From Adlayer Islands to Surface Alloy: Structural and Chemical Changes on Bimetallic PtRu/Ru(0001) Surfaces

Diemant, Thomas; Bergbreiter, Andreas; Bansmann, Joachim; Hoster, Harry E.; Behm, R. Jürgen

doi:10.1002/cphc.201000391

Cited by 29 publications

(33 citation statements)

References 55 publications

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“…For instance, specific structural elements that are present only in low concentrations in the final surface may appear in much higher concentrations during the structure formation process, allowing a better identification of their structure and of their electronic/chemical properties, which in turn may be important for the understanding of the properties of the final surface. The wealth of information available had been demonstrated, for example, for the formation of PtRu/Ru(0001),8 PtCu/Cu(111),9 PtCu/Pt(111)10–12 and PdAg/Pd(111)13, 14 surface alloys.…”

Section: Introductionmentioning

confidence: 99%

Ag on Pt(111): Changes in Electronic and CO Adsorption Properties upon PtAg/Pt(111) Monolayer Surface Alloy Formation

2015

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The electronic and chemical (adsorption) properties of bimetallic Ag/Pt(111) surfaces and their modification upon surface alloy formation, that is, during intermixing of Ag and Pt atoms in the top atomic layer upon annealing, were studied by X-ray photoelectron spectroscopy (XPS) and, using CO as probe molecule, by temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), respectively. The surface alloys are prepared by deposition of sub-monolayer Ag amounts on a Pt(111) surface at room temperature, leading to extended Ag monolayer islands on the substrate, and subsequent annealing of these surfaces. Surface alloy formation starts at ≈600-650 K, which is evidenced by core-level shifts (CLSs) of the Ag(3d5/2 ) signal. A distinct change of the CO adsorption properties is observed when going to the intermixed PtAg surface alloys. Most prominently, we find the growth of a new desorption feature at higher temperature (≈550 K) in the TPD spectra upon surface alloy formation. This goes along with a shift of the COad -related IR bands to lower wave number. Surface alloy formation is almost completed after heating to 700 K.

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Section: Introductionmentioning

confidence: 99%

Ag on Pt(111): Changes in Electronic and CO Adsorption Properties upon PtAg/Pt(111) Monolayer Surface Alloy Formation

2015

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“…In order to minimize edge effects, the surface was annealed at 700 K after Pt deposition, which leads to island sizes of 10-20 nm at 0.2 ML Pt and larger at higher coverages, respectively. [15]…”

Section: Introductionmentioning

confidence: 99%

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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“…12,21 STM images reveal that the concentration of defects such as step edges and kinks appears similar to those found on single crystal surfaces of Pt and Ru. 21 Infrared studies comparing low temperature adsorption of CO on Pt/Ru(0001) annealed at 700 K to PtRu/Ru(0001) NSAs annealed at 1300 K have been conducted previously. These studies showed bands consistent with CO adsorbed at the undercoordinated edge sites of the Pt islands following small CO exposures on the low temperature annealed surface, whereas the fully intermixed PtRu NSA formed by annealing to ∼1300 K only showed bands consistent with CO adsorption on Pt sites after fully saturating the surface alloy with CO. 21 This provides further evidence for the low concentration of defect sites of the intermixed PtRu/ Ru(0001) NSA.…”

Section: Introductionmentioning

confidence: 65%

CO Adsorption on PtRu/Ru(0001) Near Surface Alloys from Ultrahigh Vacuum to Millitorr Pressures

Starr

Bluhm

2014

J. Phys. Chem. C

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We have used ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to investigate the adsorption of CO on PtRu/Ru(0001) near surface alloys (NSA) at 300 K and pressures from ultrahigh vacuum to 0.04 Torr. We observe differences in the fraction of Pt covered by adsorbed CO with changing Pt concentrations (0.36, 0.73, and 0.94 ML) in the NSA. For all alloy compositions and CO pressures, the amount of CO adsorbed on Pt sites in the alloy is less than what is observed on pure Pt(111). Further, the fraction of Pt sites covered by CO on the 0.36 and 0.73 ML Pt NSA surfaces are similar but lower than on the 0.94 ML Pt NSA surface. These observations support the concept of a decrease in the local adsorption energy of CO on Pt sites in alloy surfaces compared to pure Pt(111). We also found a correlation between the fraction of Pt covered by CO with the binding energy of the Pt 4f 7/2 core level: the fraction of Pt covered by CO decreases with increasing Pt 4f 7/2 binding energy. This observation may provide a simple analytical test for CO tolerance of PtRu alloy catalysts used in polymer electrolyte fuel cells.

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From Adlayer Islands to Surface Alloy: Structural and Chemical Changes on Bimetallic PtRu/Ru(0001) Surfaces

Cited by 29 publications

References 55 publications

Ag on Pt(111): Changes in Electronic and CO Adsorption Properties upon PtAg/Pt(111) Monolayer Surface Alloy Formation

Ag on Pt(111): Changes in Electronic and CO Adsorption Properties upon PtAg/Pt(111) Monolayer Surface Alloy Formation

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

CO Adsorption on PtRu/Ru(0001) Near Surface Alloys from Ultrahigh Vacuum to Millitorr Pressures

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