uu.seUppsala universitets publikasjoner
Endre søk
Begrens søket
12 1 - 50 of 62
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Abdi-Jalebi, Mojtaba
    et al.
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge, England.
    Pazoki, Meysam
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Philippe, Bertrand
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Dar, M. Ibrahim
    Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photon & Interfaces, Lausanne, Switzerland.
    Alsari, Mejd
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge, England.
    Sadhanala, Aditya
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge, England.
    Diyitini, Giorgio
    Univ Cambridge, Dept Mat Sci & Met, Charles Babbage Rd, Cambridge, England.
    Imani, Roghayeh
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Lilliu, Samuele
    Univ Sheffield, Dept Phys & Astron, Sheffield, S Yorkshire, England; UAE Ctr Crystallog, Dubai, U Arab Emirates.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Rensmo, Håkan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Gratzel, Michael
    Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photon & Interfaces, Lausanne, Switzerland.
    Friend, Richard H.
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge, England.
    Dedoping of Lead Halide Perovskites Incorporating Monovalent Cations2018Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, nr 7, s. 7301-7311Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report significant improvements in the optoelectronic properties of lead halide perovskites with the addition of monovalent ions with ionic radii close to Pb2+. We investigate the chemical distribution and electronic structure of solution processed CH3NH3PbI3 perovskite structures containing Na+, Cu+, and Ag+, which are lower valence metal ions than Pb2+ but have similar ionic radii. Synchrotron X-ray diffraction reveals a pronounced shift in the main perovskite peaks for the monovalent cation-based films, suggesting incorporation of these cations into the perovskite lattice as well as a preferential crystal growth in Ag+ containing perovskite structures. Furthermore, the synchrotron X-ray photoelectron measurements show a significant change in the valence band position for Cu- and Ag-doped films, although the perovskite bandgap remains the same, indicating a shift in the Fermi level position toward the middle of the bandgap. Such a shift infers that incorporation of these monovalent cations dedope the n-type perovskite films when formed without added cations. This dedoping effect leads to cleaner bandgaps as reflected by the lower energetic disorder in the monovalent cation-doped perovskite thin films as compared to pristine films. We also find that in contrast to Ag+ and Cu+, Na+ locates mainly at the grain boundaries and surfaces. Our theoretical calculations confirm the observed shifts in X-ray diffraction peaks and Fermi level as well as absence of intrabandgap states upon energetically favorable doping of perovskite lattice by the monovalent cations. We also model a significant change in the local structure, chemical bonding of metal-halide, and the electronic structure in the doped perovskites. In summary, our work highlights the local chemistry and influence of monovalent cation dopants on crystallization and the electronic structure in the doped perovskite thin films.

  • 2.
    Barcaro, Giovanni
    et al.
    CNR, IPCF, Inst Chem & Phys Proc, Via G Moruzzi 1, I-56124 Pisa, Italy.
    Sernenta, Luca
    CNR, IPCF, Inst Chem & Phys Proc, Via G Moruzzi 1, I-56124 Pisa, Italy.
    Monti, Susanna
    CNR, ICCOM, Inst Chem Organometall Cpds, Via G Moruzzi 1, I-56124 Pisa, Italy.
    Carravetta, Vincenzo
    CNR, IPCF, Inst Chem & Phys Proc, Via G Moruzzi 1, I-56124 Pisa, Italy.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Dynamical and Structural Characterization of the Adsorption of Fluorinated Alkane Chains onto CeO22018Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 41, s. 23405-23413Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The widespread use of ceria-based materials and the need to design suitable strategies to prepare eco-friendly CeO2 supports for effective catalytic screening induced us to extend our computational multiscale protocol to the modeling of the hybrid organic/oxide interface between prototypical fluorinated linear alkane chains (polyethylene-like oligomers) and low-index ceria surfaces. The combination of quantum chemistry calculations and classical reactive molecular dynamics simulations provides a comprehensive picture of the interface and discloses, at the atomic level, the main causes of typical adsorption modes. The data show that at room temperature. a moderate. percentage` of fluorine atoms (around 25%) can enhance the interaction of the organic chains by anchoring strongly pivotal fluorines to the channels of the underneath ceria (100) surface, whereas an excessive content can remarkably reduce this interaction because of the repulsion between fluorine and the negatively charged oxygen of the surface.

  • 3.
    Broqvist, Peter
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Wolf, Matthew J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    van Duin, Adri C. T.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    ReaxFF Force-Field for Ceria Bulk, Surfaces, and Nanoparticles2015Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, nr 24, s. 13598-13609Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have developed a reactive force-field of the ReaxFF type for stoichiometric ceria (CeO2) and partially reduced ceria (CeO2-x). We describe the parametrization procedure and provide results validating the parameters in terms of their ability to accurately describe the oxygen chemistry of the bulk, extended surfaces, surface steps, and nanoparticles of the material. By comparison with our reference electronic structure method (PBE+U), we find that the stoichiometric bulk and surface systems are well reproduced in terms of bulk modulus, lattice parameters, and surface energies. For the surfaces, step energies on the (111) surface are also well described. Upon reduction, the force-field is able to capture the bulk and surface vacancy formation energies (E-vac), and in particular, it reproduces the E-vac variation with depth from the (110) and (111) surfaces. The force-field is also able to capture the energy hierarchy of differently shaped stoichiometric nanoparticles (tetrahedra, octahedra, and cubes), and of partially reduced octahedra. For these reasons, we believe that this force-field provides a significant addition to the method repertoire available for simulating redox properties at ceria surfaces.

  • 4.
    Broqvist, Peter
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Zhang, Chao
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Du, Dou
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kebede, Getachew
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Rafieefar, Ali
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Mitev, Pavlin D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Chemistry of Complex Materials2017Konferansepaper (Annet vitenskapelig)
  • 5.
    Broqvist, Peter
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Zhang, Chao
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Mitev, Pavlin D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Chemistry of Complex Materials2019Konferansepaper (Annet vitenskapelig)
  • 6.
    Castleton, Christopher
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria2007Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, nr 24, s. 244704-244704-11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in CeO2 (ceria) as a function of U in density functional theory studies with the rotationally invariant forms of the LDA+U and GGA+U functionals. The four nearest neighbor Ce ions always relax outwards, with those not carrying localized Ce4f charge moving furthest. Several quantification schemes show that the charge starts to become localized at U~3 eV and that the degree of localization reaches a maximum at ~6 eV for LDA+U or at ~5.5 eV for GGA+U. For higher U it decreases rapidly as charge is transferred onto second neighbor O ions and beyond. The localization is never into atomic corelike states; at maximum localization about 80-90% of the Ce4f charge is located on the two nearest neighboring Ce ions. However, if we look at the total atomic charge we find that the two ions only make a net gain of (0.2-0.4)e each, so localization is actually very incomplete, with localization of Ce4f electrons coming at the expense of moving other electrons off the Ce ions. We have also revisited some properties of defect-free ceria and find that with LDA+U the crystal structure is actually best described with U=3-4 eV, while the experimental band structure is obtained with U=7-8 eV. (For GGA+U the lattice parameters worsen for U>0 eV, but the band structure is similar to LDA+U.) The best overall choice is U~6 eV with LDA+U and ~5.5 eV for GGA+U, since the localization is most important, but a consistent choice for both CeO2 and Ce2O3, with and without vacancies, is hard to find.

