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Structure of water adsorbed on the open Cu(110) surface: H-up, H-down, or both?
Stockholm University, Faculty of Science, Department of Physics.
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2006 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 429, no 4-6, 415-419 p.Article in journal (Refereed) Published
Abstract [en]

We investigated the structure of the water monolayer on an open surface, Cu(1 1 0), at low temperature. We found that water adsorbs molecularly, adopting a 2:1 ratio of H-down and H-up configurations. This behavior of water on an open surface is quite different to the behavior on close-packed surfaces, such as Pt(1 1 1) and Ru(0 0 0 1), where water adsorbs primarily H-down, but can be understood on the basis of a range of different water adsorption sites across the observed (7 × 8) unit cell.

Place, publisher, year, edition, pages
2006. Vol. 429, no 4-6, 415-419 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-24765DOI: 10.1016/j.cplett.2006.08.048OAI: oai:DiVA.org:su-24765DiVA: diva2:198272
Note
Part of urn:nbn:se:su:diva-7435Available from: 2008-03-18 Created: 2008-03-18 Last updated: 2010-12-21Bibliographically approved
In thesis
1. Water-Metal Surfaces: Insights from core-level spectroscopy and density functional theory
Open this publication in new window or tab >>Water-Metal Surfaces: Insights from core-level spectroscopy and density functional theory
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Computational methods are combined with synchrotron-based techniques to analyze the structure and bonding of water and water plus hydroxyl at metal surfaces under UHV and at near-ambient conditions. Water-metal interaction plays a crucial role in a multitude of cosmic, atmospheric and biological phenomena as well as heterogeneous catalysis, electrochemistry and corrosion. A spotlight of renewed interest has recently been cast on water-metal systems due to their relevance for surface chemical reactions related to the production and utilization of hydrogen as a clean energy carrier. In particular, H2O and OH are essential reaction intermediates in the renewable production of hydrogen from sunlight and water and in fuel cell electrocatalysis.

Fuel cells are considered one of the most promising power generation technologies for a sustainable energy future. A mechanistic understanding of the oxygen reduction reaction (ORR) pathway, including the role of electronic and geometric structure of the catalyst, is essential to the design of more efficient fuel cell catalysts. This is intimately connected to fundamental factors that affect the ability to form water-metal bonds as well as the site occupation and orientation of the adsorbed H2O and OH at active metal surfaces.

Key relationships related to critical issues in the fuel cell reaction are illuminated by the synergy of theory and experiment in this thesis. We emerge with a detailed understanding of the structure of the water-metal interface and the factors that rule the wettability of a metal surface, including geometric and electronic structure effects and the influence of coadsorbed species. We show that the preferred microscopic orientation of the water monolayer has consequences for macroscopic properties, and reveal the origin of the hydrophobic water layer. Finally, we identify a cooperativity effect that drives the stability of the mixed water/hydroxyl layer at metal surfaces, an important ORR intermediate.

Place, publisher, year, edition, pages
Stockholm: Fysikum, 2008. 74 p.
Keyword
water, hydroxyl, metal, surfaces, x-ray spectroscopy, density functional theory, bonding, fuel cell
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-7435 (URN)978-91-7155-607-3 (ISBN)
Public defence
2008-04-17, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Available from: 2008-03-18 Created: 2008-03-18Bibliographically approved
2. Structure, Bonding and Chemistry of Water and Hydroxyl on Transition Metal Surfaces
Open this publication in new window or tab >>Structure, Bonding and Chemistry of Water and Hydroxyl on Transition Metal Surfaces
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The structure, bonding and chemistry of water and hydroxyl on metal surfaces are presented. Synchrotron based x-ray photoelectron- and x-ray absorption spectroscopy along with density functional theory calculations mainly form the basis of the results. Conditions span the temperature range 35 - 520 K and pressures from ultra-high vacuum (~10 fAtm) to near ambient pressures (~1 mAtm). The results provide, e.g, new insights on the importance of hydrogen bonding for surface chemical kinetics.

Water adsorbs intact on the Pt(111), Ru(001) and Cu(110) surfaces at low temperatures forming 2-dimensional wetting layers where bonding to the metal (M) mainly occurs via H2O-M and M-HOH bonds. Observed isotope differences in structure and kinetics for H2O and D2O adsorption on Ru(001) are due to qualitatively different surface chemistries. D2O desorbs intact but H2O dissociates in kinetic competition with desorption similar to the D2O/Cu(110) system. The intact water layers are very sensitive to x-ray and electron induced damage.

The mixed H2O:OH phase on Ru(001) consists of stripe-like structures 4 to 6 Ru lattice parameters wide where OH decorates the edges of the stripes. On Pt(111), two different long-range ordered mixed H2O:OH structures are found to be inter-related by geometric distortions originating from the asymmetric H-bond donor-acceptor properties of OH towards H2O.

Water adsorption on Cu(110) was studied at near ambient conditions and compared to Cu(111). Whereas Cu(111) remains clean, Cu(110) holds significant amounts of water in a mixed H2O:OH layer. The difference is explained by the differing activation barriers for water dissociation, leading to the presence of OH groups on Cu(110) which lowers the desorption kinetics of water by orders of magnitude due to the formation of strong H2O-OH bonds. By lowering the activation barrier for water dissociation on Cu(111) by pre-adsorbing atomic O, generating adsorbed OH, similar results to those on Cu(110) are obtained.

Place, publisher, year, edition, pages
Stockholm: Fysikum, 2006. 62 p.
Keyword
core-level spectroscopy, surface chemistry, water, hydroxyl, metal surfaces, adsorption, structure, hydrogen bonding
National Category
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-1246 (URN)91-7155-318-5 (ISBN)
Public defence
2006-09-26, sal FR4, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Available from: 2006-08-31 Created: 2006-08-31 Last updated: 2010-12-21Bibliographically approved

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