IFA – Institut für Innovative Fahrzeugantriebe
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- Wasserstoffantriebe; Brennstoffzellen-Antriebsstränge; Brennstoffzellenantriebe ; Brennstoffzellen (2)
- Accelerated Durability Test (1)
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- cleanEngine (1)
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PEMFC durability is still a major challenge. To overcome time-consuming durability tests, so-called accelerated durability tests (ADT) are of urgent need. This work presents our recent results in developing ADT protocols in the context of realistic operating conditions, i.e. voltage clipping at 0.85 V. A 5,500 h long-term test was carried out as reference applying a realistic automotive drive cycle. Focusing on different stressors such as temperature, relative humidity (RH) and load profile four different ADT protocols of 1,200 h duration were derived. 7-cell short stacks with 240 cm² active area were used. Comparing cell voltage as key indicator, an acceleration factor of 3 to 7 could be achieved. In situ characterization techniques such as spatially resolved current measurement, CV and EIS were employed to investigate influences of individual stressors on specific degradation mechanisms and components. Highest acceleration was observed in mass transport region of ADTs addressing RH as stressor, suggesting that RH cycling leads to increased degradation of hydrophobic surfaces. Increased temperature was found to accelerate primarily carbon support degradation. Accelerated catalyst aging seems to be low, demonstrating the effectiveness of voltage clipping conditions. Our most promising ADT shows quite homogeneous acceleration of voltage degradation across all current regions.
Durability of proton exchange membrane fuel cells (PEMFCs) in single-cell setup is often assessed using potentiostatic test protocols under inert cathode atmosphere, such as the US DOE’s accelerated stress tests (ASTs). Although these voltage-controlled protocols impose consistent electrochemical stress, they do not accurately replicate real-world operating conditions, for instance due to the lack of product water formation in the cathode or due to the generation of heat. In contrast, stress testing under hydrogen and air, which is commonly employed for PEMFC durability testing on stack level, reflect the hybrid potential- and current-controlled degradation modes which are typical of mobile applications. This is usually done galvanostatic, but can also be realized in a voltage controlled manner. There are notable differences in the ageing behaviors between those two methods: Potentiostatic testing protocols, in which the voltage remains constant throughout the test duration, induce consistent electrochemical stress regarding potential driven degradation modes such as platinum dissolution, Ostwald ripening, carbon corrosion and chemical membrane degradation due to hydrogen peroxide formation. In contrast, galvanostatic testing protocols result in a gradual decline in potential with time, thereby reducing potentially driven electrochemical stress. However, in galvanostatic mode, water production remains constant (unlike in potentiostatic mode), which is known to contribute equally to fuel cell degradation. This dynamic of varying potential driven and humidity driven stress significantly affects catalyst and membrane durability, underscoring the need to understand the degradation behavior specific to each testing method. The present study compares the impact of load-cycle and voltage-cycle protocols on PEMFC degradation. Electrochemical characterizations, such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), are used to identify the ageing behavior of the individual components. All tests were performed using commercial Gore® PRIMEA® membrane electrode assemblies (MEA) in a Baltic quickConnect high amp test cell with an active area of 12 cm². Our findings highlight the importance of testing under hydrogen and air to better replicate operational conditions and enhance PEMFC durability in practical applications.
Over the past two decades, several add-on modules for computational fluid dynamics (CFD) software focusing on modelling electrochemical processes and two-phase effects within fuel cells have been described in the literature. Most of these models are based on custom-written code that is not openly accessible to everyone. Furthermore, several commercial CFD codes offer specific modules for modelling fuel cells. Here, code modification is difficult to achieve. This work analyses and further develops the PEMFC toolbox of Kone et al. for use in OpenFOAM to simulate low temperature (LT-)PEM fuel cells. This model is freely available under the GNU GPLv3 licence. The present work focuses on enhanced physical and electrochemical modelling and improved user-friendliness. The major improvements compared to the original toolbox will be detailed in the article, together with the first results obtained. The improved PEMFC toolbox is validated using experimental data from an automotive fuel cell stack design. Furthermore, these results are compared to the original Kone model, and a commercially available CFD model. The improved toolbox reproduces both the experimentally measured polarisation curve and the current density distribution quite accurately, producing results that are fairly comparable to the more sophisticated commercial model.
