies for generated CO2 and methyl formate were calculated from Faradaic current (coulometric charge) and mass spectrometric currents (charges) at m/z=44 and m/z=60. The effects of Ru content in PtRu catalysts, catalyst loading/roughness, and the concentration of sulfuric acid as supporting electrolyte on the reaction kinetics and product distribution during methanol electrooxidation have been investigated. The results indicate that Pt-rich PtRu alloys and carbon-supported PtRu catalysts with ca. 20 atom % Ru content exhibit the highest catalytic activity for methanol electrooxidation, that is, the highest Faradaic current and the highest current efficiency for CO2 generation at low applied potentials. As the catalyst loading/roughness increases, the current efficiency for CO2 formation increases due to the further oxidation of soluble intermediates (formaldehyde and formic acid). At high concentrations of sulfuric acid, the electrooxidation of methanol was suppressed; both the oxidative current and the current efficiency of CO2 decreased, likely due to sulfate/bisulfate adsorption.

PtMo Alloy and MoOx@Pt Core−Shell Nanoparticles as Highly CO-Tolerant Electrocatalysts

PtMo alloy and MoO(x)@Pt core-shell nanoparticles (NPs) were successfully synthesized by a chemical coreduction and sequential chemical reduction method, respectively. Both the carbon-supported alloy and core-shell NPs show substantially higher CO tolerance, compared to the commercialized E-TEK PtRu alloy and Pt catalyst. These novel nanocatalysts can be potentially used as highly CO-tolerant anode electrocatalysts in proton exchange membrane fuel cells.

MnO2/CNT Supported Pt and PtRu Nanocatalysts for Direct Methanol Fuel Cells

Pt/MnO2/carbon nanotube (CNT) and PtRu/MnO2/CNT nanocomposites were synthesized by successively loading hydrous MnO2 and Pt (or PtRu alloy) nanoparticles on CNTs and were used as anodic catalysts for direct methanol fuel cells (DMFCs). The existence of MnO2 on the surface of CNTs effectively increases the proton conductivity of the catalyst, which then could remarkably improve the performance of the catalyst in methanol electro-oxidation. As a result, Pt/MnO2/CNTs show higher electrochemical active surface area and better methanol electro-oxidation activity, compared with Pt/CNTs. As PtRu alloy nanoparticles were deposited on the surface of MnO2/CNTs instead of Pt, the PtRu/MnO2/CNT catalyst shows not only excellent electro-oxidation activity to methanol with forward anodic peak current density of 901 A/gPt but also good CO oxidation ability with lower preadsorbed CO oxidation onset potential (0.33 V vs Ag/AgCl) and peak potential (0.49 V vs Ag/AgCl) at room temperature.

Catalytic activity and stability toward methanol oxidation of PtRu/CNTs prepared by adsorption in aqueous solution and reduction in ethylene glycol

In this paper, we reported an improved process for the preparation of PtRu/CNTs, which involves the adsorption of Pt and Ru ions on CNTs in aqueous solution and the reduction of the adsorbed Pt and Ru ions on CNTs in ethylene glycol. The surface morphology, structure, and compositions of the prepared catalyst were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive spectrometer. TEM observation showed that the particles size of the prepared PtRu alloy was in the range of 2–5 nm, XRD patterns confirmed a face-centered cubic crystal structure. The activity and stability of the prepared catalyst toward methanol oxidation were studied in 0.5 M H2SO4 + 1 M CH3OH solution by cyclic voltammetry, chronoamperometry, and chronopotentiometry. The electrochemical results showed that the prepared catalyst exhibited higher activity and stability toward methanol oxidation than commercial PtRu/C with the same loading amount of Pt and Ru.

Enhanced electrocatalytic oxidation of formic acid by platinum deposition on ruthenium nanoparticle surfaces

