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1
Horlick, Samuel A., Scott Swartz, David Kopechek, Geoff Merchant, Taylor Cochran, and John Funk. "Progress of Solid Oxide Electrolysis and Fuel Cells for Hydrogen Generation, Power Generation, Grid Stabilization, and Power-to-X Applications." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 152. http://dx.doi.org/10.1149/ma2023-0154152mtgabs.
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Over the past 25+ years, Nexceris has been developing solid oxide cell (SOC) technology for power generation, energy storage and hydrogen production applications. Nexceris is vertically integrated SOC technology provider that develops and manufactures solid oxide electrode materials, interconnect coatings, planar electrolyte supported cells, and solid oxide stacks. Nexceris stacks are designed for low-cost manufacture and pressurized operation, and stacks have large repeat unit area for efficient packaging into megawatt-scale systems. Nexceris’ stacks are being tested in fuel cell, electrolysis, and reversible modes, with a focus on optimizing performance, efficiency, and durability. Current work at Nexceris includes long-term electrolysis stack durability testing, breadboard system testing of reversible SOC stacks, third-party stack validation testing, and SOC system design and demonstration testing. Nexceris also is exploring solid oxide co-electrolysis for converting steam and CO2 to syngas and the conversion of this syngas to fuels and chemicals. This presentation will provide an update on Nexceris’ solid oxide cell technology development and commercialization activities.
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Ikegawa, Kazutaka, Kengo Miyara, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, and Kazunari Sasaki. "Performance and Durability of Solid Oxide Electrolysis Cell Air Electrodes Prepared By Various Conditions." ECS Transactions 109, no. 11 (September 30, 2022): 71–78. http://dx.doi.org/10.1149/10911.0071ecst.
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Fuel electrode materials are important for achieving higher performance and durability in solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), and reversible solid oxide cells (r-SOCs). On the other hand, the air electrode also faces performance and durability issues. For air electrodes, studies have been conducted on their performance and durability in SOFC operation, but the performance and durability of air electrodes in SOEC and r-SOC operation needs to be investigated in more detail. The electrochemical performance and durability of SOEC and r-SOC are evaluated by conducting electrolysis performance tests of LSCF-based air electrodes with different preparation conditions, electrolysis durability tests at the thermoneutral potential, and a 1000-cycle test in r-SOC mode.
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Ikegawa, Kazutaka, Kengo Miyara, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, and Kazunari Sasaki. "Reversible Solid Oxide Cells: Cycling and Long-Term Durability of Air Electrodes." ECS Transactions 111, no. 6 (May 19, 2023): 313–21. http://dx.doi.org/10.1149/11106.0313ecst.
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Durability and diffusion of various elements in the LSCF-based air electrode of reversible solid oxide cells (r-SOC) are studied. The r-SOC cycling durability tests are conducted by continuously switching between SOFC and SOEC operations. The performance and durability of air electrodes are verified especially after ca. 500 r-SOC cycles.
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Sahu, Sulata K., Dhruba Panthi, Ibrahim Soliman, Hai Feng, and Yanhai Du. "Fabrication and Performance of Micro-Tubular Solid Oxide Cells." Energies 15, no. 10 (May 12, 2022): 3536. http://dx.doi.org/10.3390/en15103536.
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Solid Oxide Cells (SOC) are the kind of electrochemical devices that provide reversible, dual mode operation, where electricity is generated in a fuel cell mode and fuel is produced in an electrolysis mode. Our current work encompasses the design, fabrication, and performance analysis of a micro-tubular reversible SOC that is prepared through a single dip-coating technique with multiple dips using conventional materials. Electrochemical impedance and current-voltage responses were monitored from 700 to 800 °C. Maximum power densities of the cell achieved at 800, 750, and 700 °C, was 690, 546, and 418 mW cm−2, respectively. The reversible, dual mode operation of the SOC was evaluated by operating the cell using 50% H2O/H2 and ambient air. Accordingly, when the SOC was operated in the electrolysis mode at 1.3 V (the thermo-neutral voltage for steam electrolysis), current densities of −311, −487 and −684 mA cm−2 at 700, 750 and 800 °C, respectively, were observed. Hydrogen production rate was determined based on the current developed in the cell during the electrolysis operation. The stability of the cell was further evaluated by performing multiple transitions between fuel cell mode and electrolysis mode at 700 °C for a period of 500 h. In the stability test, the cell current decreased from 353 mA cm−2 to 243 mA cm−2 in the fuel cell mode operation at 0.7 V, while the same decreased from −250 mA cm−2 to −115 mA cm−2 in the electrolysis operation at 1.3 V.
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Shang, Yijing, and Ming Chen. "Phase-Field Modelling of Microstructure Evolution in Solid Oxide Cells." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2253. http://dx.doi.org/10.1149/ma2023-02462253mtgabs.
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Solid Oxide Cell (SOC) is one of the most promising energy conversion devices due to its high efficiency, flexible fuel adaptability, and low pollutant emission. By changing the operation condition, the SOC can be operated as a solid oxide fuel cell (SOFC) to convert chemical energy to electricity or as a solid oxide electrolysis cell (SOEC) to store electricity in the way of chemical energy. However, the performance degradation of SOCs caused by microstructure evolution and phase transition during long-term operation, and the stress-induced structure damage limit the SOC’s lifetime. This is one of the most challenging problems to be tackled on the way to commercialize the SOC technology. To clarify degradation mechanisms and develop counter-acting measures, long-term testing combined with detailed post-mortem characterization is one common approach, but this is often associated with extensive amount of experimental work and long research time and thus very costly. Instead, many researchers have devoted their efforts to investigating the degradation phenomena using computational modelling or simulations. Phase field model, which has been widely employed to study microstructure evolution of alloy materials during solidification, aging etc., has also been utilized in the SOC research, to illustrate the microstructure evolution during long-term operation from micron to millimeter scale, with the possibility of taking into account the mechanical properties as well. In this article, the principle of the phase field method and different models are introduced first, following with detailed examples published in literature on phase field modeling of various (degradation) phenomena in SOCs. Finally, possible strategies coupling modelling and experimental research in optimizing SOC performance and microstructure is discussed.
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Yamada, Kei, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, and Kazunari Sasaki. "Ni-Alloy Fuel Electrodes for Reversible Solid Oxide Cells." ECS Meeting Abstracts MA2022-02, no. 47 (October 9, 2022): 1781. http://dx.doi.org/10.1149/ma2022-02471781mtgabs.
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Introduction Reversible solid oxide cells (r-SOCs, or solid oxide reversible cells) are devices that can efficiently operate in both fuel cell and electrolysis operating modes. It is expected that they can serve as a technology for green, flexible, and efficient energy systems coupled with renewable energy (1). However, a fuel electrode of r-SOCs might be degraded due to redox cycles in switching operation modes. In our research group, we have fabricated redox-resistant anodes with Ni-Co alloy cermet (2). Here in this study, we apply such alloy-based cermet to the fuel electrode, and evaluate electrochemical performance, reverse cycling durability, and the effect of Co addition. Moreover, we compare the cell performance of Ni-Co alloy cermet with conventional Ni-ScSZ fuel electrode. Experimental In this study, scandia-stabilized zirconia (ScSZ, 10mol% Sc2O3-1mol% CeO2-89mol% ZrO2) was used as the solid electrolyte. The powder prepared by mixing Ni-Co-based oxide powder prepared by ammonia co-precipitation with Ce0.9Gd0.1O2 (GDC) in a weight ratio of 48.1:51.9, was used as the fuel electrode material. Ni-Co-GDC fuel electrode with x mol% of Co added to Ni, is denoted as Ni(100 – x)Cox -GDC fuel electrode. The fuel electrodes of x = 0, 5, 10, and 20 were fabricated. Two types of Ni-GDC cermet were prepared. One was fabricated by using NiO powder by ammonia co-precipitation, and the other was by using commercial NiO powder (Kanto Chemical, Japan). We prepared the Ni-Co alloy cermet by mixing powder and binder, preparing and printing electrode paste on the electrolyte plate, followed by heat treatment. (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was used as the air electrode material. The electrochemical characteristics and r-SOC reversible cycle durability of the fuel electrodes were evaluated under the condition at an operating temperature of 800℃, while 100 ml/min of 50%-humidified hydrogen fuel was supplied to the fuel electrode, and 150 ml/min of air was supplied to the air electrode. Electrochemical characteristics were evaluated by electrochemical impedance measurements (1255WB, Solartron, UK), which separate ohmic and non-ohmic resistances. The durability in reverse r-SOC operation was evaluated by repeatedly varying current density within ± 0.2 A cm-2 at a current sweep rate of 1.56 mA cm-2 s-1 up to 1,000 cycles. The degradation was evaluated by averaging the percentage change in fuel electrode potential at ± 0.2 A cm-2. Results and discussion Figure 1 shows the initial performance of the cells with each fuel electrode. Figure 2 shows the degradation of each fuel electrode within 1,000 cycles after the r-SOC reverse durability test. The initial performance of Ni-Co-GDC was superior to Ni-ScSZ, and it increased with decreasing Co content. Two types of Ni-GDC exhibited identical performance. Similarly, the r-SOC reverse durability of Ni-Co-GDC was superior to Ni-ScSZ, and it increased with decreasing Co content. Furthermore, two types of Ni-GDC exhibited almost the same durability. These results indicate that GDC contributes to the increased cell performance and durability rather than alloying or the feature of original NiO powder. It appears that Co is not essential for r-SOC fuel electrodes in terms of r-SOC durability. However, fuel electrode materials should be selected by comprehensively considering the performance and the durability at both SOFC and SOEC modes. As Ni-Co alloy shows higher redox cycle durability compared with Ni-GDC (3), Ni-Co alloy is still one of the promising materials for r-SOC fuel electrodes. Acknowledgements A part of this study was supported by “Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration” of the New Energy and Industrial Technology Development Organization (NEDO). References N. Q. Minh and M. B. Mogensen, Electrochem. Soc. Interface, 22, 55 (2013). Y. Ishibashi, S. Futamura, Y. Tachikawa, J. Matsuda, Y. Shiratori, S. Taniguchi, and K. Sasaki, J. Electrochem. Soc., 167, 124517 (2020). K. Matsumoto, Y. Tachikawa, J. Matsuda, S. Taniguchi, and K. Sasaki, ECS Trans., 103, 1549 (2021). Figure 1
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Sasaki, Kazunari, Katsuya Natsukoshi, Kei Yamada, Kazutaka Ikegawa, Masahiro Yasutake, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, Bilge Yildiz, and Harry L. Tuller. "Reversible Solid Oxide Cells: Selection of Fuel Electrode Materials for Improved Performance and Durability." ECS Transactions 111, no. 6 (May 19, 2023): 1901–6. http://dx.doi.org/10.1149/11106.1901ecst.
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Different fuel electrodes for reversible solid oxide cells (r-SOC) are investigated with the aim of improving performance in both solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) modes, and durability in reversible operation mode. Electrodes based on gadolinium-doped ceria (GDC) as a mixed ionic electronic conductor, and lanthanum-doped strontium titanate (LST) as an electronic conductor are selected. The current-voltage characteristics of r-SOC single cells, and their cycling durability up to 1000 cycles are evaluated. LST-GDC co-impregnated with Ni and GDC prove to be highly durable in reversible operation, as a suitable fuel electrode material for r-SOCs.
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Kupecki, Jakub, Konrad Motyliński, Marek Skrzypkiewicz, Michał Wierzbicki, and Yevgeniy Naumovich. "Preliminary Electrochemical Characterization of Anode Supported Solid Oxide Cell (AS-SOC) Produced in the Institute of Power Engineering Operated in Electrolysis Mode (SOEC)." Archives of Thermodynamics 38, no. 4 (December 20, 2017): 53–63. http://dx.doi.org/10.1515/aoter-2017-0024.
