Platinum Monolayer Research Articles

Tetrahedral Palladium Nanocrystals: A New Support for Platinum Monolayer Electrocatalysts with High Activity and Stability in the Oxygen Reduction Reaction

Abstract The recent availability of tetrahedral palladium (PdTH) nanocrystals with cleaned surfaces allowed us to evaluate their facet-specific electrochemical properties as a new support of platinum monolayer (PtML) catalysts. The Pd–PtML core-shell electrocatalyst was examined by combining structural analyses and Density Functional Theory (DFT) with electrochemical techniques. The surfaces of the PdTH core are composed of (111) facets wherein the Pd atoms are highly coordinated and have low surface energy. Our results revealed that in comparison with sphere Pd (PdSP)-supported PtML or pure Pt, the PdTH-supported PtML features more surface contraction and a downshift of d-band relative to the Fermi level. These geometric- and electronic-effects determine the higher activity of PtML/PdTH/C for the oxygen reduction reaction (ORR) compared to that of PtML/PdSP/C. This shape-property interdependence illuminated new approaches to basic- and applied- research on Pt-based ORR electrocatalysts of significant importance to the widespread use of fuel cells.

Platinum Monolayer Electrocatalysts: Tunable Activity, Stability, and Self-Healing Properties

Platinum monolayer-nanostructured electrocatalysts were developed principally for the oxygen reduction reaction starting with fundamental studies on single-crystal substrates, supported by theoretical treatments, synthesizing nanoparticles, followed by scale-up syntheses and fuel cell tests. These catalysts consist of nanometer-scale core–shell particles with monolayers of platinum that are supported by metal, metal alloy, or nanostructured noble metal/non-noble metal cores. In addition to an ultralow Pt content (one monolayer) and high Pt utilization (all atoms are on the surface and can participate in the reaction), these catalysts are characterized by very high activity and stability induced by supporting nanoparticles cores, by the ability to tune the catalytic activity of a Pt monolayer depending on the properties of the top atomic layer of the cores, and by a self-healing property. The latter two properties, which open particularly broad possibilities for applications of these catalysts, will be briefly analyzed in this article. Examples of tunable activity include electrocatalysts consisting of a Pt monolayer on smooth core surfaces, Pd tetrahedral nanoparticles, Pd nanowire, and hollow Pd nanoparticle cores. The self-healing properties are illustrated by stability tests involving potential cycling. Possible future research involving these catalysts is discussed.

Electrodeposition of Metals in Catalysts Syntheses: Platinum Monolayer Electrocatalysts for the Oxygen Reduction Reaction

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Regarding the Enhanced Durability of Platinum Monolayer Electrocatalysts for the Oxygen Reduction Reaction

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Platinum Monolayer Electrocatalysts for the Oxygen Reduction Reaction

The Pt monolayer electrocatalysts for the oxygen reduction reaction is the most promising approach to reduce the content of Pt in fuel cells while meeting all the performance and durability requirements. An ample illustration of the broad possibilities of tailoring Pt monolayer properties is presented thus revealing the potential of Pt monolayer electrocatalysts for resolving problems of availability of Pt in future catalysis and electrocatalysis and removing the main obstacles to the broad scale application of fuel cell technology.

Catalytic Activity of Platinum Monolayer on Iridium and Rhenium Alloy Nanoparticles for the Oxygen Reduction Reaction

A new type of electrocatalyst with a core–shell structure that consists of a platinum monolayer shell placed on an iridium–rhenium nanoparticle core or platinum and palladium bilayer shell deposited on that core has been prepared and tested for electrocatalytic activity for the oxygen reduction reaction. Carbon-supported iridium–rhenium alloy nanoparticles with several different molar ratios of Ir to Re were prepared by reducing metal chlorides dispersed on Vulcan carbon with hydrogen gas at 400 °C for 1 h. These catalysts showed specific electrocatalytic activity for oxygen reduction reaction comparable to that of platinum. The activities of PtML/PdML/Ir2Re1, PtML/Pd2layers/Ir2Re1, and PtML/Pd2layers/Ir7Re3 catalysts were, in fact, better than that of conventional platinum electrocatalysts, and their mass activities exceeded the 2015 DOE target. Our density functional theory calculations revealed that the molar ratio of Ir to Re affects the binding strength of adsorbed OH and, thereby, the O2 reduction activity of the catalysts. The maximum specific activity was found for an intermediate OH binding energy with the corresponding catalyst on the top of the volcano plot. The monolayer concept facilitates the use of much less platinum than in other approaches. The results with the PtML/PdML/Ir2Re electrocatalyst indicate that it is a promising alternative to conventional Pt electrocatalysts in low-temperature fuel cells.

