Showing papers on "Platinum published in 2013"

Structurally ordered intermetallic platinum–cobalt core–shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts

Abstract: To enhance and optimize nanocatalyst performance and durability for the oxygen reduction reaction in fuel-cell applications, we look beyond Pt-metal disordered alloys and describe a new class of Pt-Co nanocatalysts composed of ordered Pt(3)Co intermetallic cores with a 2-3 atomic-layer-thick platinum shell. These nanocatalysts exhibited over 200% increase in mass activity and over 300% increase in specific activity when compared with the disordered Pt(3)Co alloy nanoparticles as well as Pt/C. So far, this mass activity for the oxygen reduction reaction is the highest among the Pt-Co systems reported in the literature under similar testing conditions. Stability tests showed a minimal loss of activity after 5,000 potential cycles and the ordered core-shell structure was maintained virtually intact, as established by atomic-scale elemental mapping. The high activity and stability are attributed to the Pt-rich shell and the stable intermetallic Pt(3)Co core arrangement. These ordered nanoparticles provide a new direction for catalyst performance optimization for next-generation fuel cells.

Nanostructured Nonprecious Metal Catalysts for Oxygen Reduction Reaction

Abstract: Platinum-based catalysts represent a state of the art in the electrocatalysis of oxygen reduction reaction (ORR) from the point of view of their activity and durability in harnessing the chemical energy via direct electrochemical conversion. However, because platinum is both expensive and scarce, its widespread implementation in such clean energy applications is limited. Recent breakthroughs in the synthesis of high-performance nonprecious metal catalysts (NPMCs) make replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this Account, we discuss how we can obtain highly promising M–N–C (M: Fe and/or Co) catalysts by simultaneously heat-treating precursors of nitrogen, carbon, and transition metals at 800–1000 °C. The activity and durability of resulting catalysts depend greatly on the selection of precursors and synthesis chemistry. In addition, they correlate quite well with the catalyst nanostructure. While chemists have presented n...

Active and stable carbon nanotube/nanoparticle composite electrocatalyst for oxygen reduction

Abstract: Nanostructured carbon-based materials, such as nitrogen-doped carbon nanotube arrays, Co3O4/nitrogen-doped graphene hybrids and carbon nanotube-graphene complexes have shown respectable oxygen reduction reaction activity in alkaline media. Although certainly promising, the performance of these materials does not yet warrant implementation in the energy conversion/storage devices utilizing basic electrolytes, for example, alkaline fuel cells, metal-air batteries and certain electrolysers. Here we demonstrate a new type of nitrogen-doped carbon nanotube/nanoparticle composite oxygen reduction reaction electrocatalyst obtained from iron acetate as an iron precursor and from cyanamide as a nitrogen and carbon nanotube precursor in a simple, scalable and single-step method. The composite has the highest oxygen reduction reaction activity in alkaline media of any non-precious metal catalysts. When used at a sufficiently high loading, this catalyst also outperforms the most active platinum-based catalysts.

CO Oxidation on Supported Single Pt Atoms: Experimental and ab Initio Density Functional Studies of CO Interaction with Pt Atom on θ-Al2O3(010) Surface

Abstract: Although there are only a few known examples of supported single-atom catalysts, they are unique because they bridge the gap between homogeneous and heterogeneous catalysis. Here, we report the CO oxidation activity of monodisperse single Pt atoms supported on an inert substrate, θ-alumina (Al2O3), in the presence of stoichiometric oxygen. Since CO oxidation on single Pt atoms cannot occur via a conventional Langmuir–Hinshelwood scheme (L–H scheme) which requires at least one Pt–Pt bond, we carried out a first-principles density functional theoretical study of a proposed pathway which is a variation on the conventional L–H scheme and inspired by the organometallic chemistry of platinum. We find that a single supported Pt atom prefers to bond to O2 over CO. CO then bonds with the oxygenated Pt atom and forms a carbonate which dissociates to liberate CO2, leaving an oxygen atom on Pt. Subsequent reaction with another CO molecule regenerates the single-atom catalyst. The energetics of the proposed mechanism ...

