This study presents an advanced numerical modeling approach for analyzing a 10/40 kW reversible solid oxide cell Integrated Module designed by Forschungszentrum J & uuml;lich GmbH. The present authors extend the distributed resistance analogy method using OpenFOAM to comprehensively simulate the complex physical processes within the sub-components of the Integrated Module. The model incorporates numerical techniques, including the arbitrary mesh interface for sub-component interpolation, a radiative heat transfer model for inter-component heat exchange, and a region-to-region coupling approach for surface and volume temperature coupling. Numerical predictions demonstrate good agreement with experimental measurements in both fuel cell and electrolysis modes, with maximum temperature deviations of 10-15 K observed in the middle parts of the sub-stacks. The model successfully captures the uniform performance across sub-stacks and the high efficiency of the heat exchangers. Analysis of species and current density distributions confirms that the design ensures uniform sub-stack operation, which is crucial for long-term performance. While discrepancies between predicted and reference temperatures in the heating plates are within acceptable limits, the study highlights the potential limitations of simple models in representing real-world systems. This research provides valuable insight into the Integrated Module behavior, enabling informed design optimization and operational strategies. The developed methodology offers a powerful tool for rapid and accurate characterization of reversible solid oxide cell systems, contributing to the advancement of reversible solid oxide cell technology as it scales up for industrial applications.

In this work the authors designed and experimentally evaluated different controller topologies for fuel cell operation (SOFC) of a reversible solid oxide cell (rSOC) system. Aim of the controller is to operate the SOFC system autonomously at a constant maximum temperature for maximum efficiency. The controller design incorporates an artificial neuronal network (ANN) for real time state predictions. The training data for the ANN was generated by a Digital Twin of this system. The generated training data consists of about 16,000 different steady state operating conditions.

Forschungszentrum Jülich has been operating an rSOC system in the 10/40 kW AC power class since 2021. This system uses four 20-layer sub-stacks in the mark H20 stack design. During the test campaign, a power range from 1.7 to 13 kW AC could be shown in fuel cell mode. The highest efficiency in fuel cell mode of 63.3 % was achieved at a power output of 10.4 kW AC , related to the lower heating value (LHV) of hydrogen. With a power input of -49.6 kW AC , the highest efficiency of 71.1% (LHV) was achieved in electrolysis mode. At this point, 11.7 Nm³ h -1 of hydrogen were produced. The following manuscript shows the layout and the experimental results of the rSOC demonstration system.

