九州大学 研究者情報
論文一覧
立川 雄也(たちかわ ゆうや) データ更新日:2020.02.28

助教 /  工学研究院 機械工学部門 水素利用工学


原著論文
1. 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..
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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..
8. 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..
9. 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.
10. 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), Chapter 07, A15, 2018.07.
11. 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..
12. 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..
13. 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].
14. Yuya Tachikawa, Hiroshi Kanayama, Chiaki Ishii, Hiroshi Hasegawa, 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].
15. 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..
16. 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..
17. 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..
18. 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..
19. 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..
20. 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..
21. 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..
22. 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..
23. 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..
24. 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..
25. S. Futamura, Yuya Tachikawa, Junko Matsuda, Stephen Matthew Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari 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, 2017.01, [URL], Redox-stable anodes are developed for zirconia-based electrolyte-supported SOFCs in order to improve the durability against fuel supply interruption and for higher fuel utilization, as an alternative to the conventional Ni-YSZ cermet. GDC (Ce0.9Gd0.1O2) is utilized as a mixed ionic-electronic conductor (MIEC), and combined with LST (Sr0.9La0.1TiO3) as an electronic conductor. Ni catalyst nanoparticles are incorporated via impregnation. The electrochemical characteristics of SOFC single cells using these anode materials are investigated in humidified H2 at 800°C. The stability against redox cycling and under high fuel utilization is analyzed and discussed. Ni-impregnated anodes with dispersed Ni catalyst nanoparticles on conducting oxide LST-GDC backbones exhibit lower anode non-ohmic overvoltage, and improve I-V performance. These anodes also show better redox stability compared to conventional anodes because of the isolation of Ni catalysts, preventing their agglomeration. Moreover, the co-impregnation of Ni catalysts and GDC nanoparticles further improves electrochemical characteristics due to a decrease in anode ohmic (IR) loss and non-ohmic overvoltage. This anode shows comparable I-V performance to conventional anodes for typical humidified hydrogen fuels, and is a promising redox-stable alternative for application at high fuel utilization..
26. 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..
27. M. Okumura, Z. Noda, Junko Matsuda, Yuya Tachikawa, Masamichi Nishihara, Stephen Matthew Lyth, Akari Hayashi, Kazunari 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, 2017.01, [URL], The cathode electrocatalyst layers of polymer electrolyte membrane fuel cells (PEFCs) are quantitatively investigated for different ratios of Nafion ionomer. This is achieved using focused-ion-beam coupled scanning electron microscopy (FIB-SEM) to reconstruct the three-dimensional microstructure via tomography. Parameters such as the porosity and pore size distribution were calculated from this data. The distributions of Nafion ionomer, carbon support, and platinum nanoparticles were then further clarified using transmission electron microscopy (TEM). Changes in the PEFC performance (notably the I-V characteristics, the electrochemical surface area, the activation overvoltage, and the concentration overvoltage) are thus correlated to electrode microstructure..
28. 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..
29. 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..
30. 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..
31. 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..
32. 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.
33. 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.
34. 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.
35. 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..
36. 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)..
37. Yuya Tachikawa, J. Sugimoto, M. Takada, T. Kawabata, Stephen Matthew Lyth, Yusuke Shiratori, Kazunari Sasaki, In operando visualization of SOFC electrodes by thermography and visible light imaging, ECS Electrochemistry Letters, 10.1149/2.0031511eel, 4, 11, F61-F64, 2015.01, [URL], The temperature distribution in internal reforming SOFC anodes can be visualized by thermography. However, thermal imaging techniques are limited since they cannot take into account the influence of emissivity changes caused by carbon deposition on the anode. This problem can be solved by simultaneous visualization using thermography and visible light imaging. By combining these techniques, carbon deposition can be monitored via visible light imaging, whilst temperature changes due to the reforming reaction can be monitored by thermal imaging. This in operando visualization technique enables the evaluation and prediction of the distribution of multiple chemical reactions on the SOFC electrodes..
38. 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..
39. 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..
40. 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..
41. 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..
42. 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..
43. 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..
44. 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..
45. M. Hanasaki, C. Uryu, T. Daio, T. Kawabata, Yuya Tachikawa, Stephen Matthew Lyth, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, SOFC durability against standby and shutdown cycling, Journal of the Electrochemical Society, 10.1149/2.0421409jes, 161, 9, 2014, [URL], To simulate realistic operating conditions in SOFC systems, we investigate the influence of thermal cycling on the performance of electrolyte-supported planar SOFCs. Thermal cycling is often associated with interruption of fuel supply, with three main modes; hot standby, cold standby, and shutdown. Cell performance degradation is most significant during shutdown cycles. Nickel oxidation and agglomeration are more pronounced when SOFCs are subjected to lower temperatures for longer periods of time, leading to significant performance degradation. Ostwald ripening at the anode leads to degradation as Ni grains increase in size with cycling. Ni particle precipitation on the anode zirconia grains and along electrolyte grain boundaries is found for the first time in shutdown cycling tests. When H2S is mixed with the fuel, the internal reforming reactions and electrode reactions are inhibited by sulfur poisoning of the Ni anodes, accelerating degradation. The SOFC cycling degradation mechanisms are discussed in detail..
46. Yuya Tachikawa, T. Hosoi, T. 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, [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..
47. T. Nishimura, T. 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, [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 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 coexistence of C3H8 and H2S as minor constituents in simulated prereformed CH4-based fuels..
48. 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..
49. 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..
50. 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..
51. 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..
52. 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..
53. 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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