| 立川 雄也（たちかわ ゆうや） | データ更新日：2024.04.25 |
准教授 ／
工学研究院
機械工学部門
水素利用工学
| 1. | Makoto Yoshikawa, Kotaro Yamamoto, Zhiyun Noda, Masahiro Yasutake, Tatsumi Kitahara, Yuya Tachikawa, Stephen Matthew Lyth, Akari Hayashi, Junko Matsuda, Kazunari Sasaki, Self-Supporting Microporous Layer for Polymer Electrolyte Fuel Cells, ECS Transactions, 10.1149/11204.0083ecst, 112, 4, 83-91, 2023.09, The gas diffusion layer (GDL) used in a PEFC is thicker than the electrode catalyst layer and electrolyte membrane. Thinning down the GDL can reduce gas diffusion resistance and volumetric power density of PEFC stacks. In this study, MPL/GDL is prepared by printing microporous layers (MPLs) on carbon meshes of several tens of micrometers thick as substrates for thin-layer GDLs. Through various current-voltage and overvoltage measurements and microstructural analysis of the cells using these thin-layer MPL/GDLs, cell performance has been improved, equivalent to that of the state of the MPL/GDL.. |
| 2. | Ko Yoshiga, Takeaki Okamoto, Yuya Tachikawa, Kazunari Sasaki, Effects of Current Collector on Internal Visualization of Solid Oxide Cells, ECS Transactions, 10.1149/11205.0129ecst, 112, 5, 129-140, 2023.09, 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.. |
| 3. | Yohei Nagatomo, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, Kazunari Sasaki, Distribution of Relaxation Times of Fuel Electrodes for Reversible Solid Oxide Cells Fabricated Under Various Conditions, ECS Transactions, 10.1149/11205.0121ecst, 112, 5, 121-128, 2023.09, Reversible solid oxide cells (r-SOCs) are electrochemical energy devices that can reversibly switch between power generation by solid oxide fuel cells (SOFCs), and hydrogen production by solid oxide electrolysis cells (SOECs) the reverse operation of SOFCs. For the development of high-performance and durable r-SOCs, it is essential to understand not only the I-V characteristics but also the electrode reaction processes systematically. Here in this study, Ni-GDC cermet fuel electrodes, a composite of Ni and mixed-conducting Gd-doped ceria (GDC), were prepared at different sintering temperatures and electrode thicknesses. Electrochemical impedance measurements and distribution of relaxation times (DRT) analysis were performed in both SOFC and SOEC modes to investigate the influence of fabrication conditions on the fuel electrode reaction processes.. |
| 4. | Ryota Ozaki, Kei Yamada, Kazutaka Ikegawa, Tsutomu Kawabata, Chie Uryu, Yuya Tachikawa, Junko Matsuda, Kazunari Sasaki, A Study on Electrochemical Properties of Fuel-Electrode-Supported Reversible Solid Oxide Cells, ECS Transactions, 10.1149/11205.0141ecst, 112, 5, 141-147, 2023.09, 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.. |
| 5. | Takeaki Okamoto, Masahiro Yasutake, Yuya Tachikawa, Kazunari Sasaki, In-Situ Observation of Temperature Distribution on a Planar Type SOEC During Start-Stop Cycle Operation, ECS Transactions, 10.1149/11106.0223ecst, 111, 6, 223-230, 2023.05, It is important to establish various analytical methods for solid oxide electrolysis cells (SOECs) under practical operating conditions to improve their performance and to analyze their degradation phenomena. In-situ observation of temperature distribution on a planar-type SOEC enables to reveal the distributions of electrochemical reactions and the cell degradation over time. In this study, 600-hour operation tests under start-stop cycling and constant current loading conditions have conducted using a 5 cm × 5 cm planar-type cell to evaluate the SOEC electrochemical performance and to observe the cell surface by infrared camera. The effect of cell performance degradation on the temperature distribution during operation has been evaluated. As a result, it was found that the temperature distribution on the cell surface is affected by the gas flow and current distribution, and that the temperature distribution on the cell surface changes after long-term operation even with constant-current loading operation.. |
| 6. | Kazunari Sasaki, Katsuya Natsukoshi, Kei Yamada, Kazutaka Ikegawa, Masahiro Yasutake, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, Bilge Yildiz, Harry L. Tuller, Reversible Solid Oxide Cells: Selection of Fuel Electrode Materials for Improved Performance and Durability, ECS Transactions, 10.1149/11106.1901ecst, 111, 6, 1901-1906, 2023.05, 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.. |
| 7. | Kazutaka Ikegawa, Kengo Miyara, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, Kazunari Sasaki, Reversible Solid Oxide Cells: Cycling and Long-Term Durability of Air Electrodes, ECS Transactions, 10.1149/11106.0313ecst, 111, 6, 313-321, 2023.05, 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.. |
| 8. | Tsuyoshi Takahashi, Yohsuke Kokubo, Kazuya Murata, Osamu Hotaka, Shigeki Hasegawa, Yuya Tachikawa, Masamichi Nishihara, Junko Matsuda, Tatsumi Kitahara, Stephen M. Lyth, Akari Hayashi, Kazunari Sasaki, Cold start cycling durability of fuel cell stacks for commercial automotive applications, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2022.09.172, 47, 97, 41111-41123, 2022.11, System durability is crucial for the successful commercialization of polymer electrolyte fuel cells (PEFCs) in fuel cell electric vehicles (FCEVs). Besides conventional electrochemical cycling durability during long-term operation, the effect of operation in cold climates must also be considered. Ice formation during start up in sub-zero conditions may result in damage to the electrocatalyst layer and the polymer electrolyte membrane (PEM). Here, we conduct accelerated cold start cycling tests on prototype fuel cell stacks intended for incorporation into commercial FCEVs. The effect of this on the stack performance is evaluated, the resulting mechanical damage is investigated, and degradation mechanisms are proposed. Overall, only a small voltage drop is observed after the durability tests, only minor damage occurs in the electrocatalyst layer, and no increase in gas crossover is observed. This indicates that these prototype fuel cell stacks successfully meet the cold start durability targets for automotive applications in FCEVs.. |
| 9. | Yuhei Nakashima, Yuya Tachikawa, Kanzunari Sasaki, Design Optimization of Highly Efficient SOEC Co-Electrolysis Processes, ECS Transactions, 10.1149/10911.0025ecst, 109, 11, 25-35, 2022.09, High-temperature co-electrolysis of water and carbon dioxide using solid oxide electrolysis cells (SOECs) has attracted interest as an efficient synthesis gases production method. The SOECs and a fuel synthesis reactor are usually combined to produce hydrocarbon-rich fuel. In this study, we focused on investigating the effects of H2O/CO2 ratio of feed gas to the SOEC fuel electrode and gas and heat recycles on the fuel production efficiency were evaluated by mass and heat balance analysis. The results described that the amount of fuel production depended on the feed gas composition. In the case of increasing CO2 flow rate to the fuel electrode, the maximum amount of methane was produced and the efficiency of fuel production became 93.1% when the feed gas composition was controlled as H2O/CO2 = 4.32. These results indicate that the fuel production efficiency significantly depended on the operation condition of SOEC co-electrolysis and the system design.. |
| 10. | Kei Yamada, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, Kazunari Sasaki, Ni-Alloy Fuel Electrodes for Reversible Solid Oxide Cells, ECS Transactions, 10.1149/10911.0063ecst, 109, 11, 63-69, 2022.09, Reversible solid oxide cells (r-SOCs) are devices that can operate efficiently in both fuel cell and electrolysis operation modes. Nickel is widely used as an anode in conventional solid oxide fuel cells (SOFCs), but this agglomerates due to redox cycling, leading to irreversible performance degradation, making it unsuitable for r-SOCs. Here, we apply alternative electrodes to r-SOCs, in which Ni-Co alloy functions as a catalyst and an electronic conductor, whilst Ce0.9Gd0.1O2 (GDC) functions as a mixed ionic-electronic conductor. The electrochemical performance of these Ni-Co-GDC electrodes and their reverse-operation durability in r-SOCs are evaluated, and the effect of varying the amount of Co is investigated, compared with conventional cermet fuel electrodes. These novel materials exhibit high electrochemical performance and durability against SOFC/SOEC reverse-operation cycling.. |
| 11. | Kazutaka Ikegawa, Kengo Miyara, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, Kazunari Sasaki, Performance and Durability of Solid Oxide Electrolysis Cell Air Electrodes Prepared By Various Conditions, ECS Transactions, 10.1149/10911.0071ecst, 109, 11, 71-78, 2022.09, 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.. |
| 12. | Naoki Endo, Takuro Fukumoto, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, Kazunari Sasaki, Polarization Resistance of Ceria-Containing Fuel Electrodes in Solid Oxide Cells Studied By Impedance and DRT Analysis, ECS Transactions, 10.1149/10911.0003ecst, 109, 11, 3-13, 2022.09, Solid oxide electrolysis cells (SOECs) can be used to perform steam electrolysis in a process which is the reverse of power generation using a solid oxide fuel cell (SOFCs). They are capable of highly efficient hydrogen production. In this study, various model fuel electrode materials were compared and evaluated over a wide range of current densities in both SOFC and SOEC modes. Here, we prepared three types of cells: (i) with a conventional Ni-scandia-stabilized-zirconia (Ni-ScSZ) cermet fuel electrode, (ii) with a Ni-gadolinia-doped ceria (Gd0.1Ce0.9O2, Ni-GDC) cermet fuel electrode, and (iii) with a Ni-GDC co-impregnated fuel electrode fabricated by the co-impregnation method. The electrode reactions are characterized through measurements of electrochemical impedance spectra (EIS) and subsequent analysis of distribution of relaxation times (DRT). The results suggest that the use of mixed ionic and electronic conductor GDC as a fuel electrode material is advantageous especially in SOEC operation mode.. |
| 13. | Masahiro Yasutake, Zhiyun Noda, Yuya Tachikawa, Stephen Matthew Lyth, Junko Matsuda, Masamichi Nishihara, Kohei Ito, Akari Hayashi, Kazunari Sasaki, Temperature Distribution Analysis of PEM Electrolyzer in High Current Density Operation By Numerical Simulation, ECS Transactions, 10.1149/10909.0437ecst, 109, 9, 437-450, 2022.09, An advantage of polymer electrolyte membrane water electrolysis (PEMWE) over other water electrolysis technologies is its ability to operate at high current densities. However, resistive heating during . In this study, the internal cell temperature distribution at high current densities up to 12 A cm-2 is evaluated through numerical simulation. The correlation between the temperature gradient in the cell and the flow rate of water supplied is examined. An increase in water supply is effective in minimizing high temperature gradients at higher current densities.. |
| 14. | Takuro Fukumoto, Naoki Endo, Katsuya Natsukoshi, Yuya Tachikawa, George Frederick Harrington, Stephen Matthew Lyth, Junko Matsuda, Kazunari Sasaki, Visualization and Observation of Spatial Temperature Distribution in Reversible Solid Oxide Cells through Simulation and Thermal Imaging, ECS Transactions, 10.1149/10911.0015ecst, 109, 11, 15-24, 2022.09, 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.. |
| 15. | Kohei Matsumoto, Yuya Tachikawa, Stephen M. Lyth, Junko Matsuda, Kazunari Sasaki, Performance and durability of Ni–Co alloy cermet anodes for solid oxide fuel cells, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2022.06.268, 47, 68, 29441-29455, 2022.08, Ni alloys are examined as redox-resistant alternatives to pure Ni for solid oxide fuel cell (SOFC) anodes. Among the various candidate alloys, Ni–Co alloys are selected due to their thermochemical stability in the SOFC anode environment. Ni–Co alloy cermet anodes are prepared by ammonia co-precipitation, and their electrochemical performance and microstructure are evaluated. Ni–Co alloy anodes exhibit high durability against redox cycling, whilst the current-voltage characteristics are comparable to those of pure Ni cermet anodes. Microstructural observation reveals that cobalt-rich oxide layers on the outer surface of the Ni–Co alloy particles protect against further oxidation within the Ni alloy. In long-term durability tests using highly humidified hydrogen gas, the use of a Ni–Co cermet with Gd-doped CeO2 suppresses degradation of the power generation performance. It is concluded that Ni–Co alloy cermet anodes are highly attractive for the development of robust SOFCs.. |
| 16. | Takuro Fukumoto, Naoki Endo, Katsuya Natsukoshi, Yuya Tachikawa, George F Harrington, Stephen M Lyth, Junko Matsuda, Kazunari Sasaki, Exchange current density of reversible solid oxide cell electrodes, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2022.03.164, 2022.04. |
| 17. | Tsuyoshi Takahashi, Takuya Ikeda, Kazuya Murata, Osamu Hotaka, Shigeki Hasegawa, Yuya Tachikawa, Masamichi Nishihara, Junko Matsuda, Tatsumi Kitahara, Stephen M. Lyth, Akari Hayashi, Kazunari Sasaki, Accelerated Durability Testing of Fuel Cell Stacks for Commercial Automotive Applications: A Case Study, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 10.1149/1945-7111/ac662d, 169, 4, 2022.04, System durability is crucially important for the successful commercialization of fuel cell electric vehicles (FCEVs). Conventional accelerated durability testing protocols employ relatively high voltage to hasten carbon corrosion and/or platinum catalyst degradation. However, high voltages are strictly avoided in commercialized FCEVs such as the Toyota MIRAI to minimize these degradation modes. As such, conventional durability tests are not representative of real-world FCEV driving conditions. Here, modified start-stop and load cycle durability tests are conducted on prototype fuel cell stacks intended for incorporation into commercial FCEVs. Polarization curves are evaluated at beginning of test (BOT) and end of test (EOT), and the degradation mechanisms are elucidated by separating the overvoltages at both 0.2 and 2.2 A cm(-2). Using our modified durability protocols with a maximum cell voltage of 0.9 V, the prototype fuel cell stacks easily meet durability targets for automotive applications, corresponding to 15-year operation and 200,000 km driving range. These findings have been applied successfully in the development of new fuel cell systems for FCEVs, in particular the second-generation Toyota MIRAI.. |