For a future carbon-neutral energy economy, fuel cells play an important role due their high efficiency. Especially the Solid Oxide Fuel Cell (SOFC) with demonstrated efficiencies beyond 60 % 1 can contribute to reasonable roundtrip efficiencies for hydrogen and e-fuels 2. To match the fluctuating electricity demand in a future electricity grid, dominated by renewable energy sources like wind and photovoltaic, dynamic operation of fuel cells is required. The research has shown that the degradation und therefore the lifespan of Solid Oxide Cell (SOC) stacks shows a significant dependency on the operating conditions and dynamic load changes 3. However, some research suggests that the degradation is not caused by the load changes itself but spatial temperature gradients during load changes 4–6. Therefore, controlling the temperature gradients in the stack during load changes can have a significant impact on the lifespan of SOC stacks. This is typically more dramatically for stacks with larger cell sizes or multiple cells per layer. Furthermore, a tight temperature control allows for running the stack at maximum efficiency without the risk of stack damage due to exceeding temperature limits. In this work the authors designed and experimentally evaluated different controller topologies for fuel cell operation (SOFC) of a reversible solid oxide cell (rSOC) system described previously 7. The controller design incorporates an artificial neuronal network (ANN) for real time state predictions. The training data for the ANN was generated by a dynamic model of this system. This model is implemented in Matlab Simulink and was validated against experimental data. The generated training data consists of about 1,000 simulated days of dynamic system operation with a sample interval of 10 s. Additionally, data for 16,000 different steady state operating conditions of the system were generated. One focus of this work is the robustness of the controller under real world conditions despite inaccuracies of the underlying model and SOC degradation effects over time. To compensate the aging of the stack, the ANN is trained on variable degradation states. The degradation state is then tracked by the controller during operation to maintain an accurate prediction. First system experiments showed promising results in this respect (Fig. 1). Fig 1. Maximum temperature (red) and its setpoint (red, dashed) as well as 8 other temperatures distributed over the stack (black) in response to a given current density profile (green) and the air flow (blue) set by the controller Acknowledgments The authors would like to thank their colleagues at the Forschungszentrum Jülich GmbH, who helped realize this work, and the Helmholtz Society for financing these activities as part of the Living Lab Energy Campus. References (1) Peters, Ro.; Frank, M.; Tiedemann, W.; Hoven, I.; Deja, R.; Kruse, N.; Fang, Q.; Blum, L.; Peters, R. Long-Term Experience with a 5/15kW-Class Reversible Solid Oxide Cell System. J. Electrochem. Soc. 2021, 168 (1), 014508. https://doi.org/10.1149/1945-7111/abdc79. (2) Heydarzadeh, Z.; McVay, D.; Flores, R.; Thai, C.; Brouwer, J. Dynamic Modeling of California Grid-Scale Hydrogen Energy Storage. ECS Trans. 2018, 86 (13), 245–258. https://doi.org/10.1149/08613.0245ecst. (3) Kim, Y.-D.; Lee, J.-I.; Saqib, M.; Park, K.-Y.; Hong, J.; Yoon, K. J.; Lee, I.; Park, J.-Y. Degradation of Anode-Supported Solid Oxide Fuel Cells under Load Trip and Cycle Conditions and Their Degradation Prevention Operating Logic. J. Electrochem. Soc. 2018, 165 (9), F728–F735. https://doi.org/10.1149/2.1391809jes. (4) Hagen, A.; Høgh, J. V. T.; Barfod, R. Accelerated Testing of Solid Oxide Fuel Cell Stacks for Micro Combined Heat and Power Application. Journal of Power Sources 2015, 300, 223–228. https://doi.org/10.1016/j.jpowsour.2015.09.054. (5) Nakajo, A.; Wuillemin, Z.; Van herle, J.; Favrat, D. Simulation of Thermal Stresses in Anode-Supported Solid Oxide Fuel Cell Stacks. Part I: Probability of Failure of the Cells. Journal of Power Sources 2009, 193 (1), 203–215. https://doi.org/10.1016/j.jpowsour.2008.12.050. (6) Jiang, W.; Luo, Y.; Zhang, W.; Woo, W.; Tu, S. T. Effect of Temperature Fluctuation on Creep and Failure Probability for Planar Solid Oxide Fuel Cell. Journal of Fuel Cell Science and Technology 2015, 12 (5), 051004. https://doi.org/10.1115/1.4031697. (7) Peters, R.; Tiedemann, W.; Hoven, I.; Deja, R.; Kruse, N.; Fang, Q.; Blum, L.; Peters, R. Development of a 10/40kW-Class Reversible Solid Oxide Cell System at Forschungszentrum Jülich. ECS Trans. 2021, 103 (1), 289–297. https://doi.org/10.1149/10301.0289ecst. Figure 1