Platinum Monolayer Electrocatalysts for the Oxygen Reduction Reaction

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In Situ XAS and IRRAS of Platinum Monolayer Fuel Cell Electrocatalysts

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Metal Oxide‐Supported Platinum Overlayers as Proton‐Exchange Membrane Fuel Cell Cathodes

AbstractWe investigated the activity and stability of n=(1, 2, 3) platinum layers supported on a number of rutile metal oxides (MO2; M=Ti, Sn, Ta, Nb, Hf and Zr). A suitable oxide support can alleviate the problem of carbon corrosion and platinum dissolution in Pt/C catalysts. Moreover, it can increase the activity of platinum if the interaction between the support and the metal is optimal. We found that both the activity and the stability depend on the number of platinum layers and, as expected, both converge toward platinum bulk values if the number of layers is increased. With use of a simple volcano curve for activity estimation, we found that the supported platinum layers could be active for the oxygen reduction reaction, with a few candidates possibly having an activity even greater than that of platinum. Furthermore, we established a correlation between stability and activity for supported platinum monolayers, which suggests that activity can be increased at the expense of stability and vice versa. Finally, the performance of the systems was evaluated against Pt(111) skins on Pt3X (X=Ni, Co, Fe, Ti, Sc and Y) alloys, which are the best catalysts known to date for the reaction.

Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction

Stability is one of the main requirements for commercializing fuel cell electrocatalysts for automotive applications. Platinum is the best-known catalyst for oxygen reduction in cathodes, but it undergoes dissolution during potential changes while driving electric vehicles, thus hampering commercial adoption. Here we report a new class of highly stable, active electrocatalysts comprising platinum monolayers on palladium-gold alloy nanoparticles. In fuel-cell tests, this electrocatalyst with its ultra-low platinum content showed minimal degradation in activity over 100,000 cycles between potentials 0.6 and 1.0 V. Under more severe conditions with a potential range of 0.6-1.4 V, again we registered no marked losses in platinum and gold despite the dissolution of palladium. These data coupled with theoretical analyses demonstrated that adding a small amount of gold to palladium and forming highly uniform nanoparticle cores make the platinum monolayer electrocatalyst significantly tolerant and very promising for the automotive application of fuel cells.

Bimetallic IrNi core platinum monolayer shell electrocatalysts for the oxygen reduction reaction

We synthesized a low-Pt content electrocatalyst consisting of a Pt monolayer placed on carbon-supported thermally treated IrNi core–shell structured nanoparticles using galvanic displacement of a Cu monolayer deposited at underpotentials. The Pt mass activity of the PtML/IrNi/C electrocatalyst obtained in a scale-up synthesis is approximately 3 times higher than that of the commercial Pt/C electrocatalyst. The electronic and geometrical effects of the IrNi substrate on the Pt monolayer result in its higher catalytic activity than that of Pt nanoparticles. The structure and composition of the core–shell nanoparticles were verified using transmission electron microscopy and in situX-ray absorption spectroscopy, while a potential cycling test was employed to confirm the stability of the electrocatalyst. Our experimental results, supported by the density functional calculations using a sphere-like model, demonstrate an effective way of using Pt that can resolve key problems of cathodic oxygen reduction hampering fuel cell commercialization.

Theoretical study for magnetic effect in dissociative adsorption of oxygen to a platinum monolayer on Ni(110) surface

We investigate oxygen dissociative adsorption to a platinum monolayer on Ni(110) surface (Pt/Ni(110)) by density functional theory. We have shown that the activation barrier on Pt/Ni(110) is lower than that on a clean Pt(001) surface. This may be due to the effect of magnetization of Pt surface. The reason of decrease of activation barrier can be attributed to the flow of electrons from oxygen to platinum surface because the d orbitals have spin polarization at the Fermi level where the down spin d orbitals are unoccupied.

