Ellipsometry and dems study of the electrooxidation of methanol at Pt and Ru- and Sn- promoted Pt

Frelink, T; Visscher, Whm Wil; Cox, AP; Veen, van Jar Rob

doi:10.1016/0013-4686(95)00034-c

Cited by 106 publications

(55 citation statements)

References 26 publications

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“…Apparently in the presence of methanol less Ru-oxide film is "seen" on the surface, which implies that it is removed by reaction with methanol. For Pt partially covered with Ru adatoms or with upd Sn we found a similar effect [18]; in both systems the adatom-oxide features diminish or are completely absent. The disappearance of the metal-oxide layer in the presence of methanol supports the bifunctional mechanism in which the promoting metal transfers oxygen to Pt-COH, cf.…”

Section: Measurementssupporting

confidence: 63%

On the role of Ru and Sn as promotors of methanol electro-oxidation over Pt

1995

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The role of Ru and Sn on the methanol oxidation over Pt was investigated for three different systems viz. Pt covered with adatom layers of Ru and Sn, electro-codeposited Pt-Ru and carbon supported Pt-Ru. By following the oxide growth on the Pt-promoter metal electrodes with ellipsometry it was found that in the presence of methanol the surface oxides of the promotor metal are no longer present on the surface. This supports the bifunctional model of the promotor action. DEMS measurements at Pt with submonolayer coverage of Ru or Sn revealed that the current efficiency of the methanol oxidation to CO 2 is increased in the presence of Ru or Sn and that the onset potential of the oxidation keeps lowering with increasing amounts of the promoting metal. On electrodeposited Pt-Ru systems the adsorption of methanol already takes place at potentials in the hydrogen range. These results seem to point to an electronic (ligand) effect. This is further corroborated by activity measurements at carbon supported Pt-Ru with very small particles, which show a tenfold higher activity compared with the Ru-free system.It is concluded that the promoting action of Ru and Sn may involve both a bifunctional and an electronic (ligand) effect.

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Section: Measurementssupporting

confidence: 63%

On the role of Ru and Sn as promotors of methanol electro-oxidation over Pt

1995

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“…It is also a byproduct of the electro-oxidation of small organic molecules. For both anodic electrochemical processes, bimetallic catalysts have been generated by the deposition of sub-monolayer amounts of other transition metals on well defined platinum surfaces [24,26], by alloys [17,18,21,33], or via colloidal chemistry [23,34], on highly dispersed carbon supported particles in the nanoscale range [5±9, 25,27,28,30,31]. Carbon supported Pt±Sn and Pt±Ru catalysts have been shown to be the best candidates for the electrochemical oxidation of carbon monoxide, and methanol, respectively.…”

Section: Introductionmentioning

confidence: 99%

Electro‐oxidation of Carbon Monoxide and Methanol on Carbon‐Supported Pt–Sn Nanoparticles: a DEMS Study

et al. 2002

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A comparative study between carbon supported Platinum–Tin (Pt–Snsyn), synthesized via the carbonyl route, and the commercial (Pt3Sn) from E–TEK is reported. The electro‐oxidation of methanol and adsorbed CO, in sulphuric acid medium, were used as probes to evaluate the performance of these electrocatalysts. In‐line differential mass spectrometry (DEMS) was used for this purpose. Both nanoparticulate materials had a mean particle size of = 1.68 ± 0.72 nm, and = 3.58 ± 1.94 nm, respectively. It is demonstrated that, under the same experimental conditions, our homemade Pt–Snsyn is less sensitive to poisoning by CO. This observation was again verified during the oxidation of methanol. These results are discussed in terms of the local disorder of the particles surface atoms, favourably induced by size effect and the preparation route employed.

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“…3 The superior performance of binary catalysts (Pt-Sn, Pt-Re, Pt-Mo, and Pt-Ru [4][5][6][7][8] relative to Pt has been ascribed to two effects. 9,10 In the bifunctional model, the oxophilic metal is thought to provide sites for water adsorption.…”

Section: Introductionmentioning

confidence: 99%

Structural and Electrochemical Characterization of Binary, Ternary, and Quaternary Platinum Alloy Catalysts for Methanol Electro-oxidation

et al. 1998

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The bifunctional model for methanol electro-oxidation suggests that competent catalysts should contain at least two types of surface elements: those that bind methanol and activate its C-H bonds and those that adsorb and activate water. Our previous work considered phase equilibria and relative Pt-C and M-O (M ) Ru, Os) bond strengths in predicting improved activity among single-phase Pt-Ru-Os ternary alloys. By addition of a correlation with M-C bond strengths (M ) Pt, Ir), it is possible to rationalize the recent combinatorial discovery of further improved Pt-Ru-Os-Ir quaternaries. X-ray diffraction experiments show that these quaternary catalysts are composed primarily of a nanocrystalline face-centered cubic (fcc) phase, in combination with an amorphous minor component. For catalysts of relatively high Ru content, the lattice parameter deviates positively from that of the corresponding arc-melted fcc alloy, suggesting that the nanocrystalline fcc phase is Pt-rich. Anode catalyst polarization curves in direct methanol fuel cells (DMFC's) at 60°C show that the best Pt-Ru-Os-Ir compositions are markedly superior to Pt-Ru, despite the higher specific surface area of the latter. A remarkable difference between these catalysts is revealed by the methanol concentration dependence of the current density. Although the rate of oxidation is zero order in [CH 3 OH] at potentials relevant to DMFC operation (250-325 mV vs RHE) at Pt-Ru, it is approximately first order at Pt-Ru-Os-Ir electrodes. This finding implies that the quaternary catalysts will be far superior to Pt-Ru in DMFC's constructed from electrolyte membranes that resist methanol crossover, in which higher concentrations of methanol can be used.

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Ellipsometry and dems study of the electrooxidation of methanol at Pt and Ru- and Sn- promoted Pt

Cited by 106 publications

References 26 publications

On the role of Ru and Sn as promotors of methanol electro-oxidation over Pt

On the role of Ru and Sn as promotors of methanol electro-oxidation over Pt

Electro‐oxidation of Carbon Monoxide and Methanol on Carbon‐Supported Pt–Sn Nanoparticles: a DEMS Study

Structural and Electrochemical Characterization of Binary, Ternary, and Quaternary Platinum Alloy Catalysts for Methanol Electro-oxidation

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