Scientific Approach Within the last years, the development work on reversible solid oxide cell (rSOC) systems has been intensified. This is mainly because this technology can deliver a valuable contribution to carbon-neutral energy supply by storing surplus electrical power into hydrogen and converting it again if necessary. Motivated by this application, in 2018 research by Frank et al. [1] suggests that a round trip efficiency of 50% is possible for a pressurized storage at 70 bars. Based on these results, Forschungszentrum Jülich developed an rSOC demonstration system whose design point is 10 kWAC in fuel cell mode and 40 kWAC in electrolysis mode. The system layout and the evaluation of balance of plant components (BoP) are described by Peters et al. [2]. Figure below shows on the left side the core components of the demonstrator system including the Integrated Module (IM). This IM consists of four 20-layer sub-stacks in the mark H20-design by Forschungszentrum Jülich. The fuel and air heaters are located at the top and bottom of the module. The system can be heated up by in total five heating plates which are arranged on top and below each sub-stack. These plates are also used to maintain the temperature management of the stacks during the endothermic electrolysis operation. In order to ensure the most compact system design, the BoP components are suitably arranged in the vicinity of the IM. The right side of Figure shows the core system installed in the laboratory test environment including the full thermal insulation. This environment provides the necessary media supply and disposal as well as the supporting safety equipment and control units. The system was set into operation on the first of June in 2021. The operation started with stationary operating points in fuel cell and electrolysis mode, after passing the commissioning phase. The performance and efficiency data achieved during this operating phase are shown below. An overall power range from 1.7 kWAC to 13 kWAC was achieved in fuel cell mode. At an output power of 10.4 kWAC and a fuel utilization of 98 %, a system efficiency of 63.3 % could be achieved. During the electrolysis mode, an efficiency of 71.1 % could be achieved with an input power of -49.6 kWel and a steam utilization of 80 %. An analysis of the loss mechanisms showed that in the fuel cell mode about 75 % of the losses are caused by the heat production of the stack itself. In the electrolysis mode, the largest share of about 65 % is caused by the power consumption of the steam generator. The system efficiency can be further increased by a skillful heat recovery from the fuel side off-gas into the steam generation process. Outlook In future work new methods of stack temperature control based on artificial neural networks will be investigated on basis of the presented system. Afterwards it is planned to apply realistic load profiles to the system while investigating the performance, temperature and degradation behavior. Furthermore, electricity and gas storage as well as heat decoupling for district heating application will be studied. Acknowledgement The authors would like to thank their colleagues at Forschungszentrum Jülich GmbH for their great support and the Helmholtz Society, the German Federal Ministry of Education and Research as well as the Ministry of Culture and Science of the Federal State of North Rhine-Westphalia for financing these activities as part of the Living Lab Energy Campus. References [1] Frank M, Deja R, Peters R, Blum L, Stolten D. Bypassing renewable variability with a reversible solid oxide cell plant. Applied Energy. 2018;217:101-12. [2] Peters R, Tiedemann W, Hoven I, Deja R, Kruse N, Fang Q, et al. Development of a 10/40kW-Class Reversible Solid Oxide Cell System at Forschungszentrum Jülich. ECS Transactions. 2021;103:289-97. Figure 1

This study presents the development of a scalable steam generator for a reversible solid oxide cell system with 40 kW of power in electrolysis mode. As solid oxide electrolysis can be conducted under thermal-neutral conditions, efficiency is primarily governed by the system’s heat and steam loss. The steam generator presented herein recovers heat and steam from the fuel side off-gas in order to preheat the feed water and superheat the electrically-generated saturated steam. The design is based on a pinch analysis intended to optimize the temperature levels. In the considered system, the steam generator was estimated to increase electrolysis efficiency from 70% to more than 74%.

This work describes a recently-developed numerical model for three-dimensional, steady-state simulations of reversible solid oxide cell (rSOC) stacks, taking into account a heterogeneous temperature field. The model employs a volume-averaged approach, also referred to as the distributed resistance analogy. It considers fluid flow, multi-component species diffusion, as well as heat and mass transfer, including thermal radiation and electrochemical reactions. The implementation of the computational model is based on an open-source library, OpenFOAM. An in-house designed rSOC stack, Mark-H is considered. Simulations are performed for repeating units with a 320 cm 2 active area, with both the present stack model and a one-dimensional Simulink model. Both models predict very similar voltages, with a maximum difference of 2% compared to experimental results. The present model shows a temperature distribution closer to the experimental data than the Simulink model, although a slightly longer simulation time is required.