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Abstract The article discusses the operation of solid oxide electrochemical cells (SOC) developed in the Institute of Power Engineering as prospective key components of power-to-gas systems. The fundamentals of the solid oxide cells operated as fuel cells (SOFC - solid oxide fuel cells) and electrolysers (SOEC - solid oxide fuel cells) are given. The experimental technique used for electrochemical characterization of cells is presented. The results obtained for planar cell with anodic support are given and discussed. Based on the results, the applicability of the cells in power-to-gas systems (P2G) is evaluated.
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Shang, Yijing, and Ming Chen. "Phase-Field Modelling of Microstructure Evolution in Solid Oxide Cells." ECS Transactions 112, no. 5 (September 29, 2023): 103–20. http://dx.doi.org/10.1149/11205.0103ecst.
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The performance degradation of Solid Oxide Cells (SOC) caused by microstructure evolution limits the SOC’s lifetime. Long-term testing combined with post-mortem characterization is one common approach to clarify degradation mechanisms and develop counter-acting measures, but this is associated with extensive amount of experimental work and long research time. Instead, many researchers have devoted their efforts to investigating degradation using computational methods. The phase-field model has been utilized in the SOC research to illustrate the microstructure evolution during long-term operation from micron to millimeter scale, with the possibility of taking into account the mechanical properties as well. In this article, the principle of the phase-field method and different models are introduced first, followed by examples published in literature on phase-field modeling of various degradation phenomena in SOCs. Finally, possible strategies coupling modelling and experimental research in optimizing SOC performance and microstructure are discussed.
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Zhao, Chenhuan, Yifeng Li, Wenqiang Zhang, Yun Zheng, Xiaoming Lou, Bo Yu, Jing Chen, Yan Chen, Meilin Liu, and Jianchen Wang. "Heterointerface engineering for enhancing the electrochemical performance of solid oxide cells." Energy & Environmental Science 13, no. 1 (2020): 53–85. http://dx.doi.org/10.1039/c9ee02230a.
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Lenser, Christian, Alexander Schwiers, Denise Ramler, and Norbert H. Menzler. "Investigation of the Electrode-Electrolyte Interfaces in Solid Oxide Cells." ECS Transactions 111, no. 6 (May 19, 2023): 1699–707. http://dx.doi.org/10.1149/11106.1699ecst.
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The interface between electrodes and electrolyte in a solid oxide cell (SOC) are critical locations for cell performance. These interfaces originate from the chemical interaction of two different materials during processing. Different mechanisms can degrade cell performance on the air and fuel side, which necessitates different approaches to mitigate these effects. Here, materials interaction during processing is discussed for selected materials on the air side of an SOC. A new approach to obtain barrier layers of doped ceria with submicron thickness is introduced, and it is confirmed that only the interdiffusion layer between ceria and zirconia is necessary to prevent the formation of SrZrO3. Furthermore, the effect of the microstructure of a GDC layer on the sintering of a perovskite air electrode in this layer is investigated. It is demonstrated that the morphology of the GDC layer has an impact on the quality of the interface between air electrode and barrier layer.
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Hagen, Anke, Davide Tasca, Agathe De-Faria, Federico Capotondo, Riccardo Caldogno, Bhaskar Reddy Sudireddy, and Xiufu Sun. "Reversible Metal Supported Solid Oxide Cells." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 362. http://dx.doi.org/10.1149/ma2023-0154362mtgabs.
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Solid oxide fuel cells (SOFCs) excel by high efficiencies in fuel cell as well as electrolysis modes, and by being able to operate in both modes as a reversible cell (solid oxide cell – SOC). This allows for production of electricity and heat from a green fuel, and for storage of electricity as gas or use as fuel. Lifetime and costs are major factors enabling such reversible SOCs to enter green energy systems. Metal supported SOCs (MSCs) provide cost-competitive materials within the cell. Furthermore, targeting the lower operating temperatures around 650 oC, MSCs will allow for cheaper stack and balance of plant components as well. Lowering operating temperatures leads to a reduction of thermally activated degradation processes, thereby prolonging the lifetime. The present study investigates the option to operate MSCs, fabricated at DTU Energy by tape casting, lamination, and screen-printing, in reversible mode between fuel cell (FC) and electrolysis (EC). Emphasis is on the effect of reversible operation on performance and durability of the MSC, compared to steady state operation in either mode, and to the behavior of state-of-the-art (SoA) fuel electrode supported SOC with Ni/YSZ fuel electrode. The MSCs are composed of a FeCr support, a Ni/GDC (gadolinium-doped ceria) infiltrated LSFNT (lanthanum-doped strontium iron nickel titanate) fuel electrode, a YSZ (yttria-stabilized zirconia) electrolyte, a GDC barrier layer, and an in situ sintered LSC (lanthanum-doped strontium cobaltite) air electrode. The reversible operation was carried out by switching between FC and EC modes at current densities of 0.25 and -0.25 A/cm2, respectively, at 650 oC using a gas mixture of 50/50 H2O/H2 to the fuel electrode and air to the oxygen electrode. Figure 1 shows the evolution of the cell voltages for the SoA cell and the MSC. The degradation rate of the SoA cell was larger during operation in EC as compared to FC mode. Similar observations were made previously, even though these tests were typically carried out at temperatures higher than 650 oC as in this work [1]. Furthermore, the degradation rate decreases over time, more particularly in EC mode, which is also a known phenomenon at this type of cells [2, 3]. In the final ca. 200 h, both degradation rates are in the range of 3%/1000 h, which is an interesting observation, i.e., the longer-term degradation rates are similar in both modes (EC and FC). The analysis of electrochemical impedance spectroscopy (EIS) recorded under current allowed to conclude that the main contribution to the degradation is the increase of polarization resistance, i.e., related to electrodes degradation. In the initial ca. 400 h hundred hours, the cell voltage degradation on the MSC is larger in fuel cell mode, while there is nearly no degradation in electrolysis mode. The good stability in EC mode over a few hundred hours confirms the findings of steady-state electrolysis tests with the same type of cells [4]. In the final period from ca. 600 h, both degradation rates increase but stay fairly constant with ca. 4%/1000 h in EC and ca. 16%/1000 h in FC mode, when calculated as linear increase. EIS reveals that both, the serial and the polarization resistances increase in parallel, which indicates a combination of degradation of electrode and probably corrosion and/or interface attachment. Details will be presented, including comprehensive EIS evaluation combined with micro-structural characterization. Figure 1. Cell voltage vs. operating time under current in reversible mode at 650 oC, 0.25 A/cm2 in fuel cell and -0.25 A/cm2 in electrolysis mode, 50/50 H2O/H2 fuel and air to the oxygen electrode, (a) SoA cell, (b) MSC, gaps in the cell voltage are interruptions of operation due to technical issues in the lab References [1] X. Sun, B.R. Sudireddy, X. Tong, M. Chen, K. Brodersen, A. Hauch, Optimization and Durability of Reversible Solid Oxide Cells, ECS Trans. 91 (2019) 2631. [2] A. Hagen, R. Barfod, P.V. Hendriksen, Y.-L. Liu, S. Ramousse, Degradation of anode supported SOFCs as a function of temperature and current load, J. Electrochem. Soc. 153(6) (2006) A1165. [3] A. Hauch, K. Brodersen, M. Chen, C. R. Graves, S. H. Jensen, P. S. Jørgensen, P. V. Hendriksen, M. B. Mogensen, S. Ovtar, X. Sun, A Decade of Solid Oxide Electrolysis Improvements at DTU Energy, ECS Transactions, 75(42) (2017) 3. [4] A. Hagen, R. Caldogno, F. Capotondo, X. Sun, Metal Supported Electrolysis Cells, Energies 15 (2022) 2045. Figure 1
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Langerman, Michiel, Maciej Stodolny, Eduardo da Rosa Silva, Xiaoqian Lu, Claire Ferchaud, and Frans van Berkel. "Solid Oxide Cell Performance: Spatially Resolved Oxygen Electrode Stability." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 358. http://dx.doi.org/10.1149/ma2023-0154358mtgabs.
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Solid Oxide Cell (SOC) electrolysis will play an important role in the electrification of the chemical, fertilizer, and fuel industries, contributing to the reduction of their reliance on fossil fuel feedstocks. The integration of high temperature steam and CO2-electrolyzers in industrial processes with readily available waste heat and renewable electricity allows for highly efficient green hydrogen production and methods for CO2 utilization. The development of next generation SOC electrolyzer technology at TNO aims to provide high performance and low-cost technological options for the electrification of the aforementioned chemicals and fuels industries. The ambition of the SOC technology development program is to assist the whole value chain, from cell manufacturing to end-users, by increasing the economic viability of the technology. In line with this ambition, the TNO R&D activities regarding SOC technology concentrate on cell and stack technology development coupled with techno-economic and business case studies on SOC technology integration in the industrial environment. Improvements in SOC performance and durability for electrolysis applications are of great importance for the successful industrial implementation of the technology. Hydrogen Europe targets for 2030 aim at low stack degradation rates of 0.5%/khr at thermoneutral voltage, while delivering current densities of at least 1.5 A/cm2. Therefore, lifetime improvements at high current density are one of the vocal points of SOC development efforts, which calls for a good understanding of the degradation phenomena and analytical methods to investigate the material stability in the SOC during electrolysis operation. In this contribution, the current status of SOC development and testing within TNO will be presented. Several aspects of TNO SOC performance characteristics will be discussed, with a focus on water electrolysis performance and lifetime behaviour during endurance tests of several thousand hours. Excellent water electrolysis performance of the TNO SOC cells is observed at thermoneutral voltage (1.3 V), achieving current density values of 1.75 A/cm2 at an operating temperature of 750 ºC. Lifetime assessment and material degradation of the SOC will be discussed, with a focus on the analysis of observed degradation phenomena in the oxygen electrode material. As oxygen electrode degradation can be critical for SOC performance in a stack environment, it is important to have a good understanding of the degradation processes and the ability to monitor them. At TNO, a novel high-resolution 2D mapping of the lateral conductivity of the oxygen electrode have been used as an effective tool for quality control and validation of the air electrode development. Additionally, the combination of 2D sheet resistance mapping, SEM-EDX and XRD techniques (Figure 1) provides a powerful combination of tools to obtain a spatially resolved (3D) view of the localized degradation observed in the oxygen electrode after several thousand hours of water electrolysis. Figure 1
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Njodzefon, Jean-Claude, Ulrich Sauter, and Andre Weber. "(Invited) Crosscutting Materials Innovation for Transformational Chemical and Electrochemical Energy Conversion Technologies—Solid Oxide Cells." ECS Meeting Abstracts MA2023-02, no. 48 (December 22, 2023): 2453. http://dx.doi.org/10.1149/ma2023-02482453mtgabs.
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The Solid Oxide Cell (SOC) primarily operated as Solid Oxide Fuel Cell (SOFC) converts the chemical energy of a fuel such as hydrogen directly into electricity with very high efficiencies. Reverse operation of the exact same SOCs—as Solid Oxide Electrolysis Cells (SOEC) converts electrical energy into chemical energy by using the electricity to split chemical molecules such as steam, carbon dioxide or mixtures of both into hydrogen, carbon monoxide or mixtures of both respectively. The SOC is basically a gas-tight and oxide-ion conducting solid electrolyte, sandwiched between porous oxide ion – and electron-conducting electrode materials—the oxygen electrode and the fuel electrode where the electrochemical conversions occur. Irrespective of operation mode, the choice of SOC materials and processing routes generally aim for maximum performance and lifetime at chosen conversion rate and efficiency at nominal operation. This is as much as the technology can intrinsically offer and by far not enough to guarantee either profitable production of electricity or chemicals hydrogen, carbon monoxide or both. Ultimately the materials and manufacturing costs of the cell, stack, module, and system play a key role in the involved invest. Generally, operation costs such as cost of natural gas or electricity as well as maintenance costs are much more significant in determining the profitability of the technology than the investment costs. These technology-independent factors can in turn orientate the technologist to optimize the cell for either for maximum efficiency or conversion rate capability. In this talk we will discuss specific SOC materials such as doped zirconia, doped ceria, manganates, cobaltites, and titanates. Intrinsic limitations and advantages with respect to performance, durability and costs; how they are withstanding the test of time and the ever decreasing operation temperature from micro/nano structuration, infiltration and exsolution of electrocatalysts through switching of cell supports. We will give a perspective on the dependency of cell material choices based on technology use cases and boundary conditions Figure 1
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Langerman, Michiel, Maciej Stodolny, Eduardo da Rosa Silva, Xiaoqian Lu, Claire Ferchaud, and Frans van Berkel. "Solid Oxide Cell Performance: Spatially Resolved Oxygen Electrode Stability." ECS Transactions 111, no. 6 (May 19, 2023): 2277–89. http://dx.doi.org/10.1149/11106.2277ecst.
