03 Fakultät Chemie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4
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Item Open Access Designing covalent organic framework‐based light‐driven microswimmers toward therapeutic applications(2023) Sridhar, Varun; Yildiz, Erdost; Rodríguez‐Camargo, Andrés; Lyu, Xianglong; Yao, Liang; Wrede, Paul; Aghakhani, Amirreza; Akolpoglu, Birgul M.; Podjaski, Filip; Lotsch, Bettina V.; Sitti, MetinWhile micromachines with tailored functionalities enable therapeutic applications in biological environments, their controlled motion and targeted drug delivery in biological media require sophisticated designs for practical applications. Covalent organic frameworks (COFs), a new generation of crystalline and nanoporous polymers, offer new perspectives for light‐driven microswimmers in heterogeneous biological environments including intraocular fluids, thus setting the stage for biomedical applications such as retinal drug delivery. Two different types of COFs, uniformly spherical TABP‐PDA‐COF sub‐micrometer particles and texturally nanoporous, micrometer‐sized TpAzo‐COF particles are described and compared as light‐driven microrobots. They can be used as highly efficient visible‐light‐driven drug carriers in aqueous ionic and cellular media. Their absorption ranging down to red light enables phototaxis even in deeper and viscous biological media, while the organic nature of COFs ensures their biocompatibility. Their inherently porous structures with ≈2.6 and ≈3.4 nm pores, and large surface areas allow for targeted and efficient drug loading even for insoluble drugs, which can be released on demand. Additionally, indocyanine green (ICG) dye loading in the pores enables photoacoustic imaging, optical coherence tomography, and hyperthermia in operando conditions. This real‐time visualization of the drug‐loaded COF microswimmers enables unique insights into the action of photoactive porous drug carriers for therapeutic applications.Item Open Access Interphases between alkali metals (Li, Na) and battery electrolytes : ion transport and growth behavior(2022) Lim, Kyungmi; Maier, Joachim (Prof. Dr.)Item Open Access Confirmation of siderazot, Fe3N1.33, the only terrestrial nitride mineral(2021) Bette, Sebastian; Theye, Thomas; Bernhardt, Heinz-Jürgen; Clark, William P.; Niewa, RainerSiderazot, the only terrestrial nitride mineral, was reported only once in 1876 to occur as coating on volcanic rocks in a fumarolic environment from Mt. Etna and, to date, has been neither confirmed nor structurally characterized. We have studied the holotype sample from the Natural History Museum, London, UK, originally collected by O. Silvestri in 1874, and present siderazot with epsilon-Fe3N-type crystal structure and composition of Fe3N1.33(7) according to crystal structure Rietveld refinements, in good agreement with electron microprobe analyses. Crystal structure data, chemical composition, and Raman and reflectance measurements are reported. Possible formation conditions are derived from composition and phase stability data according to synthetic samples.Item Open Access On the thermal dimorphy of the strontium perrhenate Sr[ReO4]2(2024) Conrad, Maurice; Bette, Sebastian; Dinnebier, Robert E.; Schleid, ThomasHygroscopic single crystals of a new hexagonal high‐temperature modification of Sr[ReO4]2 were prepared from a melt of Sr[ReO4]2 ⋅ H2O and SrCl2 ⋅ 6 H2O. The structure analysis of the obtained crystals by X‐ray diffraction revealed that the title compound crystallizes in the ThCd[MoO4]3‐type structure with the hexagonal space group P63/m and the lattice parameters a=1023.81(7) pm and c=646.92(4) pm (c/a=0.632) for Z=2 in its quenchable high‐temperature form. Two crystallographically independent Sr2+ cations are coordinated by oxygen atoms forming either octahedra or tricapped trigonal prisms, whereas the Re7+ cations are found in the centers of discrete tetrahedral meta‐perrhenate units [ReO4]-. Temperature‐dependent in‐situ PXRD studies of dry powder samples of Sr[ReO4]2 exhibited its thermal dimorphy with a phase‐transition temperature at 500-550 °C from literature‐known m‐Sr[ReO4]2 into the newly discovered h‐Sr[ReO4]2 (hexagonal).Item Open Access High‐performance magnesium‐sulfur batteries based on a sulfurated poly(acrylonitrile) cathode, a borohydride electrolyte, and a high‐surface area magnesium anode(2020) Wang, Peiwen; Trück, Janina; Niesen, Stefan; Kappler, Julian; Küster, Kathrin; Starke, Ulrich; Ziegler, Felix; Hintennach, Andreas; Buchmeiser, Michael R.Post‐lithium‐ion battery technology is considered a key element of future energy storage