This contribution highlights selected current activities of the SOC development at Forschungszentrum Jülich. Continued efforts are being made to gain a better understanding of degradation process in our cells and stacks. New materials are being developed to mitigate known degradation phenomena. Systems development was directed at the improvement of reversible operation, especially in electrolysis mode. On cell and stack level investigation of electrolysis operation was also intensified, focusing on CO 2 -valorization.

In this paper, a kinetic model for the catalytic dehydrogenation of perhydro dibenzyltoluene (H18-DBT), a well-established Liquid Organic Hydrogen Carrier (LOHC) compound, is presented. Kinetic parameters for hydrogen release at a Pt on alumina catalyst in a temperature range between 260 degrees C and 310 degrees C are presented. A Solid Oxide Fuel Cell (SOFC) system model was coupled to the hydrogen release from H18-DBT in order to validate the full sequence of LOHC-bound hydrogen-to-electric power. A system layout is described and investigated according to its transient operating behavior and its efficiency. We demonstrate that the maximum efficiency of LOHC-bound hydrogen-to-electricity is 45% at full load, avoiding any critical conditions for the system components. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

A 5 kW-class reversible Solid Oxide Cell (rSOC) system was developed and experimentally investigated at the Forschungszentrum Jülich in Germany. The main component of this system is the well-established Jülich Integrated Module, which consists of a 40-layer SOC stack (composed of four 10-layer sub-stacks) with an active cell area per layer of 320 cm². The other necessary system components, such as the evaporator, condenser and blowers are compactly arranged in the vicinity of the Integrated Module. In fuel cell mode, a power of 5374 WDC at 500 mA cm-2 and a maximum fuel utilization of 97.3% was achieved, which resulted in a DC electrical system efficiency of 62.7%. Furthermore, in electrolysis mode, a power of -14347 WDC was attained at 887 mA cm-2. At this operating point, the system's DC efficiency reached 70% at a steam utilization of 85%.

The primary problem renewable energy systems must overcome is that electricity cannot always be produced in accordance with demand. This is a major drawback compared to the on-demand power production capability that fossil fuels offer. New technologies can only compete, if a constant power supply is permanently guaranteed. This constitutes a critical benchmark that renewable energy technologies must meet, if they are to replace fossil fuels. Reversible solid oxide cells (rSOCs) represent a promising approach to counteracting this issue. Here we show our developed rSOC plant which incorporates both the storage via electrolysis mode and the electricity production in the reverse, fuel cell mode. In order to achieve a high level of efficiency, the plant has been investigated and optimized with respect to internal waste heat recovery and compression. The final plant design shows an efficiency of up to 67.1% in fuel cell- and 76% in electrolysis mode and therefore a round trip efficiency of 51%.

This paper presents an experimental study of catalytic hydrogen combustion that used commercial catalysts containing Pt in a honeycomb monolith reactor in a plug flow configuration. The emphasis is on determining global kinetics in the case of low hydrogen content. Measurements of the temperature and composition of the reaction product at the outlet in the steady state condition at the different initial compositions of hydrogen and total volumetric feed rates were performed. The conversion of hydrogen was determined in parallel to the composition of the reaction product at the outlet using GC as well as by means of the thermodynamic approach using material and energy balances. The influence of the flow rate and initial molar fraction of hydrogen on hydrogen conversion is shown. A kinetic expression of the Arrhenius type is proposed with the reaction first order in hydrogen and zero order in oxygen for the overall process of the oxidation of hydrogen in lean hydrogen-air mixtures. The determined activation energy was in good agreement with the desorption activation energy for O2 from graphene-covered Pt(111) surfaces using temperature-programmed desorption. This result shows transport-limitations for heterogeneous hydrogen conversion in catalytic hydrogen combustion.