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Several aspects of TNO SOC performance characteristics will be discussed, with a focus on steam electrolysis performance and lifetime behaviour during endurance tests of several thousand hours. Excellent steam electrolysis performance of the TNO SOE cells is observed at thermoneutral voltage, achieving current density values of −1.7 A/cm2 at an operating temperature of 750 °C. Lifetime assessment and material degradation of the SOC will be discussed, with a focus on the analysis of observed degradation phenomena in the oxygen electrode material. As oxygen electrode degradation can be critical for SOC performance in a stack environment, it is important to have a good understanding of the degradation processes and the ability to monitor them. At TNO, a novel approach of high-resolution 2D mapping of the lateral conductivity of the oxygen electrode has been used as an effective tool for quality control and validation of the oxygen electrode development. Additionally, the combination of 2D sheet resistance mapping, SEM-EDX and XRD techniques provides a powerful combination of tools to obtain a spatially resolved (3D) view of the localized degradation observed in the oxygen electrode after several thousand hours of steam electrolysis.
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Yu, Hyeongmin, Ha-Ni Im, and Kang Taek Lee. "High-Performance Solid Oxide Electrochemical Cells with Ultrathin and Dense Double-Doped Ceria Interlayers." ECS Transactions 111, no. 6 (May 19, 2023): 69–74. http://dx.doi.org/10.1149/11106.0069ecst.
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In this study, we utilized a La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-GDC composite oxygen electrode on a thin and dense doubly doped ceria interlayer for a high-performance solid oxide electrochemical cell (SOC). The ceria interlayers were generated via a non-vacuum solution deposition process with gelatin. The SOC achieved a high maximum power density (MPD) of 2.46 W/cm2 at 750oC along with stable operation for 30 hours in the fuel cell (FC) mode. Our results suggest that the integration of the LSCF-GDC composite and the dense ceria interlayer holds a significant promise for development of high-performance SOCs.
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Mouginn, Julie, Jérôme Laurencin, Julien Vulliet, Marie Petitjean, Elisa Grindler, Stéphane Di Iorio, Karine Couturier, et al. "Recent Highlights on Solid Oxide Cells, Stacks and Modules Developments at CEA." ECS Transactions 111, no. 6 (May 19, 2023): 1101–13. http://dx.doi.org/10.1149/11106.1101ecst.
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Solid Oxide Cell (SOC) technology is considered as an efficient electrolysis technology to produce hydrogen at large scale. It can also operate in fuel cell mode using different fuels (carbon-based or non-carbon based like ammonia), and in reversible mode. Though proofs-of concept have been achieved at different relevant scales for those operating modes, some R&D works still need to be performed to improve performance, durability and cost. Improved and upscaled cells and stacks need to be developed, with a methodology combining multiscale and multiphysics modelling, electrochemical characterization in relevant conditions and advanced post-test analysis. Their integration into modules made of several stacks is also a stepping stone in order to reach multi-MW electrolysers. CEA is working on the whole value chain of SOC technology, from cell development and optimisation to module design and operation through stack upscaling. Recent achievements on those aspects will be presented.
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Zhang, Bo, Zhizhong Leng, Yihan Ling, Hu Bai, Sha Li, Juan Zhou, and Shaorong Wang. "Nanofiber Sr2Fe1.5Mo0.5O6-δ Electrodes Fabricated by the Electrospinning Method for Solid-Oxide Cells." Crystals 12, no. 11 (November 12, 2022): 1624. http://dx.doi.org/10.3390/cryst12111624.
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Solid oxide cells (SOCs) are attracting much more attention as promising energy conversion and storage devices. One of the challenges of optimizing of solid-oxide cells’ performance is that there are not enough triple-phase boundaries (TPB) in the electrode bulk. To enhance the reaction area for SOCs, Sr2Fe1.5Mo0.5O6-δ nanofibers are synthesized by electrospinning with metal nitrate precursors and used for SOC electrodes operated in both humidified air and a hydrogen atmosphere. SFMO nanofibers display a highly porous and crystallized perovskite structure and continuous pathways by XRD analysis and SEM observation. The average diameter of the SFMO nanofibers after sintering is about 100 nm. The La0.8Sr0.2Ga0.8Mg0.2O3-δ(LSGM) electrolyte-supported symmetrical cell with the SFMO nanofiber electrode exhibits enhanced electrochemical performance in humidified air and an H2 atmosphere. Moreover, a distribution of the relaxation time method is used to analyze the impedance spectra, and the polarization peaks observed are assigned to correspond different electrochemical processes. The results indicate that the SFMO nanofiber with an improved nanostructure can be the potential material for the SOC electrode.
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Rehman, Saeed Ur, Muhammad Haseeb Hassan, Syeda Youmnah Batool, Seung Bok Lee, Hye-Sung Kim, Rak-Hyun Song, Tak-Hyoung Lim, Jong-Eun Hong, Seok Joo Park, and Dong Woo Joh. "Fabrication of Durable and High-Performance Flat Tubular Anode-Supported Solid Oxide Cells for Stack Application." ECS Transactions 111, no. 6 (May 19, 2023): 557–64. http://dx.doi.org/10.1149/11106.0557ecst.
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Solid oxide cell (SOC) technology is highly admissible for distributed power generation since it enables the most efficient and clean conversion of fuels into energy and heat. SOCs are also regarded as a potential technology for their decisive role in strengthening the hydrogen economy concept by storing renewable energy resources such as green hydrogen and synthetic fuels. In this work, high-performance and durable flat tubular anode-supported SOC is developed for SOC stack applications. NiO-8YSZ composite flat tubular anode support is fabricated by employing an extrusion process. Anode functional layer and electrolyte layers are deposited by the dip-coating technique, whereas the GDC diffusion barrier, LSCF-GDC composite cathode, and Ag-glass composite interconnect layers are fabricated by the conventional screen-printing process. Finally, the prepared flat tubular SOCs possess an active cathode area of 45 cm2 and demonstrated a high-power density of ~430 mW cm-2 at operating current density, voltage, and temperature conditions of 501 mA cm-2, 0.87 V, and 700 °C. During a long-term stability test at 700 °C for 1000 h, the SOC showed a voltage improvement of 0.013 % while operating at a fuel efficiency of 65%. The flat tubular anode-supported SOC’s high performance and durable operation showed its potential for commercial applications in distributed power generation and hydrogen production. Together with the research to further enhance the SOC’s performance and stability, the flat tubular SOC stack design and fabrication are also in progress.
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Yu, Hyeongmin, Doyeub Kim, Incheol Jeong, Ha-Ni Im, and Kang Taek Lee. "Superionic Conducting Triple-Doped Stabilized Bismuth Oxide for High Performing Reversible Solid Oxide Cells." ECS Meeting Abstracts MA2022-02, no. 47 (October 9, 2022): 1751. http://dx.doi.org/10.1149/ma2022-02471751mtgabs.
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Reversible solid oxide cells (SOCs) have drawn much attention as alternative energy conversion and storage devices owing to their high efficiency and environmental benignity. However, considering their high operating temperature involves unwanted chemical reactions, thermal stress, and high system costs it is essential to lower their operating temperature for commercial feasibility. At reduced temperature, on the other hand, the catalytic activity of oxygen reduction reactions (ORRs), oxygen evolution reactions (OERs), and oxygen ionic transport are diminished due to their thermally activated nature. For example, the most widely used yttria-stabilized zirconia (YSZ) shows significantly decreased ionic conductivity at reduced temperature (e.g. 0.003 S/cm at 600 °C), which is not sufficient for high performing SOCs. Among various alternative oxygen ionic conducting materials, rare-earth stabilized bismuth oxides have been well known as super ionic conductors which exhibit 30 times higher conductivity than that of YSZ. However, the ionic conductivity of stabilized bismuth oxides is significantly decreased due to their phase transformation from cubic phase to rhombohedral phase at 600 °C. In this regard, it is crucial to carefully utilize proper doping material for enhancing their stability while retaining their high ionic conductivity. In this study, we newly developed stabilized bismuth oxide with superior ionic conductivity and durability at 600 °C via triple-doping strategy. Initial ionic conductivity of the stabilized bismuth oxide was maintained for more than 1000 hours at 600 °C with no phase transformation. This stabilized bismuth oxide was combined with conventional La0.8Sr0.2MnO3- δ (LSM) as a novel oxygen electrode. Furthermore, a SOC with this novel air electrode showed high electrochemical performance both in the fuel cell (FC) and the electrolysis (EC) modes (e.g. 2.5 W/cm2 and 1.4 A/cm2 at 1.3V at 700 °C in the FC and the EC modes, respectively).
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Taubmann, Julian, Xiufu Sun, Christodoulos Chatzichristodoulou, and Henrik Lund Frandsen. "Tracking Localized Degradation of Solid Oxide Cells Via Multi-Physics Modelling of Impedance Spectroscopy." ECS Transactions 111, no. 6 (May 19, 2023): 955–64. http://dx.doi.org/10.1149/11106.0955ecst.
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Multi-physics models have proven valuable tools for describing and understanding degradation of solid oxide cells (SOC). One shortcoming of the approach is the restricted validation of degradation theories with only the transient voltage or current characteristics measured globally over SOCs. Such an approach disregards the additional insights via periodically measured impedance spectra that is common practice in experimental durability tests. This work overcomes these limitations by applying a combined transient-frequency domain approach permitting the description of temporal changes and the evolution of impedance spectra. It finally leads to a framework allowing trustworthy validation of degradation mechanism represented via multi-physics models. This approach is implemented for an electrode-supported SOC operated in electrolysis mode at -1 A/cm2 aiming at a separation between the different degradation modes of the Nickel/8mol% Yttria stabilized Zirconia electrode.
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Liu, Zhengrong, Yueyue Sun, Jiaming Yang, Lei Fu, Jun Zhou, and Kai Wu. "Tuning Exsolution of Nanoparticles in Defect Engineered Ruddlesden–Popper oxides for efficient CO2 electrolysis." ECS Meeting Abstracts MA2023-01, no. 26 (August 28, 2023): 1709. http://dx.doi.org/10.1149/ma2023-01261709mtgabs.
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Solid oxide cell (SOC) is the energy conversion device with a series of advantages such as high efficiency, environmental friendliness and durability, making it a promising way to deal with environmental pollution and energy crisis appearing with the development of human society. Perovskite oxides with hetero-phases which were prepared by in-situ exsolution are widely used as fuel electrode in SOC. In this work, Ni-doped perovskites Ruddlesden–Popper oxides, (La, Sr)nTinO3n-2 with n = 5, 8, and 12 (LSTNn), were synthesized to design novel exsolution materials as solid oxide fuel cell anodes and for electrochemical catalysis applications. Compared with pure LSTNn without Ni, a small A-site deficiency (10%) promoted the exsolution of Ni from the perovskite oxides of Ni-doped LSTNn. It is found that the morphology as well as electrochemical activity of LSTNn anodes can be successfully manipulated by the exsolution of Ni. Since more Ni nanoparticles are exsolved from the parent oxides, LSTN8 displays better electrochemical performance by providing more active sides during the hydrogen oxidation reaction and significantly lowering electrode polarization resistance. DRT analysis is conducted to study substeps of the whole electrode reaction, finding that in-situ precipitation improves rate-limiting steps much. The CO2 reduction reaction performance of LSTN materials is also studied, finding that in-situ grown nanoparticles on surface of LSTN significantly increases the density of surface active sites and three phase boundaries (TPBs), which are beneficial for CO2 adsorption and subsequent conversion. It is clear from these results that varying Ni-doping in Ruddlesden–Popper oxides is a key factor in controlling the electrochemical performance and catalytic activity for hydrogen oxidation reaction in solid oxide fuel cells.