| 18. | Takuro Fukumoto, Naoki Endo, Katsuya Natsukoshi, Yuya Tachikawa, George F. Harrington, Stephen M. Lyth, Junko Matsuda, Kazunari Sasaki, Exchange current density of reversible solid oxide cell electrodes, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2022.03.164, 47, 37, 16626-16639, 2022.04, Reversible solid oxide cells (r-SOCs) can be operated in either solid oxide fuel cell or solid oxide electrolysis cell mode. They are expected to become important in the support of renewable energy due to their high efficiency for both power generation and hydrogen generation. The exchange current density is one of the most important parameters in the quantification of electrode performance in solid oxide cells. In this study, four different fuel electrodes and two different air electrodes are fabricated using different materials and the microstructures are compared. The temperature, fuel humidification, and oxygen concentration at the air electrode are varied to obtain the apparent exchange current density for the different electrode materials. In contrast to ruthenium-and-gadolinia-doped ceria (Rh-GDC) as well as nickel-and-gadolinia-doped ceria (Ni-GDC) electrodes, significant differences in the apparent exchange current density were observed between electrolysis and fuel cell modes for the nickel-scandia-stabilized zirconia (Ni-ScSZ) cermet. Variation of gas concentration revealed that surface adsorption sites were almost completely vacant for all these electrodes. The apparent exchange current densities obtained in this study are useful as a parameter for simulation of the internal properties of r-SOCs.. |
| 19. | Katsuya Natsukoshi, Kengo Miyara, Yuya Tachikawa, Junko Matsuda, Shunsuke Taniguchi, George F. Harrington, Kazunari Sasakia-E, Reversible Solid Oxide Cells: Durability of fuel electrodes against voltage cycling, ECS Transactions, 10.1149/10301.0375ecst, 103, 1, 375-382, 2021.07, Reversible Solid Oxide Cells (r-SOCs) are an attractive electrochemical energy conversion technology that can act as both a Solid Oxide Fuel Cell (SOFC) for power generation, and a Solid Oxide Electrolysis Cell (SOEC) for steam electrolysis. Unfortunately, Ni-zirconia cermet, which is widely used in SOFCs, has the problem that the electronically conductive phases, Ni, agglomerates due to redox reactions and breaks the conductive path, resulting in performance degradation. In this study, we fabricated an alternative fuel electrode with a stable conductive structure using both an ionic conductor Ce0.9Gd0.1O2 (GDC) and an electronic conductor Sr0.9La0.1TiO3(LST), and we co-impregnate Ni and GDC to the fuel electrode using only Ni as an electrocatalyst. The durability of the conventional fuel electrode and our alternative fuel electrode was compared and evaluated, and the potential of the alternative fuel electrode material was demonstrated.. |
| 20. | Y. Tachikawa, Y. Matsuzaki, Y. Kawabata, S. Taniguchi, K. Sasaki, Numerical study on biogas refining system combined with proton-conducting solid oxide electrolyzer, ECS Transactions, 10.1149/10301.0845ecst, 103, 1, 845-851, 2021.07, Biogas refining system including methanation reactor and protonconducting electrolysis cell has been proposed and investigated based on the simulation including mass and heat balance analysis. Based on the calculation results, carbon deposition was predicted to still occur at the cathode outlet even with the gas humidification when a conventional oxide-ion conducting electrolyte is applied to the electrolysis cell due to the enhanced carbon activity caused by oxide-ion transport from the cathode to the anode. In the case of the proton-conducting electrolyte applied solid oxide electrolysis cell, proton transport from the anode to the cathode was found to mainly promote reverse water-gas shift reaction and methanation reaction without any carbon deposition. Even though the calculation results should be verified by comparing with experimental results, the numerical study suggested that the biogas refining system combined with p-SOEC is a promising technology for generating carbonneutral methane with a strongly suppressed risk of carbon deposition.. |
| 21. | Kohei Matsumoto, Yuya Tachikawa, Junko Matsuda, Shunsuke Taniguchi, Kazunari Sasaki, Redox Durability of Ni-Co Alloy Cermet Anodes for SOFCs, ECS Transactions, 10.1149/10301.1549ecst, 103, 1, 1549-1556, 2021.07, SOFCs are expected to be commonly used as a clean energy conversion technology. Ni-zirconia cermet, which is commonly used for SOFC anodes as an electronic conductor, has a problem that Ni agglomerates due to redox reactions disrupting the conductive path and leading to irreversible performance degradation. In this study, we fabricated anodes using Ni-Co alloy instead of Ni. By alloying Ni with Co, it was found that the same power generation performance and high redox cycle durability could be obtained.. |
| 22. | Naoki Endo, Takuro Fukumoto, Rei Ushijima, Katsuya Natsukoshi, Yuya Tachikawa, Junko Matsuda, Shunsuke Taniguchi, Kazunari Sasaki, DRT Analysis of Solid Oxide Electrolysis Cells: Polarization Resistance of Fuel Electrodes, ECS Transactions, 10.1149/10301.1981ecst, 103, 1, 1981-1989, 2021.07, Solid oxide electrolysis cells (SOECs), which enable steam electrolysis by operating solid oxide fuel cells (SOFCs) in reverse, are capable of highly efficient hydrogen production. While SOFCs and SOECs are using similar materials and cell structures, electrode reactions in SOEC operation have to be investigated in more detail. In this study, we compared and discussed conventional cells and cells fabricated by an impregnation method by characterizing the electrode reactions through measurements of electrochemical impedance spectra (EIS) and subsequent analysis of distribution of relaxation times (DRT).. |
| 23. | Takuro Fukumoto, Naoki Endo, Kouki Mori, Yuya Tachikawa, Junko Matsuda, Shunsuke Taniguchi, Kazunari Sasaki, Exchange Current Density of Solid Oxide Electrolysis Cell Electrodes, ECS Transactions, 10.1149/10301.2007ecst, 103, 1, 2007-2016, 2021.07, Solid oxide fuel cells (SOFCs) are expected to become widespread as an energy conversion technology that can directly produce electrical energy from fuel. Solid oxide electrolysis cells (SOECs) are essentially SOFCs operating in reverse to produce fuel from electricity. The exchange current density is one of the most important parameters to simulate SOEC/SOFC. In this study, experimental data was evaluated as apparent exchange current density and the effects of SOEC/SOFC operation and different electrode materials were discussed.. |
| 24. | Katsuya Miyamoto, Tsutomu Kawabata, Yuya Tachikawa, Junko Matsuda, Shunsuke Taniguchi, Yoshio Matsuzaki, Akari Hayashi, Kazunari Sasaki, Preparation of Model SOFCs with Proton-Conducting Electrolyte on Metal Support Using Pulse Laser Deposition, ECS Transactions, 10.1149/10301.2033ecst, 103, 1, 2033-2040, 2021.07, Since operating temperature of solid oxide fuel cells (SOFCs) is relatively high, SOFCs must consist of heat resistant components, such as ceramics, which results in high cost. In this study, SOFCs with a proton-conductor as the electrolyte membrane was fabricated on metal supports and examined for lower-temperature operation of SOFCs. Technological issues of such metal-supported proton-conducting SOFCs (p-SOFCs) prepared by pulse laser deposition (PLD) are analyzed through microstructural observation and electrochemical characterization.. |
| 25. | Yuto Wakita, Yuya Tachikawa, Hironori Nakajima, Shigeru Hamada, Kohei Ito, Visualization and mechanical strength of glass seal in planar type solid oxide fuel cells, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2020.05.153, 45, 41, 21754-21766, 2020.08, [URL], This study evaluated the mechanical reliability of glass seal in planar type solid oxide fuel cells and clarified the relationship between glass wettability and the mechanical reliability of glass seal. A visualization experiment was developed to observe a specific model seal in a furnace subjected to temperature variation and the relationship between the glass wettability and the seal shape was measured. The seal model consists of glass (G018-311, Schott, Germany) and interconnectors (Crofer 22 APU, VDM Metals GmbH, Germany). The visualization experiment and analysis were based on the sessile drop method to quantify glass surface tension and contact angle between glass and interconnector. The equation balance of forces with these surface properties succeeded to reproduce the seal shape observed in the visualization. Subsequently, the seal stress field was numerically solved, and the mechanical strength of the seal was quantitatively evaluated using the stress intensity factor. The analyses concluded that the stress intensity factor is 1.5 times higher than its minimum value as the contact angle raised from 90 to 130° and glass wettability decreased.. |
| 26. | Yuto Wakita, Yuya Tachikawa, Hironori Nakajima, Shigeru Hamada, Kohei Ito, Visualization and mechanical strength of glass seal in planar type solid oxide fuel cells, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2020.05.153, 45, 41, 21754-21766, 2020.08, This study evaluated the mechanical reliability of glass seal in planar type solid oxide fuel cells and clarified the relationship between glass wettability and the mechanical reliability of glass seal. A visualization experiment was developed to observe a specific model seal in a furnace subjected to temperature variation and the relationship between the glass wettability and the seal shape was measured. The seal model consists of glass (G018-311, Schott, Germany) and interconnectors (Crofer 22 APU, VDM Metals GmbH, Germany). The visualization experiment and analysis were based on the sessile drop method to quantify glass surface tension and contact angle between glass and interconnector. The equation balance of forces with these surface properties succeeded to reproduce the seal shape observed in the visualization. Subsequently, the seal stress field was numerically solved, and the mechanical strength of the seal was quantitatively evaluated using the stress intensity factor. The analyses concluded that the stress intensity factor is 1.5 times higher than its minimum value as the contact angle raised from 90 to 130° and glass wettability decreased.. |
| 27. | K. Takino, Y. Tachikawa, K. Mori, S. M. Lyth, Y. Shiratori, S. Taniguchi, K. Sasaki, Simulation of SOFC performance using a modified exchange current density for pre-reformed methane-based fuels, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2019.12.089, 45, 11, 6912-6925, 2020.02, [URL], Numerical simulations can be used to visualize and better understand various distributions such as gas concentration and temperature in solid oxide fuel cells (SOFCs) under realistic operating conditions. However, pre-existing models generally utilize an anode exchange current density equation which is valid for humidified hydrogen fuels – an unrealistic case for SOFCs, which are generally fueled by hydrocarbons. Here, we focus on developing a new, modified exchange current density equation, leading to an improved numerical analysis model for SOFC anode kinetics. As such, we experimentally determine the exchange current density of SOFC anodes fueled by fully pre-reformed methane. The results are used to derive a new phenomenological anode exchange current density equation. This modified equation is then combined with computational fluid dynamics (CFD) to simulate the performance parameters of a three-dimensional electrolyte-supported SOFC. The new modified exchange current density equation for methane-based fuels reproduces the I–V characteristics and temperature distribution significantly better than the previous models using humidified hydrogen fuel. Better simulations of SOFC performance under realistic operating conditions are crucial for the prediction and prevention of e.g. fuel starvation and thermal stresses.. |
| 28. | Yasuharu Kawabata, Tatsuya Nakajima, Kazuo Nakamura, Toru Hatae, Yuya Tachikawa, Shunsuke Taniguchi, Yoshio Matsuzaki, Kazunari Sasaki, Proposal of ultra-high-efficiency zero-emission power generation systems, Journal of Power Sources, 10.1016/j.jpowsour.2019.227459, 448, 2020.02, Solid oxide fuel cell (SOFC) and protonic ceramic fuel cell (PCFC) have strong features that enables high efficiency power generation and efficient CO2 capture. Applying these technologies to the fossil fuel and biomass power generation, we can realize ultra-high efficiency zero-emission power generation by capturing liquefied CO2 (LCO2) for easy transport and utilization (CCU) or storage(fossil fuel CCS and bio-energy CCS: BECCS). In this study, we propose LCO2 capture ultra-efficient power generation systems consist of multi-stage SOFC/PCFC, oxygen or hydrogen transport membrane, CO2 cooling and liquidizing units driven by exhaust heat and generated power by fuel cells. Net power generation efficiency is estimated through heat mass balance analysis. As the results for natural gas, proposed PCFC system is suitable and expected 64.7 %LHV net power generation efficiency with more than 99 vol% LCO2 capture. For biogas direct supply case, net power generation efficiency of proposed PCFC system is 57%LHV with 99 vol% capture of CO2 in the air. These results indicates that proposed systems have quite strong potential that enables ultra-high efficient CO2-free fossil fuel power generation with CCS and CO2-reduction biomass fuel power generation with BECCS.. |
| 29. | K. Takino, Y. Tachikawa, K. Mori, S. M. Lyth, Y. Shiratori, S. Taniguchi, K. Sasaki, Simulation of SOFC performance using a modified exchange current density for pre-reformed methane-based fuels, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2019.12.089, 45, 11, 6912-6925, 2020.02, Numerical simulations can be used to visualize and better understand various distributions such as gas concentration and temperature in solid oxide fuel cells (SOFCs) under realistic operating conditions. However, pre-existing models generally utilize an anode exchange current density equation which is valid for humidified hydrogen fuels – an unrealistic case for SOFCs, which are generally fueled by hydrocarbons. Here, we focus on developing a new, modified exchange current density equation, leading to an improved numerical analysis model for SOFC anode kinetics. As such, we experimentally determine the exchange current density of SOFC anodes fueled by fully pre-reformed methane. The results are used to derive a new phenomenological anode exchange current density equation. This modified equation is then combined with computational fluid dynamics (CFD) to simulate the performance parameters of a three-dimensional electrolyte-supported SOFC. The new modified exchange current density equation for methane-based fuels reproduces the I–V characteristics and temperature distribution significantly better than the previous models using humidified hydrogen fuel. Better simulations of SOFC performance under realistic operating conditions are crucial for the prediction and prevention of e.g. fuel starvation and thermal stresses.. |
