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  • 1. Bagger, Alexander
    et al.
    Arán-Ais, Rosa M.
    Halldin Stenlid, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Campos dos Santos, Egon
    Arnarson, Logi
    Degn Jensen, Kim
    Escudero-Escribano, Mariá
    Roldan Cuanya, Beatriz
    Rossmeisl, Jan
    Ab Initio Cyclic Voltammetry on Cu(111), Cu(100) and Cu(110) in Acidic, Neutral and Alkaline Solutions2019In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 20Article in journal (Refereed)
    Abstract [en]

    Electrochemical reactions depend on the electrochemical interface between the electrode surfaces and the electrolytes. To control and advance electrochemical reactions there is a need to develop realistic simulation models of the electrochemical interface to understand the interface from an atomistic point-of-view. Here we present a method for obtaining thermodynamic realistic interface structures, a procedure we use to derive specific coverages and to obtain ab initio simulated cyclic voltammograms. As a case study, the method and procedure is applied in a matrix study of three Cu facets in three different electrolytes. The results have been validated by direct comparison to experimental cyclic voltammograms. The alkaline (NaOH) cyclic voltammograms are described by H* and OH*, while in neutral medium (KHCO3) the CO3* species are dominating and in acidic (KCl) the Cl* species prevail. An almost one-to-one mapping is observed from simulation to experiments giving an atomistic understanding of the interface structure of the Cu facets. Atomistic understanding of the interface at relevant eletrolyte conditions will further allow realistic modelling of electrochemical reactions of importance for future eletrocatalytic studies.

  • 2. Brinck, Tore
    et al.
    Stenlid, Joakim H.
    Stockholm University, Faculty of Science, Department of Physics.
    The Molecular Surface Property Approach: A Guide to Chemical Interactions in Chemistry, Medicine, and Material Science2019In: Advanced theory and simulations, ISSN 2513-0390, Vol. 2, no 1, article id 1800149Article in journal (Refereed)
    Abstract [en]

    The current status of the molecular surface property approach (MSPA) and its application for analysis and prediction of intermolecular interactions, including chemical reactivity, are reviewed. The MSPA allows for identification and characterization of all potential interaction sites of a molecule or nanoparticle by the computation of one or more molecular properties on an electronic isodensity surface. A wide range of interactions can be analyzed by three properties, which are well-defined within Kohn-Sham density functional theory. These are the electrostatic potential, the average local ionization energy, and the local electron attachment energy. The latter two do not only reflect the electrostatic contribution to a chemical interaction, but also the contributions from polarization and charge transfer. It is demonstrated that the MSPA has a high predictive capacity for non-covalent interactions, for example, hydrogen and halogen bonding, as well as organic substitution and addition reactions. The latter results open u p applications within drug design and medicinal chemistry. The application of MSPA has recently been extended to nanoparticles and extended surfaces of metals and metal oxides. In particular, nanostructural effects on the catalytic properties of noble metals are rationalized. The potential for using MSPA in rational design of heterogeneous catalysts is discussed.

  • 3.
    Halldin Stenlid, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Campos dos Santos, Egon
    Stockholm University, Faculty of Science, Department of Physics. Universidade Federal de Minas Gerais, Brazil.
    Johansson, Adam Johannes
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    On the Nature of the Cathodic Reaction during Corrosion of Copper in Anoxic Sulfide Solutions2019In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, no 6, p. C196-C208Article in journal (Refereed)
    Abstract [en]

    Sulfide-induced corrosion is expected to be the dominating long-term corrosion process for copper containers in technical concepts for deep geological disposal of spent nuclear fuel (SNF), adapted in several waste management programs around the world. The present study investigates the atomic-scale mechanism of the cathode side of the corrosion reaction using Density Functional Theory (DFT) calculations. Despite the central role of the reaction, neither the site of reaction nor the active species has been previously established. Here we compare the cathodic reaction leading to H-2-evolution on pure copper and on chalcocite (Cu2S) surfaces. The considered H-donors are OH-/H2O and HS-/H2S which are all available at the neutral to alkaline conditions anticipated at the SNF disposal sites. Assuming Volmer-Tafel-Heyrovsky kinetics, we find that the cathodic reactions are many orders of magnitude faster on copper compared to copper sulfide. Although we find that HS-/H2S have lower reaction barriers than H2O, our kinetic analysis suggest that H2O is expected to be the main H-source for the cathodic reaction under SNF repository conditions as results of the low sulfide concentrations (less than or similar to 10 mu M) expected in SNF repositories in Sweden, Finland and Canada.

