03 Fakultät Chemie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4
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Item Open Access Sulfurized polypropylene as low‐cost cathode material for high‐capacity lithium‐sulfur batteries(2022) Du, Qian; Benedikter, Mathis; Küster, Kathrin; Acartürk, Tolga; Starke, Ulrich; Hoslauer, Jean‐Louis; Schleid, Thomas; Buchmeiser, Michael R.Among ‘beyond lithium ion’ energy storage, lithium sulfur (Li-S) batteries are one of the most promising technologies, as a result of the potential for high theoretical energy capacity at low cost. A key obstacle in exploiting the vast potential of Li-S batteries is the formation of soluble polysulfide species. Here, we report sulfurized polypropylene (S/PP‐500) synthesized in one‐step by reacting polypropylene (PP) with sulfur as a new polysulfide shuttle‐free cathode material for Li-S batteries. It exhibits a reversible capacity as high as 1000 mAh/gsulfur at 0.1 C and a sulfur loading of up to 68 wt%, which in turn allows for high sulfur loadings up to 47 % in the final cathode. The low‐cost starting materials together with the simple synthetic procedure and the good electrochemical performance in combination with a commercially available eslectrolyte make the S/PP‐500 a very promising cathode material for Li‐S batteries.Item Open Access Method of manufacturing structural, optically transparent glass fiber-reinforced polymers (tGFRP) using infusion techniques with epoxy resin systems and E-glass fabrics(2023) Heudorfer, Klaus; Bauer, Johannes; Caydamli, Yavuz; Gompf, Bruno; Take, Jens; Buchmeiser, Michael R.; Middendorf, PeterRecently, fiber-reinforced, epoxy-based, optically transparent composites were successfully produced using resin transfer molding (RTM) techniques. Generally, the production of structural, optically transparent composites is challenging since it requires the combination of a very smooth mold surface with a sufficient control of resin flow that leads to no visible voids. Furthermore, it requires a minimum deviation of the refractive indices (RIs) of the matrix polymer and the reinforcement fibers. Here, a new mold design is described and three plates of optically transparent glass fiber-reinforced polymers (tGFRP) with reproducible properties as well as high fiber volume fractions were produced using the RTM process and in situ polymerization of an epoxy resin system enclosing E-glass fiber textiles. Their mechanical (flexural), microstructural (fiber volume fraction, surface roughness, etc.), thermal (DSC, TGA, etc.), and optical (dispersion curves of glass fibers and polymer as well as transmission over visible spectra curves of the tGFRP at varying tempering states) properties were evaluated. The research showed improved surface quality and good transmission data for samples manufactured by a new Optical-RTM setup compared to a standard RTM mold. The maximum transmission was reported to be ≈74%. In addition, no detectable voids were found in these samples. Furthermore, a flexural modulus of 23.49 ± 0.64 GPa was achieved for the Optical-RTM samples having a fiber volume fraction of ≈42%.Item Open Access Toward sustainable fiber‐reinforced polymer composites(2024) Elser, Iris; Buchmeiser, Michael R.Fiber‐reinforced polymer composites (FRPCs) are versatile materials with applications in diverse fields such as transportation, construction, and electronics. With the composites market expected to reach 15.5 Mt by 2026, increasing the sustainability of FRPCs is imperative. The main factors driving the sustainability of FRPCs, namely end‐of‐life management and recyclability, the use of natural, bio‐based, and sustainable materials, as well as biodegradability and product simplification are presented and discussed.Item Open Access Hydrosilylation of alkynes under continuous flow using polyurethane‐based monolithic supports with tailored mesoporosity(2022) Acikalin, Hande; Panyam, Pradeep K. R.; Shaikh, Abdul Wasif; Wang, Dongren; Kousik, Shravan R.; Atanasova, Petia; Buchmeiser, Michael R.Non‐porous polyurethane‐based monoliths are prepared under solvent‐induced phase separation conditions. They possess low specific surface areas of 0.15 m2 g-1, pore volumes of 1 µL g-1, and a non‐permanent, solvent‐induced microporosity with pore dimensions ≤1 nm. Mesoporosity can be introduced by varying the monomers and solvents. A tuning of the average solubility parameter of the solvent mixture by increasing the macroporogen content results in a decrease in the volume fraction of micropores from 70% to 40% and an increase in the volume fraction of pores in the range of 1.7-9.6 nm from 22% to 41% with only minor changes in the volume