| 30. | Yoshio Matsuzaki, Yuya Tachikawa, Yoshitaka Baba, Koki Sato, Gen Kojo, Hiroki Matsuo, Junichiro Otomo, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Suppression of Leakage Current in Proton-Conducting BaZr0.8Y0.2O3-δ Electrolyte by Forming Hole-Blocking Layer, Journal of the Electrochemical Society, 10.1149/1945-7111/ab904f, 167, 8, 2020.01, [URL], Solid oxide fuel cells (SOFCs) with proton-conducting solid electrolyte, instead of the oxide-ion conducting solid electrolyte have attracted attentions because of their high potential to reduce operating temperatures and to enhance the electrical efficiencies of SOFCs. In addition, the proton-conducting SOFCs with multistage electrochemical oxidation configuration will be promising technology for critically-high electric efficiencies. However, it is known that there are non-negligible charge -carriers other than protons in typical proton-conducting solid oxide electrolytes at relatively high temperatures. The existence of the partial conductivities of holes and/or electrons will cause the internal leakage current that consumes fuel but never generates any electrical power output. The higher ratio of the leakage current to external current will more deteriorate the electrical efficiency. In this study, the effects of blocking -layers formed on the air side surface of base electrolyte layer consisting of BaZr0.8Y0.2O3-δ (BZY82) for suppressing the leakage current have been investigated by using electrochemical parameters of the partial conduction of the materials. The chemical potential profile and leakage current showed large dependence on the material of the blocking-layer. Lanthanum tungstate was found to play a role as unique and strong blocking-layer against the leakage current.. |
| 31. | Yusuke Ishibashi, Kohei Matsumoto, Shotaro Futamura, Yuya Tachikawa, Junko Matsuda, Stephen M. Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Improved Redox Cycling Durability in Alternative Ni Alloy-Based SOFC Anodes, Journal of the Electrochemical Society, 10.1149/1945-7111/abac87, 167, 12, 2020.01, [URL], Repeated reduction and oxidation of metallic nickel in the anodes of solid oxide fuel cell (SOFC) causes volume changes and agglomeration. This disrupts the electron conducting network, resulting in deterioration of the electrochemical performance. It is therefore desirable to develop more robust anodes with high redox stability. Here, new cermet anodes are developed, based on nickel alloyed with Co, Fe, and/or Cr. The stable phases of these different alloys are calculated for oxidizing and reducing conditions, and their electrochemical characteristics are evaluated. Whilst alloying causes a slight decrease in power generation efficiency, the Ni-alloy based anodes have significantly improved redox cycle durability. Microstructural observation reveals that alloying results in the formation of a dense oxide film on the surface of the catalyst particle (e.g. Co-oxide or a complex Fe-Ni-Cr oxide). These oxide layers help suppress oxidation of the underlying nickel catalyst particles, preventing oxidation-induced volume changes/agglomeration, and thereby preserving the electron conducting pathways. As such, the use of these alternative Ni-alloy based cermets significantly improves the redox stability of SOFC anodes.. |
| 32. | Yusuke Ishibashi, Kohei Matsumoto, Shotaro Futamura, Yuya Tachikawa, Junko Matsuda, Stephen M. Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Improved Redox Cycling Durability in Alternative Ni Alloy-Based SOFC Anodes, Journal of the Electrochemical Society, 10.1149/1945-7111/abac87, 167, 12, 2020.01, Repeated reduction and oxidation of metallic nickel in the anodes of solid oxide fuel cell (SOFC) causes volume changes and agglomeration. This disrupts the electron conducting network, resulting in deterioration of the electrochemical performance. It is therefore desirable to develop more robust anodes with high redox stability. Here, new cermet anodes are developed, based on nickel alloyed with Co, Fe, and/or Cr. The stable phases of these different alloys are calculated for oxidizing and reducing conditions, and their electrochemical characteristics are evaluated. Whilst alloying causes a slight decrease in power generation efficiency, the Ni-alloy based anodes have significantly improved redox cycle durability. Microstructural observation reveals that alloying results in the formation of a dense oxide film on the surface of the catalyst particle (e.g. Co-oxide or a complex Fe-Ni-Cr oxide). These oxide layers help suppress oxidation of the underlying nickel catalyst particles, preventing oxidation-induced volume changes/agglomeration, and thereby preserving the electron conducting pathways. As such, the use of these alternative Ni-alloy based cermets significantly improves the redox stability of SOFC anodes.. |
| 33. | Yoshio Matsuzaki, Yuya Tachikawa, Yoshitaka Baba, Koki Sato, Gen Kojo, Hiroki Matsuo, Junichiro Otomo, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Suppression of Leakage Current in Proton-Conducting BaZr |
| 34. | Yasuharu Kawabata, Tatsuya Nakajima, Kazuo Nakamura, Toru Hatae, Yuya Tachikawa, Shunsuke Taniguchi, Yoshio Matsuzaki, Kazunari Sasaki, Proposal of ultra-high-efficiency zero-emission power generation systems, Journal of Power Sources, 10.1016/j.jpowsour.2019.227459, 448, 2019.11, [URL], Solid oxide fuel cell (SOFC) and protonic ceramic fuel cell (PCFC) have strong features that enables high efficiency power generation and efficient CO2 capture. Applying these technologies to the fossil fuel and biomass power generation, we can realize ultra-high efficiency zero-emission power generation by capturing liquefied CO2 (LCO2) for easy transport and utilization (CCU) or storage(fossil fuel CCS and bio-energy CCS: BECCS). In this study, we propose LCO2 capture ultra-efficient power generation systems consist of multi-stage SOFC/PCFC, oxygen or hydrogen transport membrane, CO2 cooling and liquidizing units driven by exhaust heat and generated power by fuel cells. Net power generation efficiency is estimated through heat mass balance analysis. As the results for natural gas, proposed PCFC system is suitable and expected 64.7 %LHV net power generation efficiency with more than 99 vol% LCO2 capture. For biogas direct supply case, net power generation efficiency of proposed PCFC system is 57%LHV with 99 vol% capture of CO2 in the air. These results indicates that proposed systems have quite strong potential that enables ultra-high efficient CO2-free fossil fuel power generation with CCS and CO2-reduction biomass fuel power generation with BECCS.. |
| 35. | 立川雄也, 佐々木一成, 水素ステーションの設置・配置計画, 火力原子力発電, 70, 10, 36-41, 2019.10. |
| 36. | Yusuke Ishibashi, Shotaro Futamura, Yuya Tachikawa, Junko Matsuda, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Alternative Ni-alloy cermet anode materials for SOFCs, ECS Transactions, 10.1149/09101.1889ecst, 91, 1, 1889-1896, 2019.07, Solid oxide fuel cell (SOFC) is a promising electrochemical energy conversion device that can directly produce electricity from chemical fuels. On the other hand, in the Ni-zirconia cermet currently used for the SOFC anode, the electron conducting pathways through the Ni metal phase can be easily destroyed by redox processes, where Ni oxidation/reduction (redox) results in significant volume changes, leading to deterioration of the electrochemical performance. In this study, various anodes using Ni-based alloys as alternative materials for Ni are prepared. Their electrochemical performance and redox stability are evaluated. In particular, Ni-Co alloy cermet exhibits better durability against redox cycling.. |
| 37. | Y. Matsuzaki, Y. Tachikawa, Y. Baba, K. Sato, H. Iinuma, G. Kojo, H. Matsuo, J. Otomo, H. Matsumoto, S. Taniguchi, K. Sasaki, Leakage current and chemical potential profile in proton-conducting bi-layered solid oxide electrolyte with Bzy and hole-blocking layers, ECS Transactions, 10.1149/09101.1009ecst, 91, 1, 1009-1018, 2019.07, Solid oxide fuel cells (SOFCs) with proton-conducting solid electrolyte, instead of the oxide-ion conducting solid electrolyte have attracted attentions because of their high potential to reduce operating temperatures and to enhance the electrical efficiencies of SOFCs. In addition, the proton-conducting SOFCs with multistage electrochemical oxidation configuration will be promising technology for critically-high electric efficiencies. However, it is known that there are non-negligible charge -carriers other than protons in typical proton-conducting solid oxide electrolytes at relatively high temperatures. The existence of the partial conductivities of holes and/or electrons will cause the internal leakage current that consumes fuel but never generates any electrical power output. The higher ratio of the leakage current to external current will more deteriorate the electrical efficiency. In this study, the effects of blocking -layers formed on the air side surface of base electrolyte layer consisting of BaZr0.8Y0.2O3-δ (BZY82) for suppressing the leakage current have been investigated by using electrochemical parameters of the partial conduction of the materials. The chemical potential profile and leakage current showed large dependence on the material of the blocking -layer. Lanthanum tungstate was found to play a role as unique and strong blocking -layer against the leakage current.. |
| 38. | Shotaro Futamura, Aki Muramoto, Yuya Tachikawa, Junko Matsuda, Stephen Matthew Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, SOFC Anodes Impregnated with Noble Metal Catalyst Nanoparticles for High Fuel Utilization, ECS Transactions, 10.1149/09101.1905ecst, 91, 1, 1905-1913, 2019.07. |
| 39. | Y. Matsuzaki, Y. Tachikawa, H. Iinuma, K. Sato, Y. Baba, J. Otomo, H. Matsumoto, S. Taniguchi, K. Sasaki, Modified Energy Efficiencies of Proton-conducting SOFCs with Partial Conductions of Oxide-ions and Holes, Fuel Cells, 10.1002/fuce.201800181, 19, 4, 503-511, Chapter 07, A15, 2019.06, An analytical method to determine the electrochemical energy efficiencies of electrolytes with partial electronic conduction has been developed previously and reported in the literature. However, this analytical method does not address the effects of differing ionic species in electrolytes, i.e., the oxide-ions or protons. Therefore, we aimed to modify this analytical method to account for the effects of differing ionic species, and applied it to compare the energy efficiencies of oxide-ion conducting solid electrolytes such as yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) to proton-conducting solid electrolytes, such as yttria-doped barium zirconate (BZY). With the modification, difference in the influence of the fuel consumption between the oxide-ion conducting electrolyte and the proton-conducting electrolyte has been successfully taken into account. The energy efficiency of the BZY electrolyte relatively increased against those of YSZ or GDC electrolytes by the modification. Additionally, partial oxide-ion conduction in the proton-conducting electrolyte was successfully estimated using the modified analytical method.. |
| 40. | Y. Matsuzaki, Y. Tachikawa, H. Iinuma, K. Sato, Y. Baba, J. Otomo, H. Matsumoto, S. Taniguchi, K. Sasaki, Modified Energy Efficiencies of Proton-conducting SOFCs with Partial Conductions of Oxide-ions and Holes, Fuel Cells, 10.1002/fuce.201800181, 19, 4, 503-511, 2019.06, [URL], An analytical method to determine the electrochemical energy efficiencies of electrolytes with partial electronic conduction has been developed previously and reported in the literature. However, this analytical method does not address the effects of differing ionic species in electrolytes, i.e., the oxide-ions or protons. Therefore, we aimed to modify this analytical method to account for the effects of differing ionic species, and applied it to compare the energy efficiencies of oxide-ion conducting solid electrolytes such as yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) to proton-conducting solid electrolytes, such as yttria-doped barium zirconate (BZY). With the modification, difference in the influence of the fuel consumption between the oxide-ion conducting electrolyte and the proton-conducting electrolyte has been successfully taken into account. The energy efficiency of the BZY electrolyte relatively increased against those of YSZ or GDC electrolytes by the modification. Additionally, partial oxide-ion conduction in the proton-conducting electrolyte was successfully estimated using the modified analytical method.. |
| 41. | Tatsuya Kawasaki, Junko Matsuda, Yuya Tachikawa, Stephen Matthew Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Oxidation-induced degradation and performance fluctuation of solid oxide fuel cell Ni anodes under simulated high fuel utilization conditions, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2019.02.136, 44, 18, 9386-9399, 2019.04, [URL], High fuel utilization (Uf) conditions in a small-scale electrolyte-supported solid oxide fuel cell (SOFC) with an Ni-ScSZ anode were approximated by adjusting the gas composition to correspond to that in the downstream region of an SOFC stack. At Uf = 80%, and with a cell voltage of 0.5 V, the ohmic resistance fluctuated slightly from the early stages of operation, and became much more significant after 80 h. High current density and large polarization were found to promote Ni agglomeration, leading to insufficient connectivity of the Ni nanoparticles. At Uf = 95%, and with a cell voltage of 0.6 V, fluctuations in the polarization were observed at a much earlier stage, which are attributed to the highly humidified fuel. In particular, significant degradation was observed when the compensated anode potential (which incorporates the anode ohmic losses) approached the Ni oxidation potential. Ohmic losses in the anode are considered to influence Ni oxidation by exposing Ni near the electrolyte to a more oxidizing atmosphere with the increase in oxygen ion transport. Stable operation is therefore possible under conditions in which the compensated anode potential does not approach the Ni oxidation potential, assuming a stable interconnected Ni network.. |