  • 7.
    Castleton, Christopher W. M.
    et al.
    Nottingham Trent Univ, Sch Sci & Technol, Nottingham NG11 8NS, England;Malardalen Univ, Div Phys & Math Nat Sci Didact, Box 883, SE-72123 Vasteras, Sweden.
    Lee, Amy
    Nottingham Trent Univ, Sch Sci & Technol, Nottingham NG11 8NS, England.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Benchmarking Density Functional Theory Functionals for Polarons in Oxides: Properties of CeO22019Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 9, s. 5164-5175Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine methods for studying polarons in metal oxides with density functional theory (DFT), using the example of cerium dioxide and the functionals, local density approximation + U (LDA+U), generalized gradient approximation + U (GGA+U) in the Perdew-Burke-Ernzerhof parametrization (PBE+U), as well as the hybrid functionals B3LYP, Heyd Scuseria Ernzerhof (HSE)03, HSE06, and PBEO. We contrast the four polaron energies commonly reported in different parts of the literature: formation energy, localization/relaxation energy, density-of-states level, and polaron-hopping activation barrier. Qualitatively, all these functionals predict "small" (Holstein) polarons on the scale of a single lattice site, although LDA +U and GGA+U are more effective than the hybrids at localizing the Ce 4f electrons. The improvements over pure LDA/GGA appear because of changes in the filled Ce 4f states when using LDA/GGA+U but due to changes in the empty Ce 4f states when using the hybrids. DFT is shown to have sufficient correlation to predict both adiabatic and (approximate) diabatic hopping barriers. Overall, LDA+U = 6 eV provides the best description in comparison to the experiment, followed by GGA+U = 5 eV. The hybrids are worse, tending to overestimate the gap and significantly underestimate the polaron-hopping barriers.

  • 8.
    Deak, Peter
    et al.
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Aradi, Balint
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Frauenheim, Thomas
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Kavan, Ladislaw
    Acad Sci Czech Republic, J Heyrovsky Inst Phys Chem, Dolejkova 3, CZ-18223 Prague 8, Czech Republic..
    Water splitting and the band edge positions of TiO22016Inngår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 199, s. 27-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The possibility of splitting water by UV-light on a TiO2 electrode has created great interest in the material, however, it has been later questioned whether rutile can do the job at all without external bias. Anatase was suggested instead, but its efficiency is still a subject of debate. The problem is related to the position of the band edges, that is, of the Fermi-level (E-F), with respect to the redox potentials of water. Here we present hybrid-functional calculations to align the band structures with the vacuum level, assuming the rutile (110) and anatase (101) surface being exposed to water. Our results show that both are capable of water splitting if no adsorbates other than molecular water are present. On a fully hydroxylated surface (i.e., H+ and OH adsorption on undercoordinated surface oxygen and titanium atoms, respectively), E-F is only similar to 0.5 eV above the H+/H-2 potential in case of anatase, and - depending on the level of reduction roughly at, or below it for rutile. We also show, that the band edges (and E-F) shift up if OH+ groups dominate the surface, increasing the driving force for water splitting. This is in line with the experience on titania reduced in hydrogen. Our results are further confirmed by calculating E-F without the presence of water, and comparing it to work function measurements by photoelectron spectroscopy.

  • 9.
    Dennis Larsson, Ernst
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    DFT studies of CO2 hydrogenation on Ru/TiO2(101)2017Konferansepaper (Annet vitenskapelig)
  • 10. Dennis Larsson, Ernst
    et al.
    Pazoki, Meysam
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Computational Green Chemistry2017Konferansepaper (Annet vitenskapelig)
  • 11.
    Du, Dou
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Simulated temperature programmed reduction by H2 — a key to understanding OSC on nanoceriaManuskript (preprint) (Annet vitenskapelig)
  • 12.
    Du, Dou
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi. Uppsala Univ, Dept Chem, Angstrom Lab, Box 538, S-75121 Uppsala, Sweden.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    From Ceria Clusters to Nanoparticles: Superoxides and Supercharging2019Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 3, s. 1742-1750Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several studies have reported a dramatically increased oxygen storage capacity (OSC) for small ceria nanoparticles (∼5 nm). Both experiments and theory have correlated this effect with superoxide ion formation. In previous studies, density functional theory (DFT) calculations with the PBE+U density functional have been used, and the obtained results were only in qualitative agreement with the experimental observations. One severe problem is the underbinding of the O2 molecule upon superoxide ion formation, which suggests that such species should not exist above room temperature. In this work, we use hybrid DFT functional to resolve this problem. We find that the discrepancy between theory and experiment originates from an incorrect estimate of the energy associated with the localized f-electrons with respect to the oxygen p-levels. By using average O2 adsorption energies from hybrid DFT calculations, extrapolated to large nanoparticles (3−10 nm), in conjunction with first-order desorption kinetics, we find that superoxide ions are indeed stable on nanosized ceria well above room temperature, in accordance with experiments.

  • 13.
    Du, Dou
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kocmaruk, Bojana
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Simulated temperature programmed desorption experiments for calcined nanoceria powders2020Inngår i: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 384, s. 252-259Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory calculations (DFT), coupled with microkinetic modelling, have been used to simulate Temperature Programmed Desorption (TPD) experiments for calcined ceria nanopowders with the aim to gain insight into the chemistry governing their high redox activity. Our simulations consider two main nanoparticle models. One is a perfect ceria octahedron supercharged with adsorbed oxygen molecules turned into superoxide ions, as has previously been used to explain the enhanced oxygen storage capacity (OSC) in nanoceria. The other model is a variant where we have introduced oxygen vacancies under ridge Ce ions, thereby reducing their coordination numbers to five. The results from our microkinetic modelling suggest that including such five-coordinated Ce adsorption sites results in a TPD spectrum that better matches the experimental counterpart in terms of both peak position and width. In addition, this new structural model allows for the co-existence of Ce3+ ions, superoxide ions and O-2 molecules, as seen in experiments in the literature.

  • 14.
    Duchon, Tomas
    et al.
    Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany;Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, Prague 18000, Czech Republic.
    Hackl, Johanna
    Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany.
    Mueller, David N.
    Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Du, Dou
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Senanayake, Sanjaya D.
    Brookhaven Natl Lab, Dept Chem, Upton, NY 11973 USA.
    Mouls, Caroline
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström. Lab Nacl Luz Sincrotron, BR-13083 Campinas, SP, Brazil.
    Gottlob, Daniel M.
    Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany.
    Khan, Muhammad I.
    Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany.
    Cramm, Stefan
    Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany.
    Veltruska, Katerina
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, Prague 18000, Czech Republic.
    Matolin, Vladimir
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, Prague 18000, Czech Republic.
    Nemsak, Slavomir
    Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany;Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA 94720 USA.
    Schneider, Claus M.
    Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany;Univ Calif Davis, Dept Phys, Davis, CA 95616 USA.
    Establishing structure-sensitivity of ceria reducibility: real-time observations of surface hydrogen interactions2020Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 8, nr 11, s. 5501-5507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first Layer of atoms on an oxide cataLyst provides the first sites for adsorption of reactants and the Last sites before products or oxygen are desorbed. We employ a unique combination of morphological, structural, and chemical analyses of a model ceria cataLyst with different surface terminations under an H2 environment to unequivocally establish the effect of the Last Layer of atoms on surface reduction. (111) and (100) terminated epitaxiaL isLands of ceria are simultaneously studied in situ allowing for a direct investigation of the structure reducibility relationship under identical conditions. Kinetic rate constants of Ce4+ to Ce3+ transformation and equilibrium concentrations are extracted for both surface terminations. Unlike the kinetic rate constants, which are practically the same for both types of isLands, more pronounced oxygen release, and overall higher reducibility were observed for (100) isLands compared to (111) ones. The findings are in agreement with coordination -Limited oxygen vacancy formation energies calculated by density functional theory. The results point out the important aspect of surface terminations in redox processes, with particular impact on the catalytic reactions of a variety of catalysts.

