In 2018, a 5/15 kWDCreversible solid oxide cell system was developed and successfully operated by Forschungszentrum Jülich. Based on the knowledge gained with this first system, an optimized system in the power class of 10/40 kWACwas developed afterwards in 2019 that uses the well-established Integrated Module. This module consists of four 20-layer sub-stacks, two heat exchangers and five heating plates. It represents the main components of the system. The basic system layout was retained in general from the previous system and adjusted in accordance with the higher power level, as well as the supporting balance of plant components. The layout of the demonstrator system and its results are described. During the experimental evaluation in fuel cell mode, the system could provide an electrical output power from 1.7 to 13 kWAC. The maximum system efficiency of 63.3% based on the lower heating value (LHV) could be reached at a system power of 10.4 kWAC. This operating point was also analyzed regarding the temperature distribution in the stack and efficiency losses. In electrolysis mode, a maximum efficiency of 71.1% (LHV) was achieved with an electrical power input of −49.6 kWAC. At this operating point, about 11.7 Nm3h−1of hydrogen are generated. The stack temperature distribution and the efficiency losses are also analyzed for the electrolysis mode. Finally, the potential for the efficiency optimization through higher heat integration in this mode is experimentally evaluated and discussed.

Two once-through steam generators and a combination of a steam generator and a gas preheater for supplying feed gases to solid-oxide electrolysis stacks were evaluated for their carryover characteristics of contaminants from the feed-water into the steam phase. The concentrations of various trace impurities in the steam were determined by sampling the steam condensates and screening them with inductively coupled plasma–mass spectrometry for 19 elements and liquid ion chromatography and continuous flow analysis for chloride and ammonium. Steam-soluble species such as boric acid undergo complete volatilization and transfer into the steam phase. During unstable evaporation in the steam generators an extensive physical carryover of alloying metal species was observed. At realistic operation conditions for steam electrolysis, the gas preheater caused a considerable release of silicon into the steam phase. Two stack experiments were performed with common preheater temperatures and showed largely increased cell voltage degradation at higher operation temperatures. The post-test chemical analysis of cell samples revealed significant concentrations of silicon in the samples that are regarded as primary cause for increased degradation. These findings could partially explain the wide spread of degradation rates reported for solid-oxide steam electrolysis experiments.

As the share of distributed renewable power generation increases, high electricity prices and low feed-in tariff rates encourage the generation of electricity for personal use. In the building sector, this has led to growing interest in energy self-sufficient buildings that feature battery and hydrogen storage capacities. In this study, we compare potential technology pathways for residential energy storage in terms of their economic performance by means of a temporal optimization model of the fully self-sufficient energy system of a single-family building, taking into account its residential occupancy patterns and thermal equipment. We show for the first time how heat integration with reversible solid oxide cells (rSOCs) and liquid organic hydrogen carriers (LOHCs) in high-efficiency, single-family buildings could, by 2030, enable the self-sufficient supply of electricity and heat at a yearly premium of 52% against electricity supplied by the grid. Compared to lithium-ion battery systems, the total annualized cost of a self-sufficient energy supply can be reduced by 80% through the thermal integration of LOHC reactors and rSOC systems.

A 5/15 kW-class reversible Solid Oxide Cell (rSOC) system was developed and experimentally investigated at the Forschungszentrum Jülich GmbH. The main component of this system is the well-established Jülich Integrated Module, which consists of four 10-layer SOC sub-stacks with an active cell area per layer of 320 cm 2 . The other necessary system components, such as the evaporator, condenser and blowers are compactly arranged in the vicinity of the Integrated Module. The system’s total operation time was more than 9000 h, in detail 2607 h in fuel cells, 6043 h in electrolysis and 448 h in hot standby mode. In fuel cell mode, a power of 5374 W DC at 0.5 A cm −2 at a fuel utilization of 97.3% was delivered, which resulted in a DC electrical system’s efficiency of 62.7% (LHV). Furthermore, in electrolysis mode, a power of −14347 W DC was consumed at 0.89 A cm −2 . At this operating point, the system’s DC efficiency reached 70% at a steam utilization of 85%.

Chromium poisoning as a result of Cr evaporation from the metallic components and the subsequent deposition on the cathode (i.e., air) side is one of the most critical degradation mechanisms in solid oxide fuel cell (SOFC) stacks. Recently, the LSC cathode (i.e., La 0.6 Sr 0.4 CoO 3-δ ) exhibited more promising results in both fuel cell and electrolysis modes than the LSCF (i.e., La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ ) due to its higher ionic conductivity, despite a relatively larger thermal expansion coefficient (TEC). Furthermore, it has been reported that the oxygen surface exchange kinetics and Sr stability/activity of LSC may imply higher resistance against Cr poisoning by comparison to LSCF. For these reasons, long-term stack operation with both LSCF and LSC cathodes was performed for two different stack designs. The degradation behavior of the stacks with respect to Cr poisoning was analyzed with the support of electrochemical impedance spectroscopy and post-mortem analysis.

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%.