Biomass-derived electrocatalytic composites for hydrogen evolution

Abstract: The production of hydrogen from water electrolysis calls for an efficient non-precious-metal catalyst to make the process economically viable because of the high cost and the limited supply of the currently used platinum catalysts. Here we present such a catalyst made from earth-abundant molybdenum and common, humble soybeans (MoSoy). This catalyst, composed of a catalytic β-Mo2C phase and an acid-proof γ-Mo2N phase, drives the hydrogen evolution reaction (HER) with low overpotentials, and is highly durable in a corrosive acidic solution over a period exceeding 500 hours. When supported on graphene sheets, the MoSoy catalyst exhibits very fast charge transfer kinetics, and its performance rivals that of noble-metal catalysts such as Pt for hydrogen production. These findings prove that the soybean (as well as other high-protein biomass) is a useful material for the generation of catalysts incorporating an abundant transition metal, thereby challenging the exclusivity of platinum catalysts in the hydrogen economy.

A highly efficient electrocatalyst for the oxygen reduction reaction: N-doped ketjenblack incorporated into Fe/Fe3C-functionalized melamine foam.

Abstract: Thus,ways of increasing the ORR kinetics while maintaining fastmass transfer is a grand challenge in the development ofa new generation of metal–air batteries and fuel cells.Catalysts based on platinum and other precious metals arevery effective in facilitating the rate of ORR in batteries andfuel cells.

Ordered mesoporous porphyrinic carbons with very high electrocatalytic activity for the oxygen reduction reaction

Abstract: The high cost of the platinum-based cathode catalysts for the oxygen reduction reaction (ORR) has impeded the widespread application of polymer electrolyte fuel cells. We report on a new family of non-precious metal catalysts based on ordered mesoporous porphyrinic carbons (M-OMPC; M = Fe, Co, or FeCo) with high surface areas and tunable pore structures, which were prepared by nanocasting mesoporous silica templates with metalloporphyrin precursors. The FeCo-OMPC catalyst exhibited an excellent ORR activity in an acidic medium, higher than other non-precious metal catalysts. It showed higher kinetic current at 0.9 V than Pt/C catalysts, as well as superior long-term durability and MeOH-tolerance. Density functional theory calculations in combination with extended X-ray absorption fine structure analysis revealed a weakening of the interaction between oxygen atom and FeCo-OMPC compared to Pt/C. This effect and high surface area of FeCo-OMPC appear responsible for its significantly high ORR activity.

Highly efficient blue-emitting cyclometalated platinum(II) complexes by judicious molecular design.

Abstract: Luminescent properties of cyclometalated Ir and Pt complexes have been the focus of considerable research, driven in large part by their potential use as emitters in organic lightemitting diodes (OLEDs). This class of phosphorescent emitters has demonstrated the ability to harvest both electrogenerated singlet and triplet excitons, resulting in a theoretical 100 % electron-to-photon conversion efficiency. Driven by the technological need for full-color displays and solid-state lighting applications, the development of stable and efficient Ir and Pt complexes that emit in the range of 400–460 nm (blue region) is vital. Thus far, the approach to achieve efficient blue-phosphorescent OLEDs has focused on Irbased complexes with either high triplet energy cyclometalated ligands, such as 4,6-difluorophenylpyridine, or electronwithdrawing ancillary ligands, such as picolinate and tetrakis(1-pyrazolyl)borate. There are comparatively few reports on deep blue phosphorescent emitters with fluorine-free cyclometalating ligands, despite potential for improved optoelectronic stability compared to fluorinated derivatives. An example of such a class of materials is metal complexes cyclometalated with the methyl-2-phenylimidazole (pmi) ligand and related analogues that are coordinated to the metal through a neutral carbene. Several Ir complexes have been reported to have efficient deep blue phosphorescent emission at room temperature, including mer-tris(Ndibenzofuranyl-N-methylimidazole) iridium(III) [Ir(dbfmi)], tris(1-cyanophenyl-3-methylimidazolin-2-ylidene-C,C2’) iridium(III) [Ir(cnpmic)], and mer-tris(phenyl-methyl-benzimidazolyl) iridium(III) [m-Ir(pmb)3]. [7c] However, these complexes suffer from either long luminescent decay or relatively low quantum efficiency compared to Ir complexes based on the cyclometalated 2phenylpyridine ligand that have quantum efficiency F of 0.8– 1 and a luminescent lifetime t of 1–5 ms. This difference can be attributed to the combined effects of a high non-radiative decay rate (knr) and low radiative decay rate (kr), which are dictated by the intrinsic properties of the selected metal complex system. Thus, it will be highly desirable to identify rational design motifs that can improve the luminescent properties of deep blue phosphorescent emitters. Compared to Ir analogues, there are relatively few reports on platinum complexes cyclometalated with phenylimidazole carbene ligands. However, one such compound, platinum(II) bis(methylimidazolyl)benzene chloride (Pt-16), has demonstrated impressive device performance with a maximum external quantum efficiency (EQE) of 15.7% and Commission Internationale de L clairage (CIE) coordinates of (0.16, 0.13). Moreover, Pt complexes can provide additional structural variation owing to the square-planar configuration allowing ligands to be designed that are bidentate, tridentate and tetradentate. These variations can significantly alter the ground and excited state properties of Pt complexes. Herein, we report (pmi)Pt-based complexes that demonstrate a higher luminescent quantum yield and faster radiative decay process than published Ir carbene analogues. A new class of Pt complexes with tetradentate ligands have been synthesized. The complexes have a conventional cyclometalated fragment bridged with oxygen to an LL chelating group, where LL is an ancillary chelate, such as, phenoxyl pyridine (POPy) or carbazolyl pyridine (CbPy). The structures of Pt[pmi-O-POPy], Pt[pmi-O-CbPy], and Pt[ppz-OCbPy] are shown in Scheme 1, and are denoted as PtOO7,

