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Institute: search.filters.UBSInstitut.Fakultätsübergreifend / Sonstige EinrichtungInstitute: search.filters.UBSInstitut.Institut für Chemische VerfahrenstechnikStart date: 2024Subject: search.filters.subject.540

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Now showing 1 - 3 of 3
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    Synthesis and characterization of novel perfluoro aromatic side chain sulfonated PSU ionomers
    (2024) Martschin, Philipp; Atanasov, Vladimir; Thiele, Simon; Kerres, Jochen
    Polyethersulfone (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).
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    Gas evolution in Ruddlesden-Popper-type intercalation cathodes in all-solid-state fluoride-ion-batteries : implications on battery performance and synthesis of highly oxidized oxyfluorides
    (2025) Aalto, Tommi Hendrik; Jacobs, Jonas; Frey, Felix; Schiewe, Dörthe; Clemens, Oliver
    In this work, we report the gas evolution behavior of two common intercalation-based cathode materials for fluoride-ion-batteries (La2NiO4 and La2CoO4) by chemical fluorination and electrochemical fluorination, as well as the thermal stability of the electrochemically fluorinated active materials. Variable-temperature X-ray diffraction with coupled mass spectrometry shows that the fluorinated phases of both active materials release oxygen after oxidative fluorination using AgF. Differential electrochemical mass spectrometry revealed that significant CO2, CO and NO evolution takes place during electrochemical fluorination, but O2 evolution could not be detected. Consequently, the gas evolution observed does not compromise the long-term stability of the cell performance. Variable-temperature X-ray diffraction of the charged cathode composites reveals that the electrochemically fluorinated products decompose once heated beyond 300 °C, and then undergo similar phase evolution behavior as observed in chemical fluorination. Thus, we conclude that oxygen evolution in RP-type materials on oxidative fluorination requires thermal activation beyond the operational temperature of 170 °C, and that it can be kinetically suppressed regardless of the reduced Fermi level induced on fluorination. Our findings indicate that concepts used for the oxidative topochemical fluorination of materials need to be reconsidered: the choice of fluorination conditions must be carefully adopted to the changes of electronic structure induced and the temperature dependence of the oxygen evolution of the highly oxidized state.
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    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.