and management. Apart from high gravimetric and volumetric energy densities, economic, ecologic and safety issues become increasingly important. In that regards, both the anode and cathode materials must be easily available, recyclable, non‐toxic and safe, which renders magnesium‐sulfur (Mg-S) batteries a promising choice. Herein, we present Mg-S cells based on a sulfurated poly(acrylonitrile) composite cathode (SPAN), together with a halogen‐free electrolyte containing both Mg[BH4]2 and Li[BH4] in diglyme and a high‐specific surface area magnesium anode based on Rieke magnesium powder. These cells deliver discharge capacities of 1400 and 800 mAh/gsulfur with >99 % Coulombic efficiency at 0.1 C and 0.5 C, respectively, and are stable over at least 300 cycles. Energy densities are 470 and 400 Wh/kgsulfur at 0.1 C and 0.5 C, respectively. Rate tests carried out between 0.1 C and 2 C demonstrate good rate capability of the cells. Detailed mechanistic studies based on X‐ray photoelectron spectroscopy and electric impedance spectroscopy are presented.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 Binder-free V2O5 cathode for high energy density rechargeable aluminum-ion batteries(2020) Diem, Achim M.; Fenk, Bernhard; Bill, Joachim; Burghard, ZaklinaNowadays, research on electrochemical storage systems moves into the direction of post-lithium-ion batteries, such as aluminum-ion batteries, and the exploration of suitable materials for such batteries. Vanadium pentoxide (V2O5) is one of the most promising host materials for the intercalation of multivalent ions. Here, we report on the fabrication of a binder-free and self-supporting V2O5 micrometer-thick paper-like electrode material and its use as the cathode for rechargeable aluminum-ion batteries. The electrical conductivity of the cathode was significantly improved by a novel in-situ and self-limiting copper migration approach into the V2O5 structure. This process takes advantage of the dissolution of Cu by the ionic liquid-based electrolyte, as well as the presence of two different accommodation sites in the nanostructured V2O5 available for aluminum-ions and the migrated Cu. Furthermore, the advanced nanostructured cathode delivered a specific discharge capacity of up to ~170 mAh g-1 and the reversible intercalation of Al3+ for more than 500 cycles with a high Coulomb efficiency reaching nearly 100%. The binder-free concept results in an energy density of 74 Wh kg-1, which shows improved energy density in comparison to the so far published V2O5-based cathodes. Our results provide valuable insights for the future design and development of novel binder-free and self-supporting electrodes for rechargeable multivalent metal-ion batteries associating a high energy density, cycling stability, safety and low cost.Item Open Access Thin film growth and structural investigation of DyBa2Cu3O7-δ(2020) Putzky, Daniel; Keimer, Bernhard (Prof. Dr.)Item Open Access Defect chemistry of mixed conducting perovskites : interplay of protonic defects, oxygen vacancies and electron holes(2022) Raimondi, Giulia; Maier, Joachim (Prof. Dr.)Item Open Access Miscibility, viscoelastic reinforcement, and transport properties of blend membranes based on sulfonated poly(phenylene sulfone)s(2021) Saatkamp, Torben; Maier, Joachim (Prof. Dr.)Chemical energy that hydrogen may generate during combustion and the corresponding electrical energy are interconvertible by means of a fuel cell (FC) and by the electrolysis of water (WE), which allows for the utilization of the complementary nature of these two key energy vectors towards energy sustainability. A proton exchange membrane (PEM) made from an ionomer is commonly employed as the electrolyte in mobile fuel cell applications and in water electrolyzers that require dynamic operability and pressurized product gases. New PEM materials are needed to increase performance, reduce environmental impact, and allow for a more targeted design of PEMFC and PEMWE systems, all of which is in some way limited by the use of the established perfluorosulfonic acid (PFSA) type ionomers. This work’s focus lies on sulfonated poly(phenylene sulfone)s (sPPS), a unique group of fluorine-free cation conducting ionomers. They are unique in terms of their chemical stability and transport properties, however, typical in terms of their salt-like brittleness in the dry state and extensive swelling at high humidity and in water. To make the unique properties of sPPS available in application, the goal of this work is to take a comprehensive approach to their viscoelastic reinforcement. Therefore, the structure of this thesis