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Jang, Seungsoo, Kyung Taek Bae, Dongyeon Kim, Hyeongmin Yu, Seeun Oh, Ha-Ni Im, and Kang Taek Lee. "Microstructural Analysis of Solid Oxide Electrochemical Cells via 3D Reconstruction Using a FIB-SEM Dual Beam System." ECS Transactions 111, no. 6 (May 19, 2023): 1265–69. http://dx.doi.org/10.1149/11106.1265ecst.
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Solid oxide electrochemical cells (SOCs) have attracted increasing attention as energy conversion devices due to their high efficiency. The microstructures of SOCs play a critical role in their electrochemical performance, however, characterizing them is challenging due to their heterogeneous microstructure. This paper describes a quantitative analysis of SOC microstructures via 3D reconstruction technique using a focused ion beam-scanning electron microscope (FIB-SEM) dual beam system. The reconstructed SOC electrodes offer microstructural characteristics, including particle and pore size, tortuosity, connectivity, and triple-phase boundary (TPB) density. These in-depth analyses contribute to better understanding of the electrochemical behavior of SOCs.
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Sarner, Stephan, Norbert H. Menzler, Andrea Hilgers, and Olivier Guillon. "Recycling and Reuse Strategies for Ceramic Components of Solid Oxide Cells." ECS Transactions 111, no. 6 (May 19, 2023): 1369–78. http://dx.doi.org/10.1149/11106.1369ecst.
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The integration of solid oxide cells (SOCs) into circular economy is crucial to enable efficient preservation of critical and high-cost resources such as rare earth elements, cobalt, and nickel used in conventional SOC applications. Based on the fuel electrode-supported cell (FESC) design, a semi-closed loop recycling approach was applied for cell material from CeramTec/Forschungszentrum Jülich. We show that more than 85 wt% of the ceramic components can be successfully reprocessed to new fuel electrode-based substrate that can be further used in cell production. Reprocessing of sintered bodies requires a multi-stage procedure. Increasing the amount of recyclate in the substrate leads to changes in substrate properties such as higher porosities and reduced shrinkage.
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Sarner, Stephan, Norbert H. Menzler, Andrea Hilgers, and Olivier Guillon. "Recycling and Reuse Strategies for Ceramic Components of Solid Oxide Cells." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 210. http://dx.doi.org/10.1149/ma2023-0154210mtgabs.
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Fuel Cell and Hydrogen (FCH) applications will become crucial to enable the transition towards decarbonatization and meet the EU's zero net greenhouse gas emission targets to be achieved by 2050 (The European Green Deal, European Commission, 2019). As one part of novel FCH technologies, Solid Oxide Cells (SOCs) can be used as fuel cells and electrolyzers, enabling a fuel-flexible and adaptable range of applications. However, the Technology Readiness Level (TRL) of SOCs is currently assessed at 5–7 (H2-international, October 2022), which is lower compared to most of the technologies mentioned above. In order to achieve their market breakthrough, SOCs require scalable and cost-efficient manufacturing trails. This involves an adequate End-of-Life (EoL) material treatment, minimizing environmental impact, and avoiding landfill disposals. EoL strategies for FCH applications (including the SOC) are currently in the early stages and have not been adequately addressed. Until now, existing novel technologies and their materials are reviewed based on hazardousness, scarcity and cost. Initial considerations directly for SOC material recovery are given in two very recent publications. In these two studies, the focus was on the ceramic cell part of an SOC, aiming for the recovery of the most valuable cell fractions in a (semi-) closed loop scenario. Challenges in cell recycling arise from the diversity of structures and materials of established stack and cell designs. For industrial applications, planar stack geometry is likely to prevail, further subdivided based on the mechanical support used (fuel electrode-supported cells, FESC; electrolyte-supported cells, ESCs; metal-supported cells, MSCs). As a part of the German government-funded technology platform “H2Giga”, we are working on the re-integration of EoL FESC-type SOCs into the cell manufacturing process. The concept for FESC-recycling (Figure 1.) is based on the separation of the air-side perovskite materials (air-side electrode and contact layer) from the remaining predominant cell fraction (mechanical support, fuel electrode, electrolyte, and diffusion barrier layer).[1] Separation can be achieved by exploiting the chemical resistance of NiO and YSZ to suitable leachants such as hydrochloric acid or nitric acid. In comparison, the structure of the conventional perovskites used is more vulnerable to acid corrosion. The remaining solid fraction then undergoes a re-dispersion step and is incorporated into newly manufactured substrate. The recycled substrate is characterized in terms of electrical conductivity, mechanical stability, and microstructure. Critical components (Co, La) in the separated perovskite liquid fraction are to be recovered from the solution by precipitation. The presentation will guide the audience through the concept of multi-step recovery of the predominant cell fraction Ni(O)/YSZ, and will provide insides of the experimental results, ranging from the hydrometallurgical separation of cell fractions to suitable reprocessing techniques. [1] Sarner, S., Schreiber, A., Menzler, N. H., & Guillon, O. (2022). Recycling Strategies for Solid Oxide Cells. Advanced Energy Materials, 12(35), 2201805. Figure 1
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Sassone, Giuseppe, Ozden Celikbilek, Maxime Hubert, Katherine Develos Bagarinao, Thomas David, Laure Guetaz, Isabelle Martin, et al. "Advanced Nanoscale Characterizations of Solid Oxide Cell Electrodes." ECS Transactions 111, no. 6 (May 19, 2023): 885–98. http://dx.doi.org/10.1149/11106.0885ecst.
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Solid oxide cells (SOCs) have attracted a growing attention thanks to their high efficiency and ability to operate in both electrolysis (SOEC) and fuel cell (SOFC) modes. Despite its great potential, the current SOC technology faces significant cell degradation during long-term operation. The degradation phenomena are still not well understood as they involve complex and intricate processes arising at different length scales. Additionally, it has been shown that the degradation rate under SOEC operation is generally higher than in SOFC mode. To address this issue, durability tests were performed in SOEC mode at 750, 800 and 850 °C for 2000 h at -1 A cm-2 in 10/90 vol.% H2/H2O and dry air. The electrochemical performance of the cells was assessed using electrochemical impedance spectroscopy. In addition, advanced characterization techniques with nanometer and atomic resolution have been used to study material degradation after long-term testing.
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Liu, Zhijun, Yucun Zhou, Weilin Zhang, Jie Hou, Xueyu Hu, and Meilin Liu. "Sulfur- and Coking-Tolerant Anodes for Solid Oxide Fuel Cells." ECS Meeting Abstracts MA2022-02, no. 47 (October 9, 2022): 1761. http://dx.doi.org/10.1149/ma2022-02471761mtgabs.
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Sulfur- and Coking-tolerant Anodes for Solid Oxide Fuel Cells Zhijun Liu,1 Yucun Zhou,1 Weilin Zhang,1 Jie Hou,1 Xueyu Hu,1 Meilin Liu1, * 1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States Abstract Solid oxide fuel cells (SOFCs) have potential to be one of the most efficient systems for direct conversion of a wide variety of chemical fuels into electricity. 1-3 However, the lack of sulfur- and coking-tolerant anodes still hinders the development of direct hydrocarbon-fueled SOFCs for efficient and cost-effective operation. The conventional Ni-based anodes may suffer from carbon deposition and sulfur poisoning when they are directly exposed to sulfur-containing hydrocarbon fuels, resulting in degradation in performance or even destruction of the anodes. 4-6 In this presentation, we will report a conventional Ni-Zr0.84Y0.16O2-δ (YSZ) anode decorated with Ce and Ba-based catalyst coatings to significantly enhance the sulfur and coking tolerance. Results suggest that the enhanced sulfur tolerance is attributed to the evenly distributed Ce-based catalyst on the inner surface of the porous Ni-YSZ anode while the enhanced coking tolerance is benefited from the Ba-based catalyst layer on the top of the anode. SOFCs with the catalysts-modified Ni-YSZ anodes show minimal degradation when hydrogen with 100 ppm H2S is used as the fuel. More importantly, stable operation is demonstrated for direct utilization of sulfur-containing liquid fuels (e.g., octane and gasoline). This work demonstrates the great potential of catalyst coatings for enhancing contaminant tolerance and durability of SOFC electrodes. Z. Wang, Y. Wang, D. Qin, Y. Gu, H. Yu, S. Tao, B. Qian and Y. Chao, J. Eur. Ceram. Soc. (2022). S. Sengodan, M. Liu, T.-H. Lim, J. Shin, M. Liu and G. Kim, J. Electrochem. Soc., 161, F668 (2014). Z. Cheng, J.-H. Wang, Y. Choi, L. Yang, M. C. Lin and M. Liu, Energy Environ. Sci., 4, 4380 (2011). T. Hays, A. M. Hussain, Y.-L. Huang, D. W. McOwen and E. D. Wachsman, ACS Appl. Energy Mater., 1, 1559 (2018). Y. Chen, B. deGlee, Y. Tang, Z. Wang, B. Zhao, Y. Wei, L. Zhang, S. Yoo, K. Pei, J. H. Kim, Y. Ding, P. Hu, F. F. Tao and M. Liu, Nat. Energy, 3, 1042 (2018). L. Yang, S. Wang, K. Blinn, M. Liu, Z. Liu, Z. Cheng and M. Liu, Science, 326, 126 (2009).
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Ozaki, Ryota, Kei Yamada, Kazutaka Ikegawa, Tsutomu Kawabata, Chie Uryu, Yuya Tachikawa, Junko Matsuda, and Kazunari Sasaki. "A Study on Electrochemical Properties of Fuel-Electrode-Supported Reversible Solid Oxide Cells." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2259. http://dx.doi.org/10.1149/ma2023-02462259mtgabs.
