Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
10 results
Search Results
Item Open Access Proton-conducting membranes for the artificial leaf(2023) Bosson, Karell; Tovar, Günter E. M. (Prof.)With the aim of producing proton conducting membranes with improved proton conductivity and mechanical properties, the poly(pentafluorostyrene)-b-(butyl acrylate) (PPFS-b-PBuA) system was investigated. The study mainly focuses on the influence of the forming polymer nanostructures on the conductivity properties of the membranes. A series of well-defined PPFS-b-PBuA block copolymers (BCPs) were synthesized via nitroxide-mediated controlled radical polymerization (NMP). Spontaneous self-assembly of the BCP element was induced via a targeted change in polymer composition. Moreover, by adjusting the molar composition via enrichment of one of the blocks after synthesis, controlled self-assembly of the BCPs was realized. This was done by combining the corresponding homopolymer with the block copolymer to form a polymer blend - one of the blocks mixed to the BCP. Forming such polymer blends expanded the range of available techniques for tailoring the morphology for desired applications. Sulfonation of BCPs for the preparation of proton-conducting membranes was carried out by a para-fluoro thiol "click" reaction using sodium 3-mercapto-1-propanesulfonate (SMPS). The accessibility of fluorine in the para position of the phenylene group of PPFS provides countless opportunities for polymer functionalization by nucleophilic substitution. After modification of BCP, the self-assembly ability was retained, and higher conductivities were obtained compared to random copolymers. In addition, complementary studies were conducted on the use of printing techniques for membrane upscaling and evaluation of their life cycle.Item Open Access Discontinuous powder aerosol deposition : an approach to prepare films using smallest powder quantities(2021) Linz, Mario; Exner, Jörg; Kita, Jaroslaw; Bühner, Florian; Seipenbusch, Martin; Moos, RalfThis work shows that the powder aerosol deposition (PAD) method allows the formation of films in powder quantities of less than 60 mg, rather than the large amounts that are typically required for conventional powder aerosol deposition systems. This was achieved by changing the operation mode to a discontinuous one, resulting in operation times of several seconds. Semiconducting strontium titanate ferrate SrTi0.65Fe0.35O3-δ (STF35) was used as the powder to prove the equal behavior in terms of adhesion, film quality and electric conductivity compared to conventional powder-aerosol-deposited films.Item Open Access Synthesis and characterization of novel perfluoro aromatic side chain sulfonated PSU ionomers(2024) Martschin, Philipp; Atanasov, Vladimir; Thiele, Simon; Kerres, JochenPolyethersulfone (PSU) as a commercially available polymer offers many different opportunities for functionalization for diverse fields of application, for example, electrophilic substitutions like sulfonation and bromination or nucleophilic reactions such as lithiation. This study presents three different polysulfone derivatives, first functionalized by a lithiation reaction, followed by a reaction with carbonyl compounds containing pentafluorophenyl groups. In the last step, the pentafluorophenyl moieties of the modified PSU were sulfonated by thiolation and subsequent oxidation to sulfonic acid groups. Those novel PSU derivatives were characterized by NMR, DSC, TGA, GPC, and titration. Based on these ionomers, we show the fabrication of pure and acid-base blend membranes with promising proton conductivities. These novel sulfonic acid groups containing materials are potentially promising candidates for membranes or ionomers in electrochemical applications such as proton exchange membrane fuel cells (PEMFCs), proton exchange membrane water electrolysis (PEMWEs), or redox flow batteries (RFBs).Item Open Access Thin organic‐inorganic anti‐fouling hybrid‐films for microreactor components(2022) Neßlinger, Vanessa; Welzel, Stefan; Rieker, Florian; Meinderink, Dennis; Nieken, Ulrich; Grundmeier, GuidoDeposit formation and fouling in reactors for polymer production and processing especially in microreactors is a well‐known phenomenon. Despite the flow and pressure loss optimized static mixers, fouling occurs on the surfaces of the mixer elements. To improve the performance of such parts even further, stainless