  • 4.
    Halldin Stenlid, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Physics. KTH Royal Institute of Technology, Sweden.
    Johansson, Adam Johannes
    Brinck, Tore
    The local electron attachment energy and the electrostatic potential as descriptors of surface-adsorbate interactions2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 31, p. 17001-17009Article in journal (Refereed)
    Abstract [en]

    Two local reactivity descriptors computed by Kohn-Sham density functional theory (DFT) are used to predict and rationalize interactions of nucleophilic molecules (exemplified by CO and H2O) with transition metal (TM) and oxide surfaces. The descriptors are the electrostatic potential, V-S(r), and the local electron attachment energy, E-S(r), evaluated on surfaces defined by the 0.001 e Bohr(-3) isodensity contour. These descriptors have previously shown excellent abilities to predict regioselectivity and rank molecular as well as nanoparticle reactivities and interaction affinities. In this study, we generalize the descriptors to fit into the framework of periodic DFT computations. We also demonstrate their capabilities to predict local surface propensity for interaction with Lewis bases. It is shown that E-S(r) and V-S(r) can rationalize the interaction behavior of TM oxides and of fcc TM surfaces, including low-index, stepped and kinked surfaces spanning a wide range of interaction sites with varied coordination environments. Broad future applicability in surface science is envisaged for the descriptors, including heterogeneous catalysis and electrochemistry.

  • 5.
    Liu, Chang
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Hedström, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Stenlid, Joakim H.
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Amorphous, Periodic Model of a Copper Electrocatalyst with Subsurface Oxygen for Enhanced CO Coverage and Dimerization2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 8, p. 4961-4968Article in journal (Refereed)
    Abstract [en]

    Oxide-derived copper electrocatalysts have been found to possess excellent selectivity toward the production of multicarbon products from CO,. The presence of subsurface oxygen in these catalysts has been confirmed experimentally, but the resulting amorphous structure has yet to be captured by theoretical models. In this study, the role of subsurface oxygen atoms is investigated with density functional theory, using a disordered oxide-derived Cu surface model (d-ODCu). The presence of subsurface oxygen atoms increases the maximum adsorption coverage of the important CO intermediate but decreases that of H atoms because of electronic and geometric effects. However, this has no significant influence on the free-energy activation barrier or endothermicity of the CO-dimerization reaction step, allegedly the key to multicarbon product formation.

  • 6.
    Marks, Kess
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Besharat, Zahra
    Soldemo, Markus
    Önsten, Anneli
    Weissenrieder, Jonas
    Halldin Stenlid, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Göthelid, Mats
    Adsorption and decoposition of ethanol on Cu2O(111) and (100)2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 33, p. 20384-20392Article in journal (Refereed)
    Abstract [en]

    Ethanol dehydrogenation on metal oxides such as Cu2O is an important reaction for the production of renewable energy by fuel cells both via the production of H2 fuel and applied in direct alcohol fuel cells. To better understand this reaction we studied the adsorption, dissociation and desorption of ethanol on Cu2O(111) and (100) surfaces using high-resolution photoelectron spectroscopy (PES), vibrational sum frequency generation spectroscopy (SFG), and temperature programmed desorption (TPD) accompanied by density functional theory (DFT) calculations. On Cu2O(100) the first layer consists primarily of dissociatively adsorbed ethoxy. Second and third layers of ethanol physisorb at low temperature and desorb below 200 K. On the Cu2O(111) surface, adsorption is mixed as ethoxy, ethanol and the products following C-C cleavage, CHx and OCHx, are found in the first layer. Upon heating, products following both C-C and C-O bond breaking are observed on both surfaces and continued heating accentuates the molecular cracking. C-O cleavage occurs more on the (100) surface, whereas on the Cu2O(111) C-C cleavage dominates and occurs at lower temperatures than on the (100) surface. The increased ability of Cu2O(111) to crack ethanol is explained by the varied surface structure including both surface oxygen, electron rich O-vacancies and Cu.