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Introduction Reversible solid oxide cells (r-SOCs) enable both power generation and steam electrolysis, and have attracted attention as a solid state electrochemical energy device for a decarbonized society (1). R-SOCs have the advantage of high efficiency due to high temperature operation, but there exist various technical issues remained in materials selection, start-up and shutdown, and long-term durability. Therefore, reducing operating temperature is desirable for practical applications (2,3). Electrode-supported cells, in which the electrode acts as a structural support, enable lower temperature operation by reducing the thickness of the electrolyte, which has certain electrical resistivity. Here in this study, the current-voltage characteristics and reversible cycle durability under r-SOC operating conditions are evaluated using fuel-electrode-supported cells, with the aim of developing r-SOCs capable of highly efficient fuel cell power generation and steam electrolysis. Experimental For the experiments, fuel-electrode-supported cells were fabricated using fuel electrode-supported half-cells (Japan Fine Ceramics, Japan), schematically shown in Fig. 1. The half-cell consists of scandia-stabilized zirconia (ScSZ: 10 mol%Sc2O3-1mol%CeO2-89 mol%ZrO2) or yttria-stabilized zirconia (YSZ: 8 mol%Y2O3-92 mol%ZrO2) electrolyte and a Ni-cermet fuel electrode, such as Ni-ScSZ or Ni-YSZ. (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was applied for the air electrode, and Gd0.1Ce0.9O2 (GDC) was inserted between the electrolyte and the air electrode to suppress interdiffusion and chemical reactions. Four types of cells were used with different combinations of the electrolyte component (YSZ or ScSZ) in the electrolyte layer or the supporting fuel electrode. In electrochemical tests, 50%-humidified hydrogen (100 ml min-1) was supplied to the fuel electrode, and air (150 ml min-1) was supplied to the air electrode. R-SOC initial performance tests were conducted using an electrochemical analyzer (1255B, Solartron). Cell voltage and impedance were measured at 700-800°C at current densities ranging from -0.5 A cm-2 to +0.5 A cm-2. Positive current density means the value in SOFC mode, while negative current density means the value in SOEC mode. In r-SOC 1,000 cycle durability tests, cycles of switching between SOFC and SOEC operation were repeated 1,000 times by varying current density. The range of current density in the cycle tests was between -0.2 A cm-2 and +0.2 A cm-2. The cell impedance was measured before the cycling test and every 100 cycles. After each test, the cells were analyzed by using a focused-ion beam scanning electron microscopy (FIB-SEM) to observe and evaluate the electrode microstructure. Results and discussion Figure 2 (a) shows the r-SOC initial performance of each fuel-electrode-supported cell. The cell with the Ni-YSZ fuel electrode and the YSZ electrolyte showed better current voltage characteristics than other cells. Figure 2 (b) shows the r-SOC 1000-cycle durability of the cell with the Ni-YSZ fuel electrode and the YSZ electrolyte. The results showed a decrease in power generation and electrolysis performance with increasing the number of cycles in both SOFC and SOEC modes. Possible degradation mechanisms will be discussed. Acknowledgments This paper is based on results obtained from a project (Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration), JPNP20005, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Collaborative support by Prof. H. L. Tuller and Prof. B. Yildiz at Massachusetts Institute of Technology (MIT) is gratefully acknowledged. References (1) Venkataraman, M. Pérez-Fortes, L. Wang, Y. S. Hajimolana, C. Boigues-Muñoz, A. Agostini, S. J. Mcphail, F. Mar échal, J. V. Herle, and P. V. Aravind, J. Energy Storage, 24, 100782 (2019). (2) Subotić, S. Pofahl, V. Lawlor, N. H. Menzler, T. Thaller, and C. Hochenauer, Energy Proc., 158, 2329 (2019). (3) B. Mogensen, Current Opinion Electrochem., 21, 265 (2020). Figure 1
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Fukumoto, Takuro, Naoki Endo, Katsuya Natsukoshi, Yuya Tachikawa, George Frederick Harrington, Stephen Matthew Lyth, Junko Matsuda, and Kazunari Sasaki. "Visualization and Observation of Spatial Temperature Distribution in Reversible Solid Oxide Cells through Simulation and Thermal Imaging." ECS Transactions 109, no. 11 (September 30, 2022): 15–24. http://dx.doi.org/10.1149/10911.0015ecst.
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Understanding the phenomena which occur inside a solid oxide cell in operation is important in the development of more efficient devices. However, it is difficult to experimentally visualize the distribution of the internal power generation state due to the very high temperature operation. In this study, the performance of a reversible solid oxide cell (r-SOC) was simulated to visualize current-voltage (I-V) characteristics and internal temperature distribution. The validity of the model was verified by comparing with the I-V characteristics and temperature distribution experimentally measured by an actual cell. The establishment of this technique will eventually enable the simulation of cell stacks and systems.
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Taubmann, Julian, Xiufu Sun, Christodoulos Chatzichristodoulou, and Henrik Lund Frandsen. "Tracking Localized Degradation of Solid Oxide Cells Via Multi-Physics Modelling of Impedance Spectroscopy." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 147. http://dx.doi.org/10.1149/ma2023-0154147mtgabs.
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The global, macro-scale description of degradation phenomena in solid oxide cells (SOC) reaches limitations when dealing with localized, micro-scale processes. For example, it is established that carbon deposition and transformation of the active area in nickel containing electrodes in electrolysis mode depend strongly on the local overpotential and gas composition. The state-of-the-art long-term characterization of a full SOC however relies on macroscopic measurements of DC polarization and electrochemical impedance spectroscopy (EIS), which are capturing the average response of the entire cell. The deconvolution of impedance spectra allows to separate the electrolyte resistance from electrode electrochemistry, gas conversion, and diffusion contributions. Nonetheless, heterogeneous, and local degradation cannot be described deploying commonly used tools of EIS analysis, such as equivalent electric circuit models, transmission line models, or the analysis of distribution of relaxation times. Multi-physics based numerical models on the other hand open new opportunities in gaining advanced insights into the complex degradation mechanisms in SOCs. In the model proposed here, combining simulations of transient and frequency domain into one framework allows the description of measured long-term durability of an SOC in terms of voltage-current and impedance characteristic. In addition, the framework enables a local, micro-scale description of the degradation process based upon physical properties confirmable in experiments. The modelling framework is validated with the durability measurements of the SOC in Sun et al. [1]. In this study, a fuel electrode supported cell with an active area of 16 cm2 was tested in galvanostatic operating conditions as an electrolysis cell with the constant current of -1 A/cm2 over 4383 h. Simultaneously to the voltage measurements over the test duration, the impedance response of the cell was tracked every eight hours. The evolution of the measured impedance spectra of the cell can be seen in the attached figure. Comparing the outcomes of the model to the experimental data showcases the benefits of the model in describing the degradation induced increase in voltage over time and the evolution of impedance spectra. In particular, the effect of higher activation overpotential at the fuel inlet to the outlet of the cell is analyzed enabling the generation of local insights concerning the observed degradation. The model establishes an improved validation of equations describing degradation of SOCs encompassing overpotential gradients and relating to postmortem observed micro-structural changes. Reference [1] Sun, X., et al. "Degradation in solid oxide electrolysis cells during long term testing." Fuel Cells 19.6 (2019): 740-747. Figure 1
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Duranti, Leonardo, Anna Paola Panunzi, Umer Draz, Cadia D'Ottavi, Silvia Licoccia, and Elisabetta Di Bartolomeo. "Pt-Doped Lanthanum Ferrites as Versatile Electrode Material for Solid Oxide Cells." ECS Transactions 111, no. 6 (May 19, 2023): 2425–33. http://dx.doi.org/10.1149/11106.2425ecst.
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The tailoring of multi-tasking perovskite oxide-based electrodes for solid oxide cells has shown growing interest. The development of flexible structures represents a crucial step towards the design of symmetric and possibly SOFC/SOEC reversible systems. In this work, low (0.5 mol%) B-site Pt-doping in a lanthanum strontium ferrite is presented as a successful approach to enhance the parent perovskite properties as both SOC air and fuel electrode. Structural, morphological and electrochemical characterizations of La0.6Sr0.4Fe0.995Pt0.005O3-δ (LSFPt005) are provided and compared to the undoped compound. LSFPt005-symmetric devices are tested as CO-SOFCs and CO2-SOECs at 850 °C, respectively, obtaining a maximum power density of 301 mW/cm2 and a current density of 0.82 A/cm2 at 1.5 V. Insights of cell operating mechanisms are provided through electrochemical impedance spectroscopy.
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Mouginn, Julie, Jérôme Laurencin, Julien Vulliet, Marie Petitjean, Elisa Grindler, Stéphane Di Iorio, Karine Couturier, et al. "Recent Highlights on Solid Oxide Cells, Stacks and Modules Developments at CEA." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 168. http://dx.doi.org/10.1149/ma2023-0154168mtgabs.
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Solid Oxide Cell (SOC) technology is a versatile technology able to operate either in electrolysis mode (SOEL), to produce hydrogen at high efficiency, in fuel cell mode (SOFC) using different fuels (carbon-based or non-carbon based like ammonia), in reversible mode (rSOC) with different cycles between electrolysis and fuel cell modes depending on the use case and the type of upstream coupling with renewable energies, and finally in co-electrolysis mode (co-SOEL) to produce syngas out of steam and CO2. Though proofs-of concept have been achieved at different relevant scales for those different operating modes, some R&D works still need to be performed to improve performance, durability and cost in a concomitant way, to meet the targeted key performance indicators as set by the EU for instance. Improved and upscaled cells and stacks need to be developed, with a methodology combining multiscale and multiphysics modelling, electrochemical characterization in relevant conditions and post-test analysis. Their integration into modules made of several stacks is also a stepping stone in order to reach multi-MW electrolysers as needed to meet the targets set by the RePowerEU plan intending to install 100 GW of electrolysers in EU in 2030 [1]. CEA is working on the whole value chain of SOC technologies, from cell development and optimisation to module design and operation through stack upscaling. Regarding SOC cells, the process has been optimised to obtain a good reproducibility on the cell performances (figure 1a). A current density of – 0.8 A/cm² has been reached at the thermoneutral voltage at 700°C. Works are in progress on the electrodes microstructures and interfaces to further increase the performances. After validation at single cell level, 100 cm² and 200 cm² cells active area have been produced with a good reproducibility and validated at short stack level. As far as stack developments are concerned, CEA continued its program on upscaling [2]. In parallel, improved seals are developed to increase the stack robustness to transient operation and interconnect coatings are developed using different deposition techniques. Those components have been first validated at sample scale before integrating them into short stacks and full-stacks for validation in real configuration. For instance, the integration of interconnect protective coatings in short stacks has been evaluated over more than 4500h of operation. Finally, a 4-stack module has been developed and put in operation. Made of 4 stacks, each comprising 25 cells of 100 cm² active area, it is able to operate in electrolysis, fuel cell and reversible mode (figure 1b). [1] REPowerEU: affordable, secure and sustainable energy for Europe, 18 May 2022 [2] S. Di Iorio et al., “Solid Oxide Electrolysis Stack development and upscaling”, 15th European SOFC&SOE Forum 5-8 July 2022, Luzern A0904 (2022) Figure 1
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Yoshiga, Ko, Takeaki Okamoto, Yuya Tachikawa, and Kazunari Sasaki. "Effects of Current Collector on Internal Visualization of Solid Oxide Cells." ECS Transactions 112, no. 5 (September 29, 2023): 129–40. http://dx.doi.org/10.1149/11205.0129ecst.
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Visualization of reactions occurring inside a solid oxide cell (SOC) during operation is difficult due to the limitation of the operatable temperature to use various sensors and measurement equipment. Therefore, we are investigating a visualization method to combine three-dimensional simulation with in-operando temperature observation inside SOCs. In this study, we focused on evaluating the effect of a current collector shape on the cell performance and temperature distribution. As a result, we confirmed that the effects of several current collector shape modifications appeared in the temperature distribution. Based on the calculated temperature and current density distributions, we proposed an appropriate current collector shape for observing the temperature distribution inside the cell by experiment. Using the practical observation setup model considered in this study, the influence of sulfur poisoning on the temperature distribution was also calculated and evaluated.
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Motylinski, Konrad, Michał Wierzbicki, Stanisław Jagielski, and Jakub Kupecki. "Investigation of off-design characteristics of solid oxide electrolyser (SOE) operated in endothermic conditions." E3S Web of Conferences 137 (2019): 01029. http://dx.doi.org/10.1051/e3sconf/201913701029.
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One of the key issues in the energy production sector worldwide is the efficient way to storage energy. Currently- more and more attention is focused on Power-to-Gas (P2G) installations- where excess electric power from the grid or various renewable energy sources is used to produce different kind of fuels- such as hydrogen. In such cases- generated fuels are treated as energy carriers which- in contrast to electricity- can be easy stored and transported. Currently- high temperature electrolysers- based solid oxide cells (SOC)- are treated as an interesting alternative for P2G systems. Solid oxide electrolysers (SOE) are characterized as highly efficient (~90%) and long-term stable technologies- which can be coupled with stationary power plants. In the current work- the solid oxide cell stack was operated in electrolysis mode in the endothermic conditions. Based on the gathered experimental data- the numerical model of the SOC stack was created and validated. The prepared and calibrated model was used for generation of stack performance maps for different operating conditions. The results allowed to determine optimal working conditions for the tested stack in the electrolysis mode- thus reducing potential costs of expensive experimental analysis and test campaigns.
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Noring, Alexander, Kyle L. Buchheit, Arun Iyengar, and Gregory A. Hackett. "Techno-Economic Analysis of Reversible and Paired Solid Oxide Cell Systems for Hydrogen Production." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 376. http://dx.doi.org/10.1149/ma2023-0154376mtgabs.