| 42. | Tatsuya Kawasaki, Junko Matsuda, Yuya Tachikawa, Stephen Matthew Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Oxidation-induced degradation and performance fluctuation of solid oxide fuel cell Ni anodes under simulated high fuel utilization conditions, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2019.02.136, 44, 18, 9386-9399, 2019.04, High fuel utilization (Uf) conditions in a small-scale electrolyte-supported solid oxide fuel cell (SOFC) with an Ni-ScSZ anode were approximated by adjusting the gas composition to correspond to that in the downstream region of an SOFC stack. At Uf = 80%, and with a cell voltage of 0.5 V, the ohmic resistance fluctuated slightly from the early stages of operation, and became much more significant after 80 h. High current density and large polarization were found to promote Ni agglomeration, leading to insufficient connectivity of the Ni nanoparticles. At Uf = 95%, and with a cell voltage of 0.6 V, fluctuations in the polarization were observed at a much earlier stage, which are attributed to the highly humidified fuel. In particular, significant degradation was observed when the compensated anode potential (which incorporates the anode ohmic losses) approached the Ni oxidation potential. Ohmic losses in the anode are considered to influence Ni oxidation by exposing Ni near the electrolyte to a more oxidizing atmosphere with the increase in oxygen ion transport. Stable operation is therefore possible under conditions in which the compensated anode potential does not approach the Ni oxidation potential, assuming a stable interconnected Ni network.. |
| 43. | Shotaro Futamura, Aki Muramoto, Yuya Tachikawa, Junko Matsuda, Stephen Matthew Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, SOFC anodes impregnated with noble metal catalyst nanoparticles for high fuel utilization, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2019.01.223, 44, 16, 8502-8518, 2019.03, [URL], Redox-stable solid oxide fuel cell (SOFC) anodes are developed in order to improve durability at higher fuel utilization, as a possible alternative to conventional Ni-zirconia cermet anodes. Ce 0.9 Gd 0.1 O 2 (GDC) is utilized as a mixed ionic and electronic conductor (MIEC), in combination with Sr 0.9 La 0.1 TiO 3 (LST) as an electronic conductor. The stability of noble metals (Rh, Pt, and Pd) is analyzed via thermochemical calculation of stable phases. Noble metal catalyst nanoparticles are incorporated via co-impregnation with GDC. The electrochemical characteristics of SOFC single cells using these anode materials are investigated in highly-humidified H 2 at 800 °C. Their stability at high fuel utilization is analyzed. These co-impregnated anodes with highly dispersed noble metal catalysts on the LST-GDC conducting backbones, achieve high I[sbnd]V performance comparable to conventional Ni-cermet anodes. The co-impregnated anodes also achieve considerably high catalytic mass activity. At higher oxygen partial pressure, where the Ni catalyst can be deactivated by oxidation, these noble catalysts are thermochemically stable in the metallic state, and tolerant against oxidation. This class of alternative catalyst, impregnated with low-loading of noble metals could contribute to stable operation in the downstream region of SOFC systems. A simple cost analysis indicates a tolerance of using noble metals, provided their loading is sufficiently low.. |
| 44. | Shotaro Futamura, Aki Muramoto, Yuya Tachikawa, Junko Matsuda, Stephen M. Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, SOFC anodes impregnated with noble metal catalyst nanoparticles for high fuel utilization, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2019.01.223, 44, 16, 8502-8518, 2019.03, Redox-stable solid oxide fuel cell (SOFC) anodes are developed in order to improve durability at higher fuel utilization, as a possible alternative to conventional Ni-zirconia cermet anodes. Ce0.9Gd0.1O2 (GDC) is utilized as a mixed ionic and electronic conductor (MIEC), in combination with Sr0.9La0.1TiO3 (LST) as an electronic conductor. The stability of noble metals (Rh, Pt, and Pd) is analyzed via thermochemical calculation of stable phases. Noble metal catalyst nanoparticles are incorporated via co-impregnation with GDC. The electrochemical characteristics of SOFC single cells using these anode materials are investigated in highly-humidified H2 at 800 °C. Their stability at high fuel utilization is analyzed. These co-impregnated anodes with highly dispersed noble metal catalysts on the LST-GDC conducting backbones, achieve high I[sbnd]V performance comparable to conventional Ni-cermet anodes. The co-impregnated anodes also achieve considerably high catalytic mass activity. At higher oxygen partial pressure, where the Ni catalyst can be deactivated by oxidation, these noble catalysts are thermochemically stable in the metallic state, and tolerant against oxidation. This class of alternative catalyst, impregnated with low-loading of noble metals could contribute to stable operation in the downstream region of SOFC systems. A simple cost analysis indicates a tolerance of using noble metals, provided their loading is sufficiently low.. |
| 45. | Yuya TACHIKAWA, Yoshio MATSUZAKI, Takaaki SOMEKAWA, Koki SATO, Shunsuke TANIGUCHI, Kazunari SASAKI, Solid Oxide Electrolyzer Devices using Proton and Oxide-ion Conducting Electrolyte, Proceedings of 13th European SOFC & SOE Forum (EFCF2018), Chapter 05, A12, 2018.07. |
| 46. | Yoshio MATSUZAKI, Yuya TACHIKAWA, Hiroki IINUMA, Koki SATO, Yoshitaka BABA, Junichiro OTOMO, Hiroshige MATSUMOTO, Shunsuke TANIGUCHI, Kazunari SASAKI, Modified Energy Efficiencies of Proton-conducting SOFCs with Partial Conductions of Oxide-ions and Holes, Proceedings of 13th European SOFC & SOE Forum (EFCF2018), 07, A15, 40-49, 2018.07. |
| 47. | Yuya TACHIKAWA, Yoshio MATSUZAKI, Takaaki SOMEKAWA, Koki SATO, Shunsuke TANIGUCHI, Kazunari SASAKI, Solid Oxide Electrolyzer Devices using Proton and Oxide-ion Conducting Electrolyte, Proceedings of 13th European SOFC & SOE Forum (EFCF2018), 05, A12, 160-174, 2018.07. |
| 48. | Aki Muramoto, Yudai Kikuchi, Yuya Tachikawa, Stephen Matthew Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, High-pressure C-H-O diagrams Fuel composition, carbon deposition, and open circuit voltage of pressurized SOFCs, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2017.10.122, 42, 52, 30769-30786, 2017.12, [URL], Solid oxide fuel cells (SOFCs) can operate by using various fuel species. Pressurized SOFCs with gas/steam turbine(s) may achieve higher power generation efficiency as hybrid or triple-combined power generation systems. In this study, fuel gas composition is systematically investigated by thermochemical equilibrium calculations on the anode side of SOFCs, pressurized up to 30 bar over a wide temperature range, up to 1000 °C. Since conventional hydrogen-containing fuel gas consists mainly of carbon, hydrogen, and oxygen, high-pressure C-H-O equilibrium diagrams are numerically obtained. It is revealed that the carbon deposition region contracts in the hydrogen-rich area and expands in the oxygen-rich area with increasing total pressure. The molar fraction of each gas component, described in such C-H-O diagrams, also depends on the total pressure. The theoretical open circuit voltage (OCV) increases by pressurization. The effect of nitrogen in high-pressure SOFC fuels is also considered, which is important especially for air-blown coal gas. The minimum amount of H2O, O2, and CO2 required to prevent carbon deposition in steam reforming, partial oxidation, and CO2 (dry) reforming, respectively, is also derived up to 30 bar. The high-pressure C-H-O diagrams are also applicable to various high-temperature/high-pressure energy systems such as solid oxide electrolyzer cells (SOECs) and reversible fuel cells.. |
| 49. | Aki Muramoto, Yudai Kikuchi, Yuya Tachikawa, Stephen M. Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, High-pressure C-H-O diagrams: Fuel composition, carbon deposition, and open circuit voltage of pressurized SOFCs, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2017.10.122, 42, 52, 30769-30786, 2017.12, Solid oxide fuel cells (SOFCs) can operate by using various fuel species. Pressurized SOFCs with gas/steam turbine(s) may achieve higher power generation efficiency as hybrid or triple-combined power generation systems. In this study, fuel gas composition is systematically investigated by thermochemical equilibrium calculations on the anode side of SOFCs, pressurized up to 30 bar over a wide temperature range, up to 1000 °C. Since conventional hydrogen-containing fuel gas consists mainly of carbon, hydrogen, and oxygen, high-pressure C-H-O equilibrium diagrams are numerically obtained. It is revealed that the carbon deposition region contracts in the hydrogen-rich area and expands in the oxygen-rich area with increasing total pressure. The molar fraction of each gas component, described in such C-H-O diagrams, also depends on the total pressure. The theoretical open circuit voltage (OCV) increases by pressurization. The effect of nitrogen in high-pressure SOFC fuels is also considered, which is important especially for air-blown coal gas. The minimum amount of H2O, O2, and CO2 required to prevent carbon deposition in steam reforming, partial oxidation, and CO2 (dry) reforming, respectively, is also derived up to 30 bar. The high-pressure C-H-O diagrams are also applicable to various high-temperature/high-pressure energy systems such as solid oxide electrolyzer cells (SOECs) and reversible fuel cells.. |
| 50. | M. Okumura, Z. Noda, J. Matsuda, Y. Tachikawa, M. Nishihara, S. M. Lyth, A. Hayashi, K. Sasaki, Correlating Cathode Microstructure with PEFC Performance Using FIB-SEM and TEM, Journal of The Electrochemical Society, 10.1149/2.0581709jes, 164, 9, F928-F934, 2017.07, [URL]. |
| 51. | Takaaki Somekawa, Yoshio Matsuzaki, Mariko Sugahara, Yuya Tachikawa, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Physicochemical properties of Ba(Zr,Ce)O3-Δ-based proton-conducting electrolytes for solid oxide fuel cells in terms of chemical stability and electrochemical performance, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2017.04.267, 42, 26, 16722-16730, 2017.06, [URL], To enhance the power generation efficiency of solid oxide fuel cells (SOFCs), the use of proton-conducting solid solutions of doped BaCeO3 and doped BaZrO3, with formulas of the Ba(Zr0.1Ce0.7Y0.1X0.1)O3-δ (X = Ga, Sc, In, Yb, Gd), was investigated as SOFCs electrolyte materials with respect to both chemical stability and electrical conductivity. Regarding chemical stability, the weight changes of each material were measured under a CO2 atmosphere in a temperature range of 1200 °C–600 °C. Higher chemical stability was observed for dopant ions with smaller radii. Regarding conductivity, the dependences of the total conductivities on the oxygen partial pressure and temperature were measured in the temperature range of 600 °C–900 °C. In each material, the total conductivity was proportional to the oxygen partial pressure to the 1/4 power at high oxygen partial pressures, as previously observed for accepter-doped proton-conducting perovskite-type oxides. The derived conductivities for each type of charge carrier showed that the hole conductivity increased with the ionic conductivity. Based on the measured data, the leakage current densities were calculated for SOFCs with each of the investigated electrolyte materials and an area-specific resistance of 0.383 Ωcm2. BZCYSc showed the minimum leakage current density, with a value of 3.7% of the external current density at 600 °C. Therefore, this study indicates that BZCYSc is the most desirable among the materials investigated for use as SOFCs electrolyte. However, for BZCYSc to be used as SOFCs electrolyte material, a protective layer is needed to ensure its chemical stability.. |
| 52. | S. Futamura, Y. Tachikawa, J. Matsuda, S. M. Lyth, Y. Shiratori, S. Taniguchi, K. Sasaki, Alternative Ni-Impregnated Mixed Ionic-Electronic Conducting Anode for SOFC Operation at High Fuel Utilization, Journal of The Electrochemical Society, 10.1149/2.0071710jes, 164, 10, F3055-F3063, 2017.06, [URL]. |
| 53. | Takaaki Somekawa, Yoshio Matsuzaki, Mariko Sugahara, Yuya Tachikawa, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Physicochemical properties of Ba(Zr,Ce)O |
| 54. | S. Futamura, Yuya Tachikawa, Junko Matsuda, Stephen Matthew Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Alternative SOFC anode materials with ion- and electron-conducting backbones for higher fuel utilization, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017 ECS Transactions, 10.1149/07801.1179ecst, 78, 1179-1187, 2017.05, [URL], Redox-stable anodes are developed for zirconia-based electrolyte-supported solid oxide fuel cells (SOFCs) operating at high fuel utilization, as an alternative to the Ni yttrium-stabilized-zirconia (YSZ) cermet. Gadolinium-doped ceria (GDC, Ce0.9Gd0.1O2) is utilized as a mixed ionic electronic conductor (MIEC), and combined with lanthanum-doped strontium titanate (LST, Sr0.9La0.1TiO3) as an electronic conductor. Catalyst nanoparticles (either Ni or Rh) are incorporated via impregnation. The electrochemical characteristics of SOFC single cells using these anodes are characterized in humidified H2 at 800°C. The stability against redox cycling and under high fuel utilization is analyzed and discussed.. |
| 55. | Y. Kikuchi, Junko Matsuda, Yuya Tachikawa, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Degradation of SOFCs by various impurities Impedance spectroscopy and microstructural analysis, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017 ECS Transactions, 10.1149/07801.1253ecst, 78, 1253-1260, 2017.05, [URL], SOFC can use various kinds of fuels besides hydrogen, including city gas, coal gas, digestion gas, and biogas. On the other hand, it is known that such practical fuels contain various fuel impurities such as sulfur, phosphorus, and siloxane, affecting fuel cell performance and durability. Here, a case study for siloxane as a model SOFC fuel impurity is made to understand the impurity poisoning phenomena through both electrochemical and microstructural analysis to analyze poisoning processes, especially by applying the DRT (Distribution of Relaxation Times) analysis.. |
| 56. | Yuya Tachikawa, Y. Matsuzaki, Y. Kawabata, M. Sugahara, T. Somekawa, Shunsuke Taniguchi, Kazunari Sasaki, Effect of carbon-neutral fuel fed solid oxide fuel cell system on CO2 emission reduction, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017 ECS Transactions, 10.1149/07801.2563ecst, 78, 2563-2568, 2017.05, [URL], Carbon-neutral fuel fed solid oxide fuel cell (SOFC) system can achieve highly efficient power generation without any greenhouse gas emissions. In this paper, the influence of supplied fuel species on the SOFC performance has been evaluated by heat and mass balance analysis. The electrical efficiency of carbon-neutral fuel fed SOFCs is quantified and compared with that of conventional fuel supplied SOFCs. Then, the effect of electrical efficiency increase on CO2 emission is also quantified. Furthermore, the effect of proton-conducting ceramic materials application as an electrolyte is also discussed to evaluate the influence on electrical efficiency. The carbon-neutral fuel fed protonic ceramic fuel cells (PCFCs) had an advantage to enhance their electrical efficiencies compared with the same fuels fed typical SOFCs. Due to the increase in electrical efficiency, the CO2 emission reduction clearly appeared as CO2 emission factor.. |