  • 15.
    Gerz, Isabelle
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Mindemark, Jonas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Oligomer electrolytes for light-emitting electrochemical cells: Experimental and computational insights2018Konferansepaper (Fagfellevurdert)
  • 16.
    Gerz, Isabelle
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
    Lindh, E. Mattias
    Umea Univ, Dept Phys, Organ Photon & Elect Grp, SE-90187 Umea, Sweden.
    Thordarson, Pall
    Univ New South Wales, Australian Ctr Nanomed, Sch Chem, Sydney, NSW 2052, Australia;Univ New South Wales, ARC Ctr Excellence Convergent Bionano Sci & Techn, Sydney, NSW 2052, Australia.
    Edman, Ludvig
    Umea Univ, Dept Phys, Organ Photon & Elect Grp, SE-90187 Umea, Sweden.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Mindemark, Jonas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Oligomer Electrolytes for Light-Emitting Electrochemical Cells: Influence of the End Groups on Ion Coordination, Ion Binding, and Turn-on Kinetics2019Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, nr 43, s. 40372-40381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electrolyte is an essential constituent of the light-emitting electrochemical cell (LEC), since its operating mechanism is dependent on the redistribution of mobile ions in the active layer. Recent developments of new ion transporters have yielded high-performance devices, but knowledge about the interactions between the ionic species and the ion transporters and the influence of these interactions on the LEC performance is lacking. We therefore present a combined computational and experimental effort that demonstrates that the selection of the end group in a star-branched oligomeric ion transporter based on trimethylolpropane ethoxylate has a paramount influence on the ionic interactions in the electrolyte and thereby also on the performance of the corresponding LECs. With hydroxyl end groups, the the salt is strongly coordinated to the ion transporter, which leads to suppression of ion pairing, but the penalty is a hindered ion release and a slow turn-on for the LEC devices. With methoxy end groups, an intermediate coordination strength is seen together with the formation of contact ion pairs, but the LEC performance is very good with fast turn-on. Using a series of ion transporters with alkyl carbonate end groups, the ion transporter:cation coordination strength is lowered further, but the turn-on kinetics are slower than what is seen for devices comprising the methoxy end-capped ion transporter.

  • 17.
    Hellström, Matti
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Jorner, Kjell
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
    Bryngelsson, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
    Huber, Stefan E.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Frauenheim, Thomas
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    An SCC-DFTB Repulsive Potential for Various ZnO Polymorphs and the ZnO-Water System2013Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 33, s. 17004-17015Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have developed an efficient scheme for the generation of accurate repulsive potentials for self-consistent charge density-functional-based tight-binding calculations, which involves energy-volume scans of bulk polymorphs with different coordination numbers. The scheme was used to generate an optimized parameter set for various ZnO polymorphs. The new potential was subsequently tested for ZnO bulk, surface, and nanowire systems as well as for water adsorption on the low-index wurtzite (10 (1) over bar0) and (11 (2) over bar0) surfaces. By comparison to results obtained at the density functional level of theory, we show that the newly generated repulsive potential is highly transferable and capable of capturing most of the relevant chemistry of ZnO and the ZnO/water interface.

  • 18.
    Jolla, Kullgren
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Lu, ZS.
    Yang, ZX
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Sulfidation and Sulfur Recovery from SO2 over Ceria2014Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 31, s. 17499-17504Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sulfidation, sulfation and sulfur recovery of ceria(111) and ceria(110) surfaces are studied usingDensity Functional Theory(DFT) calculations. Under reducing atmosphere SO2 adsorption leadsto stable surface sulfate species on the (110) surface and sulfides on the (111) surface. A mechanismfor sulfur recovery from SO2 is also presented. In this mechanism SO2 reacts with a surface sulfideto form a thio-sulfite species. This thio-sulfite species is subsequently reduced by an oxygen vacancyto form a monodentate S2O structure. This structure can then be desorbed as S2 (g).

  • 19.
    Kebede, Getachew
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Mitev, Pavlin D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hydrogen-Bond Relations for Surface OH Species2018Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 9, s. 4849-4858Artikkel, omtale (Fagfellevurdert)
    Abstract [en]

    This paper concerns thin water films and their hydrogen-bond patterns on ionic surfaces. As far as we are aware, this is the first time H-bond correlations for surface water and hydroxide species are presented in the literature while hydrogen-bond relations in the solid state have been scrutinized for at least five decades. Our data set, which was derived using density functional theory, consists of 116 unique surface OH groups–intact water molecules as well as hydroxides–on MgO(001), CaO(001) and NaCl(001), covering the whole range from strong to weak to no H-bonds. The intact surface water molecules are found to always be redshifted with respect to the gas-phase water OH vibrational frequency, whereas the surface hydroxide groups are either redshifted (OsH) or blueshifted (OHf) compared to the gas-phase OH frequency. The surface H-bond relations are compared with the traditional relations for bulk crystals. We find that the “ν(OH) vs R(H···O)” correlation curve for surface water does not coincide with the solid state curve: it is redshifted by about 200 cm–1 or more. The intact water molecules and hydroxide groups on the ionic surfaces essentially follow the same H-bond correlation curve.

  • 20.
    Kettner, Miroslav
    et al.
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, V Holesovickach 2, Prague 18000 8, Czech Republic;Friedrich Alexander Univ Erlangen Nurnberg, Chair Interface Res & Catalysis, Egerlandstr 3, D-91058 Erlangen, Germany.
    Duchon, Tomas
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, V Holesovickach 2, Prague 18000 8, Czech Republic;Forschungszentrum Julich, Peter Grunberg Inst 6, D-52425 Julich, Germany.
    Wolf, Matthew J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi. Univ Bath, Dept Phys, Bath BA2 7AY, Avon, England.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Senanayake, Sanjaya D.
    Brookhaven Natl Lab, Dept Chem, Upton, NY 11973 USA.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Veltruska, Katerina
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, V Holesovickach 2, Prague 18000 8, Czech Republic.
    Nehasil, Vaclav
    Charles Univ Prague, Fac Math & Phys, Dept Surface & Plasma Sci, V Holesovickach 2, Prague 18000 8, Czech Republic.
    Anion-mediated electronic effects in reducible oxides: Tuning the valence band of ceria via fluorine doping2019Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, nr 4, artikkel-id 044701Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Combining experimental spectroscopy and hybrid density functional theory calculations, we show that the incorporation of fluoride ions into a prototypical reducible oxide surface, namely, ceria(111), can induce a variety of nontrivial changes to the local electronic structure, beyond the expected increase in the number of Ce3+ ions. Our resonant photoemission spectroscopy results reveal new states above, within, and below the valence band, which are unique to the presence of fluoride ions at the surface. With the help of hybrid density functional calculations, we show that the different states arise from fluoride ions in different atomic layers in the near surface region. In particular, we identify a structure in which a fluoride ion substitutes for an oxygen ion at the surface, with a second fluoride ion on top of a surface Ce4+ ion giving rise to F 2p states which overlap the top of the O 2p band. The nature of this adsorbate F--Ce4+ resonant enhancement feature suggests that this bond is at least partially covalent. Our results demonstrate the versatility of anion doping as a potential means of tuning the valence band electronic structure of ceria.