entails three related aspects along the process from pure materials to the optimization of robust PEMs for application. The first chapter focuses on the optimization of the intrinsic viscoelastic properties of a particularly suited sPPS (termed S360, with IEC 2.78 meq g-1, EW 360 g mol-1) which lays the groundwork for reliable and systematic further development. To achieve this, relevant properties of S360 are first characterized and viscoelastic shortcomings as seen in water uptake measurements and tensile tests under dry conditions (≤ 30% relative humidity, RH) discussed. The step-growth polymerization of S360 is optimized after finding significant inorganic contamination retained in the established purification process of the widely used monomer sulfonated difluorodiphenyl sulfone (sDFDPS), allowing for the preparation of the ionomer in reproducible high molecular weight. Relevant properties of high molecular weight S360 are characterized and an enhancement of mechanical properties at 30% RH as well as when submerged in water is found. Access to reproducible high quality of S360 enables its first-time use and study as a PEM in a completely fluorine-free WE cell. At 80 °C, record performance amongst fluorine free electrolytes in PEMWEs of 3.48 A cm-2 at 1.8 V is achieved, showcasing the potential of sPPS for application. The second chapter entails the identification and better understanding of a suitable and versatile reinforcement concept for creating robust membranes based on sPPS. To achieve this, the established homogeneously miscible acid-base polymer blends of sulfonated ionomers with poly(benzimidazole) (PBI, and its derivatives PBIO and PBIOO) are discussed in-depth and chosen for later systematic optimization in combination with sPPS. Since the origin of miscibility in PBI blends with sulfonated ionomers is insufficiently described in literature and could facilitate targeted design of new blend components, a model acid-base polymer blend system comprising pyridine-functionalized poly(sulfone) (PSU) is created. Pyridine groups of different basicity tethered to PSU in varying concentration are used to investigate the effect that interpolymer acid-base interaction strength and concentration have on miscibility in blends with 80 wt% S360, as derived from the blend membranes’ cross-sectional SEMs. High mutual compatibility is achieved at high concentration of weak interpolymer interaction, which is interpreted with regards to the observed miscibility in PBI blends. Based on the derived role that hydrogen bonds may play in PBI blends, the difference of interpolymer interaction in solution (during membrane formation) and in the dry membrane is described. This could enable the development of new blend concepts in the future. An exemplary miscible blend that comprises interpolymer hydrogen bonds only in solution but not in the final membrane is shown. The third chapter describes the optimization and balance of properties in the previously described polymer blends with PBIO, following the goal to prepare membranes which can be evaluated in fuel cells and fabricated on a wider scale in order to bring the attractive properties of sPPS into application. To achieve this, S360-blend membranes of varying PBIO content are characterized with regard to conductivity and mechanical properties in various conditions. High mechanical robustness is achieved in S360 blends with 30 wt% PBIO but is accompanied by dramatic reduction of conductivity, due to the charge-consuming acid-base interaction. The findings are translated into blends with fully sulfonated sPPS (termed S220, with IEC 4.54 meq g-1, EW 220 g mol-1) which allows for the creation of membranes that combine mechanical toughness with high conductivity at a ratio of 25 wt% PBIO in S220, making the material suited for production on a commercial casting line and fuel cell testing. Membranes based on S360 that comprise 15 wt% PBIO are designated for further studies in PEMWEs, where membrane requirements differ significantly from that in PEMFCs, highlighting the versatility of the reinforcement approach chosen in this work. Finally, first fuel cell tests of thin spray coated PBIO blend membranes are conducted, and initial durability testing of sPPS-based membranes in fuel cells is possible. Overall, the results presented in this work are strongly interrelated which underlines the importance of comprehensiveness in the successful viscoelastic reinforcement of sulfonated poly(phenylene sulfone)s. Ultimately, the blend membranes resulting from this work can be used as a platform for further development of sPPS-based PEMs in the future.