04 Fakultät Energie-, Verfahrens- und Biotechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5

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Author: search.filters.author.Morawietz, TobiasSubject: search.filters.subject.621.3

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    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. Andreas
    Anion 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.
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    Investigation of the degradation phenomena of a proton exchange membrane electrolyzer stack by successive replacement of aged components in single cells
    (2025) Kimmel, Benjamin; Morawietz, Tobias; Biswas, Indro; Sata, Noriko; Gazdzicki, Pawel; Gago, Aldo Saul; Friedrich, Kaspar Andreas
    Due to their compactness and high flexibility to operate under dynamic conditions, proton exchange membrane water electrolyzers (PEMWEs) are ideal systems for the production of green hydrogen from renewable energy sources. For the widespread implementation of PEMWEs, an understanding of their degradation mechanism is crucial. In this work, we analyze a commercial PEMWE stack via a novel approach of breaking down from the stack to the single-cell level. Therefore, the disassembled stack components are cut to fit into single cells. Then, the aged components are successively replaced with pristine or regenerated components (cleaned and polished), and electrochemical characterizations are conducted to investigate the contributions of the individual components on performance losses. In addition, several underlying degradation phenomena are identified using different physical ex-situ analysis methods. The catalyst-coated membrane (CCM) contributes the most to performance degradation because of contamination and ionomer rearrangement. Additionally, traces of calcium, likely due to insufficient water purification used during operation or for cleaning the cell components, were found. Significant oxidation was observed on the anodic components, while the electronic conductivity on the cathode side remained unchanged. The combination of electrochemical characterization with stepwise regeneration processes and physical ex-situ analysis allows to draw conclusions about the impact of different components on degradation and to analyze the underlying aging mechanisms occurring in each component.