Surface segregation energies in transition-metal alloys

Ruban, Andrei V.; Skriver, Hans Lomholt; Nørskov, Jens K.

doi:10.1103/physrevb.59.15990

Cited by 969 publications

(854 citation statements)

References 66 publications

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“…S3). The energy for the Ru(AB)-RuPt(ACBA) partial-alloy model is much higher than those of the Pt bilayer models (for example, 1,000 meV relative to the Ru(ABAB)-Pt(AB) model), indicating that the Pt atoms preferentially stay on top of the Ru surfaces, consistent with the predication based on calculated surface segregation energies 33 . Driven by entropy and with the presence of steps on real surfaces, disordered surface alloys were observed when the Ru(0001) crystals with a 0.5 to 1 Pt ML were annealed at temperatures between 800 and 1,350 K 34 .…”

Section: Resultssupporting

confidence: 74%

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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Section: Resultssupporting

confidence: 74%

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

et al. 2013

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“…have been shown to exhibit enhanced activity toward the OER. Several rationales have been proposed [48,49] including enhanced chemisorption of intermediates; a lattice change of Pt that results in the shortening of Pt Pt interatomic distances by alloying; the formation of skin Pt which has increased d-electron vacancy of the thin Pt surface layer caused by the underlying alloy and the anchor effect of alloy metals on a carbon carrier. Theoretical studies have been carried out in an effort to understand the enhanced activity of the bimetallic alloy.…”

Section: On Bimetallic Alloysmentioning

confidence: 99%

Current status of ab initio quantum chemistry study for oxygen electroreduction on fuel cell catalysts

Shi

Zhang

Liu

et al. 2006

Electrochimica Acta

143

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Recent progress in the ab initio quantum chemistry study of cathode oxygen reduction on fuel cell catalysts is reviewed with emphasis on density functional theory and ab initio molecular dynamics methods. The capabilities of these methods are illustrated using examples of oxygen adsorption on transition metals and alloys, and the reduction mechanism. Ab initio studies can calculate adsorption geometry, energy, the dissociation energy barrier, reversible potential, activation energy, and potential dependant properties for elementary electron transfer steps. Even though ab initio study in this field is still at an early stage, it has already demonstrated its predictive ability in the trend of adsorption energy on transition metals and alloys, and illustrated its potential in identifying better electrocatalysts.

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“…Theoretical studies on clean surfaces composition of binary random alloys have been carried out on the base of ab initio calculations of the surface segregation energies of transition metal impurities at the most closed-packed surfaces of other transition metals [26,27]. Calculations made in the case of a Pt matrix indicate that a solute as Ru would tend to remain in the interior of the host and vice versa, in a Ru matrix Pt would tend to segregate to the surface [28].…”

Section: Differential Heats Of Adsorptionmentioning

confidence: 99%

Synthesis and characterization of carbon black supported Pt–Ru alloy as a model catalyst for fuel cells

et al. 2004

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Surface segregation energies in transition-metal alloys

Cited by 969 publications

References 66 publications

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

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

Current status of ab initio quantum chemistry study for oxygen electroreduction on fuel cell catalysts

Synthesis and characterization of carbon black supported Pt–Ru alloy as a model catalyst for fuel cells

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