  • 21.
    Kettner, Miroslav
    et al.
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Duchon, Tomas
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Wolf, Matthew
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kus, Peter
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Sevcikova, Klara
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic.;Elettra Sincrotrone Trieste, Trieste, Italy..
    Rafaj, Zdenek
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Nehasil, Vaclav
    Charles Univ Prague, Dept Surface & Plasma Sci, Prague, Czech Republic..
    Modification of valence band of ceria via anion doping with fluorine2017Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Artikkel i tidsskrift (Annet vitenskapelig)
  • 22.
    Kim, Byung-Hyun
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Wolf, Matthew J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Multiscale modelling of CeO2 nano-interfaces2017Konferansepaper (Annet vitenskapelig)
  • 23.
    Kim, Byung-Hyun
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi. Korea Inst Energy Res, Platform Technol Lab, Daejeon, South Korea.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Wolf, Matthew J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Multiscale Modeling of Agglomerated Ceria Nanoparticles: Interface Stability and Oxygen Vacancy Formation2019Inngår i: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 7, artikkel-id 203Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interface formation and its effect on redox processes in agglomerated ceria nanoparticles (NPs) have been investigated using a multiscale simulation approach with standard density functional theory (DFT), the self-consistent-charge density functional tight binding (SCC-DFTB) method, and a DFT-parameterized reactive force-field (ReaxFF). In particular, we have modeled Ce40O80 NP pairs, using SCC-DFTB and DFT, and longer chains and networks formed by Ce40O80 or Ce132O264 NPs, using ReaxFF molecular dynamics simulations. We find that the most stable {111}/{111} interface structure is coherent whereas the stable {100}/{100} structures can be either coherent or incoherent. The formation of {111}/{111} interfaces is found to have only a very small effect on the oxygen vacancy formation energy, E-vac. The opposite holds true for {100}/{100} interfaces, which exhibit significantly lower E-vac values than the bare surfaces, despite the fact that the interface formation eliminates reactive {100} facets. Our results pave the way for an increased understanding of ceria NP agglomeration.

    Fulltekst (pdf)
    fulltext
  • 24.
    Kocmaruk, Bojana
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Computational modelling of nanosystems2019Konferansepaper (Annet vitenskapelig)
  • 25.
    Kocmaruk, Bojana
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Computational modelling of nanosystems2019Konferansepaper (Annet vitenskapelig)
  • 26.
    Krishna, Akshay
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Wadbro, Eddie
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys.
    Kholer, Christof
    Mitev, Pavlin D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    A material chemistry tool for generating two body potentials2019Konferansepaper (Annet vitenskapelig)
  • 27.
    Krishna Ammothum Kandy, Akshay
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Can water affect the shape of CeO2 nanopartiles?2017Konferansepaper (Annet vitenskapelig)
  • 28.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Oxygen Vacancy Chemistry in Ceria2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Cerium(IV) oxide (CeO2), ceria, is an active metal oxide used in solid oxide fuel cells and for the purification of exhaust gases in vehicle emissions control. Behind these technically important applications of ceria lies one overriding feature, namely ceria's exceptional reduction-oxidation properties. These are enabled by the duality of the cerium ion which easily toggles between Ce4+ and Ce3+. Here the cerium 4f electrons and oxygen vacancies (missing oxygen ions in the structure) are key players. In this thesis, the nature of ceria's f electrons and oxygen vacancies are in focus, and examined with theoretical calculations.

    It is shown that for single oxygen vacancies at ceria surfaces, the intimate coupling between geometrical structure and electron localisation gives a multitude of almost degenerate local energy mimima. With many vacancies, the situation becomes even more complex, and not even state-of-the-art quantum-mechanical calculations manage to predict the experimentally observed phenomenon of vacancy clustering. Instead, an alternative set of computer experiments managed to produce stable vacancy chains and trimers consistent with experimental findings from the literature and revealed a new general principle for surface vacancy clustering.

    The rich surface chemistry of ceria involves not only oxygen vacancies but also other active oxygen species such as superoxide ions (O2). Experiments have shown that nanocrystalline ceria demonstrates an unusually large oxygen storage capacity (OSC) and an appreciable low-temperature redox activity, which have been ascribed to superoxide species. A mechanism explaining these phenomena is presented.

    The ceria surface is also known to interact with SOx molecules, which is relevant both in the context of sulfur poisoning of ceria-based catalysts and sulfur recovery from them. In this thesis, the sulfur species and key mechanisms involved are identified.

    Delarbeid
    1. Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria
    Åpne denne publikasjonen i ny fane eller vindu >>Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria
    2007 (engelsk)Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, nr 24, s. 244704-244704-11Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in CeO2 (ceria) as a function of U in density functional theory studies with the rotationally invariant forms of the LDA+U and GGA+U functionals. The four nearest neighbor Ce ions always relax outwards, with those not carrying localized Ce4f charge moving furthest. Several quantification schemes show that the charge starts to become localized at U~3 eV and that the degree of localization reaches a maximum at ~6 eV for LDA+U or at ~5.5 eV for GGA+U. For higher U it decreases rapidly as charge is transferred onto second neighbor O ions and beyond. The localization is never into atomic corelike states; at maximum localization about 80-90% of the Ce4f charge is located on the two nearest neighboring Ce ions. However, if we look at the total atomic charge we find that the two ions only make a net gain of (0.2-0.4)e each, so localization is actually very incomplete, with localization of Ce4f electrons coming at the expense of moving other electrons off the Ce ions. We have also revisited some properties of defect-free ceria and find that with LDA+U the crystal structure is actually best described with U=3-4 eV, while the experimental band structure is obtained with U=7-8 eV. (For GGA+U the lattice parameters worsen for U>0 eV, but the band structure is similar to LDA+U.) The best overall choice is U~6 eV with LDA+U and ~5.5 eV for GGA+U, since the localization is most important, but a consistent choice for both CeO2 and Ce2O3, with and without vacancies, is hard to find.

    Emneord
    Other nonmetals, Point defects and defect clusters, Density functional theory, local density approximation, gradient and other corrections
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-12806 (URN)10.1063/1.2800015 (DOI)000251987800030 ()
    Tilgjengelig fra: 2008-01-15 Laget: 2008-01-15 Sist oppdatert: 2019-02-19bibliografisk kontrollert
    2. B3LYP calculations of cerium oxides
    Åpne denne publikasjonen i ny fane eller vindu >>B3LYP calculations of cerium oxides
    Vise andre…
    2010 (engelsk)Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, nr 5, s. 054110-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this paper we evaluate the performance of density functional theory with the B3LYP functional for calculations on ceria (CeO2) and cerium sesquioxide (Ce2O3). We demonstrate that B3LYP is able to describe CeO2 and Ce2O3 reasonably well. When compared to other functionals, B3LYP performs slightly better than the hybrid functional PBE0 for the electronic properties but slightly worse for the structural properties, although neither performs as well as LDA+U(U = 6 eV) or PBE+U(U = 5 eV). We also make an extensive comparison of atomic basis sets suitable for periodic calculations of these cerium oxides. Here we conclude that there is currently only one type of cerium basis set available in the literature that is able to give a reasonable description of the electronic structure of both CeO2 and Ce2O3. These basis sets are based on a 28 electron effective core potential (ECP) and 30 electrons are attributed to the valence space of cerium. Basis sets based on 46 electron ECPs fail for these materials

