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| Hauptseite > Publikationsdatenbank > Solid Oxide Electrolysis and Fuel Cells at Forschungszentrum Jülich: An Overview and Recent Advances |
| Hauptseite > Publikationsdatenbank > Solid Oxide Electrolysis and Fuel Cells at Forschungszentrum Jülich: An Overview and Recent Advances |
| Contribution to a conference proceedings/Contribution to a book | FZJ-2026-00938 |
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2025
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Please use a persistent id in citations: doi:10.1149/MA2025-03139mtgabs
Abstract: Solid Oxide Cell (SOC) technology is currently experiencing a high level of interest, as the capabilities and the potential of the technology are well aligned with the global efforts to achieve zero emissions. Forschungszentrum Jülich has been heavily involved in the SOC research for more than three decades and has become a cornerstone of the global SOC research community. Selected historical highlights of this research include Jülich’s contributions to the development of the fuel electrode-supported design with material innovations and the advancement of the design for scalability in cells and stacks [1, 2], the development of the Crofer 22 APU alloy in close cooperation with industrial partners [3, 4] and the long-term operation of a short stack in fuel cell mode for more than 100,000 hours [5]. Today, the SOC research at Jülich is organized in five institutes and is characterized by a multidisciplinary approach to solving current fundamental and applied challenges in order to further develop the technology for various application areas. This comprehensive approach covers all aspects from materials to systems, including synthesis, fabrication, modeling, testing, demonstration, and post-test analysis. This contribution provides a general overview of these activities addressing current research topics and recent advances.Sustainability & cost reductionMaking SOC technology more economically attractive is an important goal, which can be achieved in different ways. One approach is to use cheaper steel grades, e.g. DIN1.4509 or DIN1.4016 that were not originally optimized for SOC application, but whose performance could be improved by coatings retaining Cr-evaporation. As part of a European project, long-term oxidation studies were carried out on coated steels [6], revealing excellent adhesion and microstructure stability of the coating systems. In addition, new coatings based on Mn-Co-Fe or Mn-Cu-Fe-spinels applied by electrophoresis (EPD) have been developed. EPD could be a more sustainable alternative to plasma spraying, especially suitable for thin-film cassette-type interconnects. Scale-up to real stack sizes and comparison with wet powder spraying [7] are currently underway.Another way to reduce costs is to minimize efforts to purify reactants (water, air, etc.). For this case the effect of pollutants such as Cl or S on the microstructure and properties of the cell components has been studied [8], revealing important degradation mechanisms. Cell degradation studies can be complemented with recently developed FIB/SEM and X-ray computed tomography [9]. Furthermore, approaches for the recycling of SOC metallic constituents have been developed with the aim of producing different Cr- and Ni-containing stainless steel grades, supported by thermodynamic modeling [10].A recycling strategy for operated stacks and especially also for the cell fraction has been implemented in a large German funded R&D project [11, 12]. The developed cell recycling route starts with a reoxidation step of the metallic Ni, the acidic leaching of the air electrode and the remaining contact layer material. The resulting fraction then consists of NiO, 8YSZ and remnants from GDC. This material mixture could then be post-processed (milling) and re-dispersed into a tape casting slurry for the fuel support up to amounts of 50% of recyclate. Full cells were fabricated and showed similar performance to the state-of-the-art fuel-electrode supported cells. The leached fraction could be separated into La-phase and a residual phase. The La could be re-processed. The ongoing work focuses on the remaining leached fraction.Cell development & modelingExtensive studies of long-term SOC operation and degradation at Jülich show that a ceramic material substitution is necessary to achieve a long lifetime of the SOC technology. The efforts include the development of proton conducting ceramic cells [13] and new electrode materials for oxygen conducting ceramics [14]. Finally, the driving force is to lower the application temperature to reduce the impact of degradation mechanisms.Since Ni-YSZ cermets have shown high degradation rates in steam electrolysis due to Ni migration, there is a strong focus on replacing Ni-YSZ in fuel electrode-supported cells. To enable a Ni-GDC cermet electrode, a three-layer electrolyte (GDC-YSZ-GDC) has been developed using a combination of screen-printing and magnetron sputtering. Excellent cell/stack performance can be achieved by avoiding interdiffusion between YSZ and GDC at the electrode/electrolyte interface, but cell processing needs to be optimized. Other efforts to replace Ni-YSZ include the development of an all-ceramic electrode made of SrTi0.5Fe0.5O3-d (STF), and the development of perovskite oxides with exsolved Ni particles.To gain a fundamental understanding of the degradation of electrode structures, a hierarchical model was developed that relates changes at the level of