| 1. |
S. Taniguchi, K. Miyara, T. Kawabata, C. Uryu, Y. Inoue, J.-T Chou, K. Sasaki
, Stability of nickel/scandia-doped-stabilized-zirconia composite anode
under high fuel utilization conditions
, 17th International Symposium on Solid Oxide Fuel Cells, 2021.07. |
| 2. |
H. C. Pham, S. Taniguchi, Y. Inoue, J. T. Chou, K. Sasaki, Semiconductive α-Al2O3/Sr3Al2O6 Oxide Layer formed on Fe-Cr-Al Alloy, 16th International Symposium on Solid Oxide Fuel Cells, SOFC 2019, 2019.01, Surface oxide layer of Fe-Cr-Al alloy was investigated to apply for metal support material of SOFCs. We already found that electrical resistance of the surface oxide layer can be decreased by La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) coating and heat-treatment. The morphology of the surface oxide layer changed to a columnar structure consisting of γ-Al2O3 polycrystal and Sr3Al2O6 growing outward in the same direction. In this study, we investigated heat-treatment condition to increase durability of the oxide layer. The Fe-Cr-Al alloy was firstly coated with LSCF and pre-heat treated in a vacuum at 1000oC for 1 h. Stability of mass gain and electrical resistance in air at 700oC was significantly improved. The morphology of the surface oxide layer was a complex structure consisting of α-Al2O3/Sr3Al2O6.. |
| 3. |
S. Futamura, A. Muramoto, Y. Tachikawa, J. Matsuda, S. M. Lyth, Y. Shiratori, S. Taniguchi, K. Sasaki, SOFC anodes impregnated with noble metal catalyst nanoparticles for high fuel utilization, 16th International Symposium on Solid Oxide Fuel Cells, SOFC 2019, 2019.01, In order to improve the stability under high fuel utilization, alternative anodes are fabricated with ionic (mixed) conducting GDC (Ce0.9Gd0.1O2) and electronic conducting LST (Sr0.9La0.1TiO3), both of which act as stable ion- and electron-conducting frameworks against reduction-oxidation (redox) cycles, respectively. Noble metal catalyst nanoparticles (Rh, Pt, or Pd) are incorporated via impregnation with GDC on the LST-GDC backbones. The electrochemical characteristics, such as the stability against redox cycling and under high fuel utilization, of SOFC single cells using these anodes are characterized in humidified H2 at 800°C. Moreover, the changes of the noble metal catalyst nanoparticles before/after the high fuel utilization durability tests are analyzed and discussed.. |
| 4. |
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, 16th International Symposium on Solid Oxide Fuel Cells, SOFC 2019, 2019.01, 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.. |
| 5. |
Y. Inoue, J. T. Chou, T. Kawabata, J. Matsuda, S. Taniguchi, K. Sasaki, Influence of current load on the growth of SrZrO3 at the GDC/YSZ interface, 16th International Symposium on Solid Oxide Fuel Cells, SOFC 2019, 2019.01, The influence of current load on the growth of SrZrO3 formed at the interface of a gadolinia-doped ceria (GDC) interlayer and yttria-stabilized zirconia (YSZ) electrolyte was analyzed using high-resolution electron microscopy. A cell with LNF (LaNi0.6Fe0.4O3) cathode was prepared after removing the LSCF cathode using HCl. The LNF cathode was used to eliminate the effect of Sr diffusion during cell operation. These cells were operated under 0.2 A cm−2 at 800°C. For the cell with the LNF cathode, no significant change was observed in the amount of SrZrO3. At the SrZrO3/GDC interface, crystal orientation was the same from the GDC side to the SrZrO3 side. Before cell operation, the GDC grain had some defects and no clear boundary was distinguished between GDC and SrZrO3. After cell operation, the SrZrO3/GDC interface was clearer and crystallization of SrZrO3 proceeded.. |
| 6. |
Yusuke Ishibashi, Shotaro Futamura, Yuya Tachikawa, Junko Matsuda, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Alternative Ni-alloy cermet anode materials for SOFCs, 16th International Symposium on Solid Oxide Fuel Cells, SOFC 2019, 2019.01, 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.. |
| 7. |
H.-C Pham, S. Taniguchi, Y. Inoue, J.-T Chou, J. Matsuda, K. Sasaki, Investigation of Fe-Cr-Al Alloy for Metal Supported SOFC, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017, 2017.05. |
| 8. |
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, 2015.07, 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.. |
| 9. |
