04 Fakultät Energie-, Verfahrens- und Biotechnik

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

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Institute: search.filters.UBSInstitut.Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)Author: search.filters.author.Kube, Alexander

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Now showing 1 - 4 of 4
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    Wetting behavior of aprotic Li-air battery electrolytes
    (2021) Kube, Alexander; Bienen, Fabian; Wagner, Norbert; Friedrich, Kaspar Andreas
    The open architecture of cathodes in Li–air batteries implies the need for open porosity with adequate pore size distribution and surface energy optimization with regard to the electrolyte. The interaction of liquid and cathode material, especially the wetting properties, which depend on cathode material, roughness and porosity, and electrolyte properties, needs to be understood properly to avoid flooding and assure high active areas. In this work, contact angle goniometry, capillary rise method, and pressure saturation curves are used to investigate the wetting properties of dimethyl sulfoxide (DMSO), tetraethylene glycol dimethyl ether (Tetraglyme), a 1:1 mixture of ethylene carbonate and dimethyl carbonate (EC:DMC) and water on a gas diffusion layer (GDL) Sigracet 39BC, and a pure flat polytetrafluorethylene (PTFE) foil. Contact angle measurement shows that all three organic solvents wet the GDL hydrophobic agent PTFE. Capillary rise measurements show that all sample liquids slowly imbibe into the porous network. While for Tetraglyme an efficient penetration is limited by the high viscosity, water flow rate is slowed down by the hydrophobic pore network of the GDL. Pressure saturation curves for DMSO, Tetraglyme, and EC:DMC can be obtained for the first time and are compared with the water pressure saturation curve.
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    Advanced impedance analysis for performance degradation during low-temperature CO2 electroreduction
    (2024) Chen, Qinhao; Kube, Alexander; Kopljar, Dennis; Friedrich, Kaspar Andreas
    Electrochemical impedance spectroscopy (EIS) is a powerful tool commonly used to study electrochemical systems. Nevertheless, its application in CO2 electroreduction has been so far limited due to its complex reaction mechanism and environment. Although initial findings have demonstrated the viability of applying EIS analysis in CO2 electrolyzers, the assignment of individual processes in the impedance spectra remains ambiguous. Therefore, a more detailed investigation, especially focused on its application in evaluating degradation mechanisms, is essential. In this study, a stable gas diffusion electrode (GDE) system was developed for a comprehensive EIS and distribution of relaxation time (DRT) evaluation to assess key degradation mechanisms under accelerated stress conditions such as high current density and low operating temperature. Validated by post-mortem analysis and complementary methods, we demonstrate the viability of this approach for operando monitoring of CO2 electroreduction by assigning individual mechanistic processes in the GDE and linking them to performance degradation over time.
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    A segmented cell measuring technique for current distribution measurements in batteries, exemplified by the operando investigation of a Zn-air battery
    (2021) Kube, Alexander; Meyer, Jens; Kopljar, Dennis; Wagner, Norbert; Friedrich, Kaspar Andreas
    A transimpedance amplifier circuit as well as an instrumental amplifier circuit were used to measure current densities of a zinc-air battery with an integrated segmented current collector foil. Error calculation showed that the transimpedance amplifier is superior to the used instrumental amplifier, but both methods provide valuable and consistent results. They both showed comparable results with operando insight into the current distribution of the battery. The knowledge about those distributions is essential to avoid fast degradation of battery materials and irreversible capacity loss due to heterogeneous dissolution of the anode during discharge. In this work we showed that oxygen starvation as well as gas flow rate leads to large current gradients. It was also demonstrated that heterogeneous current distributions on cathode side induces also a heterogenous dissolution behavior on the anode, resulting in irreversible capacity loss.
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    Scalable fabrication of multi-layered Cu-based electrodes via solvent-free method for the selective electrochemical conversion of CO2 to C2+ products
    (2024) Chen, Qinhao; Kube, Alexander; Rana, Bhawna; Biswas, Indro; Morawietz, Tobias; Kopljar, Dennis; Friedrich, Kaspar Andreas
    In the research field of CO2 electroreduction, gas diffusion electrodes (GDEs) are predominantly manufactured through solvent-based processes. Meanwhile, the solvent-free method has gained heightened attention due to its potential to reduce operational and production expenses, while considering ecological aspects such as solvent evaporation, circulation, and waste treatment. Drawing from its successful applications in other fields, we have specifically developed a solvent-free manufacturing method to produce multi-layered Cu-based GDEs for CO2 electroreduction. The procedure is compatible with industrial production lines, specifically through a roll-to-roll process. By evaluating the interplay between production parameters and electrochemical performance of GDEs via various characterization methods, key factors, i.e., hydrophobicity, gas permeability, thickness, and pore size, were adjusted and applied to achieve a highly selective GDE towards C2+ products (alcohols and ethylene) at industrial relevant currents up to 300 mA cm-2 (ethylene ∼40%, ethanol ∼10%, n-propanol ∼15%).