The current interest in solid oxide fuel cells (SOFC) technology lies mainly in its high power generation/conversion efficiency and its low or zero emissions. Their application in stationary power generation systems indicate their maturity to date. However, the stability and performance of the cells or stacks could be affected due to the adverse conditions to which they are exposed. One of the most concerning conditions for Ni-based anode-supported cells (ASC) is when the stack is subjected to unplanned reduction-oxidation (Redox) cycles, which can lead to irreversible damage to the cell. During a Redox cycle, the anode undergoes changes in its volume, due to the oxidation of nickel (Ni) to nickel oxide (NiO), which causes microstructural damages to the anode itself or to the electrolyte or to both. Previous study has shown that the cell performance decreased after redox cycling above 600 °C, mainly based on voltage-current curve or electrochemical impedance measurements. However, there is little information on the application of acoustic emission (AE) techniques in the study of redox cycling. Therefore, the purpose of this work is to investigate the redox process and stability of a SOFC stack through the application of the AE monitoring. The research will include the analysis of the AE signals, the AE cumulative energy as well as an analysis in the frequency domain. This is expected to contribute to the understanding of the redox process inside stack and failure modes of the cell.

Solid oxide fuel cells (SOFCs) provide electrical energy through a highly efficient direct transformation of chemical energy stored in fuels. The sealing between the stacked components of the SOFC has to prevent gas leakage towards the environment as well as mixing of fuel gas and oxidant in order to ensure a reliable long-term operability. Hence, the understanding of the sealing loading conditions and the failure assessment plays a major role regarding the improvement of current and future SOFC designs. In the present study, glass ceramics sealing failure is investigated by means of a current SOFC design. For this purpose, the stresses in the sealings are firstly examined by employing a fully parameterized three-dimensional finite element model. On the basis of a canonical example, the underlying physical mechanisms, which are responsible for the occurrence of stresses, are identified and their influence is discussed. Since the initiation of sealing failure is complex and depends on several parameters, a methodology for failure assessment is proposed. In this context, the glass transition temperature is of superordinate importance. Since the material properties differ significantly depending on whether the operating temperature is below or above the glass transition temperature, several competing failure mechanisms must be considered.

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.

Compared to low-temperature electrolysis techniques, solid oxide cell (SOC) technology has attracted growing interest in Power-to-X scenarios based on renewable energy due to its high efficiency, reversibility, and the possibility of simultaneously converting CO2 and H2O into syngas, a chemical precursor for synthetic fuels or intermediates such as methanol. Furthermore, SOCs can also be operated in CO2 electrolysis mode in order to produce pure CO, which is in great demand in the chemical and steel industries. Based on previous experience with fuel cell, steam,- and co-electrolysis operation, the electrochemical performance and durability of planar fuel electrode-supported SOC stacks are investigated with a focus on CO2 electrolysis. Their current-voltage characteristics and electrochemical impedance have been measured in both CO2 and co-electrolysis modes. The main aim of these investigations was to gain insights into the electrochemical processes and limitations of the currently used electrodes during CO2 electrolysis, and to understand the general degradation mechanisms of cells under different conditions. Using state-of-the-art cells, the stack can be operated at 800°C with a current density of -1000 mA cm-2 below cell voltages of 1.4 V in a CO2/CO (1:1) mixture. Based on the findings thus far, some promising approaches with respect to the optimization of fuel electrode microstructures and reaction kinetics to increase the performance and durability of the cells under CO2 electrolysis operation are discussed.

The mechanical integrity of the sealant material is of key importance for the long-term, reliable operation of solid oxide fuel/electrolysis cell stacks. However, in-situ monitoring and detection of potential failures in sealing materials using classical electrochemical characterization techniques are difficult tasks. Therefore, in this work, the acoustic emission (AE) technique is applied to monitor and characterize the failure process of a glass-ceramic sealant exposed to torsional shear strength at both room and typical stack operation temperature (750 degrees C). Hourglass-shaped steel specimens are produced for the tests. A glass-ceramic material with two different porosities is used to join the specimens. The failure process is characterized in terms of AE peak amplitude, AE cumulative hits and AE energy, as well as the average frequency content of the signals. The results indicate that the degree of microscopic damage can be determined from the analysis of the AE energy and the fracture mechanisms can be found by statistical analysis of the average frequency of the signals. The fractured surfaces are visualized by optical microscopy to unveil that specimens with high porosity showed a fully cohesive fracture pattern, while specimens with low porosity showed a partially fracture pattern. As a result, AE method promises to be a potential in-operando technique for monitoring mechanical failure processes inside solid oxide cell stacks. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Flexible, system-oriented operating strategies are becoming increasingly important in terms of achieving a climate-neutral energy system transformation. Solid-oxide electrolysis (SOEC) can play an important role in the production of green synthesis gas from renewable energy in the future. Therefore, it is important to investigate the extent to which SOEC can be used flexibly and which feedback effects and constraints must be taken into account. In this study, we derived a specific load profile from an energy turnaround scenario that supports the energy system. SOEC short-stacks were operated and we investigated the impact that the load profile has on electrical stack performance and stack degradation as well as the product gas composition by means of Fourier-transform infrared spectroscopy. The stacks could follow the grid-related requirement profiles of secondary control power and minute reserves very well with transition times of less than two minutes per 25% of relative power. Only short-term disturbances of the H2/CO ratio were observed during transitions due to the adjustment of feed gases. No elevated degradation effects resulting from flexible operation were apparent over 1300 h, although other causes of degradation were present.