Built-In Open Circuit Reference Electrodes in a PEM Water Electrolysis Cell – A Proof of Concept
(2025)
This study presents a proof of concept for the integration of open circuit reference electrodes (OC-REs) in proton-exchange membrane water electrolysis (PEMWE) cells to understand electrode performance and loss mechanisms, allowing for unequivocal assignment of these losses to anode and cathode. OC-REs, which are non-invasive to cell performance and share the same environment as the working electrodes (WEs), are assessed for stability and reproducibility while their performance is investigated across varying current densities and membrane thicknesses. Results demonstrate the significant impact of hydrogen crossover on the potential of the anode RE, impact that was modeled by calculating a current-density-dependent mixed potential. When comparing half-cell and full-cell polarization, the latter shows significantly higher reproducibility, with proper electrode alignment being crucial to minimize differences in half-cell polarization curves. Conversely, no significant impact from alignment on half-cell electrochemical impedance spectroscopy (EIS) was observed, making this technique the more consistent approach. The half-cell EIS revealed a significant contribution from the cathode to the overall loss, contrary to indications from most studies lacking this half-cell insight. These findings illustrate the potential of OC-REs as effective sensors for assessing electrode contributions, paving the way for future investigations into optimizing PEMWE.
Power demand and dynamic response are primary control objectives for automotive fuel cell systems (FCSs). Their operational impact in fuel cell electric transporters is underexplored, with most studies limited to simulations and optimization-based energy management systems (EMSs) that lack practical interpretability. This study presents experimental analysis on a powertrain test bench with components of a light commercial transporter, employing rule-based EMS to derive design guidelines. The analysis considers FCS operating range, dynamic response, and power distribution. Results show that narrowing the operating range from 65 to 45 kW improves average efficiency by 1.4%. Varying the dynamic response between 5–30 kW/s does not affect efficiency. A 5% efficiency span is observed across load-following, charge-sustaining, and average-power strategies. Sizing guidelines are derived from battery stress analysis. An operating range of 45 kW with ramp rates of 5–10 kW/s (positive) and −30 kW/s (negative) is recommended for EMS design.
Ein Ziel im Projekt "cleanEngine" war es, eine hoch innovative Entwicklungsplattform zur dynamisch-energetischen Optimierung von Brennstoffzellenantrieben für leichte Nutzfahrzeuge zu schaffen. Die Fokusse lagen in der Erhöhung der Reichweite, der Steigerung der Energieeffizienz und Untersuchungen zur Skalierbarkeit. Dabei standen die Anpassungsfähigkeit an verschiedene Betriebsbedingungen, einschließlich dynamischer Lastzyklen und Temperaturschwankungen, im Mittelpunkt.
Ein Ziel im Projekt "cleanEngine" war es, eine hoch innovative Entwicklungsplattform zur dynamisch-energetischen Optimierung von Brennstoffzellenantrieben für leichte Nutzfahrzeuge zu schaffen. Die Fokusse lagen in der Erhöhung der Reichweite, der Steigerung der Energieeffizienz und Untersuchungen zur Skalierbarkeit. Dabei standen die Anpassungsfähigkeit an verschiedene Betriebsbedingungen, einschließlich dynamischer Lastzyklen und Temperaturschwankungen, im Mittelpunkt.
We present a physical degradation model which simulates the evolution of the cathode catalyst layer nanomorphology and associated catalyst surface area in the course of potential-induced ageing. By coupling to the morphology model featured in Part I, the effects of the pore, particle and ionomer distributions and resulting nanoscale interfaces in each individual material are taken into account. Specifically, the model discriminates between catalyst ageing on the support surface and inside primary pores of the support. For model validation, catalyst utilization data in terms of active surface area measured at varying relative humidity is used. These data are sensitive to a variety of electrode properties such as support porosity, catalyst loading and size and ionomer loading. Simulations are compared against data from 15 samples manufactured in-house using different materials and aged in different conditions. In-depth analysis of simulation results identifies the model as a valuable tool to establish a link between electrode composition and nanomorphology as well as between nanomorphology and expected degradation.