Impact of Platinum Loading and Catalyst Layer Structure on PEMFC Performance

Abstract: For a hydrogen-powered fuel cell vehicle to be cost competitive, Pt loading must be reduced to lower than 0.15 gPt kW. Therefore, fuel cell researchers are exploring the limits of Pt loading with established catalyst structures in parallel with advanced catalyst research. It is observed that reducing the cathode Pt loading results in significant voltage loss, which can be partly explained by the Pt-oxide coverage dependent oxygen reduction reaction (ORR) kinetics. For ionomer coated catalysts, an additional transport resistance from the electrode pore to the Pt surface (i.e. local resistance) has been reported that is much higher than oxygen permeability through bulk ionomer.

The Role of Platinum in Proton Exchange Membrane Fuel Cells

Abstract: Johnson Matthey, Orchard Road, Royston, Hertfordshire SG8 5HE, UK Email: *oliver.holton@matthey.com; **joe.stevenson@matthey.com Proton exchange membrane fuel cells (PEMFCs) dominate the transportation fuel cell market and platinum (Pt) is the catalyst material used for both anode and cathode. This review sets out the fundamentals of activity, selectivity, stability and poisoning resistance which make Pt or its alloys the best available materials to use in this application. It is clear that Pt is the only element which can meet the requirements for performance while avoiding slow reaction kinetics, proton exchange membrane (PEM) system degradation due to hydrogen peroxide (H2O2) formation and catalyst degradation due to metal leaching. Some of the means by which the performance of Pt can be enhanced are also discussed.

Atomic Layer Deposition of Platinum Catalysts on Nanowire Surfaces for Photoelectrochemical Water Reduction

Abstract: The photocathodic hydrogen evolution reaction (HER) from p-type Si nanowire (NW) arrays was evaluated using platinum deposited by atomic layer deposition (ALD) as a HER cocatalyst. ALD of Pt on the NW surface led to a highly conformal coating of nanoparticles with sizes ranging from 0.5 to 3 nm, allowing for precise control of the Pt loading in deep submonolayer quantities. The catalytic performance was measured using as little as 1 cycle of Pt ALD, which corresponded to a surface mass loading of ∼10 ng/cm2. The quantitative exploration of the lower limits of Pt cocatalyst loading reported here, and its application to high-surface-area NW photoelectrodes, establish a general approach for minimizing the cost of precious-metal cocatalysts for efficient and affordable solar-to-fuel applications.

Investigation of Catalytic Finite-Size-Effects of Platinum Metal Clusters.

Abstract: In this paper, we use density functional theory (DFT) calculations on highly parallel computing resources to study size-dependent changes in the chemical and electronic properties of platinum (Pt) for a number of fixed freestanding clusters ranging from 13 to 1415 atoms, or 0.7-3.5 nm in diameter. We find that the surface catalytic properties of the clusters converge to the single crystal limit for clusters with as few as 147 atoms (1.6 nm). Recently published results for gold (Au) clusters showed analogous convergence with size. However, this convergence happened at larger sizes, because the Au d-states do not contribute to the density of states around the Fermi-level, and the observed level fluctuations were not significantly damped until the cluster reached ca. 560 atoms (2.7 nm) in size.

