PtxRu1−x/Ru(0001) surface alloys—formation and atom distribution

Hoster, Harry E.; Bergbreiter, Andreas; Erne, Petra M.; Häger, Tobias; Rauscher, Hubert; Behm, R. Jürgen

doi:10.1039/b802169d

Cited by 79 publications

(153 citation statements)

References 82 publications

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“…While the number of Pd surface concentrations investigated is too low for a conclusive statement, the data provide at least clear evidence that at the freezing temperature of the surface alloy, i.e., at the temperature where surface diffusion becomes too slow to reach the equilibrium configuration during cool down, effective mutual interactions between the different surface species do not significantly affect the distribution of surface atoms. 60 This result fits well to the miscibility of PdAu alloys, furthermore it allows us to estimate ensemble size distributions also for other Pd surface concentrations in this range of Au surface concentrations assuming a statistical distribution of surface atoms.…”

Section: Structure Of Pdau-pd(111) Surface Alloyssupporting

confidence: 73%

Hydrogen adsorption on bimetallic PdAu(111) surface alloys: minimum adsorption ensemble, ligand and ensemble effects, and ensemble confinement

Takehiro

Liu

Bergbreiter

et al. 2014

Phys. Chem. Chem. Phys.

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The adsorption of hydrogen on structurally well defined PdAu-Pd(111) monolayer surface alloys was investigated in a combined experimental and theoretical study, aiming at a quantitative understanding of the adsorption and desorption properties of individual PdAu nanostructures. Combining the structural information obtained by high resolution scanning tunneling microscopy (STM), in particular on the abundance of specific adsorption ensembles at different Pd surface concentrations, with information on the adsorption properties derived from temperature programmed desorption (TPD) spectroscopy and high resolution electron energy loss spectroscopy (HREELS) provides conclusions on the minimum ensemble size for dissociative adsorption of hydrogen and on the adsorption energies on different sites active for adsorption. Density functional theory (DFT) based calculations give detailed insight into the physical effects underlying the observed adsorption behavior. Consequences of these findings for the understanding of hydrogen adsorption on bimetallic surfaces in general are discussed.

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Section: Structure Of Pdau-pd(111) Surface Alloyssupporting

confidence: 73%

Hydrogen adsorption on bimetallic PdAu(111) surface alloys: minimum adsorption ensemble, ligand and ensemble effects, and ensemble confinement

Takehiro

Liu

Bergbreiter

et al. 2014

Phys. Chem. Chem. Phys.

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“…The shift can involve the top one (left part) or two (right part) layers. In other words, the first Pt layer can occupy either the C or A site with little energy difference (33 meV), a fact that is supported by an experimental observation of Pt sub-ML islands in two orientations associated with fcc and hcp stacking sequence on the Ru(0001) single crystal surface 34 . We excluded the scenario wherein a Ru layer is shifted, because the energy cost for such a shift is high, that is, 466 or 612 meV (Supplementary Table S1).…”

Section: Resultsmentioning

confidence: 55%

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

et al. 2013

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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 (H 2 with CO impurity) as the fuel. O ne major goal in electrocatalysis studies is to produce highly active, durable catalysts, while minimizing the use of precious noble metals, especially platinum (Pt). This is the key requirement for the large-scale commercialization of proton exchange membrane (PEM) fuel cells 1,2 . An effective approach is to fabricate core-shell nanoparticles (NPs) that have active, corrosion-resistant Pt atoms on the surface, with tunable reactivity through their interactions with other metal cores to assure optimal catalytic performances. At the cathode, Pt monolayer (ML) catalysts with Pd or Pd 9 Au alloy cores exhibited enhanced activity and durability for the oxygen reduction reaction compared with Pt NPs 3 . Furthermore, both experimental and theoretical studies verified that lattice contraction 4-7 , high-coordination (111) facets 8-10 and smooth surface morphology 11 are beneficial structural factors in enhancing oxygen reduction reaction activity and the catalysts' durability.For the hydrogen oxidation reaction (HOR) at the anode, a negligible overpotential loss was achieved with pure hydrogen using 50 mg cm À 2 Pt NPs 12,13 . However, the challenge remains in employing inexpensive reformate hydrogen, wherein the p.p.m.-level of carbon monoxide (CO) impurities can severely deactivate the Pt catalysts [14][15][16] . In addition, although the anode operates at relatively low potentials, its nanocatalysts must be dissolution resistant because of the high potentials experienced during startups and shutdowns 17,18 . For developing CO-tolerant HOR catalysts, ruthenium (Ru) was used to support spontaneously deposited sub-ML Pt 19,20 . With about a one-to two-ML-thick Ru(core)-Pt(shell) (denoted as Ru@Pt) NPs, theoretical calculations and temperatureprogrammed measurements showed preferential CO oxidation in hydrogen feeds on Ru@Pt NPs compared with that of Ru-Pt nano-alloys 21 and of Pt shells with other metal core 22 . Besides being a promoter of CO tolerance of Pt surface, Ru ...