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The United States (U.S.) Department of Energy (DOE) National Energy Technology Laboratory (NETL) has been pursuing the development of solid oxide cell (SOC) technology to enable future power generation systems with high efficiencies and low emissions. Government and industry net-zero goals are driving interest in approaches to decarbonize challenging sectors of the economy, such as industrial applications. Hydrogen (H2) – including that produced by SOC technology-based high-temperature electrolysis – is one promising route. At present, low prices for low-greenhouse gas intensity electrical power (i.e., renewable sources such as wind and solar) are available intermittently (at low-capacity factors), complicating the economics of clean hydrogen produced by electrolysis. Reversible solid-oxide cell (r-SOC) based power to gas systems have the potential to address this challenge by producing power when electricity prices are high and hydrogen when they are low. Plants with the ability to co-generate power from solid oxide fuel cells (SOFC) and hydrogen from solid oxide electrolysis cells (SOEC) are of particular interest for their dual revenue streams and the flexibility they can provide to the grid. This study investigates the cost and performance of two configurations of co-generating SOC plants. The first includes an r-SOC stack that alternates between power and hydrogen production. The second plant contains paired SOFC and SOEC stacks that are each dedicated to generating a single product when operated. For the purposes of this study, the plants are primarily intended to generate hydrogen, only switching to power production mode when market conditions are favorable. The study aims to elucidate expected tradeoffs between the higher capital cost of the paired SOFC/SOEC plant and the higher degradation rate of the r-SOC. The anticipated tradeoff of a reversible system is an increased degradation rate for lower capital costs. This is due to the paired systems being optimized for either fuel cell or electrolysis operation while the reversible system is not optimized for either. To quantify the impact of this, a base case where the SOFC, SOEC, and r-SOC all degrade performance-wise at the same rate (0.2% per 1000 h). The degradation rate of the r-SOC is then allowed to float to where the levelized cost of hydrogen (LCOH) of the two systems is at parity, which does not occur at the base case assumptions. Additional sensitivity analyses are performed on natural gas price and cost of imported power to determine which system is more favorable under different assumptions. In summary, the results show that the total plant cost of the paired SOFC/SOEC system is about 5% higher than the reversible system. The additional cost of having two separate SOC modules is largely diluted by the balance of plant costs. The LCOH of the r-SOC and paired SOFC/SOEC are ≈$3.60/kg and ≈$3.30/kg H2, respectively as shown in Figure 1. Despite the higher capital cost, the paired SOFC/SOEC has a more favorable LCOH. This is due to the SOFC’s ability to generate electricity cheaper than the assumed $60/MWh grid purchase price. Sensitivity analyses show how the assumed cost of grid power and natural gas price affects the disposition of hydrogen versus electron generation. As an example, the LCOH of the r-SOC becomes more favorable than the paired SOFC/SOEC at natural gas prices above $12/MMBtu and at electricity purchase prices below $27/MWh. In conclusion, this investigation shows that depending on the market situation and final application, reversible SOC units warrant consideration for inclusion in advanced integrated energy systems as grid electricity prices continue to decrease over time. For the purposes of this study, natural gas is used as the fuel for power generation operation, and the systems are equipped with high rate (≈98%) carbon capture. In future work, stored hydrogen may be examined as the fuel for power generation. Future analyses may also examine the use of industrial or other waste heat sources, as well as perform life cycle analyses for the cradle-to-gate greenhouse gas intensity for select system configurations and applications. Figure 1
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Minh, Nguyen Q. "(Invited) Development of Thin-Film Solid Oxide Cells for Power Generation and Hydrogen Production." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2273. http://dx.doi.org/10.1149/ma2023-02462273mtgabs.
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Thin-film solid oxide cells (TF-SOCs) fabricated by sputtering have been developed for power generation and hydrogen production applications. TF-SOCs have been considered for cell configuration in this development because of the potential for efficient operation at reduced temperatures (≤700oC). Reduced temperature operation allows a wider choice of cell and ancillary materials, minimizes elemental migration/interaction, and reduces thermal stresses, thus improving cell reliability and durability. Sputtering has been considered for fabrication of TF-SOCs because the technique can create dense or porous films as required for the cell components. In addition, a fabrication process based on sputtering is readily scaled to large cell sizes and large volume production. All-sputtered TF-SOC cells have been shown to exhibit exceptionally high performance in both power generation and electrolysis modes, for example, a peak power density of 2.7W/cm2 (fuel cell mode) and a current density of 2.6A/cm2 at 1.3V (electrolysis mode) at 650oC with 50%H2-50%H2O. TF-SOC cells as large as 15 cm x 15 cm size have been fabricated by sputtering. This paper discusses the development of the sputtering process for making TF-SOCs and evaluation of cell performance characteristics in power generation and hydrogen production operating modes.
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Bianchi, Fiammetta Rita, Arianna Baldinelli, Linda Barelli, Giovanni Cinti, Emilio Audasso, and Barbara Bosio. "Multiscale Modeling for Reversible Solid Oxide Cell Operation." Energies 13, no. 19 (September 25, 2020): 5058. http://dx.doi.org/10.3390/en13195058.
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Solid Oxide Cells (SOCs) can work efficiently in reversible operation, allowing the energy storage as hydrogen in power to gas application and providing requested electricity in gas to power application. They can easily switch from fuel cell to electrolyzer mode in order to guarantee the production of electricity, heat or directly hydrogen as fuel depending on energy demand and utilization. The proposed modeling is able to calculate effectively SOC performance in both operating modes, basing on the same electrochemical equations and system parameters, just setting the current density direction. The identified kinetic core is implemented in different simulation tools as a function of the scale under study. When the analysis mainly focuses on the kinetics affecting the global performance of small-sized single cells, a 0D code written in Fortran and then executed in Aspen Plus is used. When larger-scale single or stacked cells are considered and local maps of the main physicochemical properties on the cell plane are of interest, a detailed in-home 2D Fortran code is carried out. The presented modeling is validated on experimental data collected on laboratory SOCs of different scales and electrode materials, showing a good agreement between calculated and measured values and so confirming its applicability for multiscale approach studies.
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Park, Beom-Kyeong, Roberto Scipioni, Qian Zhang, Dalton Cox, Peter W. Voorhees, and Scott A. Barnett. "Tuning electrochemical and transport processes to achieve extreme performance and efficiency in solid oxide cells." Journal of Materials Chemistry A 8, no. 23 (2020): 11687–94. http://dx.doi.org/10.1039/d0ta04555a.
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A new SOC that utilizes a very thin GDC/YSZ bi-layer electrolyte, support with enhanced porosity, and electrode surface modification via PrOx and GDC nanocatalysts pushes the limits of cell polarizations, exceeding fuel cell power density ∼3 W cm−2 and electrolysis current density ∼4 A cm−2.
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Kunz, Felix, Roland Peters, Dominik Schäfer, Shidong Zhang, Nicolas Kruse, L. G. J. (Bert) de Haart, Vaibhav Vibhu, et al. "Progress in Research and Development of Solid Oxide Cells, Stacks and Systems at Forschungszentrum Jülich." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 257. http://dx.doi.org/10.1149/ma2023-0154257mtgabs.
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The defossilization of the energy sector requires the transfer of sustainable, carbon-neutral technologies and processes into application. Along with the development of a global hydrogen economy, technologies that generate, store, distribute and use hydrogen and derivatives are particularly relevant. Considerable potential in this sense is offered by the solid oxide cell (SOC), which can be operated as a fuel cell (SOFC), as an electrolysis cell (SOEC) and reversible (rSOC). Forschungszentrum Jülich has been involved in the research and development of SOCs for more than 30 years. In addition to material and cell development, stack and system development and understanding degradation effects are among the main topics today. Recently, an rSOC system with an output power of 10kW in fuel cell mode and input power of 40kW in electrolysis mode was developed. Four SOC stacks, separated and surrounded by a total of five heating plates plus an air preheater at one end and a fuel preheater at the other end, form the Integrated Module of the system; each stack has 20 layers with an active cell area of 19x19 cm². A compact and optimized design could be realized, which achieves a system efficiency of 63.3 % and 71.1 % in fuel cell mode and electrolysis mode, respectively. The system has already been tested in stationary operation modes. Current developments focus on the operating strategy, in particular on the temperature control of the stack in fuel cell mode and during the transient operation of the system. With a focus on the SOC stack, progress was made both in the area of actual stack development and in the area of clarification and optimization of performance and lifetime relevant processes. The role of contaminants, foremost silicon species and sulfur dioxide in feed gases, was investigated to support technical applications. Headway was also made in applying advanced measuring technology like fibre-optic sensors for temperature measurements in air channels. Degradation processes were investigated both experimentally and simulatively in fuel cells as well as in steam and co-electrolysis operation. On the one hand, machine learning approaches were pursued to analyze degradational patterns in SOC stacks, utilizing a specifically consolidated and curated set of long-term experiments and EIS measurements. On the other hand, a multiphysical stack model was developed that allows the relevant physical processes within the stack to be analyzed individually and coupled and thus to optimize the overall operation of the stack. In the area of the development and investigation of cells and materials, the performance of the SOC in the fuel cell mode as well as in the electrolysis mode was in the focus. In addition to operation in steam and co-electrolysis modes, operation in pure CO2 electrolysis was also researched. On single cell level the degradation behavior in the different modes of electrolysis operation was investigated. Different alternative materials were examined both on the fuel side and on the air side as well. A hierarchical degradation model framework was developed that relates changes at the level of electrode particles to changes in electrode structure, resulting materials properties and overall lifetime-performance. Model-based diagnostic allows the extraction of model parameters from experimental data, model verification as well as identification and quantification of different degradation mechanisms. Overall, therefore, significant progress can be observed in the field of cell as well as in the field of stack and system development of SOCs in fuel cell, electrolysis and reversible operation at Forschungszentrum Jülich.
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Ozaki, Ryota, Kei Yamada, Kazutaka Ikegawa, Tsutomu Kawabata, Chie Uryu, Yuya Tachikawa, Junko Matsuda, and Kazunari Sasaki. "A Study on Electrochemical Properties of Fuel-Electrode-Supported Reversible Solid Oxide Cells." ECS Transactions 112, no. 5 (September 29, 2023): 141–47. http://dx.doi.org/10.1149/11205.0141ecst.
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Reversible solid oxide cells (r-SOCs) enable both fuel cell power generation and steam-electrolysis hydrogen production by changing the direction of the current in the cells. They are attractive electrochemical devices because of their ability to regulate power supply derived from renewable energy sources. In this study, initial performance was evaluated, and an electrolyte-supported cell and fuel-electrode-supported cells were compared and evaluated with changing operating temperatures. The performances for fuel-electrode-supported cells with various combinations of fuel electrode and electrolyte materials were also evaluated. In addition, the Ni-YSZ/YSZ fuel-electrode-supported cell, which exhibited the highest current-voltage characteristics, was subjected to r-SOC cycling tests to evaluate the cycle durability.
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Zhang, Shidong, Kai Wang, Shangzhe Yu, Nicolas Kruse, Roland Peters, Felix Kunz, and Rudiger-A. Eichel. "Multiscale and Multiphysical Numerical Simulations of Solid Oxide Cell (SOC)." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 144. http://dx.doi.org/10.1149/ma2023-0154144mtgabs.