| 57. | K. Takino, Yuya Tachikawa, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Effect of exchange current density on current distribution at planar-type SOFC anodes, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017 ECS Transactions, 10.1149/07801.1523ecst, 78, 1523-1531, 2017.05, [URL], Cell stack structure of solid oxide fuel cells (SOFCs) affects their performance; its optimization is important to realize highly efficient SOFCs. In this study, we focus on the numerical simulation method combined with experimentally obtained exchange current density. Deriving the anode exchange current density for fully pre-reformed methane-fueled SOFCs, the effect on the current distribution is evaluated. Current distribution was calculated using variable anode exchange current density after taking into account the pressures of CO and CO2.. |
| 58. | A. Muramoto, Y. Kikuchi, Yuya Tachikawa, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Fuel composition in pressurized SOFCs, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017 ECS Transactions, 10.1149/07801.2497ecst, 78, 2497-2504, 2017.05, [URL], Pressurized SOFCs operate at high temperatures and generate electricity by using various fuel species. SOFCs can be applied for large-scale power generation combined with gas and steam turbine(s) under high pressure. In this study, fuel gas composition is systematically considered by thermochemical calculations on the anode side of the SOFCs pressurized up to 30 bar in a wide temperature range up to 1000oC. In general, fuel gas consists mainly of carbon, hydrogen, and oxygen, so that the C-H-O equilibrium diagrams have been calculated for different cases. It is revealed that carbon deposition region contracts in the hydrogenrich area and expands in the oxygen-rich area with increasing the total pressure. The molar fraction of each gas component also depends also on the total pressure.. |
| 59. | Y. Wakita, Yuya Tachikawa, Hironori Nakajima, Kohei Ito, Glass shape change during firing for improving the seal of planar SOFCs, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017 ECS Transactions, 10.1149/07801.1731ecst, 78, 1731-1737, 2017.05, [URL], Secure sealing is vital for planar type SOFCs to avoid the performance degradation and achieve long-term stable operation. Here we focus on the sheet type glass sealing which is produced by tape-casting method. High wettability of the glass is essential to avoid the stress concentration because low wettability increases the contact angle of the glass and makes the notch at the edge of glass sealing interface. We have evaluated the effect of temperature rising rate on the wettability of the sealing glass and the edge shape of it using the visualization test system. High temperature rising rate led to small contact angle of the sealing glass in some cases and can mitigate the stress concentration.. |
| 60. | Y. Kawabata, Yuya Tachikawa, Shunsuke Taniguchi, Y. Matsuzaki, Kazunari Sasaki, New applications of SOFC-MGT hybrid power generation system for low-carbon society, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017 ECS Transactions, 10.1149/07801.0197ecst, 78, 197-208, 2017.05, [URL], Solid oxide fuel cell (SOFC) is one of the efficient power generation technologies which have high applicability to use various kinds of fuels including city gas, coal, and biomass. As SOFC can transport oxygen ions from the cathode side to the anode side, the exhaust anode off-gas contains CO2 and H2O only, so that CO2 can be captured simply by cooling the exhaust gas. This means that we can, in principle, develop highly-efficient CO2-capture SOFC power generation system by integrating efficient oxygen production system and exhaust gas cooling system. In this paper, we propose CO2-capture SOFC-Micro Gas Turbine (MGT) hybrid power generation system as a new application towards low-carbon society. Results of feasibility study and performance analysis indicated great potential and high applicability of efficient CO2-capture power generation solutions.. |
| 61. | Y. Matsuzaki, Yuya Tachikawa, T. Somekawa, K. Sato, Y. Kawabata, M. Sugahara, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Relationship between electrochemical properties and electrolyte partial conductivities of proton-conducting ceramic fuel cells, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017 ECS Transactions, 10.1149/07801.0441ecst, 78, 441-450, 2017.05, [URL], The electrochemical properties of the proton-conducting ceramic fuel cells (PCFCs) with BaZr0.1Ce0.7Y0.1X0.1O3-δ (BZCYX, X = Ga, Sc, In, Yb, or Gd) electrolytes have been investigated. BZCYX materials were found to have various partial conductivities of charge-carriers such as ion, hole, and electron. The electrochemical properties exhibited strong dependences on operation conditions. When ASR and external current density were fixed at 0.4 Ω cm2 and 0.25 A cm-2, respectively, the electrical efficiency, η(X), was found to have the following sequential order: η(Sc) > η(In) > η(Ga) > η(Yb) > η(Gd). On the other hand, when ASR was not fixed but the thickness of the electrolyte was fixed at 25 μm, large variations appeared in the leakage current of the cells with the BZCYX electrolytes. The sequential order of the electrical efficiency with the fixed thickness was different from that with the fixed ASR as described in the above inequality expression, and depends on the operating temperature. The ratios of the leakage current with X = Yb or Gd were higher than those with X = Ga, Sc, or In. These high ratios were found to cause the serious drop in the electrical efficiency at an external current density of 0.25 A cm-2. We have successfully found out the candidates for the X element in BZCYX, by which high-efficient power generation would be expected.. |
| 62. | S. Futamura, Y. Tachikawa, J. Matsuda, S. M. Lyth, Y. Shiratori, S. Taniguchi, K. Sasaki, Alternative SOFC anode materials with ion- and electron-conducting backbones for higher fuel utilization, ECS Transactions, 10.1149/07801.1179ecst, 78, 1, 1179-1187, 2017.05, Redox-stable anodes are developed for zirconia-based electrolyte-supported solid oxide fuel cells (SOFCs) operating at high fuel utilization, as an alternative to the Ni yttrium-stabilized-zirconia (YSZ) cermet. Gadolinium-doped ceria (GDC, Ce0.9Gd0.1O2) is utilized as a mixed ionic electronic conductor (MIEC), and combined with lanthanum-doped strontium titanate (LST, Sr0.9La0.1TiO3) as an electronic conductor. Catalyst nanoparticles (either Ni or Rh) are incorporated via impregnation. The electrochemical characteristics of SOFC single cells using these anodes are characterized in humidified H2 at 800°C. The stability against redox cycling and under high fuel utilization is analyzed and discussed.. |
| 63. | Y. Kikuchi, J. Matsuda, Y. Tachikawa, Y. Shiratori, S. Taniguchi, K. Sasaki, Degradation of SOFCs by various impurities: Impedance spectroscopy and microstructural analysis, ECS Transactions, 10.1149/07801.1253ecst, 78, 1, 1253-1260, 2017.05, SOFC can use various kinds of fuels besides hydrogen, including city gas, coal gas, digestion gas, and biogas. On the other hand, it is known that such practical fuels contain various fuel impurities such as sulfur, phosphorus, and siloxane, affecting fuel cell performance and durability. Here, a case study for siloxane as a model SOFC fuel impurity is made to understand the impurity poisoning phenomena through both electrochemical and microstructural analysis to analyze poisoning processes, especially by applying the DRT (Distribution of Relaxation Times) analysis.. |
| 64. | Y. Tachikawa, Y. Matsuzaki, Y. Kawabata, M. Sugahara, T. Somekawa, S. Taniguchi, K. Sasaki, Effect of carbon-neutral fuel fed solid oxide fuel cell system on CO |
| 65. | K. Takino, Y. Tachikawa, Y. Shiratori, S. Taniguchi, K. Sasaki, Effect of exchange current density on current distribution at planar-type SOFC anodes, ECS Transactions, 10.1149/07801.1523ecst, 78, 1, 1523-1531, 2017.05, Cell stack structure of solid oxide fuel cells (SOFCs) affects their performance; its optimization is important to realize highly efficient SOFCs. In this study, we focus on the numerical simulation method combined with experimentally obtained exchange current density. Deriving the anode exchange current density for fully pre-reformed methane-fueled SOFCs, the effect on the current distribution is evaluated. Current distribution was calculated using variable anode exchange current density after taking into account the pressures of CO and CO2.. |
| 66. | A. Muramoto, Y. Kikuchi, Y. Tachikawa, Y. Shiratori, S. Taniguchi, K. Sasaki, Fuel composition in pressurized SOFCs, ECS Transactions, 10.1149/07801.2497ecst, 78, 1, 2497-2504, 2017.05, Pressurized SOFCs operate at high temperatures and generate electricity by using various fuel species. SOFCs can be applied for large-scale power generation combined with gas and steam turbine(s) under high pressure. In this study, fuel gas composition is systematically considered by thermochemical calculations on the anode side of the SOFCs pressurized up to 30 bar in a wide temperature range up to 1000oC. In general, fuel gas consists mainly of carbon, hydrogen, and oxygen, so that the C-H-O equilibrium diagrams have been calculated for different cases. It is revealed that carbon deposition region contracts in the hydrogenrich area and expands in the oxygen-rich area with increasing the total pressure. The molar fraction of each gas component also depends also on the total pressure.. |
| 67. | Y. Wakita, Y. Tachikawa, H. Nakajima, K. Ito, Glass shape change during firing for improving the seal of planar SOFCs, ECS Transactions, 10.1149/07801.1731ecst, 78, 1, 1731-1737, 2017.05, Secure sealing is vital for planar type SOFCs to avoid the performance degradation and achieve long-term stable operation. Here we focus on the sheet type glass sealing which is produced by tape-casting method. High wettability of the glass is essential to avoid the stress concentration because low wettability increases the contact angle of the glass and makes the notch at the edge of glass sealing interface. We have evaluated the effect of temperature rising rate on the wettability of the sealing glass and the edge shape of it using the visualization test system. High temperature rising rate led to small contact angle of the sealing glass in some cases and can mitigate the stress concentration.. |
| 68. | Y. Kawabata, Y. Tachikawa, S. Taniguchi, Y. Matsuzaki, K. Sasaki, New applications of SOFC-MGT hybrid power generation system for low-carbon society, ECS Transactions, 10.1149/07801.0197ecst, 78, 1, 197-208, 2017.05, Solid oxide fuel cell (SOFC) is one of the efficient power generation technologies which have high applicability to use various kinds of fuels including city gas, coal, and biomass. As SOFC can transport oxygen ions from the cathode side to the anode side, the exhaust anode off-gas contains CO2 and H2O only, so that CO2 can be captured simply by cooling the exhaust gas. This means that we can, in principle, develop highly-efficient CO2-capture SOFC power generation system by integrating efficient oxygen production system and exhaust gas cooling system. In this paper, we propose CO2-capture SOFC-Micro Gas Turbine (MGT) hybrid power generation system as a new application towards low-carbon society. Results of feasibility study and performance analysis indicated great potential and high applicability of efficient CO2-capture power generation solutions.. |
| 69. | Y. Matsuzaki, Y. Tachikawa, T. Somekawa, K. Sato, Y. Kawabata, M. Sugahara, H. Matsumoto, S. Taniguchi, K. Sasaki, Relationship between electrochemical properties and electrolyte partial conductivities of proton-conducting ceramic fuel cells, ECS Transactions, 10.1149/07801.0441ecst, 78, 1, 441-450, 2017.05, The electrochemical properties of the proton-conducting ceramic fuel cells (PCFCs) with BaZr0.1Ce0.7Y0.1X0.1O3-δ (BZCYX, X = Ga, Sc, In, Yb, or Gd) electrolytes have been investigated. BZCYX materials were found to have various partial conductivities of charge-carriers such as ion, hole, and electron. The electrochemical properties exhibited strong dependences on operation conditions. When ASR and external current density were fixed at 0.4 Ω cm2 and 0.25 A cm-2, respectively, the electrical efficiency, η(X), was found to have the following sequential order: η(Sc) > η(In) > η(Ga) > η(Yb) > η(Gd). On the other hand, when ASR was not fixed but the thickness of the electrolyte was fixed at 25 μm, large variations appeared in the leakage current of the cells with the BZCYX electrolytes. The sequential order of the electrical efficiency with the fixed thickness was different from that with the fixed ASR as described in the above inequality expression, and depends on the operating temperature. The ratios of the leakage current with X = Yb or Gd were higher than those with X = Ga, Sc, or In. These high ratios were found to cause the serious drop in the electrical efficiency at an external current density of 0.25 A cm-2. We have successfully found out the candidates for the X element in BZCYX, by which high-efficient power generation would be expected.. |
| 70. | T. Somekawa, Y. Matsuzaki, Yuya Tachikawa, Shunsuke Taniguchi, Kazunari Sasaki, Characterization of yttrium-doped ceria with various yttrium concentrations as cathode interlayers of SOFCs, Ionics, 10.1007/s11581-016-1816-9, 23, 1, 95-103, 2017.01, [URL], This study focuses on enhancing the efficiency of solid oxide fuel cells (SOFCs) by modulating the thickness of the highly resistive solid solution layer of (Ce,Zr)O2 formed between the yttria-stabilized zirconia (YSZ) electrolyte and the CeO2-based interlayer on the cathode side. The effects of the concentration of dopant in CeO2 on the thickness of the solid solution were analyzed. Yttrium-doped CeO2 (YDC) interlayers were studied, with dopant concentrations in the range of 5–40 mol%. The results revealed that the thickness of the solid solution decreased with increasing dopant concentration up to 20 mol% and then saturated at higher dopant concentrations. In addition, the electrical conductivities of yttrium-doped ceria (YDC) and the solid solution of YSZ and YDC were measured. YDC with a dopant concentration of 20 mol% exhibited the highest conductivity. The conductivities of the YSZ/YDC solid solution decreased compared to those of YDC and YSZ for each dopant concentration, and the extent of the reductions was approximately the same for all dopant concentrations. These results indicate that a dopant concentration of 20 mol% is optimal to minimize the internal resistance of SOFCs when YDC is used as the interlayer material.. |
