06 Fakultät Luft- und Raumfahrttechnik und Geodäsie

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7

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2024 - 20253

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Institute: search.filters.UBSInstitut.Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)Author: search.filters.author.Egert, FranzAuthor: search.filters.author.Razmjooei, Fatemeh

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    Hydroxyl-conductive 2D hexagonal boron nitrides for anion exchange membrane water electrolysis and sustainable hydrogen production
    (2025) Kaur, Jasneet; Schweinbenz, Matthew; Ho, Kane; Malekkhouyan, Adel; Ghotia, Kamal; Egert, Franz; Razmjooei, Fatemeh; Ansar, Syed Asif; Zarrin, Hadis
    In response to the urgent global call to transition from polluting fossil fuels to sustainable energy alternatives, hydrogen emerges as a promising and widely accessible energy source if it can be efficiently produced through water splitting and electrolysis. Anion exchange membrane (AEM) water electrolyzers (AEMWEs) have potential for large scale H2 production at a low cost. However, the development of alkaline membranes with high hydroxide conductivity, improved stability and better performance is a significant challenge for the commercial application of advanced AEMWEs. In this work, a novel structure for hydroxide-ion conductive membranes based on surface-engineered two-dimensional (2D) hexagonal boron nitrides (h-BN) is designed and validated in a highly active and durable AEMWE cell with non-precious metal Ni-based electrodes. Among two samples, the high-loaded 2D hBN nanocomposite membrane (M2) showed significantly high hydroxide-ion conductivity (190 mS cm-1) with improved electrochemical and mechanical stability. The AEMWE cell assembled with the M2 membrane exhibited superior cell performance, achieving 1.78 V at 0.5 A cm-2 compared to the cell utilizing the lower loading hBN nanocomposite membrane (M1). Additionally, its performance closely approached that of the cell employing a commercial membrane. During a long-term stability test conducted at a constant load of 0.5 A cm-2 for 250 hours, the M2 membrane maintained satisfactory electrolysis voltage without any notable failure. These findings demonstrate that 2D hBN nanocomposite membranes hold great promise for use in advanced AEMWEs.
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    Intensification of alkaline electrolyzer with improved two‑phase flow
    (2025) Egert, Franz; Ullmer, Dirk; Marx, Sven; Taghizadeh, Ehsan; Morawietz, Tobias; Gerle, Martina; Le, Thi Anh; Campo Schneider, Lucia Paula; Biswas, Indro Shubir; Wirz, Richard E.; Spieth, Philipp; Marquard‐Möllenstedt, Tonja; Brinner, Andreas; Faccio, Ricardo; Fernández‐Werner, Luciana; Esteves, Martín; Razmjooei, Fatemeh; Ansar, Syed Asif
    Green hydrogen produced through water electrolysis offers a promising pathway to global decarbonization. Among various electrolyzers, alkaline water electrolysis (AWE) is the most established and commercially mature. To reduce the cost of hydrogen production from AWE, it is crucial to increase operational current density while maintaining or lowering voltage to increase hydrogen yield and reduce energy consumption. Such efforts are focused on reducing the ohmic resistance at high current densities through the implementation of alkaline membranes. However, this work underlines that the ohmic resistance at high current densities is also influenced by the losses associated with the evolution of bubbles at the electrode surface and two‐phase mass transfer. This is shown by investigating the impact of tortuosity and bubble point of porous electrodes on AWE performance. Low‐tortuosity porous nickel electrodes are fabricated and analyzed for their ability to reduce capillary pressure and bubble point, resulting in lower energy losses and improved efficiency. The cell reaches an industrially appealing relevant current density of 2 A cm -2 at ≈2 V. Besides test in single cells, the advantageous effect of these low tortuosity porous nickel electrodes are also validated in a kW‐class AWE stack, confirming their effectiveness in enhancing overall system performance.
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    Proton exchange membrane-like alkaline water electrolysis using flow-engineered three-dimensional electrodes
    (2024) Rocha, Fernando; Georgiadis, Christos; Van Droogenbroek, Kevin; Delmelle, Renaud; Pinon, Xavier; Pyka, Grzegorz; Kerckhofs, Greet; Egert, Franz; Razmjooei, Fatemeh; Ansar, Syed-Asif; Mitsushima, Shigenori; Proost, Joris
    For high rate water electrolysers, minimising Ohmic losses through efficient gas bubble evacuation away from the active electrode is as important as minimising activation losses by improving the electrode’s electrocatalytic properties. In this work, by a combined experimental and computational fluid dynamics (CFD) approach, we identify the topological parameters of flow-engineered 3-D electrodes that direct their performance towards enhanced bubble evacuation. In particular, we show that integrating Ni-based foam electrodes into a laterally-graded bi-layer zero-gap cell configuration allows for alkaline water electrolysis to become Proton Exchange Membrane (PEM)-like, even when keeping a state-of-the-art Zirfon diaphragm. Detailed CFD simulations, explicitly taking into account the entire 3-D electrode and cell topology, show that under a forced uniform upstream electrolyte flow, such a graded structure induces a high lateral velocity component in the direction normal to and away from the diaphragm. This work is therefore an invitation to start considering PEM-like cell designs for alkaline water electrolysis as well, in particular the use of square or rectangular electrodes in flow-through type electrochemical cells.