    sted, utgiver, år, opplag, sider
    American Institute of Physics, 2010
    HSV kategori
    Forskningsprogram
    Kemi med inriktning mot oorganisk kemi
    Identifikatorer
    urn:nbn:se:uu:diva-121560 (URN)10.1063/1.3253795 (DOI)000274319900011 ()
    Tilgjengelig fra: 2010-03-25 Laget: 2010-03-25 Sist oppdatert: 2019-02-19bibliografisk kontrollert
    3. Many Competing Ceria (110) Oxygen Vacancy Structures: From Small to Large Supercells
    Åpne denne publikasjonen i ny fane eller vindu >>Many Competing Ceria (110) Oxygen Vacancy Structures: From Small to Large Supercells
    2012 (engelsk)Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, nr 4, s. 044705-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We present periodic "DFT+U" studies of single oxygen vacancies on the CeO2(110) surface using a number of different supercells, finding a range of different local minimum structures for the vacancy and its two accompanying Ce(III) ions. We find three different geometrical structures in combination with a variety of different Ce(III) localization patterns, several of which have not been studied before. The desired trapping of electrons was achieved in a two-stage optimization procedure. We find that the surface oxygen nearest to the vacancy either moves within the plane towards the vacancy, or rises out of the surface into either a symmetric or an unsymmetric bridge structure. Results are shown in seven slab geometry supercells, p(2 x 1), p(2 x 2), p(2 x 3), p(3 x 2), p(2 x 4), p(4 x 2), and p(3 x 3), and indicate that the choice of supercell can affect the results qualitatively and quantitatively. An unsymmetric bridge structure with one nearest and one next-nearest neighbour Ce(III) ion (a combination of localizations not previously found) is the ground state in all (but one) of the supercells studied here, and the relative stability of other structures depends strongly on supercell size. Within any one supercell the formation energies of the different vacancy structures differ by up to 0.5 eV, but the same structure can vary by up to similar to 1 eV between supercells. Furthermore, finite size scaling suggests that the remaining errors (compared to still larger supercells) can also be similar to 1 eV for some vacancy structures.

    Emneord
    DFT, Ceria, (110), Vacancies, Supercell approximation
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-167996 (URN)10.1063/1.4723867 (DOI)000307611500053 ()
    Tilgjengelig fra: 2012-02-03 Laget: 2012-02-03 Sist oppdatert: 2019-02-19bibliografisk kontrollert
    4. Oxygen Vacancy Clustering at the Ceria(111) surface
    Åpne denne publikasjonen i ny fane eller vindu >>Oxygen Vacancy Clustering at the Ceria(111) surface
    Vise andre…
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Oxygen vacancy clustering at the ceria(111) surface have been studied with both force-field and density function theory methods. Two of the methods predict that stable clusters of surface oxygen vacancies should form on these surface, as seen in numerous experimental studies. We propose that vacancy clustering of both surface and sub-surface vacancies follow the simple principle of sharing their Ce(III) neighbors. For surface oxygen vacancies this leads to compact clusters separated by one surface lattice constant. On the other hand for sub-surface this leads to sparse clusters separated by two surface lattice constants.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-168002 (URN)
    Tilgjengelig fra: 2012-02-03 Laget: 2012-02-03 Sist oppdatert: 2014-07-25
    5. Supercharged Low-Temperature Oxygen Storage Capacity of Ceria at the Nanoscale
    Åpne denne publikasjonen i ny fane eller vindu >>Supercharged Low-Temperature Oxygen Storage Capacity of Ceria at the Nanoscale
    2013 (engelsk)Inngår i: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, nr 4, s. 604-608Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We provide an explanation for the experimental finding of a dramatically enhancedlow-temperature oxygen storage capacity for small ceria nanoparticles. At low temperature, small octahedral ceria nanoparticles will be understoichiometric at both oxidizing and reducing conditions without showing explicit oxygen vacancies. Instead, rather than becoming stoichiometric at oxidizing conditions, such particles are stabilized through oxygen adsorption forming superoxo (O-2(-)) ions and become in this way supercharged with oxygen. Thesupercharging effect is size-dependent and largest for small nanoparticles where it gives a direct increase in the oxygen storage capacity and simultaneously provides a source of active oxygenspecies at low temperatures.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-168004 (URN)10.1021/jz3020524 (DOI)000315432000010 ()
    Tilgjengelig fra: 2012-02-03 Laget: 2012-02-03 Sist oppdatert: 2019-02-19bibliografisk kontrollert
    6. SOx on ceria from adsorbed SO2
    Åpne denne publikasjonen i ny fane eller vindu >>SOx on ceria from adsorbed SO2
    Vise andre…
    2011 (engelsk)Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, nr 18, s. 184703-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Results from first-principles calculations present a rather clear picture of the interaction of SO2 with unreduced and partially reduced (111) and (110) surfaces of ceria. The Ce3+/Ce4+ redox couple, together with many oxidation states of S, give rise to a multitude of SOx species, with oxidation states from + III to + VI. SO2 adsorbs either as a molecule or attaches via its S-atom to one or two surface oxygens to form sulfite (SO32-) and sulfate (SO42-) species, forming new S-O bonds but never any S-Ce bonds. Molecular adsorption is found on the (111) surface. SO32- structures are found on both the (111) and (110) surfaces of both stoichiometric and partially reduced ceria. SO42-structures are observed on the (110) surface together with the formation of two reduced Ce3+ surface cations. SO2 can also partially heal the ceria oxygen vacancies by weakening a S-O bond, when significant electron transfer from the surface (Ce4f) into the lowest unoccupied molecular orbital of the SO2 adsorbate takes place and oxidizes the surface Ce3+ cations. Furthermore, we propose a mechanism that could lead to monodentate sulfate formation at the (111) surface.

    HSV kategori
    Forskningsprogram
    Kemi med inriktning mot oorganisk kemi
    Identifikatorer
    urn:nbn:se:uu:diva-154547 (URN)10.1063/1.3566998 (DOI)000290589900035 ()
    Tilgjengelig fra: 2011-06-07 Laget: 2011-06-07 Sist oppdatert: 2019-02-19bibliografisk kontrollert
    7. Sulfidation of ceria surfaces from sulfur and sulfur diffusion
    Åpne denne publikasjonen i ny fane eller vindu >>Sulfidation of ceria surfaces from sulfur and sulfur diffusion
    2012 (engelsk)Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 15, s. 8417-8425Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Even very low levels of sulfur contaminants can degrade the catalytic performance of cerium oxide. Here, the interaction of atomic sulfur with the ceria (111) and (110) surfaces has been studied using first-principles methods. Two sulfoxy species are identified: oxido-sulfate(2-) species (SO2-) on both the CeO2 (111) and (110) surfaces and hyposulfite (SO22-) on the (110) surface. Sulfide (S2-) is formed when a surface or a subsurface oxygen atoms is replaced by sulfur. These sulfide species are most stable at the surface. Furthermore, sulfite (SO32-) structures are found when sulfur is made to replaces one Ce in the ceria (111) and (110) surfaces. The calculated sulfur diffusion barriers are larger than 1.4 eV for both surfaces and thus sulfur is essentially immobile, providing a possible explanation for the sulfidation phenomena of the ceria-based catalysis. Thus we find three different species from interaction of S with Ceria which are all, due to their strong binding, capable of poisoning the surface, reduced or unreduced. Our results suggest that under reducing conditions, sulfur is likely to be found in the (111) surface (replacing oxygen) but on the (110) surface (as SO22-).

