Interaction of CO and deuterium with bimetallic, monolayer Pt-island/film covered Ru(0001) surfaces

Hartmann, Heinrich; Diemant, Thomas; Bansmann, Joachim; Behm, R. Jürgen

doi:10.1039/c2cp41434a

Cited by 22 publications

(48 citation statements)

References 59 publications

(130 reference statements)

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“…0.8 ML, is possible also under UHV conditions by using a different adsorption channel. It follows a previous publication, [11] where we speculated on the existence of such spill-over behavior based on temperature programmed desorption (TPD) measurements. Such spill-over processes are well known from heterogeneous catalysis [10] and have also been discussed for adsorption on bimetallic surfaces; direct quantitative evidence for that, however, remains scarce.…”

Section: Introductionsupporting

confidence: 62%

Kinetically Limited CO Adsorption: Spill‐Over as a Highly Effective Adsorption Pathway on Bimetallic Surfaces

2013

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We demonstrate that the (local) adsorbed carbon monoxide, COad , coverage on the Pt-free areas of bimetallic Pt/Ru(0001) surfaces (a Ru(0001) substrate partly covered by Pt monolayer islands) can be increased to ∼0.80 monolayers (ML), well above the established saturation COad coverage of 0.68 ML, even under ultrahigh vacuum conditions by using spill-over of CO adsorbed on the Pt islands to the Ru areas as an highly effective adsorption channel. The apparent COad saturation coverage of 0.68 ML on pure Ru(0001) is identified as due to kinetic limitations, hindering further uptake from the gas phase, rather than being caused by thermodynamic reasons. This spill-over mechanism is proposed to be a general phenomenon for adsorption on bimetallic surfaces.

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Section: Introductionsupporting

confidence: 62%

Kinetically Limited CO Adsorption: Spill‐Over as a Highly Effective Adsorption Pathway on Bimetallic Surfaces

2013

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“…[78] will make the adsorption energy less negative by roughly 0.1 eV as compared to 0.25 ML H ad . This is in agreement with trends found in thermal desorption experiments (also known as temperature programmed desorption, TPD) of deuterium on Ru(0001) in UHV [79][80][81], as well as the discussion in the previous section, in which a constant coverage of 0.5 ML was assumed for the potential region E < 0.2 V in H 2 -saturated electrolyte and E < 0.1 V in H 2 -free electrolyte. D 2 is commonly used in place of H 2 in TPD experiments, because its background signal from the residual gas in the vacuum chamber of the mass spectrometer is much lower.…”

Section: Ru(0001): Cyclic Voltammetry In Perchloric Acidsupporting

confidence: 76%

“…Reproduced with permission from refs. [80,81] surface alloy formation, as shown elsewhere [7,44,83,84]. Since the adsorption energies on mixed PtRu sites will be similar to those on the Pt bilayer [40,60], however, those two influences cannot be properly disentangled.…”

Section: Ru(0001): Cyclic Voltammetry In Perchloric Acidmentioning

confidence: 96%

“…D 2 is commonly used in place of H 2 in TPD experiments, because its background signal from the residual gas in the vacuum chamber of the mass spectrometer is much lower. Figure 7a shows a set of thermal desorption spectra of D 2 from Ru(0001) recorded after increasing gas dosages [80,81]. The leading edges of the spectra indicates the temperature region where desorption sets in at relevant rates.…”

Section: Ru(0001): Cyclic Voltammetry In Perchloric Acidmentioning

confidence: 99%

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Electrochemical Kinetics: a Surface Science-Supported Picture of Hydrogen Electrochemistry on Ru(0001) and Pt/Ru(0001)

Mercer

Hoster

2017

Electrocatalysis

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In this short review, we compare the kinetics of hydrogen desorption in vacuum to those involved in the electrochemical hydrogen evolution/oxidation reactions (HER/ HOR) at two types of atomically smooth model surfaces: bare Ru(0001) and the same surface covered by a 1.1 atomic layer thick Pt film. Low/high H 2 (D 2 ) desorption rates at room temperature in vacuum quantitatively correspond to low/high exchange current densities for the HOR/HER in electrochemistry. In view of the Bvolcano plot^concept, these represent two surfaces that adsorb hydrogen atoms, H ad , too strongly and too weakly, respectively. Atomically smooth, vacuum annealed model surfaces are the closest approximation to the idealized slab geometries typically studied by density functional theory (DFT). A predictive volcano plot based on DFT-based adsorption energies for the H ad intermediates agrees well with the experiments if two things are considered: (i) the steady-state coverage of H ad intermediates and (ii) local variations in film thickness. The sluggish HER/HOR kinetics of Ru(0001) allows for excellent visibility of cyclic voltammetry (CV) features even in H 2 -saturated solution. The CV switches between a H ad -and a OH ad -/O ad -dominated regime, but the presence of H 2 in the electrolyte increases the H ad -dominated potential window by a factor of two. Whereas in plain electrolyte two electrochemical adsorption processes compete in forming adlayers, it is one electrochemical and one chemical one in the case of H 2 -saturated electrolyte. We demonstrate and quantitatively explain that dissociative H 2 adsorption is more important than H + discharge for H ad formation in the low potential regime on Ru(0001).

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“…S5). However, what weakens CO adsorption also lessens the adsorption of H and O species 23,24,38 , thereby lowering the HOR activity per site and the oxidative removal of CO. Therefore, a dedicated balance is needed to assure optimal performance.…”

Section: Resultsmentioning

confidence: 99%

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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Interaction of CO and deuterium with bimetallic, monolayer Pt-island/film covered Ru(0001) surfaces

Cited by 22 publications

References 59 publications

Kinetically Limited CO Adsorption: Spill‐Over as a Highly Effective Adsorption Pathway on Bimetallic Surfaces

Kinetically Limited CO Adsorption: Spill‐Over as a Highly Effective Adsorption Pathway on Bimetallic Surfaces

Electrochemical Kinetics: a Surface Science-Supported Picture of Hydrogen Electrochemistry on Ru(0001) and Pt/Ru(0001)

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

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