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Electrochemical applications play a key role for the topic of “green hydrogen” for the de-carbonization of the energy and mobility sectors. Electrochemical systems and processes, including fuel cells and electrolysers, have witnessed several benefits over conventional combustion-based technologies currently being widely used in power plants and vehicles. The ceramic high-temperature technologies by means of SOC exhibits high efficiencies, with a thermoelectric conversion efficiency as high as 60% and a total efficiency of up to 90% in fuel cell operation and even higher in electrolysis mode. The SOC technology, therefore, sees a promising future in the production of green hydrogen and electricity. Providing high operating temperature, over 600 oC, the SOC system shows the capability to operate with diverse types of gas mixtures, for example, hydrogen, ammonia, and carbon-containing mixtures such as methane (CH4), carbon monoxide (CO) in fuel cell operation (SOFC) and steam and/or carbon dioxide (CO2) in electrolysis operation (SOEC). The design of the SOC stack enables a reversible operation (rSOC) between fuel cell and electrolysis modes. It indicates the SOC system can perform with high efficiencies in both operating modes, which also widens the scope of possible applications. Challenges remain when it comes to commercialization of the SOC technology, in both the investment costs (CAPEX) and operating costs (OPEX) aspects. From the technological and scientific point of view, the physical transport phenomena in SOCs need to be understood which can be done by the help of experimental and numerical investigations. Cheaper and long-lasting material alternatives may be found for the cell, stack and system development afterwards. Detailed experimental investigations usually require a lot of effort in time and data analysis. To promote the scientific and technological studies on the SOC technology, numerical investigations by using multiscale and multiphysical models are carried out in this work. The models include an in-house designed/written phase field model (PFM) 1, and an open-source based computational fluid dynamics (CFD) model, openFuelCell2 2 (based on OpenFOAM). The former accounts for the microstructure evolution of the Ni/YSZ composition. The latter addresses the multiphysical transport processes in different phases, i.e., ionic transfer in YSZ, electronic transfer in Ni, and the gas diffusion in the gas phase. The figure below shows the computational domain and different phases in the numerical simulations. The evolution of Ni/YSZ composition can be predicted by the PFM. It is supposed to reproduce the Ni agglomeration that has been observed in SOFC long-term experiments 3. The simulation result shown at the left-most is obtained by performing the PFM simulation (with 96 x 96 x 96 voxels) representing the microstructure change for a certain time duration. The computational domain (192 x 192 x 192 voxels) consists of three phases, namely, YSZ, Ni, and gas, as shown in the middle and on the right side. It is refined in each direction to better capture the triple phase regions (lower right) shared by the three phases, which refers to the active sites that enable the electrochemical reaction to be conducted. By applying different governing equations on these phases, the CFD model, openFuelCell2, can describe the transport phenomena numerically. Hence, the performance degradation of a SOFC due to Ni agglomeration can be captured by carrying out the simulations for different time durations. The effective properties may be derived as well so that they can be used in numerical simulations with larger scales. 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 Q. Li, L. Liang, K. Gerdes, and L.-Q. Chen, Appl. Phys. Lett., 101, 033909 (2012). S. Zhang, S. Hess, H. Marschall, U. Reimer, S. B. Beale, and W. Lehnert, Computer Physics Communications, to be submitted (2023). C. E. Frey, Q. Fang, D. Sebold, L. Blum, and N. H. Menzler, J. Electrochem. Soc., 165, F357 (2018). Figure 1
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Kruse, Nicolas, Wilfried Tiedemann, Ingo Hoven, Rober Deja, Roland Peters, Felix Kunz, and Rudiger-A. Eichel. "Design and Experimental Investigation of Temperature Control for a 10 kW SOFC System Based on an Artificial Neuronal Network." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 83. http://dx.doi.org/10.1149/ma2023-015483mtgabs.
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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
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Kee, Robert J., Huayang Zhu, Sandrine Ricote, and Greg Jackson. "(Invited) Mixed Conduction in Ceramic Electrolytes For Intermediate-Temperature Fuel Cells and Electrolyzers." ECS Meeting Abstracts MA2023-02, no. 46 (December 22, 2023): 2216. http://dx.doi.org/10.1149/ma2023-02462216mtgabs.
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High-temperature fuel cells and electrolyzers (e.g., T > 700 ˚C) rely on oxide electrolytes such as stabilized cubic zirconia that conduct a single defect, oxygen vacancies. Intermediate-temperature electrochemical cells (e.g., T < 650 ˚C) utilize mixed conducting ceramic electrolytes, that conduct multiple defects. Operating at T < 600 ˚C facilitates lower-cost interconnect materials and balance-of-plant components, but the mixed conductor behavior can reduce fuel cell voltages and lower electrolyzer faradaic efficiencies. Predicting behavior of these mixed conductors, even at open-circuit voltage, requires modeling the coupled transport of the multiple conducting defects in the electrolyte. Detailed models of mixed conductors coupled to porous electrode models can simulate cell performance over a broad range of operating conditions. This presentation highlights models of two types of cells with mixed conducting oxide electrolytes. Firstly, gadolinium-doped ceria (GDC) primarily conducts oxygen vacancies but also some electrons via a reduced-ceria small polaron, but it performs well in intermediate temperature solid-oxide fuel cells [1]. Secondly, yttrium-doped barium zirconates (BZY) primarily conducts protons but also oxygen vacancies and small polarons, which contribute to electronic leakage. Variants of BZY electrolytes perform well in fuel cells and electrolyzers [2-4]. This paper focuses on cell-level models of these mixed-conductors and how to identify favorable regions for high performance in fuel cells and electrolyzers. Zhu, A. Ashar, R.J. Kee, R.J. Braun, G.S. Jackson, “Physics-based model to represent the membrane-electrode assemblies of solid-oxide fuel cells based on gadolinium-doped ceria,” J. Electrochem. Soc., Under revision, 2023. J. Kee, S. Ricote, H. Zhu, R.J. Braun, G. Carins, J.E. Persky, “Perspectives on technical challenges and scaling considerations for tubular protonic-ceramic electrolysis cells and stacks ,” J. Electrochem. Soc. 169:054525 (2022). Zhu, Y. Shin, S. Ricote, R.J. Kee, “Defect incorporation and transport in dense BaZr0.8Y0.2O3-d membranes and their impact on hydrogen separation and compression,” J. Electrochem. Soc., Under revision, 2023. Zhu, S. Ricote, R.J. Kee, “Thermodynamics, transport, and electrochemistry in proton-conducting ceramic electrolysis cells,” in High Temperature Electrolysis, W. Sitte and R. Merkle, Editors, IOP Publishing, 2023.
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Anelli, Simone, Luis Moreno-Sanabria, Federico Baiutti, Marc Torrell, and Albert Tarancón. "Solid Oxide Cell Electrode Nanocomposites Fabricated by Inkjet Printing Infiltration of Ceria Scaffolds." Nanomaterials 11, no. 12 (December 18, 2021): 3435. http://dx.doi.org/10.3390/nano11123435.
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The enhancement of solid oxide cell (SOC) oxygen electrode performance through the generation of nanocomposite electrodes via infiltration using wet-chemistry processes has been widely studied in recent years. An efficient oxygen electrode consists of a porous backbone and an active catalyst, which should provide ionic conductivity, high catalytic activity and electronic conductivity. Inkjet printing is a versatile additive manufacturing technique, which can be used for reliable and homogeneous functionalization of SOC electrodes via infiltration for either small- or large-area devices. In this study, we implemented the utilization of an inkjet printer for the automatic functionalization of different gadolinium-doped ceria scaffolds, via infiltration with ethanol:water-based La1−xSrxCo1−yFeyO3−δ (LSCF) ink. Scaffolds based on commercial and mesoporous Gd-doped ceria (CGO) powders were used to demonstrate the versatility of inkjet printing as an infiltration technique. Using yttrium-stabilized zirconia (YSZ) commercial electrolytes, symmetrical LSCF/LSCF–CGO/YSZ/LSCF–CGO/LSCF cells were fabricated via infiltration and characterized by SEM-EDX, XRD and EIS. Microstructural analysis demonstrated the feasibility and reproducibility of the process. Electrochemical characterization lead to an ASR value of ≈1.2 Ω cm2 at 750 °C, in the case of nanosized rare earth-doped ceria scaffolds, with the electrode contributing ≈0.18 Ω cm2. These results demonstrate the feasibility of inkjet printing as an infiltration technique for SOC fabrication.
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Jang, Seungsoo, Kyung Taek Bae, Dongyeon Kim, Hyeongmin Yu, Seeun Oh, Ha-Ni Im, and Kang Taek Lee. "Microstructural Analysis of Solid Oxide Electrochemical Cells via 3D Reconstruction Using a FIB-SEM Dual Beam System." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 194. http://dx.doi.org/10.1149/ma2023-0154194mtgabs.
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The 3D reconstruction based on tomography technology enables quantitative and qualitative microstructural analysis of complex multiphase oxide structures. This powerful approach is widely investigated in diverse areas, in particular, gaining more importance in solid oxide electrochemical cells (SOCs) fields. SOCs are promising energy conversion devices with high efficiency, however, they have complex and porous/dense multilayered microstructures, which are closely related to the electrochemical reaction in the electrodes, thus, one of the major factors determining overall output performance of SOCs. Therefore, it is necessary to quantify the microstructural parameters of the cell. A focused ion beam-scanning electron microscope (FIB-SEM) dual beam system is one well-established method to obtain tomographic images to reconstruct 3D microstructures. It has an appropriate scale of tenth of nm to μm-level with high spatial resolution to represent the microstructural characteristics of the SOC electrodes. This presentation is intended to introduce our progress on 3D reconstruction techniques to quantitatively analyse SOCs, obtaining microstructural features such as particle size, connectivity, tortuosity, contact area, and triple phase boundary density. These in-depth analyses are helpful in extensively understanding electrochemical behavior in SOC electrodes.
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Cox, Dalton, and Scott A. Barnett. "Time-Resolved Characterization of Electrochemically-Induced Solid Oxide Cell Microstructure Evolution." ECS Meeting Abstracts MA2022-01, no. 37 (July 7, 2022): 1620. http://dx.doi.org/10.1149/ma2022-01371620mtgabs.
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Solid oxide cells (SOC) are exciting both for their capability of fuel-flexible electricity generation and their promise in the production of green H2; however, their degradation and long-term performance remain important questions. Operating individual button cells to characterize these changes is prone to cell-to-cell variations, whereas large-area cell/stack life testing requires considerable resources. In both cases, full cell characterization usually must wait until the completion of the life test, which may delay getting results for months or years. While progress has been made in observing microstructural changes over time (termed here time-resolved characterization) using techniques like non-destructive transmission x-ray microscope tomography, such experiments are difficult to implement, especially the effect of current is unexplored due to geometrical and gas environmental limitations of the system. Presented here is a method to rapidly obtain time-resolved microstructural information of the same cell in tandem with electrochemical measurements. While SOC degradation arises due to a range of processes, this work focuses on the microstructural evolution of Ni-YSZ fuel electrodes that occurs during electrolysis operation, which is known to be a key issue. Two key experimental features allowed time-resolved characterization of multiple cells simultaneously: (1) the use of Ni-YSZ symmetric cells allows multiple cells of different size in a single test by avoiding the need for gas seals, and (2) the use of laser milling to allow controlled removal of a portion of each cell during the test. Here we illustrate the method for the case of low steam content and high current density, designed to exacerbate and accelerate electrolysis degradation due to the highly reducing conditions achieved. Tape-cast planar electrode-supported Ni-YSZ symmetric cells were laser cut into precise geometries with well-defined projected areas and easily removable sections. Four cells with projected areas of 1, 1, 0.75, and 0.5 cm2 were connected in series within the same furnace at 800 C and a gas environment of 97% H2 and 3% H2O. A current of 0.75 A was run through three of the cells, resulting in current densities of 0.75, 1.0, and 1.5 A/cm2, while one was maintained with no current. The life test lasted for 500 h, and the microstructure was observed at 0, 200, and 500 hours. Figure 1 shows the microstructures observed at the highest current density by polished cross-sectional SEM and FIB-polished sections under conditions that provided Ni/YSZ contrast. Microstructural degradation had occurred by 200 h and became immense at 500 h, due to high current density in these reducing conditions. By 200 hours, grain boundaries become enriched with Ni, likely due to the formation of Ni-Zr intermetallics in the ultra-low pO2 induced by local overpotential as reported by Chen[1] and Szasz[2]. Additionally, the electrode-electrolyte interface becomes nanoporous and a Ni enriched fracture is present ~2 μm into the electrolyte. By 500 hours, the Ni rich nanoporosity has progressed more than 10 μm into the electrolyte and created islands of large grains surrounded by Ni-rich deposits. Electrochemical impedance spectroscopy measurements show a clear initial decrease in polarization resistance followed by an overall impedance increase by 200 hours. These correspond to the initial electrochemical boost from the production of a nanoporous structure, followed by the deactivation of areas of the cell due to the large fractures through the electrolyte. [1] M. Chen et al., “Microstructural Degradation of Ni/YSZ Electrodes in Solid Oxide Electrolysis Cells under High Current,” J. Electrochem. Soc., vol. 160, no. 8, pp. F883–F891, 2013, doi: 10.1149/2.098308jes. [2] J. Szász et al., “High-Resolution Studies on Nanoscaled Ni/YSZ Anodes,” Chem. Mater., vol. 29, no. 12, pp. 5113–5123, 2017, doi: 10.1021/acs.chemmater.7b00360. Figure 1: Microstructural and electrochemical changes of a symmetric Ni-YSZ SOC undergoing 1.5 A/cm2 in reducing conditions at 0, 200, and 500 hours. Cathode is on the left in all images; anode is on the right. a, b, c) Backscatter electron imaging reveals destruction of the dense YSZ electrolyte over the lifetime of the experiment. Lines of brighter phases on the anode side of fractures are Ni deposits. d, e, f) Focused Ion Beam cross sections reveal nanoporosity forming in the first 10 μm from the cathode-electrolyte interface at 200 and 500 hours. Charging is evident as a result of curtaining from the nanoporous features in the electrolyte. g) Electrochemical impedance spectroscopy shows the initial decrease in resistance from 0 to 48 hours followed by increasing resistance due to microstructure evolution. Figure 1
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Nami, Hossein, Arash Nemati, and Henrik Lund Frandsen. "Ammonia Driven Reversible Solid Oxide Cell As Large-Scale Grid Energy Storage System." ECS Meeting Abstracts MA2022-01, no. 3 (July 7, 2022): 504. http://dx.doi.org/10.1149/ma2022-013504mtgabs.