PtRu alloy nanoparticles were prepared by the spontaneous adsorption of Pt(acac) 2 on the surface of freshly prepared octanethiolate-protected ruthenium (RuSC8) nanoparticles. UV–vis spectroscopic measurements suggested that the adsorption was facilitated by the strong affinity of the platinum metal center to the ruthenium surface. Scanning tunneling spectroscopic studies showed that the resulting PtRu nanoparticles exhibited enhanced conductance as compared to the original ruthenium nanoparticles, where the adsorbed Pt centers might serve as the effective sites for electron-tunneling across the tip/particle/substrate junction. The nanoparticles were then loaded onto a glassy carbon (GC) electrode and their catalytic activities in the electro-oxidation of formic acid were examined and compared. Remarkably, despite the presence of an organic protecting monolayer on the particle surface, apparent electrocatalytic activity was observed. Voltammetric measurements suggested that a Pt skin layer was formed on the Ru nanoparticle surface, most likely as a result of electro-reduction of the adsorbed Pt(acac) 2. On the basis of the onset potential and current density in the electro-oxidation of HCOOH, the resulting PtRu nanoparticles displayed much higher electrocatalytic activity than the Ru counterparts and commercial PtRu nanoparticle catalysts from BASF. It was also found that the electrocatalytic activity of the PtRu nanoparticles was comparable to that of FePt alloy nanoparticles and PtRu bulk electrocatalysts, despite a minimal loading of Pt in the catalysts. Consistent responses were observed in electrochemical impedance spectroscopic measurements, where the charge-transfer resistance on PtRu/GC was found to be at least an order of magnitude smaller than that on Ru/GC and commercial PtRu catalysts. These measurements suggest that the PtRu thin-layer nanoparticles might be used as a promising candidate for the electrocatalytic oxidation of formic acid.

Electrocatalytic properties of nanoporous PtRu alloy towards the electrooxidation of formic acid

The electrooxidation of formic acid has been investigated as a probe of the electrocatalytic properties of PtRu alloy having high surface area and regular nanoporous structure using cyclic voltammetry and chronoamperometry. Compared to nanostructured Pt electrocatalyst, adding Ru to Pt significantly enhances the electrocatalytic activity towards the formic acid oxidation and substantially changes the reaction kinetics. The electrocatalytic decomposition pathway of HCOOH is strongly dependent upon electrochemical driving forces. At room temperature and low potential of around 0.3 V vs. RHE, the direct dehydrogenation of HCOOH to CO 2 dominates and strongly adsorbed CO formed through the dehydration of HCOOH acts as a poison responsible for chronoamperometric current decays. At higher potential and/or higher temperature, the indirect oxidation of HCOOH with the adsorbed CO as a reactive intermediate is triggered and gradually becomes dominant with increasing driving forces. At 60 °C and in the potential range of 0.28–0.48 V, the instantaneous reaction rate ratio of the indirect oxidation of HCOOH to the direct dehydrogenation of HCOOH is 2.38 ± 0.22, derived from fitting data. At increased temperature, current oscillations have been observed under both potentiostatic and potentiodynamic conditions and have been correlated to the nanoporous structure of the PtRu alloy. These should be considered for the design of formic acid fuel cell electrocatalysts and the elucidation of the electrooxidation of small organic molecules.

A volcano curve: optimizing methanol electro-oxidation on Pt-decorated Ru nanoparticles

Controlled Pt adlayers were deposited on commercial Ru nanoparticles (NPs) using an industrially scalable one-pot ethylene glycol (EG) reduction based method and were characterized by X-ray diffraction (XRD), electrochemical (EC) CO stripping voltammetry, inductively-coupled plasma optical emission spectrometry (ICP-OES), X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM). Compared with the previously used "spontaneous deposition", the wet chemistry-based EG method is less technically demanding, i.e. no need to handle high-temperature hydrogen reduction, offers a better control of the Pt packing density (PD), enables the formation of stable, segregated Pt surface adlayers for optimal tuning and use of Pt, and effectively prevents NPs sintering. Two batches of a total of 11 (8 vs. 3) samples with different values of Pt PD ranging from 0.05 to 0.93 were prepared, with a time interval of more than 18 months between the sytheses of the two batches of samples, and an excellent reproducibility of results was observed. All samples were investigated in terms of methanol (MeOH) electro-oxidation (EO) by cyclic voltammetry (CV) and chronoamperometry (CA). Although the peak current of CV increased as the Pt content increased, the long-term steady-state MeOH electro-oxidation current density of the Pt-decorated Ru NPs measured by CA showed a volcano curve as a function of the Pt PD, with the maximum appearing at the PD of 0.31. The optimal peak activity was approximately 150% higher than that of the industrial benchmark PtRu (1 : 1) alloy NPs and could deliver the same performance at half the electrode material cost. Fundamentally, such a volcano curve in the reaction current is the result of two competing processes of the EO of MeOH: the triple dehydrogenation of MeOH that prefers more Pt ensemble sites, and the elimination of poisonous CO that is enhanced by more adjacent Ru/Pt sites via the so-called bifunctional mechanism and also by possible electronic effects at low Pt coverages.