11. Ceramic synthesis of disordered lithium rich oxyfluoride materialsJean-Marcel Ateba Mba, Iztok Arčon, Gregor Mali, Elena Tchernychova, Ralf Witte, Robert Kruk, Miran Gaberšček, Robert Dominko, 2020, izvirni znanstveni članek Opis: Disordered lithium-rich transition metal oxyfluorides with a general formula Li1þxMO2Fx (M being a transition
metal) are gaining more attention due to their high specific capacity which can be delivered from the facecentered
cubic (fcc) structure. The most common synthesis procedure involves use of mechanosynthesis. In
this work, ceramic synthesis of lithium rich iron oxyfluoride and lithium rich titanium oxyfluoride are reported.
Two ceramic synthesis routes are developed each leading to the different level of doping with Li and F and
different levels of cationic disorder in the structure. Three different Li1þxMO2Fx samples (x ¼ 0.25, 0.3 and 1) are
compared with a sample prepared by mechanochemical synthesis and non-doped LiFeO2 with fcc structure. The
obtained lithium rich iron oxyfluoride are characterized by use of M€ossbauer spectroscopy, X-ray absorption
spectroscopy, NMR and TEM. Successful incorporation of Li and F have been confirmed and specific capacity that
can be obtained from the samples is in the correlation with the level of disorder introduced with doping,
nevertheless oxidation state of iron in all samples is very similar. Conclusions obtained from lithium rich iron
oxyfluoride are validated by lithium rich titanium oxyfluoride.
Ključne besede: Lithium batteries
Face centered-cubic
Oxyfluoride
Li-rich
Disorder
Objavljeno v RUNG: 05.06.2020; Ogledov: 4452; Prenosov: 0
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12. Study of water adsorption on EDTA dealuminated zeolite YO. L. Pliekhov, Olena Pliekhova, Iztok Arčon, Federica Bondino, Elena Magnano, Gregor Mali, Nataša Zabukovec Logar, 2020, izvirni znanstveni članek Opis: Zeolite Y was synthesized and modified with EDTA dealumination procedure. The modified zeolites were
analyzed by X-ray diffraction, X-ray absorption spectroscopy, chemical analysis and water adsorption measurements.
We demonstrated that dealumination with bulk organic acid such as EDTA is able to reduce the
original intense water affinity. Furthermore, it was found that dealumination with EDTA, in contrast with
steaming and HCl dealumination, provides fully controllable, predictable and secure process of Al removal from
the zeolites’ frameworks. The shift of the adsorption isotherm in the low partial pressure range represents an
interesting result for adsorption-based applications.
Ključne besede: Zeolite Y
Water sorption
Dealumination
Al XANES
EDTA treatment
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13. Effects of a Mixed O/F Ligand in the Tavorite-Type LiVPO4O StructureSorour Semsari Parapari, Jean-Marcel Ateba Mba, Elena Tchernychova, Gregor Mali, Iztok Arčon, Gregor Kapun, Mehmet Ali Gülgün, Robert Dominko, 2020, izvirni znanstveni članek Opis: We report the synthesis and detailed structural
and chemical characterization including electrochemical
properties of a lithium vanadium oxy/fluoro-phosphate
material. To the best of our knowledge, we have for the first
time synthesized a LiVPO4O-type phase with a mixed O/F
ligand. In the synthesis procedure, the LiVPO4O precursor
compound was fluorinated via LiF incorporation, with
preservation of the LiVPO4O framework structure. The
operating potential of the synthesized material is increased
compared to that of the LiVPO4O precursor (4.12 V vs 3.95 V
versus metallic lithium, respectively). The related increase in
operating potential was assigned to the effect of the
intermixing O/F ligand, which is attained via the successful
fluorine incorporation into the LiVPO4O structure. A characterization of the investigated materials was performed using
microscale-covering XRD, XANES, and NMR techniques as well as nanoscale spatially resolved imaging and analytical STEM
techniques. The obtained oxy/fluoro-phosphate phase is isostructural to LiVPO4O; however, the presence of the mixed O/F
ligand promoted a higher symmetry of vanadium octahedra. These variations of the vanadium local environment along with the
observed inhomogeneous distribution of the incorporated fluorine gave rise to the minor local deviations in vanadium valence.
Our results clearly emphasize the connection among the fluorine ligand incorporation, its local distribution, and the
electrochemical properties of the material.
Ključne besede: LiVPO4O, XRD, SEM, V XANES, Tavorite-Type, electrochemical properties
Objavljeno v RUNG: 17.02.2020; Ogledov: 2920; Prenosov: 0
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14. Unraveling the arrangement of Al and Fe within the framework explains the magnetism of mixed-metal MIL-100(Al,Fe)Gregor Mali, Matjaž Mazaj, Iztok Arčon, Darko Hanžel, Denis Arčon, Zvonko Jagličić, 2019, izvirni znanstveni članek Opis: Properties of mixed-metal MOFs depend on the distribution of different
metals within their frameworks. Determination of this distribution is often very
challenging. Using an example of aluminum- and iron-containing MIL-100, we
demonstrate that 27Al NMR spectroscopy, when combined with first-principles
calculations and magnetic, X-band electron paramagnetic resonance, Fe K-edge extended
X-ray absorption fine structure, and Mössbauer measurements, enables one to accurately
determine the arrangement of Al and Fe within the metal trimers, which are the basic
building units of MIL-100. In this particular material, the incorporation of Fe and Al on
the framework metal sites is random. Crucial for deciphering the arrangement is detecting
NMR signals, shifted because of the strong hyperfine interaction between the 27Al nuclei
and the unpaired electronic spins of Fe3+ ions, assigning the shifted signals aided by first-principles calculations of hyperfine
couplings, and quantitatively evaluating the NMR intensities and the measured effective magnetic moment.
Ključne besede: Fe EXAFS, XANES, MIL100, MOF, magnetizem
Objavljeno v RUNG: 26.03.2019; Ogledov: 3232; Prenosov: 0
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15. High-temperature stabilization of bulk amorphous Al2O3Andraž Mavrič, Mattia Fanetti, Gregor Mali, Matjaž Valant, 2018, izvirni znanstveni članek Opis: We present a method for high temperature stabilization of bulk amorphous aluminium oxide. The stabilization is achieved by dispersing polysilane dendritic molecules in aluminium hydroxide gel, which upon thermal treatment gives amorphous aluminium oxide stable up to 900 °C. The dispersed macromolecules covalently bind to the alumina matrix and induce homogeneously distributed strain fields that keep the alumina amorphous. The thermal conversion of the precursor system was followed by thermogravimetry with an evolved gas analysis, infrared spectroscopy and 29Si NMR. The amorphous structure of aluminium oxide was confirmed with an X-ray and electron diffraction. Additionally, the amorphous state was supported by presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by a UV–visible absorption spectroscopy.
Ključne besede: Amorphous aluminium oxide, Polysilane, Nanocomposite, Stabilization
Objavljeno v RUNG: 30.07.2018; Ogledov: 4328; Prenosov: 16
 Celotno besedilo (2,67 MB) |
16. A Mechanistic Study of Magnesium Sulfur BatteriesAna Robba, Alen Vižintin, Jan Bitenc, Gregor Mali, Iztok Arčon, Matjaž Kavčič, Matjaž Žitnik, Klemen Bučar, Giuliana Aquilanti, Charlotte Martineau-Corcos, Anna Randon-Vitanova, Robert Dominko, 2017, izvirni znanstveni članek Opis: Magnesium sulfur batteries are considered as attractive energy storage devices due to the
abundance of electrochemically active materials and high theoretical energy density. Here we
report the mechanism of a Mg-S battery operation, which was studied in the presence of
simple and commercially available salts dissolved in a mixture of glymes. The electrolyte
offers high sulfur conversion into MgS in the first discharge with low polarization. The
electrochemical conversion of sulfur with magnesium proceeds through two well-defined
plateaus, which correspond to the equilibrium between sulfur and polysulfides (high-voltage
plateau) and polysulfides and MgS (low-voltage plateau). As shown by XANES, RIXS and
NMR studies, the end discharge phase involves MgS with Mg atoms in a tetrahedral
environment resembling the wurtzite structure, while chemically synthesized MgS crystalizes
in the rock-salt structure with octahedral coordination of magnesium.
Ključne besede: magnesium, sulfur, rechargeable batteries, XAS, NMR
Objavljeno v RUNG: 19.10.2017; Ogledov: 4417; Prenosov: 0
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18. Growth mechanism and structure of electrochemically synthesized dendritic polymethylsilane moleculesAndraž Mavrič, Artem Badasyan, Gregor Mali, Matjaž Valant, 2017, izvirni znanstveni članek Opis: The study of an electrochemical synthesis of polymethylsilane from trifunctional trichloro-
methylsilane monomers identified a single polymerization pathway involving reduction of the
monomer to silyl anions and their addition to the growing polymer. The sizes of the synthesized
macromolecules, measured with dynamic light scattering, are much larger than the theoretical
size estimated for an ideal dendrimer. The reason for this, found by NMR analysis, is in a large
number of branching irregularities (defects) contained in the molecular structure, which can be
described as a hyperbranched dendritic polymer. Theoretical estimates of sizes for an ideal
dendrimer were corrected assuming a branching defect is a cavity with the volume of one
monomer. Appropriateness of the theoretical and experimental models was confirmed with a
good quantitative agreement between the experimental densities and the theoretically calculated
values.
Ključne besede: Polymethylsilane
Dendritic polymer
Electropolymerization
Objavljeno v RUNG: 20.03.2017; Ogledov: 4330; Prenosov: 14
Celotno besedilo (705,04 KB) |