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-167999 (URN)10.1021/jp2092913 (DOI)000302924900010 ()
    Tilgjengelig fra: 2012-02-03 Laget: 2012-02-03 Sist oppdatert: 2019-02-19bibliografisk kontrollert
    8. Sulfidation and Sulfur Recovery from SO2 over Ceria
    Åpne denne publikasjonen i ny fane eller vindu >>Sulfidation and Sulfur Recovery from SO2 over Ceria
    2014 (engelsk)Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 31, s. 17499-17504Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Sulfidation, sulfation and sulfur recovery of ceria(111) and ceria(110) surfaces are studied usingDensity Functional Theory(DFT) calculations. Under reducing atmosphere SO2 adsorption leadsto stable surface sulfate species on the (110) surface and sulfides on the (111) surface. A mechanismfor sulfur recovery from SO2 is also presented. In this mechanism SO2 reacts with a surface sulfideto form a thio-sulfite species. This thio-sulfite species is subsequently reduced by an oxygen vacancyto form a monodentate S2O structure. This structure can then be desorbed as S2 (g).

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-168001 (URN)10.1021/jp4094673 (DOI)000340222300036 ()
    Tilgjengelig fra: 2012-02-03 Laget: 2012-02-03 Sist oppdatert: 2019-02-19bibliografisk kontrollert
    Fulltekst (pdf)
    fulltext
  • 29.
    Kullgren, Jolla
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Castleton, Christopher W. M.
    Müller, Carsten
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Ramo, David Muñoz
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    B3LYP calculations of cerium oxides2010Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, nr 5, s. 054110-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we evaluate the performance of density functional theory with the B3LYP functional for calculations on ceria (CeO2) and cerium sesquioxide (Ce2O3). We demonstrate that B3LYP is able to describe CeO2 and Ce2O3 reasonably well. When compared to other functionals, B3LYP performs slightly better than the hybrid functional PBE0 for the electronic properties but slightly worse for the structural properties, although neither performs as well as LDA+U(U = 6 eV) or PBE+U(U = 5 eV). We also make an extensive comparison of atomic basis sets suitable for periodic calculations of these cerium oxides. Here we conclude that there is currently only one type of cerium basis set available in the literature that is able to give a reasonable description of the electronic structure of both CeO2 and Ce2O3. These basis sets are based on a 28 electron effective core potential (ECP) and 30 electrons are attributed to the valence space of cerium. Basis sets based on 46 electron ECPs fail for these materials

  • 30.
    Kullgren, Jolla
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Ceria chemistry at the nanoscale: effect of the environment2013Inngår i: Solar Hydrogen And Nanotechnology Viii / [ed] Yosuke Kanai and David Prendergast, 2013, s. 88220D-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We use theoretical simulations to study how oxidative and humid environments affect the chemical composition, shape and structure of ceria nanoparticles. Based on our calculations, we predict that small stoichiometric ceria nanoparticles will have a very limited stability range when exposed to these environments. Instead, we find that reduced ceria nanoparticles are stabilized without changing their inherent shape through the adsorption of oxygen molecules in the form of superoxo species and water in the form of hydroxo species. Based on our results, we propose a redox-cycle for meta-stable ceria nanoparticles without the formation of explicit oxygen vacancies, which is important for understanding the low-temperature oxygen chemistry of ceria at the nanoscale.

  • 31.
    Kullgren, Jolla
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Supercharged Low-Temperature Oxygen Storage Capacity of Ceria at the Nanoscale2013Inngår i: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, nr 4, s. 604-608Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We provide an explanation for the experimental finding of a dramatically enhancedlow-temperature oxygen storage capacity for small ceria nanoparticles. At low temperature, small octahedral ceria nanoparticles will be understoichiometric at both oxidizing and reducing conditions without showing explicit oxygen vacancies. Instead, rather than becoming stoichiometric at oxidizing conditions, such particles are stabilized through oxygen adsorption forming superoxo (O-2(-)) ions and become in this way supercharged with oxygen. Thesupercharging effect is size-dependent and largest for small nanoparticles where it gives a direct increase in the oxygen storage capacity and simultaneously provides a source of active oxygenspecies at low temperatures.

  • 32.
    Kullgren, Jolla
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Castleton, Christopher
    School of Science and Technology, Nottingham Trent University.
    Many Competing Ceria (110) Oxygen Vacancy Structures: From Small to Large Supercells2012Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, nr 4, s. 044705-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present periodic "DFT+U" studies of single oxygen vacancies on the CeO2(110) surface using a number of different supercells, finding a range of different local minimum structures for the vacancy and its two accompanying Ce(III) ions. We find three different geometrical structures in combination with a variety of different Ce(III) localization patterns, several of which have not been studied before. The desired trapping of electrons was achieved in a two-stage optimization procedure. We find that the surface oxygen nearest to the vacancy either moves within the plane towards the vacancy, or rises out of the surface into either a symmetric or an unsymmetric bridge structure. Results are shown in seven slab geometry supercells, p(2 x 1), p(2 x 2), p(2 x 3), p(3 x 2), p(2 x 4), p(4 x 2), and p(3 x 3), and indicate that the choice of supercell can affect the results qualitatively and quantitatively. An unsymmetric bridge structure with one nearest and one next-nearest neighbour Ce(III) ion (a combination of localizations not previously found) is the ground state in all (but one) of the supercells studied here, and the relative stability of other structures depends strongly on supercell size. Within any one supercell the formation energies of the different vacancy structures differ by up to 0.5 eV, but the same structure can vary by up to similar to 1 eV between supercells. Furthermore, finite size scaling suggests that the remaining errors (compared to still larger supercells) can also be similar to 1 eV for some vacancy structures.

  • 33.
    Kullgren, Jolla
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kim, Byung-Hyun
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    SCC-DFTB simulations of ceria surfaces and nanoparticles2017Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    First principles modelling, using e.g. the density functional theory (DFT), has become a valuable tool in materials research. However, today’s computer resources limit the size and time scales that can be studied with such techniques, thereby hindering the full utilization of computational chemistry for large-scale systems in practice. Thus, new developments of reliable approximate and/or parameterized methods are needed.

    One promising approximate method, conceptually similar to the DFT, is the self-consistent charge density functional based tight binding method (SCC-DFTB). SCC-DFTB calculations are parameterized against DFT data (see illustration in Figure 1) and are at least two orders of magnitude faster than a standard semi-local DFT calculation. However, to obtain an accuracy comparable to DFT for complex oxides is a task that has proven to be a challenge.

    In this talk, I will present our SCC-DFTB parameterization effort for the technologically important reducible oxide CeO2.1 I will discuss the strategy we have developed for the parameterization and the special complication that follows with reducible oxides. Furthermore, I will demonstrate the applicability of the generated parameters and show results from validation by comparing to data obtained from DFT calculations for CeO2. I will show results for oxygen vacancy formation in various ceria structures of different dimensionality, ranging from 0D (nano) to 3D (bulk) and for oxygen adsorption on ceria nanoparticles and preliminary results regarding ceria nanoparticle agglomeration.