  • 7. Tissot, Heloise
    et al.
    Wang, Chunlei
    Halldin Stenlid, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Brinck, Tore
    Weissenrieder, Jonas
    The Surface Structure of Cu2O(100): Nature of Defects2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 13, p. 7696-7704Article in journal (Refereed)
    Abstract [en]

    The Cu2O(100) surface is most favorably terminated by a (3,0;1,1) reconstruction under ultrahigh-vacuum conditions. As most oxide surfaces, it exhibit defects, and it is these sites that are focus of attention in this study. The surface defects are identified, their properties are investigated, and procedures to accurately control their coverage are demonstrated by a combination of scanning tunneling microscopy (STM) and simulations within the framework of density functional theory (DFT). The most prevalent surface defect was identified as an oxygen vacancy. By comparison of experimental results, formation energies, and simulated STM images, the location of the oxygen vacancies was identified as an oxygen vacancy in position B, located in the valley between the two rows of oxygen atoms terminating the unperturbed surface. The coverage of defects is influenced by the surface preparation parameters and the history of the sample. Furthermore, using low-energy electron beam bombardment, we show that the oxygen vacancy coverage can be accurately controlled and reach a complete surface coverage (1 per unit cell or 1.8 defects per nm(2)) without modification to the periodicity of the surface, highlighting the importance of using local probes when investigating oxide surfaces.

  • 8. Tissot, Heloise
    et al.
    Wang, Chunlei
    Halldin Stenlid, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Panahi, Mohammad
    Kaya, Sarp
    Soldemo, Markus
    Yazdi, Milad Ghadami
    Brinck, Tore
    Weissenrieder, Jonas
    Interaction of Atomic Hydrogen with the Cu2O(100) and (111) Surfaces2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 36, p. 22172-22180Article in journal (Refereed)
    Abstract [en]

    Reduction of Cu2O by hydrogen is a common preparation step for heterogeneous catalysts; however, a detailed understanding of the atomic reaction pathways is still lacking. Here, we investigate the interaction of atomic hydrogen with the Cu2O(100):(3,0;1,1) and Cu2O(111):(root 3 x root 3)R30 degrees surfaces using scanning tunneling microscopy (STM), low-energy electron diffraction, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). The experimental results are compared to density functional theory simulations. At 300 K, we identify the most favorable adsorption site on the Cu2O(100) surface: hydrogen atoms bind to an oxygen site located at the base of the atomic rows intrinsic to the (3,0;1,1) surface. The resulting hydroxyl group subsequently migrates to a nearby Cu trimer site. TPD analysis identifies H-2 as the principal desorption product. These observations imply that H-2 is formed through a disproportionation reaction of surface hydroxyl groups. The interaction of H with the (111) surface is more complex, including coordination to both Cu+ and O-CUS sites. STM and XPS analyses reveal the formation of metallic copper clusters on the Cu2O surfaces after cycles of hydrogen exposure and annealing. The interaction of the Cu clusters with the substrate is notably different for the two surface terminations studied: after annealing, the Cu clusters coalesce on the (100) termination, and the (3,0;1,1) reconstruction is partially recovered. Clusters formed on the (111) surface are less prone to coalescence, and the (root 3 x root 3)R30 degrees reconstruction was not recovered by heat treatment, indicating a weaker Cu cluster to support interaction on the (100) surface.

  • 9. Wang, Chunlei
    et al.
    Tissot, Heloise
    Halldin Stenlid, Joakim
    Stockholm University, Faculty of Science, Department of Physics. KTH Royal Institute of Technology, Sweden.
    Kaya, Sarp
    Weissenrieder, Jonas
    High-Density Isolated Fe1O3 Sites on a Single-Crystal Cu2O(100) Surface2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 23, p. 7318-7323Article in journal (Refereed)
    Abstract [en]

    Single-atom catalysts have recently been subject to considerable attention within applied catalysis. However, complications in the preparation of well-defined single-atom model systems have hampered efforts to determine the reaction mechanisms underpinning the reported activity. By means of an atomic layer deposition method utilizing the steric hindrance of the ligands, isolated Fe1O3 motifs were grown on a single-crystal Cu2O(100) surface at densities up to 0.21 sites per surface unit cell. Ambient pressure X-ray photoelectron spectroscopy shows a strong metal-support interaction with Fe in a chemical state close to 3+. Results from scanning tunneling microscopy and density functional calculations demonstrate that isolated Fe1O3 is exclusively formed and occupies a single site per surface unit cell, coordinating to two oxygen atoms from the Cu2O lattice and another through abstraction from O-2. The isolated Fe1O3 motif is active for CO oxidation at 473 K. The growth method holds promise for extension to other catalytic systems.

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