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, 2015.07, 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.. |
| 10. |
S. Kanae, Y. Toyofuku, T. Kawabata, Y. Inoue, T. Daio, Junko Matsuda, J. T. Chou, Yusuke Shiratori, Shunsuke Taniguchi, Kazunari Sasaki, Microstructural characterization of SrZrO3 formation and the influence to SOFC performance, 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, 2015.07, One of the major phenomena to shorten SOFC durability is the formation of insulating phases, such as SrZrO3, between the cathode and the electrolyte. It is known that SrZrO3 is formed and grown during sintering processes as well as during long-term operation. A systematic study is made to examine the SrZrO3 formation mechanisms and their influence on electrochemical properties.. |
| 11. |
Daiki Ishibashi, Eunjoo Park, Shunsuke Taniguchi, Yuko Inoue, Jyh Tyng Chou, Kazunari Sasaki, Influence of cathode polarization change on chromium deposited on electrolyte surface near cathode reaction sites of SOFC, 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, 2015.07, It has been clarified that Cr deposition occurs significantly on the electrolyte surface near cathode reaction sites as a consequence of cathode polarization. In this study, we investigated the influence of a change in the cathode polarization on the Cr deposited on the electrolyte surface by using NiO/YSZ or NiO/GDC as the cathode material. The deposited Cr segregated at the interface of NiO and YSZ in the case of the NiO/YSZ cathode after a decrease in the cathode polarization, which suggests nucleation under a cathode polarization of 200 mV and growth of Cr compounds after decreasing the cathode polarization. In contrast, the amount of deposited Cr decreased in the case of the NiO/GDC cathode after decreasing the cathode polarization.. |
| 12. |
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, 2015.07, 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.. |
| 13. |
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, 2015.07, 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.. |
| 14. |
H. C. Pham, Shunsuke Taniguchi, Y. Inoue, J. T. Chou, T. Izumi, K. Matsuoka, Kazunari Sasaki, Electrical and oxidation resistance of surface oxide of porous Fe-Cr-Al alloy for the application of metal supported SOFCs, 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, 2015.07, We have investigated the property of Fe-Cr-Al-type stainless steel as a porous alloy substrate for metal-supported SOFCs especially on the cathode side. We confirmed not only good heat resistance but also low electrical resistance at the interface between the porous substrate and a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) coating at 700°C in air. Long-term durability of the oxidation resistance of the LSCF-coated Fe-Cr-Al alloy at 700°C was investigated by measuring the mass gain, surface oxide thickness, and electrical resistance at different temperatures from 700 to 900°C.. |
| 15. |
T. Hatae, K. Sato, T. Somekawa, Y. Matsuzaki, S. Amaha, M. Yoshikawa, Y. Mugikura, K. Miyara, T. Oshima, Shunsuke Taniguchi, Kazunari Sasaki, M. Shimazu, Y. Takahashi, A. Kawakami, N. Mori, H. Yokokawa, Durability assessment of SOFC stacks with several types of structures for thermal cycles during their lifetimes on residential use, 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, 2015.07, We have been developing a rapid evaluation method for durability of SOFC stacks for thermal cycles during their lifetimes based on the assumption of residential use. The durability for thermal cycles is expected to be affected by the degradation during their long-term operation. In order to accelerate the evaluation, treatments to intentionally cause degradation were investigated. A degradation factor was determined depending on the SOFC stacks with different structures respectively because each degradation mechanism during their long-term operation also depends on them. The SOFC stacks were supplied by four SOFC stack manufactures in Japan. In this work, we investigated the Cr poisoning treatment to tubular SOFC (TOTO) and the S poisoning treatment to singlestep co-fired planar SOFC (Murata Manufacturing). As results of both cases, 10 years' worth of degradation was successful to be intentionally caused in short period.. |
| 16. |