We present a physical model of the cathode catalyst layer morphology which simulates the electrochemically active catalyst surface area at varying degrees of humidification. The model considers pore, particle and ionomer distributions and resulting interfaces on the nanoscale to create a unique mathematical representation of each material. Specifically, the model discriminates between catalyst particles on the support surface and inside primary pores of the support and their respective connection to the proton-conducting phase.
Catalyst particles may be protonically activated by coverage with ionomer or water or be protonically inaccessible. The exact configuration depends on the particle size and location as well as the cell operating conditions, sensitizing the simulated catalyst utilization to these properties.
Model results are compared against data for five samples with different support materials and ionomer loadings manufactured in-house. Further, trends in catalyst utilization which were observed in recent literature are reproduced with the model. This work provides a comprehensive analysis of material configurations and simulations at begin of test. In Part II, the presented model is integrated into a degradation model to predict the evolution of the electrode morphology and catalyst utilization during ageing.
Entwicklungsplattform cleanEngine: Dynamisch-energetische Optimierung von leichten BZ-Nutzfahrzeugen
(2024)
Das Forschungsverbundprojekt „cleanEngine“ zielte darauf ab, eine innovative Entwicklungsplattform zur dynamisch-energetischen Optimierung von Brennstoffzellenantrieben (BZ-Antrieben) für leichte Nutzfahrzeuge zu schaffen. Hierfür wurden virtuelle und reale Testverfahren zusammengeführt, um modellbasierte Entwicklungen zu verifizieren und zu validieren. An der Hochschule Kempten wurde ein Hardware-in-the-Loop-Teststand (HiL) für eine maximale Antriebsleistung von 250 kW realisiert, der durch einen digitalen Zwilling, in Form einer Model-in-the-Loop-Simulation (MiL), ergänzt wurde. Ein prototypischer BZ-Antriebsstrang wurde in einen Versuchsträger implementiert, um die Ergebnisse aus Fahrversuchen mit denen aus Simulationen und Teststandmessungen zu vergleichen.
Die Herausforderungen bestanden in der fahrzeug- und anwendungsspezifischen Dimensionierung der Antriebskomponenten, einschließlich der Brennstoffzellenleistung, der Dynamik des BZ-Systems, der Wasserstoffspeicherkapazität, der Leistung der Hochvoltbatterie und des Antriebsmotors. Durch iterative und rekursive Verfahren wurde die Reproduzierbarkeit der Ergebnisse sichergestellt, wodurch für die entwickelten Methoden der Funktionsnachweis erbracht wurde.
Ein zentrales Ergebnis des Projekts ist die Erkenntnis, dass die Ladeleistungsgrenze der Batterie ein kritischer Faktor für die Effizienz des Antriebsstrangs ist. Dies unterstreicht die Notwendigkeit der Weiterentwicklung von Batteriesystemen für wasserstoffelektrische Antriebe. Darüber hinaus wurde ein intelligenter Energieflussregler entwickelt, der die Energieflüsse zwischen Brennstoffzelle, Batterie und Antriebsmotor optimiert und so den Wasserstoffverbrauch minimiert.
Die Ergebnisse zeigen, dass die entwickelten Methoden und Tools eine ganzheitliche Betrachtung von Brennstoffzellensystemen ermöglichen, von der Komponentenebene bis hin zum Gesamtfahrzeug. Dies trägt dazu bei, die Entwicklungszeiten und -kosten für kleine und mittlere Unternehmen erheblich zu reduzieren.
Das Projekt „cleanEngine“ wurde vom Bundesministerium für Digitales und Verkehr (BMDV) gefördert und in Zusammenarbeit mit der Hochschule RheinMain (HSRM) und der ABT e-Line GmbH durchgeführt. Die Ergebnisse sind für die Weiterentwicklung wasserstoffelektrischer Antriebe von fundamentaler Bedeutung und unterstreichen das Potenzial der H2-Technologie für eine nachhaltige Mobilität.