Our contribution demonstrates the technological potential of coupling Liquid Organic Hydrogen Carrier (LOHC)-based hydrogen storage and hydrogen -based Solid Oxide Fuel Cell (SOFC) operation. As SOFC operation creates waste heat at a temperature level of more than 600 degrees C, clever heat transfer from the SOFC operation to the LOHC dehydrogenation process is possible and results in an overall efficiency of 45% (electric output of SOFC vs. lower heating value of LOHC-bound hydrogen). Moreover, we demonstrate that LOHC vapour does not harm the operational stability of a typical 150 W SOFC short stack. By operating the stack with LOHC-saturated hydrogen, operation times of more than 10 years have been simulated without noticeable degradation of SOFC performance. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Solid oxide fuel cell systems with an anode off-gas recirculation have the potential for high electrical efficiency. The anode off-gas recirculation within an SOFC system has two significant advantages. Firstly, a part of the unused fuel at the stack outlet is returned to the stack inlet, where it can again participate in the electrochemical reaction. Therefore, the amount of fresh fuel fed into the system can be reduced. This increases the system fuel utilization and leads to a significant increase in efficiency. Secondly, the recirculated electrochemically produced steam can be used for the steam reforming process. Thus, during operation an external steam supply is no longer necessary. A challenge is the high anode off-gas temperature of at least 700°C, which prohibits the use of commercially available blower units. At Forschungszentrum Jülich GmbH an SOFC subsystem with an anode off-gas recirculation loop was developed and tested using methane as the fuel. The off-gas recirculation loop consists of two heat exchangers in combination with a low temperature blower, which operates at temperatures up to 200°C. With this setup, tests were carried out to study the influence of e.g. recirculation rate and fuel utilization on the system operation behavior and performance. During the tests the system fuel utilization was driven up to 93%. The test results indicate that changes in recirculation rate affect the cell voltage, the amount of excess air for cooling and the electrical efficiency. At constant current density high recirculation rates decrease the cell voltage, but also the amount of excess air. Therefore, high electrical efficiency could be achieved with high system fuel utilization at moderate recirculation rates.

A solid oxide fuel cell (SOFC) is a promising all-solid-state energy conversion device that produces electricity by electrochemically combining a fuel with an oxidant across an oxide electrolyte. To optimize SOFC performance, it is necessary to investigate the effects of the design and operating parameters on system components such as pre-reformers and afterburners. In pursuit of this, a multi-component SOFC design based on a planar stack was developed. Two specially designed planar-type steam pre-reformers (the first consisting of five layers with air heating and the other of one with electric heating) utilizing nickel yttria-stabilized zirconia (Ni/YSZ) as catalyst were built to investigate the kinetics of steam reforming with methane. Whereas experimental results on the global reaction kinetics of a Ni-based catalyst in the 5-layer planar pre-reformers within a temperature range of between 350 degrees C and 610 degrees C have been published, this work reports the results of reforming kinetics using a 1-layer reformer as a flow reactor in a higher temperature range (500 degrees C-740 degrees C), as well as on reforming kinetics in combination with anode off-gas recycling. The results confirm the proposed kinetic expression of the Arrhenius type (second order with respect to the mole fraction of methane and first order with respect to the mole fraction of water) for different steam-to-carbon ratios and also for anode off-gas recycling. The activation energy for methane steam reforming corresponds to the desorption energy of CO or H2O from the catalyst surface depending on the inlet composition of the mixture. (C) 2016 Elsevier B.V. All rights reserved.

This study analyzes different hydrogen-fueled solid oxide fuel cell (SOFC) system layouts. It begins with a simple system layout without any anode off-gas recirculation, continues with a configuration equipped with off-gas recirculation, including steam condensation and then considers a layout with a dead-end anode off-gas loop. Operational parameters such as stack fuel utilization, as well as the recirculation rate, are modified, with the aim of achieving the highest efficiency values. Drawing on experiments and the accumulated experience of the SOFC group at the Forschungszentrum Jülich, a set of operational parameters were defined and applied to the simulations. It was found that anode off-gas recirculation, including steam condensation, improves electrical efficiency by up to 11.9 percentage-points compared to a layout without recirculation of the same stack fuel utilization. A system layout with a dead-end anode off-gas loop was also found to be capable of reaching electrical efficiencies of more than 61%.