A study is performed on the manufacturing costs of planar Jülich Solid Oxide Fuel Cell (SOFC) stacks, based on anode-supported cells (ASC). The manufacturing of two ASC concepts with different design approaches (referred to as standard and light-weight) are evaluated on the basis of stacks that have undergone performance and degradation testing. A bottom-up cost model for 5 kWel is constructed to estimate the costs at production volumes of 1 MWel, 10 MWel and 25 MWel per annum. The direct costs of manufacturing are estimated as 2737–1210 €kWel−1 for the standard design, and 2170–580 €kWel−1 for the light-weight design, depending on production volume. For the evaluated concepts, the material costs are estimated to be dominant over the other factors (at the 25 MWel per annum scale > 65%) which is in accordance with most previous studies. The effect of the different design types on the costs is discussed. The steel components are found to be the most cost-intensive, benefiting the light-weight design. Cost sensitivity analyses to manufacturing parameters, power density and degradation are performed, as well as a theoretical scenarios calculated based on low-cost steel type SS441 replacing the costly Crofer materials and co-sintering replacing sequential sintering. The results are compared to previous studies. Strategies for cost-saving are discussed based on 20 years of experience with stack building and testing in Jülich.

The performance of a planar SOFC stack using anode-supported cells (ASC) specifically developed for low temperature operation is discussed. The performance in single cell tests is compared to the stack performance, and important issues leading to a loss of performance in the stack are discussed. Based on the analysis of the contribution of the cell components to the decreasing performance below 600 degrees C, it is demonstrated that the thin electrolyte contributes only a small fraction of the ohmic resistance in stack operation, and that further improvement of the electrolyte may yield insignificant improvements in stack performance. The anode has the largest contribution to cell impedance in both cell and stack tests. The implications of a cell optimized for low-temperature operation on the stack sealing and anode reduction procedures are briefly discussed, exemplified by the performance loss of the cathode during stack sealing. In addition, an unusual breakaway-type oxidation is found on a thin Crofer 22 APU foil in the cathode air compartment, which is likely related to the low operation temperature of the stack. These findings highlight the most pressing issues of cell and stack development for low temperature applications, and provide a guide toward stack operation at 500 degrees C.

A four-layer solid oxide fuel cell stack consisting of standard anode-supported cells was assembled to investigate long-term stability, but at higher current densities and/or fuel utilization compared to previous investigations. The stack was operated within a furnace temperature range of 700 °C–750 °C with hydrogen fuel at a current density of up to 1 A·cm−2 and fuel utilization of up to 80% for more than 10,000 h. The average voltage degradation rate was approximately 0.6%kh−1. Increases in the ohmic resistance and anode polarization dominated the degradation behavior. An increase in the current density and fuel utilization under current testing conditions did not fundamentally influence the degradation rate. However, the possible modification in the nickel structure by local higher fuel utilization may have had a long-term impact on the lifetime of the stack. The complexity of the degradation analysis of stacks resulting from an inhomogeneous contact inside the stack was analyzed with the support of impedance measurements and a post-mortem analysis.

One of the essential components for ensuring the long service life of solid oxide cell (SOC) stacks is the sealant used. Therefore, in this work, an experimental investigation of the glass ceramic sealant (GCS) fracture process was carried out using an Acoustic Emission (AE) based approach. A series of tensile tests at room temperature were performed and the acoustic activity emitted was recorded by two AE sensors. An AE signal analysis was then performed using two approaches: wave mode identification and frequency content analysis. To understand the fracture process of the GCS, the analysis was supported with prior knowledge of the GCS microstructure and a post-test visual analysis. This demonstrated the presence of low-frequency failure mechanisms (50-400 kHz) such as debonding, fiber pull-out and matrix cracking, and high-frequency mechanisms (>400 kHz) such as fiber breakage. The results confirm the suitability of using the acoustic emission approach for monitoring failure events and show its potential application in SOC stacks monitoring. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Stationary applications of Solid Oxide Fuel Cell systems require operating times of 40,000 to 80,000 h for market introduction. Therefore, extended lifetime tests are essential for learning about the long-term behavior and various degradation mechanisms and to foster ideas about accelerated stack testing. The Forschungszentrum Julich has been gradually extending the testing time, resulting in successful short-stack operating times of between 20,000 and 40,000 h. This work highlights the results of these long-term tests and compares the observations for different material combinations, operating temperatures of 700 and 800 degrees C, including different fuel utilizations and gas compositions. An increase of temperature from 700 to 800 degrees C leads to an acceleration of the degradation rate by a factor of 1.5-2. Meanwhile, an increase in fuel utilization from 40 to 80% did not result in increased degradation. The same was found for higher current densities of up to 1 Acm(-2). (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.