Junko Matsuda, S. Kanae, T. Kawabata, J. T. Chou, Y. Inoue, Shunsuke Taniguchi, Kazunari Sasaki, TEM and ETEM study of SrZrO3 formation at LSCF/GDC/YSZ interfaces, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017, 2017.05, Transmission electron microscopic (TEM) studies have revealed SrZrO3 formation and growth at La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)/Ce0.9Gd0.1O2 (GDC)/yttria-stabilized zirconia (YSZ) interfaces in solid oxide fuel cells (SOFCs). SrZrO3 forms first at the GDC/YSZ interface: at the interface between the GDC dense layer and the YSZ, at grain boundaries in the GDC dense layer, and on the surface of the GDC dense layer during the sintering of LSCF at 1100°C. Then, SrZrO3 grows to both sides of the YSZ electrolyte and the porous GDC layer. Electron energy loss spectroscopy revealed the inter-diffusion of La, Ce, and Gd as well as Sr and Zr in the vicinity of the GDC/YSZ interface. La was a solute in SrZrO3, and SrZrO3 exhibited a tetragonal crystal structure with a double pseudo-cubic perovskite sub-cell. Nucleation and growth of the SrZrO3 orthorhombic phase was observed at 800°C under an O2 atmosphere in an environmental TEM.. |
| 17. |
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, 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.. |
| 18. |
Hung-Cuong Pham, Shunsuke Taniguchi, Yuko Inoue, Jyh-Tyng Chou, Toru Izumi, Koji Matsuoka, Kazunari Sasaki, Modification of Surface Oxide of Porous Fe-Cr-Al Alloy by Coating and Heat-Treatment for the Application of Metal Supported SOFCs, SSI-20, 2015.06, Fe-Cr-Al alloy was investigated for the porous support material of metal supported SOFCs on the cathode side. We found that surface oxide layer of the porous Fe-Cr-Al alloy shows low electrical resistance when the porous alloy was coated with La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) first, and then heat-treated at 700 oC in air. Small amount of Sr included in the Al2O3-rich surface oxide layer may change microstructure and contribute to electronic conduction. In this study, we investigated effect of coating materials using La0.8Sr0.2MnO3 (LSM), LaNi0.6Fe0.4O3 (LNF), Pr0.8Sr0.2MnO3 (PrSM), Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF), Nd0.8Sr0.2MnO3 (NdSM), La0.8Ca0.2CrO3(LCC), or Li0.025Ni 0.975O (LNO). Relatively low contact resistances were obtained in all cases when these materials were coated on the porous alloy first, and then heat-treated at 700 oC in air. Morphology and crystal structure of the surface oxide layer of the alloy was analyzed by STEM-EDS and TEM in detail to clarify the cause of low electrical resistance. . |
| 19. |
Hung-Cuong Pham, Shunsuke Taniguchi, Yuko Inoue, Jyh-Tyng Chou, Toru Izumi, Koji Matsuoka, Kazunari Sasaki, Electrical and Oxidation Resistance of Surface Oxide of Porous Fe-Cr-Al Alloy for the Application of Metal Supported SOFCs, SOFC-14, 2015.07, We have investigated the property of Fe-Cr-Al-type stainless steel as a porous alloy substrate for metal-supported SOFCs especially on the cathode side. We confirmed not only good heat resistance but also low electrical resistance at the interface between the porous substrate and a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) coating at 700 °C in air. Long-term durability of the oxidation resistance of the LSCF-coated Fe-Cr-Al alloy at 700 °C was investigated by measuring the mass gain, surface oxide thickness, and electrical resistance at different temperatures from 700 to 900 °C.. |
| 20. |
Daiki Ishibashi, Eunjoo Park, Shunsuke Taniguchi, Yuko Inoue, Jyh-Tyng Chou, Kazunari Sasaki, Influence of Cathode Polarization Change on Chromium Deposited on Electrolyte Surface Near Cathode Reaction Sites of SOFC, SOFC-14, 2015.07, It has been clarified that Cr deposition occurs significantly on the electrolyte surface near cathode reaction sites as a consequence of cathode polarization. In this study, we investigated the influence of a change in the cathode polarization on the Cr deposited on the electrolyte surface by using NiO/YSZ or NiO/GDC as the cathode material. The deposited Cr segregated at the interface of NiO and YSZ in the case of the NiO/YSZ cathode after a decrease in the cathode polarization, which suggests nucleation under a cathode polarization of 200 mV and growth of Cr compounds after decreasing the cathode polarization. In contrast, the amount of deposited Cr decreased in the case of the NiO/GDC cathode after decreasing the cathode polarization.. |