steel substrates are coated with ultra‐thin films which have low surface energy, good adhesion, and high durability. Perfluorinated organosilane (FOTS) films deposited via chemical vapor deposition (CVD) are compared with FOTS containing zirconium oxide sol‐gel films regarding the prevention of deposit formation and fouling during polymerization processes in microreactors. Both film structures led to anti‐adhesive properties of microreactor component surfaces during aqueous poly(vinylpyrrolidone) (PVP) synthesis. To determine the morphology and surface chemistry of the coatings, different characterization methods such as X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy as well as microscopic methods such as field‐emission scanning electron microscopy (FE‐SEM) and atomic force microscopy (AFM) are applied. The surface free energy and wetting properties are analyzed by means of contact angle measurements. The application of thin film‐coated mixing elements in a microreactor demonstrates a significant lowering in pressure increase caused by a reduced deposit formation.Item Open Access Proton-conducting (blend) membranes based on sulfonated/phosphonated and basic polymers(2024) De Azpiazu Nadal, Ignasi; Tovar, Günter (Prof.)Aiming at new proton-conducting membranes, this thesis deals with the syntheses and characterizations of highly sulfonated poly(arylene sulfides) and other polysulfides for application as polymer electrolytes. The study focuses mainly on the analysis of the polymer structures that would improve the conductivity of current proton conducting membranes while maintaining their mechanical stability. In a first step, several polymers are obtained from which poly(arylene sulfide)s polymers look more promising for further functionalization. They are obtained by using mild reaction conditions of a polycondensation reaction between 4,4 ́-thiobisbenzenethiol (TBBT) and decafluorobiphenyl. Optimization of this reaction allows for the obtainment of higher molecular weights than the ones reported in the literature. In a second step, poly(arylene sulfides) were phosphonated and sulfonated by a nucleophilic aromatic substitution (SNAr) displacement reaction of the fluorine atoms of the fluorinated polymer sub-units using different agents. Highly sulfonated polymers were obtained when using sodium 3-mercapto-1-propanesulfonate and resulted in water soluble ionomers. Kinetic studies of this reaction were performed and several new sulfonated poly(arylene sulfides) were obtained. Finally, stable polymer electrolyte membrane (PEM) with enhanced mechanical and chemical stability were obtained by blending these obtained ionomers with polybenzimidazole (PBIOO). These membranes were further characterized and in the best case a PEM with new sulfonated ionomer showed a conductivity 40 % higher than Nafion 212, used as a golden reference material. The best performing PEM’s obtained were further used in an electrolytic cell being part of eSCALED, a H2020 (MSC-ITN-2017. GA# 765376) European project which aim is to obtain a device that does the artificial photosynthesis in a more efficient way than the current devices.Item Open Access Carbon‐methanol based adsorption heat pumps : identifying accessible parameter space with carbide‐derived carbon model materials(2020) Träger, Lisa; Gläsel, Jan; Scherle, Marc; Hartmann, Julian; Nieken, Ulrich; Etzold, Bastian J. M.In adsorption heat pumps, the properties of the porous adsorbent and the refrigerant determine the performance. Major parameters for this working pair are the total uptake of the adsorptive, its kinetics, and the heat transfer characteristics. In the technical application despite powdered adsorbents, thin consolidated layers of the adsorbent can be attractive and obtained by a binder‐based approach but likely result in competing material properties. Thus, for a process optimization, the accessible parameter space and interdependencies have to be known and were deduced in this work for model porous carbons (carbide‐derived carbons derived from TiC and ZrC) and methanol as well as the addition of different amounts of boron nitride, silver, and graphite as heat‐conductive agents and the use of two binders.Item Open Access UV/VIS-spectroscopic inline measurement for the detection of fouling processes during the polymerization of N-vinylpyrrolidone(2023) Spoor, Erik; Welzel, Stefan; Nieken, Ulrich; Rädle, MatthiasWith the goal to