Ambient Surfactantless Synthesis, Growth Mechanism, and Size-Dependent Electrocatalytic Behavior of High-Quality, Single Crystalline Palladium Nanowires

In this report, we utilize the U-tube double diffusion device as a reliable, environmentally friendly method for the size-controlled synthesis of high-quality, single crystalline Pd nanowires. The nanowires grown in 200 and 15 nm polycarbonate template pores maintain diameters of 270 ± 45 nm and 45 ± 9 nm, respectively, and could be isolated either as individual nanowires or as ordered free-standing arrays. The growth mechanism of these nanowires has been extensively explored, and we have carried out characterization of the isolated nanowires, free-standing nanowire arrays, and cross sections of the filled template in order to determine that a unique two-step growth process predominates within the template pores. Moreover, as-prepared submicrometer and nanosized wires were studied by comparison with ultrathin 2 nm Pd nanowires in order to elucidate the size-dependent trend in oxygen reduction reaction (ORR) electrocatalysis. Subsequently, the desired platinum monolayer overcoating was reliably deposited onto the surface of the Pd nanowires by Cu underpotential deposition (UPD) followed by galvanic displacement of the Cu adatoms. The specific and platinum mass activity of the core-shell catalysts was found to increase from 0.40 mA/cm(2) and 1.01 A/mg to 0.74 mA/cm(2) and 1.74 A/mg as the diameter was decreased from the submicrometer size regime to the ultrathin nanometer range.

Electrodeposition of Metals in Catalysts Syntheses: A Case of Platinum Monolayer Electrocatalysts

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Enhanced Stability of Platinum Monolayer on Palladium-Gold Nanoparticle Electrocatalysts in Long-Term Fuel Cell Tests

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Deposition of platinum monolayers on gold

Deposition of small amount of Pt is reported onto polycrystalline Au from H2PtCl6-containing solutions. Spontaneous deposition, yielding about 5% of a full-packed monolayer, has been found at the steady-state open circuit potential. Formation of a somewhat more dense, but still a partial monolayer could be observed at potentials between the steady-state open circuit potential and that of the onset of bulk deposition. A specific difference of monolayer and bulk deposition is that Pt surface area levels off with time and keeps increasing for the former and latter types of deposition, respectively. Pt monolayers with quite high coverages can be formed in a rather narrow, 20–30 mV potential region only. The surface areas of Pt and of the Pt-free Au have been simultaneously measured as cyclic voltammetry peak charges. From these measurements, the site requirement of the Pt atoms was determined to be around four; that is, each Pt atom blocks the oxidation of about four underlying/neighbouring Au atoms, implying their distant positions. Based on the results, Au surfaces coated with monoatomic Pt layers of quite high coverages can be prepared.

The structure formed by the deposition of a sub-monolayer quantity of platinum onto Cu(110) investigated using medium energy ion scattering

The structure of 0.35 monolayers of platinum deposited onto Cu(110) has been investigated using medium energy ion scattering. Quantitative analysis of the data has been performed using the VEGAS routine. It was found that platinum atoms mostly occupy the second layer with a first interlayer distance of d 12 = 123 ± 4 pm and a separation of first and third layers of d 13= 142 − 10 + 4 pm. These represent a contraction of 4% and an expansion of 11% respectively from the ideal termination of the Cu(110) surface. There is clear evidence of the presence of some platinum in the third layer.

Platinum Monolayer on IrFe Core–Shell Nanoparticle Electrocatalysts for the Oxygen Reduction Reaction

We synthesized high activity and stability platinum monolayer on IrFe core–shell nanoparticle electrocatalysts. Carbon-supported IrFe core–shell nanoparticles were synthesized by chemical reduction and subsequent thermal annealing. The formation of Ir shells on IrFe solid-solution alloy cores has been verified by scanning transmission electron microscopy coupled with energy-loss spectroscopy (EELS) and in situ X-ray absorption spectroscopy. The Pt monolayers were deposited on IrFe core-shell nanoparticles by galvanic replacement of underpotentially deposited Cu adatoms on the Ir shell surfaces. The specific and Pt mass activities for the ORR on the Pt monolayer on IrFe core-shell nanoparticle electrocatalyst are 0.46 mA/cm2 and 1.1 A/mgPt, which are much higher than those on a commercial Pt/C electrocatalyst. High durability of PtML/IrFe/C has also been demonstrated by potential cycling tests. These high activity and durability observed can be ascribed to the structural and electronic interaction between the Pt monolayer and the IrFe core–shell nanoparticles.

Catalytic Activity of Platinum Monolayer on Iridium and Rhenium Alloy Nanoparticles for Oxygen Reduction Reaction

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Tetrahedral Palladium Nanocrystals - A New Support of Platinum Monolayer Electrocatalysts Having Improving Activity and Stability in Oxygen Reduction Reaction

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