    Fulltekst (pdf)
    fulltext
  • 34.
    Kullgren, Jolla
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Wolf, Matthew J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Koehler, Christof
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Aradi, Balint
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Frauenheim, Thomas
    Univ Bremen, Bremen Ctr Computat Mat Sci, POB 330440, D-28334 Bremen, Germany..
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) Parameters for Ceria in 0D to 3D2017Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 8, s. 4593-4607Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reducible oxides such as CeO2 are challenging to describe with standard density-functional theory (DFT) due to the mixed valence states of the cations; they often require the use of non-standard correction schemes, and/or more computationally expensive methods. This adds a new layer of complexity when it comes to the generation of Slater-Koster tables and the corresponding repulsive potentials for self-consistent density-functional based tight-binding (SCC-DFTB) calculations of such materials. In this work, we provide guidelines for how to set up a parametrization scheme for mixed valence oxides within the SCC-DFTB framework, with a focus on reproducing structural and electronic properties as well as redox reaction energies calculated using a reference DFT method. This parametrization procedure was here used to generate parameters for Ce-O systems, with Ce in its +III or +IV formal oxidation states. The generated parameter set is validated by comparison with DFT calculations for various ceria (CeO2) and reduced ceria (CeO2-x) systems of different dimensionalities ranging from 0D (nanoparticles) to 3D (bulk). As oxygen vacancy defects in ceria are of crucial importance to many technological applications, special focus is directed toward the capability of describing such defects accurately.

  • 35.
    Kullgren, Jolla
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Wolf, Matthew J.
    Mitev, Pavlin D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Briels, Wim J.
    Computational Biophysics, University of Twente, Box 217, 7500 AE Enschede, The Netherlands, Forschungszentrum Jülich, ICS 3, D-52425 Jülich, Germany.
    Defect cluster at the CeO2(111) surface: A combined DFT and Monte-Carlo study2017Konferansepaper (Annet vitenskapelig)
    Download (pdf)
    sammanfattning
  • 36.
    Kullgren, Jolla
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Wolf, Matthew J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Mitev, Pavlin D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Briels, Wim J.
    Univ Twente, Computat Biophys, Box 217, NL-7500 AE Enschede, Netherlands.;Forschungszentrum Julich, ICS 3, D-52425 Julich, Germany..
    DFT-based Monte Carlo Simulations of Impurity Clustering at CeO2(111)2017Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 28, s. 15127-15134Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interplay between energetics and entropy in determining defect distributions at ceria(111) is studied using a combination of DFT+U and lattice Monte Carlo simulations. Our main example is fluorine impurities, although we also present preliminary results for surface hydroxyl groups. A simple classical force-field model was constructed from a training set of DFT+U data for all symmetrically inequivalent (F-)(n)(Ce3+)(n) nearest-neighbor clusters with n = 2 or 3. Our fitted model reproduces the DFT energies well. We find that for an impurity concentration of 15% at 600 K, straight and hooked linear fluorine clusters are surprisingly abundant, with similarities to experimental STM images from the literature. We also find that with increasing temperature the fluorine cluster sizes show a transition from being governed by an attractive potential to being governed by a repulsive potential as a consequence of the increasing importance of the entropy of the Ce3+ ions. The distributions of surface hydroxyl groups are noticeably different.

  • 37.
    Källquist, Ida
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Naylor, Andrew J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Baur, Christian
    Helmholtz Inst Ulm, Helmholtzstr 11, D-89081 Ulm, Germany.
    Chable, Johann
    Helmholtz Inst Ulm, Helmholtzstr 11, D-89081 Ulm, Germany.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Fichtner, Maximilian
    Helmholtz Inst Ulm, Helmholtzstr 11, D-89081 Ulm, Germany;Karlsruhe Inst Technol, Inst Nanotechnol, Box 3640, D-76021 Karlsruhe, Germany.
    Edström, Kristina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Brandell, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hahlin, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Degradation Mechanisms in Li2VO2F Li-Rich Disordered Rock-Salt Cathodes2019Inngår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, nr 16, s. 6084-6096Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The increased energy density in Li-ion batteries is particularly dependent on the cathode materials that so far have been limiting the overall battery performance. A new class of materials, Li-rich disordered rock salts, has recently been brought forward as promising candidates for next-generation cathodes because of their ability to reversibly cycle more than one Li-ion per transition metal. Several variants of these Li-rich cathode materials have been developed recently and show promising initial capacities, but challenges concerning capacity fade and voltage decay during cycling are yet to be overcome. Mechanisms behind the significant capacity fade of some materials must be understood to allow for the design of new materials in which detrimental reactions can be mitigated. In this study, the origin of the capacity fade in the Li-rich material Li2VO2F is investigated, and it is shown to begin with degradation of the particle surface that spreads inward with continued cycling.

  • 38.
    Langhammer, David
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Mitev, Pavlin D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Österlund, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    SO2 adsorption on rutile TiO2(110): An infrared reflection-absorption spectroscopy and density functional theory study2018Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 677, s. 46-51Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of SO2 on single crystalline TiO2(110) has been investigated by means of polarized infrared reflection-absorption spectroscopy (IRRAS) experiments and density functional theory (DFT) calculations. IR absorption bands were detected at 1324 cm(-1) and 985 cm(-1) with p-polarized light incident along both the [110] and [001] crystallographic directions at 123 K. When the temperature was increased to 153 K, the peak at 1324 cm(-1) disappears, while a new, weak band appears at 995 cm(-1). Simultaneously, a band at 995 cm(-1) also emerges with s-polarized light along the [110] direction. Based on the symmetry properties of the IRRAS spectra and accompanying ab initio simulations of the spectra employing a three layer model (vacuum-adsorbate-substrate), it is shown that the low temperature absorption IRRAS bands can be attributed to an SO3-like adsorbate structure. This is also the most stable adsorption structure (E-ad = - 0.58 eV) on the stoichiometric surface. The combined IRRAS and DFT results show that the band appearing at 995 cm(-1) is associated with a surface sulfite specie which is stabilized by residual surface water. The DFT calculations also revealed that a stable adsorption structure exists on a reduced TiO2 surface, where SO2 binds strongly to an oxygen vacancy site. It is suggested that this is an intermediate that form surface sulfate upon further reactions with water, although it was not observed on the stoichiometric surface studied in this work.

  • 39. Lu, Zhansheng
    et al.
    Müller, Carsten
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Yang, Zongxian
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    SOx on ceria from adsorbed SO22011Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, nr 18, s. 184703-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Results from first-principles calculations present a rather clear picture of the interaction of SO2 with unreduced and partially reduced (111) and (110) surfaces of ceria. The Ce3+/Ce4+ redox couple, together with many oxidation states of S, give rise to a multitude of SOx species, with oxidation states from + III to + VI. SO2 adsorbs either as a molecule or attaches via its S-atom to one or two surface oxygens to form sulfite (SO32-) and sulfate (SO42-) species, forming new S-O bonds but never any S-Ce bonds. Molecular adsorption is found on the (111) surface. SO32- structures are found on both the (111) and (110) surfaces of both stoichiometric and partially reduced ceria. SO42-structures are observed on the (110) surface together with the formation of two reduced Ce3+ surface cations. SO2 can also partially heal the ceria oxygen vacancies by weakening a S-O bond, when significant electron transfer from the surface (Ce4f) into the lowest unoccupied molecular orbital of the SO2 adsorbate takes place and oxidizes the surface Ce3+ cations. Furthermore, we propose a mechanism that could lead to monodentate sulfate formation at the (111) surface.