| 71. | T. Somekawa, Y. Matsuzaki, Y. Tachikawa, S. Taniguchi, K. Sasaki, Characterization of yttrium-doped ceria with various yttrium concentrations as cathode interlayers of SOFCs, Ionics, 10.1007/s11581-016-1816-9, 23, 1, 95-103, 2017.01, This study focuses on enhancing the efficiency of solid oxide fuel cells (SOFCs) by modulating the thickness of the highly resistive solid solution layer of (Ce,Zr)O2 formed between the yttria-stabilized zirconia (YSZ) electrolyte and the CeO2-based interlayer on the cathode side. The effects of the concentration of dopant in CeO2 on the thickness of the solid solution were analyzed. Yttrium-doped CeO2 (YDC) interlayers were studied, with dopant concentrations in the range of 5–40 mol%. The results revealed that the thickness of the solid solution decreased with increasing dopant concentration up to 20 mol% and then saturated at higher dopant concentrations. In addition, the electrical conductivities of yttrium-doped ceria (YDC) and the solid solution of YSZ and YDC were measured. YDC with a dopant concentration of 20 mol% exhibited the highest conductivity. The conductivities of the YSZ/YDC solid solution decreased compared to those of YDC and YSZ for each dopant concentration, and the extent of the reductions was approximately the same for all dopant concentrations. These results indicate that a dopant concentration of 20 mol% is optimal to minimize the internal resistance of SOFCs when YDC is used as the interlayer material.. |
| 72. | Takaaki Somekawa, Yoshio Matsuzaki, Yuya Tachikawa, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Physicochemical properties of proton-conductive Ba(Zr0.1Ce0.7Y0.1Yb0.1)O3−δ solid electrolyte in terms of electrochemical performance of solid oxide fuel cells, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2016.07.265, 41, 39, 17539-17547, 2016.10, [URL], Previously, most studies of proton-conductive electrolytes for SOFCs were conducted to achieve lower-temperature operation. In this study, we investigate a proton-conductive electrolyte to realize high-efficiency SOFCs. To this end, the dependencies of the total conductivity of Ba(Zr0.1Ce0.7Y0.1Yb0.1)O3−δ on the oxygen partial pressure and temperature under wet and dry conditions were measured. Based on the measurement data, we analyzed the ratio of ionic current density to electronic current density in the temperature range of 550–900 °C. Assuming that the area-specific resistance of the electrolyte and the external current density were 0.383 Ω cm2 and 0.25 A cm−2, respectively, the leakage current densities caused by the minority carriers were calculated to be 5.4% and 9.7% of the external current density at 550 °C and 600 °C, respectively. This study developed a method to evaluate proton-conductive electrolyte materials and established guidelines for the development of new materials for high-efficiency SOFCs.. |
| 73. | Takaaki Somekawa, Yoshio Matsuzaki, Yuya Tachikawa, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Physicochemical properties of proton-conductive Ba(Zr |
| 74. | Ryohei Torii, Yuya Tachikawa, Kazunari Sasaki, Kohei Ito, Anode gas recirculation for improving the performance and cost of a 5-kW solid oxide fuel cell system, Journal of Power Sources, 10.1016/j.jpowsour.2016.06.045, 325, 229-237, 2016.09, [URL], Solid oxide fuel cells (SOFCs) have the potential to efficiently convert chemical energy into electricity and heat and are expected to be implemented in stationary combined heat and power (CHP) systems. This paper presents the heat balance analysis for a 5-kW medium-sized integrated SOFC system and the evaluation of the effect of anode gas recirculation on the system performance. The risk of carbon deposition on an SOFC anode due to anode gas recirculation is also assessed using the C-H-O diagram obtained from thermodynamic equilibrium calculations. These results suggest that a higher recirculation ratio increases net fuel utilization and improves the electrical efficiency of the SOFC system. Furthermore, cost simulation of the SOFC system and comparison with the cost of electricity supply by a power grid indicates that the capital cost is sufficiently low to popularize the SOFC system in terms of the total cost over one decade.. |
| 75. | Ryohei Torii, Yuya Tachikawa, Kazunari Sasaki, Kohei Ito, Anode gas recirculation for improving the performance and cost of a 5-kW solid oxide fuel cell system, Journal of Power Sources, 10.1016/j.jpowsour.2016.06.045, 325, 229-237, 2016.09, Solid oxide fuel cells (SOFCs) have the potential to efficiently convert chemical energy into electricity and heat and are expected to be implemented in stationary combined heat and power (CHP) systems. This paper presents the heat balance analysis for a 5-kW medium-sized integrated SOFC system and the evaluation of the effect of anode gas recirculation on the system performance. The risk of carbon deposition on an SOFC anode due to anode gas recirculation is also assessed using the C-H-O diagram obtained from thermodynamic equilibrium calculations. These results suggest that a higher recirculation ratio increases net fuel utilization and improves the electrical efficiency of the SOFC system. Furthermore, cost simulation of the SOFC system and comparison with the cost of electricity supply by a power grid indicates that the capital cost is sufficiently low to popularize the SOFC system in terms of the total cost over one decade.. |
| 76. | Hiroki Anai, Junko Matsuda, Zyiyun Noda, Yuya Tachikawa, Akari Hayashi, Kohei Ito, Kazunari Sasaki, Preparation of Iridium-SnO2/VGCF Electrocatalysts for Water Electrolysis, ECS Transactions, 10.1149/07514.1129ecst, 75, 14, 1129-1135, 2016.08, Novel iridium-based electrocatalysts supported on SnO2/Vapor-Grown Carbon Fiber (VGCF) have been developed and characterized by FESEM, STEM, and XPS. The membrane electrode assembly (MEA) made with the IrO2/Sn0.98Nb0.02O2/VGCF electrocatalyst exhibited a decrease in overvoltage especially under the low current density compared to the MEA made with conventional IrO2/Ti electrocatalyst. Iridium-based SnO2/VGCF can be a good candidate for anode catalysts of water electrolysis cells.. |
| 77. | Yoshio Matsuzaki, Yuya Tachikawa, Takaaki Somekawa, Kouki Sato, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Potential for critically-high electrical efficiency of multi-stage SOFCs with proton-conducting solid electrolyte, Proceedings of 12th European SOFC & SOE Forum (EFCF2016), A1208, 2016.07. |
| 78. | Yuya Tachikawa, Yoshio Matsuzaki, Takaaki Somekawa, Shunsuke Taniguchi, Kazunari Sasaki, Multi-stage highly-efficient SOFC system using proton and oxide-ion conducting electrolyte, Proceedings of 12th European SOFC & SOE Forum (EFCF2016), B1112, 2016.07. |
| 79. | Y. Matsuzaki, Yuya Tachikawa, T. Hatae, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Symbolic Analysis of Multi-Stage Electrochemical Oxidation for Enhancement of Electric Efficiency of SOFCs, Ceramic Transactions, 10.1002/9781119234531.ch4, 255, 41-46, 2016.05, [URL], SOFCs have the solid-state ceramic construction and operate at high-temperatures, with flexibility in fuel choice, high efficiency, stability, and reliability. The most attractive characteristics of SOFCs should be high fuel-to-electricity conversion efficiencies of as high as 50 to 60 percent LHV. For further improving the electrical efficiencies, preceding studies on multi-stage electrochemical oxidation with SOFCs have been reported. However, there are many parameters for the multi-stage oxidation, and effects of the parameters on the efficiency remains to be identified. We have investigated the multi-stage oxidation by using a symbolic analysis method. In the case of n-stage electrochemical oxidation, the fuel utilization ratio in the individual stage was found to decrease with increasing the n value at a fixed fuel utilization ratio of an entire system, resulting in the enhancement of robustness against the operation at a high fuel utilization ratio of the entire system as well as against a gas-leakage.. |
| 80. | Y. Matsuzaki, Y. Tachikawa, T. Hatae, H. Matsumoto, S. Taniguchi, K. Sasaki, Symbolic Analysis of Multi-Stage Electrochemical Oxidation for Enhancement of Electric Efficiency of SOFCs, Ceramic for Energy Conversion, Storage, and Distribution Systems, 10.1002/9781119234531.ch4, 255, 41-46, 2016.05, SOFCs have the solid-state ceramic construction and operate at high-temperatures, with flexibility in fuel choice, high efficiency, stability, and reliability. The most attractive characteristics of SOFCs should be high fuel-to-electricity conversion efficiencies of as high as 50 to 60 percent LHV. For further improving the electrical efficiencies, preceding studies on multi-stage electrochemical oxidation with SOFCs have been reported. However, there are many parameters for the multi-stage oxidation, and effects of the parameters on the efficiency remains to be identified. We have investigated the multi-stage oxidation by using a symbolic analysis method. In the case of n-stage electrochemical oxidation, the fuel utilization ratio in the individual stage was found to decrease with increasing the n value at a fixed fuel utilization ratio of an entire system, resulting in the enhancement of robustness against the operation at a high fuel utilization ratio of the entire system as well as against a gas-leakage.. |
| 81. | H. Anai, Junko Matsuda, Z. Noda, Yuya Tachikawa, Akari Hayashi, Kohei Ito, Kazunari Sasaki, Preparation of iridium/SnO2/VGCF electrocatalysts for water electrolysis, Symposium on Polymer Electrolyte Fuel Cells 16, PEFC 2016 - PRiME 2016/230th ECS Meeting Polymer Electrolyte Fuel Cells 16, PEFC 16, 10.1149/07514.1129ecst, 75, 1129-1135, 2016, [URL], Novel iridium-basedelectrocatalysts supported on SnO2/Vapor-Grown Carbon Fiber (VGCF)havebeendevelopedand characterized by FESEM, STEM, and XPS.The membraneelectrode assembly (MEA)made withtheIrO2/Sn0.98Nb0.02O2/VGCFelectrocatalystexhibited a decrease inovervoltageespeciallyunderthelow current densitycompared to the MEA made withconventionalIrO2/Ti electrocatalyst.Iridium-based SnO2/VGCF can bea good candidate for anode catalystsof water electrolysis cells.. |
| 82. | Yuya Tachikawa, 松崎 良雄, Kazunari Sasaki, 新規材料とシステム開発の融合による革新的新規高性能SOFCの創出, Fine ceramics report, 34, 1, 27-31, 2016. |
| 83. | 松崎 良雄, Yuya Tachikawa, 染川 貴亮, 佐藤 洸基, Hiroshige Matsumoto, 谷口 俊介, Kazunari Sasaki, 電気化学的多段酸化を用いた固体酸化物形燃料電池(SOFC)による革新的高効率発電の可能性, エネルギーと動力, 66, 286, 50-57, 2016. |
| 84. | 松崎 良雄, Yuya Tachikawa, 染川 貴亮, 革新的高効率SOFCに向けた取り組み, 燃料電池, 15, 3, 63-68, 2016. |
| 85. | Yuya Tachikawa, Conceptual design for critically-high power generation efficiency by using multi-stage solid oxide fuel cells (SOFCs) or proton-conducting ceramic fuel cells (PCFCs), Science Proceedings, 10.14800/sp.1272, 2016, [URL]. |
| 86. | T. Somekawa, Y. Matsuzaki, Yuya Tachikawa, Shunsuke Taniguchi, Kazunari Sasaki, Study of the solid-state reaction at the interface between lanthanoid-doped ceria and yttria-stabilized zirconia for solid-oxide fuel cell applications, Solid State Ionics, 10.1016/j.ssi.2015.09.005, 282, 1-6, 2015.12, [URL], To develop more highly-efficient SOFCs, we have investigated the thickness of highly resistive layer which consist of solid solutions of CeO2-ZrO2 system generally observed between YSZ electrolyte and cathode-interlayer made of doped CeO2. In terms of the effect of the dopant in the CeO2-based interlayer materials on the thickness of the solid solution, the use of YDC or LDC for the interlayer results in a thinner solid solution compared to that obtained when a GDC interlayer was used. When adapted into SOFCs, I-V tests at 800 °C indicated that the cell with a YDC interlayer exhibited substantially better performance than the cell with a GDC interlayer.. |
| 87. | T. Somekawa, Y. Matsuzaki, Y. Tachikawa, S. Taniguchi, K. Sasaki, Study of the solid-state reaction at the interface between lanthanoid-doped ceria and yttria-stabilized zirconia for solid-oxide fuel cell applications, Solid State Ionics, 10.1016/j.ssi.2015.09.005, 282, 1-6, 2015.12, To develop more highly-efficient SOFCs, we have investigated the thickness of highly resistive layer which consist of solid solutions of CeO2-ZrO2 system generally observed between YSZ electrolyte and cathode-interlayer made of doped CeO2. In terms of the effect of the dopant in the CeO2-based interlayer materials on the thickness of the solid solution, the use of YDC or LDC for the interlayer results in a thinner solid solution compared to that obtained when a GDC interlayer was used. When adapted into SOFCs, I-V tests at 800 °C indicated that the cell with a YDC interlayer exhibited substantially better performance than the cell with a GDC interlayer.. |
| 88. | Makito Okumura, Yohei Nagamatsu, Zhiyun Noda, Yuya Tachikawa, Takeshi Daio, Akari Hayashi, Kazunari Sasaki, A FIB-SEM Study on Correlations between PEFC Electrocatalyst Microstructure and Cell Performance, ECS Transactions, 10.1149/06917.0709ecst, 69, 17, 709-714, 2015.09, PEFC electrocatalyst microstructure strongly influences cell performance. In this study, Nafion ionomer content in the cathode electrocatalyst layer is systematically varied to modify the electrocatalyst microstructure. Current-voltage characteristics of the membrane-electrode-assemblies are measured and then the electrocatalyst microstructure is observed by the focused-ion-beam coupled scanning electron microscopy (FIB-SEM) to examine the correlations between the 3D microstructure and the cell performance. Although technical limitation was found for FIB-SEM analysis, certain correlations were also established.. |
| 89. | Y. Tachikawa, J. Sugimoto, M. Takada, T. Kawabata, S. M. Lyth, Y. Shiratori, K. Sasaki, In Operando Visualization of SOFC Electrodes by Thermography and Visible Light Imaging, ECS Electrochemistry Letters, 10.1149/2.0031511eel, 4, 11, F61-F64, 2015.08, [URL]. |