fraction of larger mesopores in the range of 9.6–50 nm. The polymeric monoliths are functionalized with quaternary ammonium groups, which allowed for the immobilization of an ionic liquid that contained the ionic Rh‐catalyst [1‐(pyrid‐2‐yl)‐3‐mesityl)‐imidazol‐2‐ylidene))(η4‐1,5‐cyclooctadiene)Rh(I) tetrafluoroborate]. The supported catalyst is used in the hydrosilylation of 1‐alkynes with dimethylphenylsilane under continuous flow using methyl‐tert‐butyl ether as second liquid transport phase. E/Z‐selectivity in hydrosilylation is compared to the one of the analogous biphasic reactions. The strong increase in Z‐selectivity is attributed to a confinement effect provided by the small mesopores.Item Open Access Structure evolution in polyethylene‐derived carbon fiber using a combined electron beam‐stabilization‐sulphurization approach(2021) Frank, Erik; Muks, Erna; Ota, Antje; Herrmann, Thomas; Hunger, Michael; Buchmeiser, Michael R.A new approach is described for the production of poly(ethylene) (PE) derived carbon fibers (CFs) that entails the melt spinning of PE fibers from a suitable precursor, their cross-linking by electron beam (EB) treatment, and sulphurization with elemental sulphur (S8), followed by pyrolysis and carbonization. Instead of focusing on mechanical properties, analysis of CF structure formation during all process steps is carried out by different techniques comprising solid-state nuclear magnetic resonance spectroscopy, thermogravimetric analysis coupled to mass spectrometry/infrared spectroscopy, elemental analysis, energy dispersive X-ray scattering, scanning electron microscopy, Raman spectroscopy, and wide-angle X-ray diffraction. A key step in structure formation is the conversion of PE into poly(thienothiophene)s during sulphurization; these species are stabile under inert gas up to 700 °C as confirmed by Raman analysis. Above this temperature, they condense into poly(napthathienophene)s, which are then converted into graphite-type structures during pyrolysis.Item Open Access Predicting catalytic activity from 13CCH alkylidene chemical shift in cationic tungsten oxo alkylidene N‐heterocyclic carbene complexes(2021) Musso, Janis V.; Schowner, Roman; Falivene, Laura; Frey, Wolfgang; Cavallo, Luigi; Buchmeiser, Michael R.A series of cationic tungsten oxo alkylidene N‐heterocyclic carbene (NHC) complexes was synthesized and structurally characterized by single crystal X‐ray diffraction. The 13C NMR chemical shifts of the alkylidene C atoms of these complexes were correlated with the diamagnetic, paramagnetic and spin‐orbit chemical shifts calculated by DFT. A good correlation (R2=0.90) between the DFT isotropic chemical shifts and the experimental chemical shift as well as a strong correlation between the DFT isotropic chemical shifts and the TOF1min for the RCM of 1,7‐octadiene was found. Further, a comparison of the catalyst geometries allowed for assigning tetracoordinate pseudotetrahedral catalysts to the most deshielded alkylidenes and to the highest TOF1min, pentacoordinate square‐planar catalysts to the intermediate deshielded alkylidenes and intermediate TOF1min, and hexacoordinate and octahedral catalyst to the most shielded alkylidene and lowest TOF1min. Analysis of the magnetic shielding tensors allowed for ascribing variations in the chemical shifts to electronic transitions between occupied molecular orbitals corresponding to the alkylidene‐C and alkylidene‐H σ‐bonds and the empty molecular orbital corresponding to the W‐alkylidene σ*‐bond.Item Open Access A sodium bis(perfluoropinacol) borate-based electrolyte for stable, high-performance room temperature sodium-sulfur batteries based on sulfurized poly(acrylonitrile)(2021) Murugan, Saravanakumar; Klostermann, Sina V.; Frey, Wolfgang; Kästner, Johannes; Buchmeiser, Michael R.A new type of electrolyte salt based on a weakly coordinating anion (Na-PPB) for RT Na-SPAN batteries has been developed. Na-PPB was synthesized in bulk via a one-pot reaction. NMR spectroscopy reveals high purity of the salt and stability even under ambient atmospheric conditions. Single-crystal X-ray analysis confirmed the molecular structure of Na-PPB with Na+ coordinated by one DME molecule. The electrolyte containing Na-PPB with PC + 10 wt% FEC showed high oxidative stability on Al current collector exceeding 5.5 V. In a Na-SPAN cell, the Na-PPB electrolyte allows for an initial and final discharge capacity (500 cycles) of 1140 mAh/gsulfur and 965 mAh/gsulfur respectively, obtained at 2C (3.35 A/gsulfur). The excellent electrochemical performance and good chemical stability of Na-PPB offers access to the design of novel electrolyte salts for RT Na-SPAN