Ordered macroporous platinum electrode and enhanced mass transfer in fuel cells using inverse opal structure.

Abstract: Inverse opal structures are desirable for fuel cell electrodes, but application of such structures in polymer electrolyte membrane fuel cells is yet to be realised. Kim et al. report fabrication of a platinum catalyst layer with an inverse opal structure, and show improved fuel cell performance.

An iron complex with pendent amines as a molecular electrocatalyst for oxidation of hydrogen

Abstract: Electricity can be produced by the oxidation of hydrogen in fuel cells, but the best catalyst for this is platinum, a precious metal of low abundance. Now a molecular complex of iron, a very abundant, inexpensive metal, has been rationally designed for the oxidation of H2 at room temperature.

Ordered bilayer ruthenium–platinum core-shell nanoparticles as carbon monoxide-tolerant fuel cell catalysts

Abstract: Fabricating subnanometre-thick core-shell nanocatalysts is effective for obtaining high surface area of an active metal with tunable properties. The key to fully realize the potential of this approach is a reliable synthesis method to produce atomically ordered core-shell nanoparticles. Here we report new insights on eliminating lattice defects in core-shell syntheses and opportunities opened for achieving superior catalytic performance. Ordered structural transition from ruthenium hcp to platinum fcc stacking sequence at the core-shell interface is achieved via a green synthesis method, and is verified by X-ray diffraction and electron microscopic techniques coupled with density functional theory calculations. The single crystalline Ru cores with well-defined Pt bilayer shells resolve the dilemma in using a dissolution-prone metal, such as ruthenium, for alleviating the deactivating effect of carbon monoxide, opening the door for commercialization of low-temperature fuel cells that can use inexpensive reformates (H2 with CO impurity) as the fuel.

Unidirectional suppression of hydrogen oxidation on oxidized platinum clusters

Abstract: Solar-driven water splitting to produce hydrogen may be an ideal solution for global energy and environment issues. Among the various photocatalytic systems, platinum has been widely used to co-catalyse the reduction of protons in water for hydrogen evolution. However, the undesirable hydrogen oxidation reaction can also be readily catalysed by metallic platinum, which limits the solar energy conversion efficiency in artificial photosynthesis. Here we report that the unidirectional suppression of hydrogen oxidation in photocatalytic water splitting can be fulfilled by controlling the valence state of platinum; this platinum-based cocatalyst in a higher oxidation state can act as an efficient hydrogen evolution site while suppressing the undesirable hydrogen back-oxidation. The findings in this work may pave the way for developing other high-efficientcy platinum-based catalysts for photocatalysis, photoelectrochemistry, fuel cells and water-gas shift reactions.

Tungsten Carbide Nanoparticles as Efficient Cocatalysts for Photocatalytic Overall Water Splitting

Abstract: Tungsten carbide exhibits platinum-like behavior, which makes it an interesting potential substitute for noble metals in catalytic applications. Tungsten carbide nanocrystals (≈5 nm) are directly synthesized through the reaction of tungsten precursors with mesoporous graphitic C(3)N(4) (mpg-C(3)N(4)) as the reactive template in a flow of inert gas at high temperatures. Systematic experiments that vary the precursor compositions and temperatures used in the synthesis selectively generate different compositions and structures for the final nanocarbide (W(2)C or WC) products. Electrochemical measurements demonstrate that the WC phase with a high surface area exhibits both high activity and stability in hydrogen evolution over a wide pH range. The WC sample also shows excellent hydrogen oxidation activity, whereas its activity in oxygen reduction is poor. These tungsten carbides are successful cocatalysts for overall water splitting and give H(2) and O(2) in a stoichiometric ratio from H(2)O decomposition when supported on a Na-doped SrTiO(3) photocatalyst. Herein, we present tungsten carbide (on a small scale) as a promising and durable catalyst substitute for platinum and other scarce noble-metal catalysts in catalytic reaction systems used for renewable energy generation.