| 90. | Yoshio Matsuzaki, Yuya Tachikawa, Takaaki Somekawa, Toru Hatae, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Effect of proton-conduction in electrolyte on electric efficiency of multi-stage solid oxide fuel cells, Scientific Reports, 10.1038/srep12640, 5, 2015.07, [URL], Solid oxide fuel cells (SOFCs) are promising electrochemical devices that enable the highest fuel-to-electricity conversion efficiencies under high operating temperatures. The concept of multi-stage electrochemical oxidation using SOFCs has been proposed and studied over the past several decades for further improving the electrical efficiency. However, the improvement is limited by fuel dilution downstream of the fuel flow. Therefore, evolved technologies are required to achieve considerably higher electrical efficiencies. Here we present an innovative concept for a critically-high fuel-to-electricity conversion efficiency of up to 85% based on the lower heating value (LHV), in which a high-temperature multi-stage electrochemical oxidation is combined with a proton-conducting solid electrolyte. Switching a solid electrolyte material from a conventional oxide-ion conducting material to a proton-conducting material under the high-temperature multi-stage electrochemical oxidation mechanism has proven to be highly advantageous for the electrical efficiency. The DC efficiency of 85% (LHV) corresponds to a net AC efficiency of approximately 76% (LHV), where the net AC efficiency refers to the transmission-end AC efficiency. This evolved concept will yield a considerably higher efficiency with a much smaller generation capacity than the state-of-the-art several tens-of-MW-class most advanced combined cycle (MACC).. |
| 91. | Yoshio Matsuzaki, Yuya Tachikawa, Takaaki Somekawa, Toru Hatae, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, Effect of proton-conduction in electrolyte on electric efficiency of multi-stage solid oxide fuel cells, Scientific Reports, 10.1038/srep12640, 5, 2015.07, Solid oxide fuel cells (SOFCs) are promising electrochemical devices that enable the highest fuel-to-electricity conversion efficiencies under high operating temperatures. The concept of multi-stage electrochemical oxidation using SOFCs has been proposed and studied over the past several decades for further improving the electrical efficiency. However, the improvement is limited by fuel dilution downstream of the fuel flow. Therefore, evolved technologies are required to achieve considerably higher electrical efficiencies. Here we present an innovative concept for a critically-high fuel-to-electricity conversion efficiency of up to 85% based on the lower heating value (LHV), in which a high-temperature multi-stage electrochemical oxidation is combined with a proton-conducting solid electrolyte. Switching a solid electrolyte material from a conventional oxide-ion conducting material to a proton-conducting material under the high-temperature multi-stage electrochemical oxidation mechanism has proven to be highly advantageous for the electrical efficiency. The DC efficiency of 85% (LHV) corresponds to a net AC efficiency of approximately 76% (LHV), where the net AC efficiency refers to the transmission-end AC efficiency. This evolved concept will yield a considerably higher efficiency with a much smaller generation capacity than the state-of-the-art several tens-of-MW-class most advanced combined cycle (MACC).. |
| 92. | Yoshio Matsuzaki, Yuya Tachikawa, Toru Hatae, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, A Parametric Study of SOFC Performances with Multi-Stage Electrochemical Oxidation for Enhancement of Electric Efficiency, ECS Transactions, 10.1149/06801.1961ecst, 68, 1, 1961-1968, 2015.06, The solid-state ceramic construction of SOFCs enables high fuel to electricity conversion efficiencies of as high as 50 to 60 percent LHV in high temperature operation, and allows more flexibility in fuel choice. In this study, we have developed a symbolic analysis method to investigate the availability of variable parameters appeared in multi-stage electrochemical oxidation mechanism that is expected to further improve the electric efficiencies of SOFCs. In the flow system of the multi-stage oxidation, the fuel utilization, Uf, at the most downstream stack, UfM, is expressed as a function of number of stacks, n, and total fuel utilization, UfT. When n = 10 and UfT = 85%, UfM is calculated to be 36%, which is much smaller than UfT. Therefore, if the most downstream stack has high robustness against lean fuel gas, UfT could be set to be higher values without serious degradation by using this flow system.. |
| 93. | Tatsuya Kawasaki, Junki Sugimoto, Yuya Tachikawa, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Oxidation-Induced Degradation of SOFC Ni Anodes at High Fuel Utilizations, ECS Transactions, 10.1149/06801.1345ecst, 68, 1, 1345-1352, 2015.06, In the downstream of SOFC systems, higher oxygen partial pressure can cause oxidation-induced Ni anode degradation. In this study, we have investigated cell performance at high fuel utilizations for simulating situations around the system downstream. When the anode voltage was higher than a voltage threshold, the cell performance was stable. On the other hand, it became unstable associated with cell voltage oscillation when anode voltage was around or less than the threshold value. The threshold value was consistent with the anode potential derived from the oxygen partial pressure at the phase boundary at which both Ni and NiO coexist.. |
| 94. | Yuya Tachikawa, Yoshio Matsuzaki, Toru Hatae, Shunsuke Taniguchi, Kazunari Sasaki, Process Analysis for Achieving Highly Enhanced Total Efficiency on Multi-Stage Fuel Supplied SOFC System, ECS Transactions, 10.1149/06801.3107ecst, 68, 1, 3107-3113, 2015.06, A multi-stage fuel supply SOFC system is studied, which has additional fuel supply inlets between each SOFC stack. The anode offgas from the first stack is supplied to the next stack as reformed fuel gas being mixed with additional fresh fuel. In this paper, the effect of the additional fuel flow ratio is evaluated. The electric efficiency and the fuel utilization of the system can be improved in applying multi-stage fuel supply design.. |
| 95. | Kazunari Sasaki, Shunsuke Taniguchi, Yusuke Shiratori, Akari Hayashi, Toshihiro Oshima, Masamichi Nishihara, Yuya Tachikawa, Takeshi Daio, Tsutomu Kawabata, Miki Fujita, Ayumi Zaitsu, Smart Fuel Cell Demonstration Project: A Challenge to Realize SOFC-Powered Campus, ECS Transactions, 10.1149/06801.0171ecst, 68, 1, 171-178, 2015.06, This paper introduces a challenge to realize a fuel-cell-powered campus at Kyushu University where SOFC technology plays a major role. The Smart Fuel Cell Demonstration Project, supported by Cabinet Secretariat/Office of Japan, enables us to install one 250 kW SOFC power generation system, other SOFC units, and the world-first university-owned fuel cell vehicle to which renewable hydrogen gas is supplied from the hydrogen refueling station in this campus using electrolyzers. The experience in this demonstrative project is described along with related efforts to accelerate industry-academia collaborations and fundamental scientific studies using advanced analytical facilities.. |
| 96. | Yuya Tachikawa, Tsutomu Kawabata, Yusuke Shiratori, Kazunari Sasaki, Visualization of SOFC Anode by Dual Imaging Method Using Infrared and Visible Light Cameras, ECS Transactions, 10.1149/06801.1115ecst, 68, 1, 1115-1120, 2015.06, Thermography imaging can be applied for the surface of an SOFC electrode to evaluate the spatial distribution of reforming and electrode reactions. For getting a correct temperature distribution by thermography, emissivity change on the object surface caused by chemical reactions or material coverage must be precisely evaluated. In-situ observation using both infrared and visible light dual cameras enables us to obtain precise emissivity change and thus temperature distribution, because the influence of emissivity change can be corrected by the visible light imaging technique. In this study, this imaging method is applied for an anode material which was exposed to a fuel flow causing coke formation, and the information on the carbon distribution was successfully separated on the anode surface to obtain the true temperature distribution.. |
| 97. | T. Kawasaki, J. Sugimoto, Yuya Tachikawa, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Oxidation-induced degradation of SOFC Ni anodes at high fuel utilizations, 14th International Symposium on Solid Oxide Fuel Cells, SOFC 2015; held as part of the Electrochemical Society, ECS Conference on Electrochemical Energy Conversion and Storage Solid Oxide Fuel Cells 14, SOFC 2015, 10.1149/06801.1345ecst, 68, 1345-1352, 2015.01, [URL], In the downstream of SOFC systems, higher oxygen partial pressure can cause oxidation-induced Ni anode degradation. In this study, we have investigated cell performance at high fuel utilizations for simulating situations around the system downstream. When the anode voltage was higher than a voltage threshold, the cell performance was stable. On the other hand, it became unstable associated with cell voltage oscillation when anode voltage was around or less than the threshold value. The threshold value was consistent with the anode potential derived from the oxygen partial pressure at the phase boundary at which both Ni and NiO coexist.. |
| 98. | Makito Okumura, Yohei Nagamatsu, Zhiyun Noda, Yuya Tachikawa, Takeshi Daio, Akari Hayashi, Kazunari Sasaki, A FIB-SEM study on correlations between PEFC electrocatalyst microstructure and cell performance, Symposium on Polymer Electrolyte Fuel Cells 15, PEFC 2015 - 228th ECS Meeting Polymer Electrolyte Fuel Cells 15, PEFC 15, 10.1149/06917.0709ecst, 69, 709-714, 2015, [URL], PEFC electrocatalyst microstructure strongly influences cell performance. In this study, Nafion ionomer content in the cathode electrocatalyst layer is systematically varied to modify the electrocatalyst microstructure. Current-voltage characteristics of the membrane-electrode-assemblies are measured and then the electrocatalyst microstructure is observed by the focused-ion-beam coupled scanning electron microscopy (FIB-SEM) to examine the correlations between the 3D microstructure and the cell performance. Although technical limitation was found for FIBSEM analysis, certain correlations were also established.. |
| 99. | Y. Matsuzaki, Yuya Tachikawa, T. Hatae, Hiroshige Matsumoto, Shunsuke Taniguchi, Kazunari Sasaki, A parametric study of SOFC performances with multi-stage electrochemical oxidation for enhancement of electric efficiency, 14th International Symposium on Solid Oxide Fuel Cells, SOFC 2015; held as part of the Electrochemical Society, ECS Conference on Electrochemical Energy Conversion and Storage Solid Oxide Fuel Cells 14, SOFC 2015, 10.1149/06801.1961ecst, 68, 1961-1968, 2015, [URL], The solid-state ceramic construction of SOFCs enables high fuel to electricity conversion efficiencies of as high as 50 to 60 percent LHV in high temperature operation, and allows more flexibility in fuel choice. In this study, we have developed a symbolic analysis method to investigate the availability of variable parameters appearing in multi-stage electrochemical oxidation mechanism that is expected to further improve the electric efficiencies of SOFCs. In the flow system of the multi-stage oxidation, the fuel utilization, Uf, at the most downstream stack, UfM, is expressed as a function of number of stacks, n, and total fuel utilization, UfT. When n = 10 and UfT = 85%, UfM is calculated to be 36%, which is much smaller than UfT. Therefore, if the most downstream stack has high robustness against lean fuel gas, UfT could be set to higher values without serious degradation by using this flow system.. |
| 100. | Yuya Tachikawa, Y. Matsuzaki, T. Hatae, Shunsuke Taniguchi, Kazunari Sasaki, Process analysis for achieving highly enhanced total efficiency on multi-stage fuel supplied SOFC system, 14th International Symposium on Solid Oxide Fuel Cells, SOFC 2015; held as part of the Electrochemical Society, ECS Conference on Electrochemical Energy Conversion and Storage Solid Oxide Fuel Cells 14, SOFC 2015, 10.1149/06801.3107ecst, 68, 3107-3113, 2015, [URL], A multi-stage fuel supply SOFC system is studied, which has additional fuel supply inlets between each SOFC stack. The anode offgas from the first stack is supplied to the next stack as reformed fuel gas being mixed with additional fresh fuel. In this paper, the effect of the additional fuel flow ratio is evaluated. The electric efficiency and the fuel utilization of the system can be improved in applying multi-stage fuel supply design.. |
| 101. | Kazunari Sasaki, Shunsuke Taniguchi, Yusuke Shiratori, Akari Hayashi, T. Oshima, Masamichi Nishihara, Yuya Tachikawa, T. Daio, T. Kawabata, M. Fujita, A. Zaitsu, Smart fuel cell demonstration project A challenge to realize SOFC-powered campus, 14th International Symposium on Solid Oxide Fuel Cells, SOFC 2015; held as part of the Electrochemical Society, ECS Conference on Electrochemical Energy Conversion and Storage Solid Oxide Fuel Cells 14, SOFC 2015, 10.1149/06801.0171ecst, 68, 171-178, 2015, [URL], This paper introduces a challenge to realize a fuel-cell-powered campus at Kyushu University where SOFC technology plays a major role. The Smart Fuel Cell Demonstration Project, supported by Cabinet Secretariat/Office of Japan, enables us to install one 250 kW SOFC power generation system, other SOFC units, and the world-first university-owned fuel cell vehicle to which renewable hydrogen gas is supplied from the hydrogen refueling station on the campus using electrolyzers. The experience in this demonstrative project is described along with related efforts to accelerate industry-academia collaborations and fundamental scientific studies using advanced analytical facilities.. |
| 102. | Yuya Tachikawa, T. Kawabata, Yusuke Shiratori, Kazunari Sasaki, Visualization of SOFC anode by dual imaging method using infrared and visible light cameras, 14th International Symposium on Solid Oxide Fuel Cells, SOFC 2015; held as part of the Electrochemical Society, ECS Conference on Electrochemical Energy Conversion and Storage Solid Oxide Fuel Cells 14, SOFC 2015, 10.1149/06801.1115ecst, 68, 1115-1120, 2015, [URL], Thermography imaging can be applied for the surface of an SOFC electrode to evaluate the spatial distribution of reforming and electrode reactions. For getting a correct temperature distribution by thermography, emissivity change on the object surface caused by chemical reactions or material coverage must be precisely evaluated. In-situ observation using both infrared and visible light dual cameras enables us to obtain precise emissivity change and thus temperature distribution, because the influence of emissivity change can be corrected by the visible light imaging technique. In this study, this imaging method is applied for an anode material which was exposed to a fuel flow causing coke formation, and the information on the carbon distribution was successfully separated on the anode surface to obtain the true temperature distribution.. |