batteries.Item Open Access Lignin/poly(vinylpyrrolidone) multifilament fibers dry‐spun from water as carbon fiber precursors(2023) Kreis, Philipp; Frank, Erik; Clauß, Bernd; Bauch, Volker; Stolpmann, Heiko; Kuske, Lisa; Schneck, Tanja; König, Simon; Buchmeiser, Michael R.The preparation of lignin-based carbon fibers by dry spinning from aqueous solution followed by stabilization and continuous carbonization to endless yarns is reported. The influence of carbonization temperature and draw ratio on the morphology and mechanical properties of the final carbon fibers is investigated by single-fiber testing, wide-angle X-ray scattering, scanning electron microscopy, and Raman spectroscopy. A draw ratio of 5% (1.05) with a carbonization temperature of 1400 °C leads to the best mechanical properties. The resulting multifilament carbon fibers have an average diameter between 10-12 µm, an average tensile strength of 1.30 ± 0.32 GPa, a Young's modulus of 101 ± 18 GPa, and an elongation at break of 1.31 ± 0.23%. The maximum Weibull strength (𝜎0) is 1.04 GPa with a Weibull modulus (m) of 5.1. The use of a water-soluble system is economically advantageous; also, unlike melt-spun lignin fibers, the dry-spun precursor fibers can be thermally converted without any additional crosslinking step.Item Open Access Molybdenum alkylidyne silyloxy N‐heterocyclic carbene complexes : highly active alkyne metathesis catalysts that can be handled in air(2022) Musso, Janis V.; Gramm, Vincent; Stein, Sarjano; Frey, Wolfgang; Buchmeiser, Michael R.A series of molybdenum alkylidyne silyloxy N‐heterocyclic carbene (NHC) complexes of the general formula [Mo(≡C(R))(OSiPh3)3(NHC)] (R=tBu, 4‐methoxyphenyl, 2,4,6‐trimethylphenyl; NHC = 1,3‐diisopropylimidazol‐2‐ylidene, 1,3‐dicyclohexylimidazol‐2‐ylidene, 1,3‐dicyclohexyl‐4,5‐dihydroimidazol‐2‐ylidene, 1,3‐dimethylimidazol‐2‐ylidene, 1,3‐dimethyl‐4,5‐dichloroimidazol‐2‐ylidene) was synthesized. Single crystal X‐ray analyses revealed that with increasing steric demand of the alkylidyne group, enhanced air‐stability of the complexes in the solid‐state is achieved with the most stable complex (R=2,4,6‐trimethylphenyl, NHC = 1,3‐diisopropylimidazol‐2‐ylidene) being stable in air for 24 h without showing signs of decomposition in 1H NMR. In contrast to previously reported air‐stable molybdenum‐based complexes, the novel catalysts proved to be highly active in alkyne metathesis, allowing for turnover numbers (TONs) of up to 6000 without further activation, and tolerant towards several functional groups such as tosyl, ether, ester, thioether and nitro moieties. Their air stability allows for facile handling of the catalysts in air and even after exposure to ambient atmosphere for one week, the most stable representative still displayed high productivity in alkyne metathesis.Item Open Access Synthetic and structural peculiarities of neutral and cationic molybdenum imido and tungsten oxo alkylidene complexes bearing weakly coordinating N‐heterocyclic carbenes(2024) Buchmeiser, Michael R.; Wang, Dongren; Schowner, Roman; Stöhr, Laura; Ziegler, Felix; Sen, Suman; Frey, WolfgangThe syntheses of the neutral molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes of the general formula [Mo(NAr)(CHCMe2Ph)(NHC)XY] (Ar=2-tBu-C6H4, 2-CF3-C6H4, 2,6-Me2-C6H3, 2,6-Cl2-C6H3, adamantyl; X, Y=OTf, OC(CF3)3, OCH(CF3)2, OC6F5, SC6F5, 2,5-bis(pentafluorophenyl)phen-1-yl) bearing electron-withdrawing NHCs (1,3-dimethyl-4,5-dichloroimidazol-2-ylidene (IMeCl2), 1,3,4-triphenyl-1,2,4-triazol-5-ylidene (TPT)) are reported. Complementary, the corresponding cationic molybdenum imido alkylidene NHC complexes of the general formula [Mo(NAr)(CHCMe2R)(NHC)X+][B(ArF)4−/Al(OC(CF3)3)4−] (R=Me, Ph; B(ArF)4-=tetrakis (3,5-bis(trifluoromethyl)phenyl)borate) have been prepared. Aiming at tungsten oxo complexes, reaction of [W(O)Cl2(CHCMe2Ph)(PMe2Ph)2] with [1,3-dimethyl-4,5-dichloroimidazol-2-ylidene⋅AgI] (IMeCl2⋅AgI) followed by the addition of lithium terphenoxide yields [W(O)(CHCMe2Ph)(IMeCl2)(DPPO)2]. For comparison, [W(O)Cl(CHCMe2Ph)(IMes)(OSi(OtBu)3)] was prepared via reaction of [W(O)Cl2(CHCMe2Ph)(PMe2Ph)(IMes)] with KOSi(OtBu)3. [W(O)(CHCMe2Ph)(IMeCl2)(DPPO)(Et2O)+][B(ArF)4−] (DPPO=2,6-diphenylphenoxide) became accessible via reaction of [W(O)(DPPO)2(CHCMe2Ph)(IMeCl2)] with anilinium B(ArF)4-. The structural peculiarities of selected complexes are reported. Benchmark ring-closing metathesis and homometathesis reactions revealed that the neutral complexes bearing weakly coordinating NHCs such as IMeCl2 and TPT possessed only moderate activity, which could, however, be improved by preparing the corresponding cationic metal alkylidene complexes.