electrode particles to the evolution of the electrode structure and resulting material properties, and ultimately to the overall lifetime performance. In the fuel electrode, it was found that the limited ion conduction leads to a locally enhanced degradation rate close to the electrolyte side, until the breakdown of the percolating nickel particle network and thus of the electron conductivity is reached, resulting in a movement of the degradation zone deeper into the electrode. This creates a moving degradation front at the microstructural level, which leaves a fingerprint in the electrochemical impedance spectra. Overall, the model can be easily modified and extended (e.g. by including Ni migration). Since its computational time is low, it could be used as a concomitant analyzing tool during the operation of the SOC.Another challenge that is being addressed is the impact of different fuel sources (ammonia, biogas and their impurities) [15] on the functional properties and lifetime of fuel cells. Similarly, different types of components (e.g. sodium chloride) in water sources can affect the application of solid oxide electrolyzers. As access to high purity water is an issue and electrolysis should not contribute to further depletion of drinking water sources, the development of wastewater or saltwater electrolysis is an important sustainability goal for the hydrogen economy.Stack technology & characterizationOne of the 20-layer stacks assembled with the prospect of being used in the rSOC system showed a short circuit after the initial joining process and cell reduction. To avoid the disposal of the stack, dismantling was carried out level by level for six repeating units until the damaged layer could be removed. A green foil of the glass-based composite sealant was placed on the residuals of the broken joint and a second joining process was performed against a new top plate. After this repair process, the stack operation could be started with promising results.In the field of electrochemical stack characterization, the research focuses on the development of innovative measurement and analysis techniques. Fiber optic sensors are used for precise and compact temperature measurements under highly dynamic SOC operating conditions. A combined approach using electrochemical impedance spectroscopy (EIS) and total harmonic distortion provides detailed insight into the performance of a co-electrolysis stack. A novel data-driven methodology was developed using 2,600 EIS measurements from SOC stacks operated in various modes for over 47,000 hours. This method allows reconstruction of the EIS from sparse frequency sampling [16]. Long-term degradation effects are studied in a multi-stack configuration consisting of six sub-stacks operated under co-electrolysis conditions, revealing the effect of operating time with a common history of all samples. Additional degradation analysis focuses on one stack under steam electrolysis at reduced temperatures, with variations in current density and feed gas composition over four 1,000-hour phases. Modeling efforts include a CFD-based sulfur poisoning analysis of the co-electrolysis and a predictive performance evaluation method coupling phase field modeling with CFD. At the system level, the rSOC system design in the 10/40 kW power class demonstrated reliable operation for over 11,500 h at temperature, with ongoing optimization of control strategies for cyclic operation and realistic load profiles. A digital twin of the integrated module of the rSOC system, developed using OpenFOAM, was validated and supports fast, accurate characterization.Post-test analysisPost-test analyses provide critical insight into failure modes and degradation processes, including electrical behavior, material interactions, and operational influences. Failure mechanisms such as short circuits, leakage, and external factors are characterized alongside degradation phenomena such as chromium poisoning and sealant degradation. Key operating parameters such as temperature, current density, and fuel composition, are evaluated for their impact on performance and material stability. An SOC-stack autopsy methodology has been developed that demonstrates the disassembly of a module for the subsequent post-test analysis.The Jülich long-term test in fuel cell operation, which lasted about 10 years, was investigated immediately after the end of the test [17, 18]. The results showed relatively few changes, interactions or damage considering the long operating time. One of the main conclusions was that the interface between the LSCF air electrode and the GDC barrier layer was somewhat changed. Secondary phase formation was observed, leading to tiny nanocrystals and partial incorporation of Cr into the LSCF grains. The secondary formed crystals were also found in the pores of the GDC layer. Additional advanced characterization tools such as Raman spectroscopy and µ-Laue diffraction revealed similar results compared to the SEM characterizations. However, one simple question remained unanswered. None of the techniques applied could verify or falsify whether the LSCF perovskite was still a perovskite or had transformed into another crystal structure after such a long time. Thus, additional high-resolution TEM investigations were performed. Finally, it was proven that the entire air-electrode volume, from the interface to the GDC to the bulk layer, is still a perovskite. This result proves the chemical stability of the perovskite structure.
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