| 103. | Yoshinori Kobayashi, Kenichiro Kosaka, Takashi Yamamoto, Yuya Tachikawa, Kohei Ito, Kazunari Sasaki, A solid polymer water electrolysis system utilizing natural circulation, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2014.07.153, 39, 29, 16263-16274, 2014.10, [URL], Solid Polymer Water Electrolysis (SPWE) is a method to efficiently produce high-purity hydrogen gas using a polymer electrolyte membrane-based system. SPWE systems that utilize natural water circulation (resulting from a difference in buoyancy) are a promising technology, which need no additional circulation pump for water supply to the electrolysis cells, and generate no pressure difference between the hydrogen generation and oxygen generation chambers. However, despite not needing an accurate pressure control, gas bubbles formed and trapped within the cell stacks can inhibit heat convection, leading to hot-spot formation and consequent destructive degradation. Improving the reliability is therefore one of the most important technological issues in natural circulation SPWEs. In this study, hot-spot formation is studied both by numerical heat and flow analysis, and by experimental in-situ visualization. This leads to insights into the degradation mechanisms of SPWE stacks, and their possible solutions. An improved design for an SPWE cell stack is successfully fabricated, and reliable operation up to 5000 h is demonstrated.. |
| 104. | Yoshinori Kobayashi, Kenichiro Kosaka, Takashi Yamamoto, Yuya Tachikawa, Kohei Ito, Kazunari Sasaki, A solid polymer water electrolysis system utilizing natural circulation, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2014.07.153, 39, 29, 16263-16274, 2014.10, Solid Polymer Water Electrolysis (SPWE) is a method to efficiently produce high-purity hydrogen gas using a polymer electrolyte membrane-based system. SPWE systems that utilize natural water circulation (resulting from a difference in buoyancy) are a promising technology, which need no additional circulation pump for water supply to the electrolysis cells, and generate no pressure difference between the hydrogen generation and oxygen generation chambers. However, despite not needing an accurate pressure control, gas bubbles formed and trapped within the cell stacks can inhibit heat convection, leading to hot-spot formation and consequent destructive degradation. Improving the reliability is therefore one of the most important technological issues in natural circulation SPWEs. In this study, hot-spot formation is studied both by numerical heat and flow analysis, and by experimental in-situ visualization. This leads to insights into the degradation mechanisms of SPWE stacks, and their possible solutions. An improved design for an SPWE cell stack is successfully fabricated, and reliable operation up to 5000 h is demonstrated.. |
| 105. | M. Hanasaki, C. Uryu, T. Daio, T. Kawabata, Y. Tachikawa, S. M. Lyth, Y. Shiratori, S. Taniguchi, K. Sasaki, SOFC Durability against Standby and Shutdown Cycling, Journal of The Electrochemical Society, 10.1149/2.0421409jes, 161, 9, F850-F860, 2014.06, [URL]. |
| 106. | Yuya Tachikawa, Takami Hosoi, Takashi Nishimura, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Computational Study of Performance Drop Phenomena Based on Sulfur Adsorption and Desorption Model in Planar-Type SOFCs, ECS Transactions, 10.1149/05701.2841ecst, 57, 1, 2841-2848, 2013.10, [URL], For solid oxide fuel cell (SOFC) systems operating with practical fuels, it is important to simulate the distribution of sulfur poisoning and its dependence on the operating conditions in planar-type SOFCs. In this paper, by taking into account the sulfur poisoning effect and its distribution in planar-type SOFC simulation, numerical analysis is performed using anode exchange current density data and Temkin-like sulfur adsorption isotherm on Ni surface. From this numerical analysis, it is found that the distribution of current density after sulfur poisoning is changed, depending on operating temperature and fuel utilization.. |
| 107. | Takashi Nishimura, Tsutomu Kawabata, Yuya Tachikawa, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, In-Plane Distribution of Carbon Deposition on SOFCs, ECS Transactions, 10.1149/05701.1593ecst, 57, 1, 1593-1598, 2013.10, [URL], SOFC can directly utilize not only hydrogen but also various fuels such as city gas, kerosene, and others by internal reforming reaction on anodes. However, impurities and un-reformed hydrocarbon in fuels can cause degradation associated with e.g. carbon deposition. In this study, in-plane distribution of carbon deposition was evaluated using planar cells with an electrode area of 4 cm by 4 cm. The 2-dimensional distribution of deposited carbon has been visualized, where the carbon deposition was accelerated in the simultaneous presence of C3H8 and H2S as minor constituents in simulated pre-reformed CH4-based fuels.. |
| 108. | Eunjoo Park, Shunsuke Taniguchi, Jyh-Tyng Chou, Yuya Tachikawa, Yusuke Shiratori, Kazunari Sasaki, Influence of Cathode Polarization on the Chromium Poisoning of SOFC Cathodes Consisting of LSM, LSCF and LNF, ECS Transactions, 10.1149/05030.0021ecst, 50, 30, 21-25, 2013.04, Chromium poisoning phenomena were compared among three SOFC cathodes consisting of La0.8Sr0.2MnO3 (LSM), La0.6Sr0.4Fe0.8Co0.2O3(LSCF) and LaNi0.6Fe0.4O3 (LNF) under relatively large cathode polarization conditions. Deposition of chromium near the cathode/electrolyte interface seems to be affected only by the cathode polarization, not by the cathode materials nor the current density.. |
| 109. | Yuya Tachikawa, Zhiyun Noda, Akari Hayashi, Yusuke Shiratori, Kazunari Sasaki, Numerical analysis for evaluating the effect of hydrophilic anode support for water management in polymer electrolyte fuel cells, Theoretical and Applied Mechanics Japan, 61, 161-172, 2013, Much attempt was made to improve PEFC perfonnance to optimize its operating condition and its structure by experimental and numerical trials. One of the most critical issues about PEFC improvement is the durability enhancement at its membrane electrode assembly (MEA) to keep its robust control. The objective of this study is to keep the optimal water distribution at MEA with applying the hydrophilic anode support. In this study, the influence of modification to use two hydrophilic support materials is calculated by the case of weak hydrophilized carbon support and strong hydrophilic SnC>2 support. The distribution of liquid water shows that hydrophilic anode support has the effect to hold the liquid water in anode catalyst layer under the low humidification, and water saturation ratio in cathode catalyst layer is also controlled by the use of hydrophilic materials. Hydrophilic anode support works as a water transport pathway to anode across polymer electrolyte membrane. Its effect also prevents from drying-up of the anode and flooding of the cathode.. |
| 110. | Eunjoo Park, Shunsuke Taniguchi, Jyh Tyng Chou, Yuya Tachikawa, Yusuke Shiratori, Kazunari Sasaki, Influence of cathode polarization on the chromium poisoning of SOFC cathodes consisting of LSM, LSCF and LNF, Symposium on Materials Degradation in Energy Systems: Corrosion and Hydrogen-Material Interactions - 22nd ECS Meeting/PRiME 2012 Materials Degradation in Energy Systems: Corrosion and Hydrogen-Material Interactions, 10.1149/05030.0021ecst, 50, 21-25, 2012, [URL], Chromium poisoning phenomena were compared among three SOFC cathodes consisting of Lai0.8Sr0.2MnO3 (LSM), Lai 0.06Sri0.4Fei0.8Co0.2O3 (LSCF) and LaNii0.06Fei0.4O3 (LNF) under relatively large cathode polarization conditions. Deposition of chromium near the cathode/electrolyte interface seems to be affected only by the cathode polarization, not by the cathode materials nor the current density.. |
| 111. | T. Yonekura, Yuya Tachikawa, T. Yoshizumi, Yusuke Shiratori, Kohei Ito, Kazunari Sasaki, Exchange current density of solid oxide fuel cell electrodes, 12th International Symposium on Solid Oxide Fuel Cells, SOFC-XII - 219th ECS Meeting Solid Oxide Fuel Cells 12, SOFC XII, 10.1149/1.3570081, 35, 1007-1014, 2011.12, [URL], It is desired to develop computational procedures to simulate internal current density, anode/cathode gas concentrations, and temperature distribution in solid oxide fuel cell (SOFC) systems. In this study, the influences of various operational conditions on the exchange current density, the essential parameter to simulate SOFC performance, are revealed and discussed. The anodic exchange current density depended strongly on the humidity of H 2-based fuel gas, and it exhibited the highest value at around 40% H 2O. The cathodic exchange current density was strongly affected by the operational temperature. Parameters necessary to describe dependencies of exchange current density on various operational parameters were determined by fitting measured exchange current density values with empirical equations.. |
| 112. | Takahiro Yonekura, Yuya Tachikawa, Tomoo Yoshizumi, Yusuke Shiratori, Kohei Ito, Kazunari Sasaki, Exchange Current Density of Solid Oxide Fuel Cell Electrodes, ECS Transactions, 10.1149/1.3570081, 35, 1, 1007-1014, 2011.04, It is desired to develop computational procedures to simulate an internal current density, anode/cathode gas concentrations and a temperature distribution in solid oxide fuel cell (SOFC) systems. In this study, the influences of various operational conditions on the exchange current density which is the essential parameter to simulate SOFC performance were discussed. The anodic exchange current density depended strongly on the humidity of H2, and it exhibited the highest value at around 40% H2O. The cathodic exchange current density was strongly affected by the operational temperature. Parameters necessary to describe dependences of exchange current density on the operational conditions were determined by fitting measured exchange current density with the empirical equations.. |
| 113. | Yuya Tachikawa, Yuya Matsuda, Hiroshi Kanayama, Numerical Analysis of a Three-Dimensional Sandwich Model for Investigating the Effect of Using the Pore Size Distribution, Journal of Computational Science and Technology, 10.1299/jcst.4.89, 4, 2, 89-104, 2010, [URL], To investigate the effect of liquid water saturation on the efficiency of polymer electrolyte fuel cells, it is important to determine the exact relationship between the liquid water saturation profile and other parameters. In this paper, the pore size distribution (PSD) is used to calculate the liquid water saturation in a fuel cell. Using the PSD, liquid water saturation is calculated from experimental data for the capillary pressure on a porous media. Numerical analysis is used to analyze and evaluate the liquid water pressure and temperature profiles in a fuel cell. This paper uses two-phase, three-dimensional analysis to determine the effects of using the PSD.. |
| 114. | TACHIKAWA Yuya, KANAYAMA Hiroshi, ISHII Chiaki, HASEGAWA Hiroshi, Finite Element Analysis of a Two-Dimensional Sandwich Model for the Inspection of Fuel Cell Internal Characteristics, Journal of Computational Science and Technology, 10.1299/jcst.3.488, 3, 2, 488-498, 2009.07, [URL], In this paper, numerical modeling methods for a fuel cell are explained. The aim of this study is to make an analysis system to perform investigation on the whole behavior of a fuel cell with higher precision. Through numerical analysis, the effects of changing the structure and the control can be made clear. Liquid water distribution and temperature distribution inside the fuel cell are analyzed and evaluated in general under various situations. This paper describes through a two-phase two-dimensional analysis effects of pressure and temperature for liquid water distribution in fuel cells.. |
| 115. | Yuya Tachikawa, Hiroshi Kanayama, Chiaki Ishii, Hiroshi Hasegawa, Finite element analysis of a two-dimensional sandwich model for inspection of fuel cell inside characteristics, Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.75.754_1357, 75, 754, 1357-1362, 2009.06, In this paper, numerical modeling methods for a fuel cell are explained. The aim of this study is to make an analysis system to perform investigation on the whole behavior of a fuel cell with higher precision. Through numerical analysis, the effects of changing the structure and the control will be able to be made clear. Liquid water distribution and temperature distribution inside the fuel cell are analyzed and evaluated in general under various situations. This paper describes through a two-phase two-dimensional analysis effects of pressure and temperature for liquid water distribution in fuel cells.. |
| 116. | Yuya Tachikawa, Hiroshi Kanayama, Chiaki Ishii, Hiroshi Hasegawa, Finite element analysis of a two-dimensional sandwich model for inspection of fuel cell inside characteristics, Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.75.754_1357, 75, 754, 1357-1362, 2009.01, [URL], In this paper, numerical modeling methods for a fuel cell are explained. The aim of this study is to make an analysis system to perform investigation on the whole behavior of a fuel cell with higher precision. Through numerical analysis, the effects of changing the structure and the control will be able to be made clear. Liquid water distribution and temperature distribution inside the fuel cell are analyzed and evaluated in general under various situations. This paper describes through a two-phase two-dimensional analysis effects of pressure and temperature for liquid water distribution in fuel cells.. |
| 117. | Yuya Tachikawa, 金山 寛, 石井 千明, 長谷川 弘, 燃料電池内部特性検証用二次元サンドイッチモデルの有限要素解析(熱工学,内燃機関,動力など), Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.75.754_1357, 75, 754, 1357-1362, 2009, [URL], In this paper, numerical modeling methods for a fuel cell are explained. The aim of this study is to make an analysis system to perform investigation on the whole behavior of a fuel cell with higher precision. Through numerical analysis, the effects of changing the structure and the control will be able to be made clear. Liquid water distribution and temperature distribution inside the fuel cell are analyzed and evaluated in general under various situations. This paper describes through a two-phase two-dimensional analysis effects of pressure and temperature for liquid water distribution in fuel cells.. |
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QIR 九州大学学術情報リポジトリ システム情報科学研究院
工学部・工学研究院
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