Novel cobalt/nickel–tungsten-sulfide catalysts for electrocatalytic hydrogen generation from water

Abstract: The potential of water (photo)electrolysis technology to provide hydrogen as a fuel on a large scale depends on how viable electrocatalysts for the water oxidation reaction (WOR) and the hydrogen evolution reaction (HER) are and whether they can be constructed from elements which are abundant in the Earth's crust. Here we show that ternary sulfides of cobalt–tungsten and nickel–tungsten (MWSx where M is Co or Ni) are efficient and robust electrocatalysts for the HER in water over a wide pH range. These novel ternary sulfides were readily grown on a conducting electrode surface by employing a scalable electrodeposition process from aqueous solutions of [M(WS4)2]2−. In terms of HER activity, the MWSx catalysts represent attractive alternatives to platinum. Moreover, we show that the HER activity is governed by the nature of the metal M within M–S–W heterobimetallic sulfide centres, located in the WS2-like layered structure of MWSx. Our work provides structural and mechanistic keys to understand how HER activity is promoted in previously described nickel and cobalt-doped molybdenum and tungsten sulfide materials.

Self-terminating growth of platinum by electrochemical deposition

Abstract: A self-terminating rapid process for controlled growth of platinum or platinum alloy monolayer films from a K2PtCl4—NaCl—NaBr electrolyte. Using the present process, platinum deposition may be quenched at potentials just negative of proton reduction by an alteration of the double layer structure induced by a saturated surface coverage of underpotential deposited hydrogen. The surface may be reactivated for platinum deposition by stepping the potential to more positive values where underpotential deposited hydrogen is oxidized and fresh sites for absorption of platinum chloride become available. Periodic pulsing of the potential enables sequential deposition of two dimensional platinum layers to fabricate films of desired thickness relevant to a range of advanced technologies, from catalysis to magnetics and electronics.

Oxygen Reduction Catalyzed by Platinum Nanoparticles Supported on Graphene Quantum Dots

Abstract: Nanosized graphene quantum dots were prepared by acid etching of carbon fibers and used as effective substrate supports for platinum nanoparticles which were synthesized by thermolytic reduction of platinum(II) chloride in ethylene glycol. Transmission electron microscopic measurements showed that the resulting nanocomposite (Pt/G) particles exhibited an average diameter of 2.79 ± 0.38 nm, with clearly defined lattice fringes of 0.23 nm that might be assigned to the interlayer spacing of the (111) crystal planes of fcc Pt. In addition, the Pt nanoparticles were found to be wrapped with a low-contrast halo that likely arose from the poorly crystalline graphene quantum dots. X-ray diffraction studies confirmed the composite nature of the Pt/G nanoparticles, and the average size of the crystal domains of the Pt/G nanoparticles was found to be close to the nanoparticle physical dimensions, whereas for commercial Pt/C nanoparticles the size of the crystal domains was only half that of the nanoparticle diameter...

Stable platinum nanoclusters on genomic DNA-graphene oxide with a high oxygen reduction reaction activity

Abstract: Platinum nanoclusters are well-known catalysts for the oxygen reduction reaction, although the performance of clusters smaller than 2 nm is poorly studied. Here, the authors report 1.4 nm platinum clusters supported on DNA–graphene oxide composites and demonstrate promising electrochemical activity and stability.

Monofunctional and Higher-Valent Platinum Anticancer Agents

Abstract: Platinum compounds represent one of the great success stories of metals in medicine. Following the serendipitous discovery of the anticancer activity of cisplatin by Rosenberg, a large number of cisplatin variants have been prepared and tested for their ability to kill cancer cells and inhibit tumor growth. These efforts continue today with increased realization that new strategies are needed to overcome issues of toxicity and resistance inherent to treatment by the approved platinum anticancer agents. One approach has been the use of so-called “non-traditional” platinum(II) and platinum(IV) compounds that violate the structure–activity relationships that governed platinum drug-development research for many years. Another is the use of specialized drug-delivery strategies. Here we describe recent developments from our laboratory involving monofunctional platinum(II) complexes together with a historical account of the manner by which we came to investigate these compounds and their relationship to previous...

Stabilization of copper catalysts for liquid-phase reactions by atomic layer deposition.

Abstract: Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid-phase catalytic reactions (e.g., hydrogenation of biomass-derived furfural in alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid-phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X-ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ-Al2O3. Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under-coordinated copper atoms on the nanoparticle surface.