  • 40.
    Marchiori, Cleber
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Amber, Mace
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Multiscale Modeling of Battery Materials2019Konferansepaper (Annet vitenskapelig)
  • 41.
    Meier de Andrade, Ageo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    On the Importance of Dispersion in Electronic Structure Calculations of NanoAlloys2019Konferansepaper (Annet vitenskapelig)
  • 42.
    Meier de Andrade, Ageo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Rationalizing Results from Density Functional Theory in Terms of Exchange Energy and Dispersion Interactions2019Konferansepaper (Annet vitenskapelig)
  • 43.
    Meier de Andrade, Ageo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    vdW FUNCTIONALS AND DISPERSION CORRECTIONS IMPROVE ACCURACY IN DFT CALCULATIONS OF A BIMETALLIC CATALYST2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    There is high demand for versatile materials today, i.e. materials with flexible composition and tunable properties, but at the same time, affordable.  Nanoalloys, which can be tailored all the way down to the atomic scale, meet these requirements, and is expected to be a material class of great importance in many future technologies. One example is heterogeneous catalysis, where bimetallic nanoalloys have been used for long time to enhance catalytic processes, both when it comes to activity and selectivity for many chemical reactions.

    The tailoring of nanoalloys at the atomic scale requires detailed knowledge of how the structure and the composition (and size and shape) affects the desired properties. Here, experiments alone are too obtuse to decipher the often very complex relation between atomic level structure and properties; theory have an important role to fill here.

    The most popular theoretical methods used in materials science today is the density functional theory (DFT) [1].  The success of standard DFT to describe and predict bulk properties of metals and many complex alloys cannot be underestimated. However, for surfaces and nanoparticles, and some special alloys, the accuracy of the method is still questionable and here the lack of non-local correlation (dispersion) and inaccurate exchange description is believed to be the critical shortcomings. One way forward is therefore to improve upon these.

    In this work, we focus on the Ni-Sn bimetallic alloys, which improves the selectivity in hydrogenation reactions.  For the Ni-Sn system, we have systematically investigated the capability of several DFT functionals which explicitly accounts for dispersion, either through an a posteriori correction (Grimme D3 corrections) [2], or by integrating it self-consistently into the functional (vdW class of functionals) [3]. We have both modelled bulk phases along with the most important surface structures, and compared how the different methods describes structural, energetic and electronic properties. We find that the inclusion of dispersion mainly affects the structural and energetic properties, leading to better agreement to experimental data. Interestingly, the improved structural description also gives slightly modified electronic properties, both in terms of the d-band levels, and work functions.  

    Acknowledgements

    This work was carried out with the financial support of the Swedish Research Council (VR), the Swedish Foundation for International Cooperation in Research and Higher Education, STINT, Åforsk foundation and by the Swedish national strategic e-Science program eSSENCE. The simulations were performed using computational resources provided by the Swedish National Infrastructure for Computing (SNIC) at HPC2N and PDC.

    The authors are grateful to The Swedish Foundation for International Cooperation in Research and Higher Education, “Swedish Research Council” and and ÅForsk foundation for the financial support

    References

    [1] Klimes, J., Michaelides, A. J. Chem. Phys. 137, p 120901 (2012)

    [2] Grimme, S., et. al., J. Chem. Phys. 132, p 154104 (2010)

    [3] Berland, K, Hyldgaard, P., Phys. Rev. B, 89, p 035412 (2014)

  • 44.
    Meier de Andrade, Ageo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    vdW FUNCTIONALS AND DISPERSION CORRECTIONS IMPROVE ACCURACY IN DFT CALCULATIONS OF A BIMETALLIC CATALYST2019Konferansepaper (Annet vitenskapelig)
  • 45.
    Meier de Andrade, Ageo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    vdW FUNCTIONALS AND DISPERSION CORRECTIONS IMPROVE ACCURACY IN DFT CALCULATIONS OF A BIMETALLIC CATALYSTvdW FUNCTIONALS AND DISPERSION CORRECTIONS IMPROVE ACCURACY IN DFT CALCULATIONS OF A BIMETALLIC CATALYST2019Konferansepaper (Annet vitenskapelig)
  • 46.
    Meier de Andrade, Ageo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    What the eyes cannot see: The chemistry of a catalyst2017Konferansepaper (Annet vitenskapelig)
  • 47.
    Meier de Andrade, Ageo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Sá, Jacinto
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Insights into reactive nanoparticles2018Konferansepaper (Annet vitenskapelig)
  • 48.
    Meier de Andrade, Ageo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Sá, Jacinto
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Insights into reactive nanoparticles2019Konferansepaper (Annet vitenskapelig)
  • 49.
    Mirsakiyeva, Amina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Ebadi, Mahsa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Brandell, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Initial Steps in PEO Decomposition on a Li Metal Electrode2019Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 37, s. 22851-22857Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Poly(ethylene oxide) (PEO) is the most widely used compound as a solid-state (solvent-free) polymer electrolyte for Li batteries, mainly due to its low glass transition temperature (T-g) and ability to dissolve Li salts. It is also frequently suggested that its cathodic stability renders it possible to operate with Li metal anodes in the design of high energy density storage devices. However, little is still known about the true interfacial chemistry between Li metal and PEO and how these two materials interact with each other. We are here exploring this relationship by the means of density functional theory (DFT)-based modeling. Using bulk structures and isolated PEO chains, we have found that there is a strong thermodynamic driving force to oxidize Li metal into lithium oxide (Li2O) when PEO is decomposed into C2H4 and H-2, irrespectively of the PEO oligomer length. Explicit modeling of PEO on a Li(100) surface reveals that all steps in the decomposition are exothermic and that the PEO/Li metal system should have a layer of Li2O between the polymer electrolyte and the metal surface. These insights and the computational strategy adopted here could be highly useful to better tailor polymer electrolytes with favorable interfacial properties.

  • 50.
    Pazoki, Meysam
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Jacobsson, Jesper T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi.
    Cruz, Silver
    Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photomol Sci, CH-1015 Lausanne, Switzerland.; Benemerita Univ Autonoma Puebla, CIDS, Ave San Claudio & 18 Sur,Ciudad Univ,POB 1067, Puebla 72570, Mexico.
    Johansson, Malin B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Imani, Roghayeh
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Kullgren, Jolla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hagfeldt, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Johansson, Erik M. J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Boschloo, Gerrit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Photon Energy-Dependent Hysteresis Effects in Lead Halide Perovskite Materials2017Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 47, s. 26180-26187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lead halide perovskites have a range of spectacular properties and interesting phenomena and are a serious candidate for the next generation of photovoltaics with high efficiencies and low fabrication costs. An interesting phenomenon is the anomalous hysteresis often seen in current-voltage scans, which complicates accurate performance measurements but has also been explored to obtain a more comprehensive understanding of the device physics. Herein, we demonstrate a wavelength and illumination intensity dependency of the hysteresis in state-of-the-art perovskite solar cells with 18% power conversion efficiency (PCE), which gives new insights into ion migration. The perovskite devices show lower hysteresis under illumination with near band edge (red) wavelengths compared to more energetic (blue) excitation. This can be rationalized with thermalization-assisted ion movement or thermalization-assisted vacancy generation. These explanations are supported by the dependency of the photovoltage decay with illumination time and excitation wavelength, as well as by impedance spectroscopy. The suggested mechanism is that high-energy photons create hot charge carriers that either through thermalization can create additional vacancies or by release of more energetic phonons play a role in overcoming the activation energy for ion movement. The excitation wavelength dependency of the hysteresis presented here gives valuable insights into the photophysics of the lead halide perovskite solar cells.

    Fulltekst (pdf)
    fulltext
12 1 - 50 of 62
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf