03 Fakultät Chemie

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Institute: search.filters.UBSInstitut.Max-Planck-Institut für FestkörperforschungInstitute: search.filters.UBSInstitut.Institut für MaterialwissenschaftStart date: 2024End date: 2024

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Now showing 1 - 3 of 3
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    Asymmetric Rh diene catalysis under confinement : isoxazole ring‐contraction in mesoporous solids
    (2024) Marshall, Max; Dilruba, Zarfishan; Beurer, Ann‐Katrin; Bieck, Kira; Emmerling, Sebastian; Markus, Felix; Vogler, Charlotte; Ziegler, Felix; Fuhrer, Marina; Liu, Sherri S. Y.; Kousik, Shravan R.; Frey, Wolfgang; Traa, Yvonne; Bruckner, Johanna R.; Plietker, Bernd; Buchmeiser, Michael R.; Ludwigs, Sabine; Naumann, Stefan; Atanasova, Petia; Lotsch, Bettina V.; Zens, Anna; Laschat, Sabine
    Covalent immobilization of chiral dienes in mesoporous solids for asymmetric heterogeneous catalysis is highly attractive. In order to study confinement effects in bimolecular vs monomolecular reactions, a series of pseudo‐C2‐symmetrical tetrahydropentalenes was synthesized and immobilized via click reaction on different mesoporous solids (silica, carbon, covalent organic frameworks) and compared with homogeneous conditions. Two types of Rh‐catalyzed reactions were studied: (a) bimolecular nucleophilic 1,2‐additions of phenylboroxine to N‐tosylimine and (b) monomolecular isomerization of isoxazole to 2H‐azirne. Polar support materials performed better than non‐polar ones. Under confinement, bimolecular reactions showed decreased yields, whereas yields in monomolecular reactions were only little affected. Regarding enantioselectivity the opposite trend was observed, i. e. effective enantiocontrol for bimolecular reactions but only little control for monomolecular reactions was found.
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    Insights into the first multi-transition-metal containing Ruddlesden-Popper-type cathode for all-solid-state fluoride ion batteries
    (2024) Vanita, Vanita; Waidha, Aamir Iqbal; Vasala, Sami; Puphal, Pascal; Schoch, Roland; Glatzel, Pieter; Bauer, Matthias; Clemens, Oliver
    Promising cathode materials for fluoride-ion batteries (FIBs) are 3d transition metal containing oxides with Ruddlesden-Popper-type structure. So far, the multi-elemental compositions have not been investigated, but it could alternate the electrochemical performance similar to what has been found for cathode materials for lithium-ion batteries. In this study, we investigate RP type La2Ni0.75Co0.25O4.08 as an intercalation-based active cathode material for all-solid-state FIBs. We determine the structural changes of La2Ni0.75Co0.25O4.08 during fluoride intercalation/de-intercalation by ex situ X-ray diffraction, which showed that F- insertion leads to transformation of the parent phase to three different phases. Changes in the Ni and Co oxidation states and coordination environment were examined by X-ray absorption spectroscopy and magnetic measurements in order to understand the complex reaction behaviour of the phases in detail, showing that the two transition metals behave differently in the charging and discharging process. Under optimized operating conditions, a cycle life of 120 cycles at a critical cut-off capacity of 40 mA h g-1 against Pb/PbF2 was obtained, which is one of the highest observed for intercalation electrode materials in FIBs so far. The average coulombic efficiencies ranged from 85% to 90%. Thus, La2Ni0.75Co0.25O4.08 could be a promising candidate for cycling-stable high-energy cathode materials for all-solid-state FIBs.
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    Realization of a classical Ruddlesden Popper type bilayer nickelate in Sr3Ni2-xAlxO7-δ with unusual Ni4+
    (2024) Yilmaz, Hasan; Küster, Kathrin; Starke, Ulrich; Clemens, Oliver; Isobe, Masahiko; Puphal, Pascal
    The discovery of 80 K superconductivity in bilayer La3Ni2O7 at pressures greater than 14 GPa presents a unique opportunity to study a novel class of high-temperature superconductors. Therefore, other bilayer nickelates following the classical (T4+) Ruddlesden-Popper (RP) series of Sr3Ni2O7 would present an interesting new candidate. In this work, we study the stabilization of RP n = 2 phase in Sr3Ni2-xAlxO7-δ, via floating zone growth of crystals. With powder and single-crystal XRD, we study the stability range of the RP-type phase. Our Thermogravimetric Analysis (TGA), X-ray photoelectron spectroscopy (XPS) and gas extraction studies reveal a remarkably high oxidation state of Ni4+ stabilized by chemical strain from Al. The obtained black crystals are insulating in transport and show a magnetic transition around 12 K.