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Sökning: WFRF:(Jeschke S.)

  • Resultat 1-7 av 7
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  • Chernenkaya, A., et al. (författare)
  • Microscopic origin of the charge transfer in single crystals based on thiophene derivatives : A combined NEXAFS and density functional theory approach
  • 2016
  • Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606. ; 145:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the charge transfer mechanism in single crystals of DTBDT-TCNQ and DTBDT-F4TCNQ (where DTBDT is dithieno[2,3-d;2′,3′-d′] benzo[1,2-b;4,5-b′]dithiophene) using a combination of near-edge X-ray absorption spectroscopy (NEXAFS) and density functional theory calculations (DFT) including final state effects beyond the sudden state approximation. In particular, we find that a description that considers the partial screening of the electron-hole Coulomb correlation on a static level as well as the rearrangement of electronic density shows excellent agreement with experiment and allows to uncover the details of the charge transfer mechanism in DTBDT-TCNQ and DTBDT-F4 TCNQ, as well as a reinterpretation of previous NEXAFS data on pure TCNQ. Finally, we further show that almost the same quality of agreement between theoretical results and experiment is obtained by the much faster Z+1/2 approximation, where the core hole effects are simulated by replacing N or F with atomic number Z with the neighboring atom with atomic number Z+1/2.
  • Lindberg, S., et al. (författare)
  • Charge storage mechanism of alpha-MnO2 in protic and aprotic ionic liquid electrolytes
  • 2020
  • Ingår i: Journal of Power Sources. - : ELSEVIER. - 0378-7753 .- 1873-2755. ; 460
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we have investigated the charge storage mechanism of MnO2 electrodes in ionic liquid electrolytes. We show that by using an ionic liquid with a cation that has the ability to form hydrogen bonds with the active material (MnO2) on the surface of the electrode, a clear faradaic contribution is obtained. This situation is found for ionic liquids with cations that have a low pKa, i.e. protic ionic liquids. For a protic ionic liquid, the specific capacity at low scan rate rates can be explained by a densely packed layer of cations that are in a standing geometry, with a proton directly interacting through a hydrogen bond with the surface of the active material in the electrode. In contrast, for aprotic ionic liquids there is no interaction and only a double layer contribution to the charge storage is observed. However, by adding an alkali salt to the aprotic ionic liquid, a faradaic contribution is obtained from the insertion of Li+ into the surface of the MnO2 electrode. No effect can be observed when Li+ is added to the protic IL, suggesting that a densely packed cation layer in this case prevent Li-ions from reaching the active material surface.
  • Cznotka, E., et al. (författare)
  • 3D laser scanning confocal microscopy of siloxane-based comb and double-comb polymers in PVDF-HFP thin films
  • 2016
  • Ingår i: Journal of Coatings Technology and Research. - 1945-9645. ; 13:4, s. 577-587
  • Tidskriftsartikel (refereegranskat)abstract
    • Currently, atomic force microscopy is the preferred technique to determine roughness on membrane surfaces. In this paper, a new method to measure surface roughness is presented using a 3D laser scanning confocal microscope for high-resolution topographic analysis and is compared to conventional SEM. For this study, the surfaces of eight samples based on a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) host polymer with different liquid interpenetrating components were analyzed. Polymethylhydrosiloxane, triethylene glycolallylmethyether, (3,3,3-trifluoropropyl) methylcyclotrisiloxane (D-3-C2H4CF3), polysiloxane-comb-propyloxymethoxytriglycol (PSx), poly-siloxane-comb-propyl-3,3,3-trifluoro (PSx-C2H4CF3), poly [bis(2-(2-methoxyethoxy) ethoxy) phosphazene, or poly [bis(trifluoro) ethoxy] phosphazene was chosen as interpenetrating compound to investigate the impact of comb and double-comb-structured polymer backbones, as well as their dipolar or fluorous residues on the PVDF-HFP-miscibility. Different phases of the constituting ingredients were identified via their thermal properties determined by DSC. Additionally, the COSMO-RS method supported the experimental results, and with regard to computed sigma-profiles, new modified structures for polysiloxane and polyphosphazene synthesis were suggested.
  • Jeschke, Steffen, 1986, et al. (författare)
  • Catching TFSI: A Computational–Experimental Approach to β-Cyclodextrin-Based Host–Guest Systems as electrolytes for Li-Ion Batteries
  • 2018
  • Ingår i: ChemSusChem. - 1864-5631 .- 1864-564X. ; 11:12, s. 1942-1949
  • Tidskriftsartikel (refereegranskat)abstract
    • Cyclodextrins (CDs) are pyranoside-based macromolecules with a hydrophobic cavity to encapsulate small molecules. They are used as molecular vehicles, for instance in pharmaceutical drug delivery or as solubility enhancer of monomers for their polymerization in aqueous solution. In this context, it was discovered about 10 years ago that the bis(trifluoromethylsulonyl)imide (TFSI) anion forms host–guest complexes with βCD in aqueous media. This sparked interest in using the TFSI anion in lithium-based battery electrolytes open for its encapsulation by βCD as an attractive approach to increase the contribution of the cation to the total ion conductivity. By using semi-empirical quantum mechanical (SQM) methods and the conductor-like screening model for a real solvent (COSMO-RS), a randomly methylated βCD (RMβCD) is here identified as a suitable host for TFSI when using organic solvents often used in battery technology. By combining molecular dynamics (MD) simulations with different NMR and FTIR experiments, the formation of the corresponding RMβCD–TFSI complex was investigated. Finally, the effects of the addition RMβCD to a set of electrolytes on the ion conductivity are measured and explained using three distinct scenarios.
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  • Resultat 1-7 av 7

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