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The global agreement on the reduction of greenhouses entails increased use of intermittent renewable energy sources such as wind and solar. In this contest, there is a huge need for efficient and cost-effective energy storage systems. Currently, different types of grid energy storage systems are under operation worldwide. However, few of them have the capacity of storing several MWhs of electricity. Large-scale energy storage systems will play a vital role in grid stabilization by reducing imbalances between energy production and demand. Solid oxide cells (SOC) are promising and efficient technologies operating both on electrolyzer and fuel cell modes applicable for energy storage and production. The efficiency of SOC can be further increase by utilization of excess high temperature steam from other processes like ammonia synthesis when it is operating as electrolyzer. In this way, part of the energy needed for electrlozer is covered and less input energy is required, which leads to higher efficiency. This is the main reason behind combining solid oxide cells with the ammonia synthesis process. In the present work, we propose a large-scale electricity storage system operating with reversible solid oxide cells (RSOC) to store electricity as synthetic ammonia. Ammonia can be easily produced, when RSOC operates as an electrolyzer, and stored in the liquid form during off-peak demand. During the peak demand, stored ammonia can be fed into the RSOC, when RSOC operates as a fuel cell, to produce green electricity. Besides the RSOC, the proposed system mainly consists of an air separation unit (ASU) and a Haber-Bosch loop (HBL). Besides large-scale storing of grid electricity, such a system can create an efficient link between electricity and ammonia markets. The system performance is evaluated at a component level thermodynamic analysis showing that a round-trip storage efficiency higher than 50% is achievable.
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Kupecki, Jakub, Anna Niemczyk, Stanisław Jagielski, Agnieszka Zurawska, Ryszard Kluczowski, and Magdalena Kosiorek. "Experimental and Numerical Studies of the Effect of Microstructure of Ionic Conductors on Generation of Hydrogen in Solid Oxide Electrochemical Cells (SOC)." ECS Meeting Abstracts MA2022-01, no. 39 (July 7, 2022): 1737. http://dx.doi.org/10.1149/ma2022-01391737mtgabs.
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Ceramic ionic conductors are applied in innovative systems for highly efficient and clean power generation. The oxygen separation membranes and solid oxide fuel cells (SOFC) and solid oxide electrolyzers (SOE) can be the examples. Influence of various structural properties of ceramic ionic conductors which are used for solid oxide fuel cells was well-defined and described using several mathematical models. Such parameters as ionic and electronic conductivity, porosity, tortuosity, shape and distribution of pores were included. In case of solid oxide electrolysis cells, effects of these parameters on the electrolysis reaction remain unclear and obscure. There is no clearly defined correlation, neither there is an optimization tool for modification of the parameters to maximize the performance of solid oxide cell operating in regenerative mode. For that reason it is necessary to perform a complete comprehensive analysis combining both the experimental and numerical techniques to identify the key microstructural parameters and their correlation with the performance of electrochemical reaction. The work was aimed at verification of data presented in earlier studies which advised that porosity of electrodes of SOEs needs to be different than in the case of SOFCs, however different values were claimed. Mingyi et al. [1] indicated that optimum porosity for SOEC is about 45%, however several other studies advised on different values. This paper presents results of numerical simulations and correlation of material properties with operational characteristic of a solid oxide electrochemical cell which were followed by initial experimental investigations towards validation of the numerical model, including the analysis of selected operational states. Model was established on the basis of theoretical correlations between microstructural parameters and macro-level performance. It was used for performing variant analysis of different modes of operation under varied conditions. The outcomes of the numerical investigations made it possible to define the requirements for fabrication of modified cells for high temperature electrolysis which were studied. The work presents preliminary results of electrochemical characterization of modified cells and an attempt to generalize the model of SOC customized to highly efficient electrolysis. The general concept of optimizing the performance of SOE by fine-tuning of the microstructure which was proposed earlier [2] is assessed throughout experiments using in-house 50 mm x 50 mm cells fabricated in the Institute of Power Engineering. The proposed path for tailoring the microstructural properties is presented and discussed. References [1] L. Mingyi, Y. Bo, X. Jingming, Ch. Jing, Int J Hydrogen Energy. 2010,35,2670-2674. [2] J. Kupecki, J. Milewski, ECS Trans. 2018,83(1),171-178. Figure 1
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Rosner, Fabian, and Scott Samuelsen. "Techno-Economic Optimization of SOC Design and Operating Conditions in a Solid Oxide Fuel Cell-Gas Turbine Hybrid System." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 104. http://dx.doi.org/10.1149/ma2023-0154104mtgabs.
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In a circular economy, highly efficient energy conversion systems are paramount to maximize resource utilization and minimize waste production, including carbon dioxide emissions. Solid oxide fuel cell-gas turbine hybrid systems, which can reach efficiencies of greater than 75%-LHV, have demonstrated to be a promising technology on the way to cleaner power generation. During the energy transition period, solid oxide fuel cell-gas turbine hybrid systems are likely to be operated on natural gas, however, their scalability allows these systems to reach very high efficiencies even at small scales, enabling the use of distributed resources such as biogas. In this presentation the authors will discuss key performance and economic metrics of small-scale (10 MW) advanced solid oxide fuel cell-gas turbine hybrid systems and their relation to cell design and system design elements. Current challenges in solid oxide fuel cell development include thermal cell management and production cost. This presentation presents findings of how cell design parameters influence thermal gradients and specific solid oxide cell costs on a $/kW-basis under hybrid system operating conditions. Moreover, specific cell components are identified, and effects will be discussed that can synergistically reduce thermal stress and specific cell cost at the same time. Informed by this analysis, the optimized cell design is integrated into a solid oxide fuel cell-gas turbine hybrid system in order to provide a comprehensive analysis of system operating conditions under consideration of thermal cell gradients, and new insights into economics and levelized cost of electricity are provided. The presentation will discuss the impact of fuel utilization, operating voltage, and operating pressure upon the heat integration, system’s operating window, and power output. A discussion of economic parameters will highlight cost driving factors to inform research on the next generation of solid oxide cells.
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Ikegawa, Kazutaka, Kengo Miyara, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, and Kazunari Sasaki. "Reversible Solid Oxide Cells: Cycling and Long-Term Durability of Air Electrodes." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 44. http://dx.doi.org/10.1149/ma2023-015444mtgabs.
Full textAbstract:
Introduction Reversible solid oxide cell (r-SOC) enables both power generation and electrolysis, when the cell can be operated as a solid oxide fuel cell (SOFC) and as a solid oxide electrolysis cell (SOEC). Many studies are being conducted to improve their performance and durability (1,2). Lanthanum strontium cobalt ferrite (LSCF) is an air electrode material with a perovskite-type crystal structure which exhibits high electronic and ionic conductivity, oxygen diffusivity, and electrocatalytic activity (3). However, performance and durability of the cells with Sr-containing oxide air electrodes have to be carefully analyzed, as Sr ions tend to easily diffuse during sintering and in long-term operation, reacting with Zr ions from the solid electrolyte to form a highly resistance reaction layer such as SrZrO3 (4-6). While the performance and durability of LSCF-based air electrodes and the Sr diffusion in SOFC operation have been studied, there are still limited number of studies on the SOEC operation, and especially on the r-SOC operation. The diffusion of constituent ions such as Co and Fe may not be negligible in SOCs. Here in this study, we fabricate YSZ electrolyte-supported r-SOCs and conduct durability studies in both SOFC and SOEC modes. STEM-EDS observation of the air electrode materials is also made to investigate the durability and diffusion of various elements in the LSCF-based air electrode of r-SOCs. Experimental R-SOCs with yttria stabilized zirconia electrolytes (YSZ, 200 µm thick) were prepared. Ni-GDC co-impregnated fuel electrode was prepared, where a mixture of La0.1Sr0.9TiO3 (LST) and Gd0.1Ce0.9O2 (GDC) at a volume ratio of 50:50 was used as the porous electrode backbone, onto which Ni-containing solution of 1 µL was impregnated for Ni loading of 0.167 mg cm-2 (7). Gd0.1Ce0.9O2 (GDC) buffer layer was prepared between the electrolyte and the air electrode to prevent elemental diffusion (8). La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) was used for the air electrode. In addition, a Pt reference electrode was deposited onto the electrolyte on the fuel electrode side. The voltage measurement terminals of the electrochemical measurement setup were connected between the reference electrode and the air electrode to evaluate the air electrode potential. 50%-humidified hydrogen (100 ml min-1) was supplied to the fuel electrode, and air (150 ml min-1) was supplied to the air electrode. Negative current density means the value in the SOEC mode, while positive current density in the SOFC mode. Results and discussion As shown in Fig. 2 describing one cycle, current density was varied at 800°C for the 1000-cycle durability tests in the r-SOC operation. The range of current density was between -0.2 A cm-2 and 0.2 A cm-2. The air electrode potential at different current densities and the electrode impedance in every 100 cycles were measured. For the 1000-hour electrolysis durability test in the SOEC mode, current density of -0.2 A cm-2 was applied for 1000 hours at 800°C. The air electrode potential and the impedance in every 100 hours were measured (9). It has been found that a gradual degradation of the r-SOCs associated with an increase in air electrode potential in the SOEC mode and a decrease in the potential in the SOFC mode could be distinguished. However, such degradation tended to be stabilized with the number of cycles. STEM-EDS observations were performed to analyze the elemental distribution around the air electrode and the electrolyte in the cell. It was found that such elemental diffusion could occur during sintering and durability experiments. Acknowledgments A part of this study was supported by “Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration” of the New Energy and Industrial Technology Development Organization (NEDO) (Project No. JPNP20005). Collaborative support by Prof. H. L. Tuller, and Prof. B. Yildiz at Massachusetts Institute of Technology (MIT) for their continuous support is gratefully acknowledged. Figure 1