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“…27 In conclusion, we have proposed Fe MLs on hexagonal surfaces of late 4d and 5d TMs as promising systems to study experimentally the magnetic interactions in TMs, e.g., by proving the influence of spin interactions beyond the Heisenberg model. Alloying of the substrate, e.g., PtRu͑0001͒, 29 may allow an additional fine tuning of the degree of disorder in 2D systems as proposed in Ref. 26.…”

mentioning

confidence: 99%

Complex magnetism of iron monolayers on hexagonal transition metal surfaces from first principles

Hardrat¹,

Al-Zubi

Ferriani³

et al. 2009

Phys. Rev. B

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Using first-principles calculations, we demonstrate that an Fe monolayer can assume very different magnetic phases on hcp ͑0001͒ and fcc ͑111͒ surfaces of 4d-and 5d-transition metals. Due to the substrates' d-band filling, the nearest-neighbor exchange coupling of Fe changes gradually from antiferromagnetic ͑AFM͒ for Fe films on Tc, Re, Ru, and Os to ferromagnetic on Rh, Ir, Pd, and Pt. In combination with the topological frustration on the triangular lattice of these surfaces the AFM coupling results in a 120°Néel structure for Fe on Re and Ru and an unexpected double-row-wise AFM structure on Rh, which is a superposition of left-and right-rotating 90°spin spirals. DOI: 10.1103/PhysRevB.79.094411 PACS number͑s͒: 75.70.Ak, 71.15.Mb Triggered by the discovery of the giant-magnetoresistance effect and the demand to realize spintronic device concepts, 1 magnetic nanostructures on surfaces have been a focus of experimental and theoretical research for more than 20 years now. In particular, there has been a tremendous effort to grow ultrathin transition-metal films on metal surfaces and to characterize and explain their magnetic properties. It is now generally believed that these structurally simple systems are well understood and more complex nanostructures such as atomic chains, clusters, or molecules on surfaces have moved into the spotlight of today's research. [2][3][4][5][6][7] Therefore, it came as a big surprise when it was experimentally shown that the prototypical ferromagnet Fe becomes a two-dimensional ͑2D͒ antiferromagnet on the W͑001͒ surface. 8 Combining spin-polarized scanning tunneling microscopy and first-principles calculations, it has been further demonstrated that complex magnetic order can be obtained even in single monolayer ͑ML͒ magnetic films on nonmagnetic substrates. For example, recently a spin-spiral state was discovered for a Mn ML on W͑110͒ ͑Ref. 9͒ and for a Mn ML on W͑001͒ ͑Ref. 10͒ and a nanoscale magnetic structure was found for an Fe ML on Ir͑111͒. 11 Surfaces of 4d-and 5d-transition metals ͑TMs͒ such as W, Re, Ru, or Ir have been particularly attractive from an experimental point of view as ultrathin 3d-TM films can often be grown pseudomorphically and without intermixing. 12-16 However, there has been controversy in the past about reports concerning dead magnetic layers and absence of magnetic order in ultrathin films on these surfaces. 14,15 The fundamental key to many unresolved puzzles may be the itinerant character of TMs resulting in competing exchange interactions beyond nearest neighbors and higher-order spin interactions beyond the Heisenberg model. The latter interactions have been proposed to play a role in transition metals; however, to our knowledge, no unambiguous proof of their importance has been given.Here, we use first-principles calculations to demonstrate that a hexagonal Fe ML can assume very different magnetic phases on a triangular lattice provided by hcp ͑0001͒ and fcc ͑111͒ surfaces of 4d-and 5d-transition metals, which are also experimentally accessib...

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PtxRu1−x/Ru(0001) surface alloys—formation and atom distribution

Cited by 79 publications

References 82 publications

Hydrogen adsorption on bimetallic PdAu(111) surface alloys: minimum adsorption ensemble, ligand and ensemble effects, and ensemble confinement

Hydrogen adsorption on bimetallic PdAu(111) surface alloys: minimum adsorption ensemble, ligand and ensemble effects, and ensemble confinement

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

Complex magnetism of iron monolayers on hexagonal transition metal surfaces from first principles

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