better process the monitoring of occurring fouling, a backscatter probe was developed to perform in-line measurements in a half-shell reactor during the reaction of N-vinylpyrrolidone (NVP) to polyvinylpyrrolidone (PVP). The measurement technique detects the changes of bands in the UV range, which allows a direct correlation with the concentration. Thus, the measured absorbance signal allows a conclusion on the accumulation of fouling in the reactor and on changes in the conversion at the measurement location.Item Open Access Modeling strategies for the propagation of terminal double bonds during the polymerization of N‐vinylpyrrolidone and experimental validation(2020) Zander, Christian; Hungenberg, Klaus‐Dieter; Schall, Thomas; Schwede, Christian; Nieken, UlrichBased on a recently suggested reaction mechanism, which involves the production and propagation of terminal double bonds (TDBs), kinetic models for the polymerization of N‐vinylpyrrolidone in aqueous solution are developed. Two modeling strategies, the classes and the pseudodistribution approach, are applied to handle the multidimensional property distributions that result from this reaction mechanism and to get detailed structural property information, e.g., on the chain length distribution and the distribution of TDBs. The structural property information is then used to develop reduced models with significantly lower computational effort, which can be used for process design, on‐line applications or coupled to computational fluid dynamic simulations. To validate the derivations, the models are first compared against each other and finally to experimental results from a continuous stirred tank reactor. The evolution of monomer conversion and molecular weight average data as well as molecular weight distributions can be represented very well by the models that are derived in this article. These results support the correctness of the reaction mechanism predicted by quantum mechanical simulations.Item Open Access Novel pyrrolidinium-functionalized styrene-b-ethylene-b-butylene-b-styrene copolymer based anion exchange membrane with flexible spacers for water electrolysis(2023) Xu, Ziqi; Delgado, Sofia; Atanasov, Vladimir; Morawietz, Tobias; Gago, Aldo Saul; Friedrich, K. AndreasAnion exchange membranes (AEM) are core components for alkaline electrochemical energy technologies, such as water electrolysis and fuel cells. They are regarded as promising alternatives for proton exchange membranes (PEM) due to the possibility of using platinum group metal (PGM)-free electrocatalysts. However, their chemical stability and conductivity are still of great concern, which is appearing to be a major challenge for developing AEM-based energy systems. Herein, we highlight an AEM with styrene-b-ethylene-b-butylene-b-styrene copolymer (SEBS) as a backbone and pyrrolidinium or piperidinium functional groups tethered on flexible ethylene oxide spacer side-chains (SEBS-Py2O6). This membrane reached 27.8 mS cm-1 hydroxide ion conductivity at room temperature, which is higher compared to previously obtained piperidinium-functionalized SEBS reaching up to 10.09 mS cm-1. The SEBS-Py206 combined with PGM-free electrodes in an AWE water electrolysis (AEMWE) cell achieves 520 mA cm-2 at 2 V in 0.1 M KOH and 171 mA cm-2 in ultra-pure water (UPW). This high performance indicates that SEBS-Py2O6 membranes are suitable for application in water electrolysis.Item Open Access Validation of an extended kinetic model of free‐radical N‐vinylpyrrolidone polymerization(2023) Welzel, Stefan; Burmeister, Jule; Höppchen, Oliver; Nieken, UlrichTo predict the polymer properties produced by free-radical polymerization of N-vinylpyrrolidone (NVP) in aqueous solution a detailed kinetic model has been developed. The kinetic model allows to calculate the chain length distribution, the number of branching points, and the number of terminal double bonds (TDB). The latter is accounted for since TDBs are a precondition for branching. While monomer conversion can be predicted sufficiently using independently determined rate constants for propagation and termination, here the predictions of structural properties by a newly developed extended kinetic model to experimental findings are compared. Polymer produced in a continuous stirred tank reactor is analyzed by gel permeation chromatography (GPC), field flow fractionation (FFF), and high-pressure liquid chromatography (HPLC).