| 1. |
Y. INOUE, J.-T CHOU, T. KAWABATA, J. MATSUDA, S. TANIGUCHI, K. SASAKI, Influence of Current Load on the Grouwth of SrZrO3 at the GDC/YSZ Interface, ECS Transactions, 91 (1), pp. 847-852 (2019) , 2020.07. |
| 2. |
H.-C PHAM, S. TANIGUCHI, Y. INOUE, J.-T CHOU, K. SASAKI, Semi-conductive α-Al2O3/Sr3Al2O6 Oxide Layer formed on Fe-Cr-Al Alloy, ECS Transactions, 91 (1), pp. 2299-2305 (2019), 2020.06. |
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Eunjoo Park, Shunsuke Taniguchi, Takeshi Daio, Jyh Tyng Chou, Kazunari Sasaki, Influence of cathode polarization on the chromium deposition near the cathode/electrolyte interface of SOFC, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2013.11.030, 39, 3, 1463-1475, 2014.01, Chromium poisoning phenomena were compared among three SOFC cathodes using (La0.8Sr0.2)0.98MnO3 (LSM), La 0.6Sr0.4Fe0.8Co0.2O3 (LSCF) and LaNi0.6Fe0.4O3 (LNF) at 700 C by changing cathode polarization (0-400 mV). Chromium vapor deposited near the electrolyte for LSM and LNF, and the amount of the deposition increased with increasing cathode polarization. In the case of LSCF, chromium deposited near the cathode surface under smaller cathode polarization (≤200 mV). Under larger cathode polarization (≥300 mV), however, chromium deposition near the cathode/electrolyte interface similarly increased for the three cathodes. Cathode polarization facilitated the chromium deposition and there seemed to be no correlation with the current density. Microscopic distribution of the deposited chromium, which was located on the surface of LSM, LSCF, LNF grains, and also on the surface of zirconia and ceria, seemed to correspond to the distribution of oxygen vacancy by cathode polarization at the electrode reaction sites. Chromium deposition on the zirconia surface seemed to be assisted by metal oxides segregated from the cathode material, which can conduct electron required for generating oxygen vacancy continuously. Oxygen deficiency on the surface of the deposited chromium was confirmed and interdiffusion of chromium and zirconium caused by cathode polarization was also suggested.. |
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Eunjoo Park, Shunsuke Taniguchi, Takeshi Daio, Jyh Tyng Chou, Kazunari Sasaki, Comparison of chromium poisoning among solid oxide fuel cell cathode materials, Solid State Ionics, 10.1016/j.ssi.2014.01.047, 262, 421-427, 2014.09, Chromium poisoning phenomena of solid oxide fuel cells (SOFCs) were investigated using (La0.8Sr0.2)0.98MnO 3 (LSM), Pr0.8Sr0.2MnO3 (PrSM), Nd0.8Sr0.2MnO3 (NdSM), and Br 0.5Sr0.5Co0.8Fe0.2O3 (BSCF) for the cathode materials and yttria-stabilized zirconia (YSZ) as the electrolyte material at 700 °C under constant cathode polarization conditions. Deposition of chromium increased with increasing cathode polarization similarly for the four cathodes, although position of the deposition was different for the BSCF cathode. Chromium deposited near the cathode/electrolyte interface for the LSM cathode, the PrSM cathode and the NdSM cathode. Chromium deposition on the surface of the zirconia electrolyte was observed for the PrSM cathode and the NdSM cathode as previously observed in the LSM cathode. Oxygen deficiency in the deposited chromium on the surface of the zirconia electrolyte was also observed, thus the reaction mechanism of chromium vapor with the oxygen vacancy induced by cathode polarization was supported. The oxygen vacancy on the surface of the zirconia electrolyte seemed to be generated via metal oxides such as manganese oxide or neodymium oxide segregated from the cathode materials. Chromium deposited on the surface of the BSCF cathode. Cathode polarization seems to increase reactivity of BSCF and enhance trapping of chromium vapor near the cathode surface.. |
| 5. |
Hung Cuong Pham, Shunsuke Taniguchi, Yuko Inoue, Jyh Tyng Chou, Toru Izumi, Koji Matsuoka, Kazunari Sasaki, Decrease in electrical resistance of surface oxide of iron-chromium-aluminium alloy by La0.6Sr0.4Co0.2Fe0.8O3 coating and heat treatment for the application of metal-supported solid oxide fuel cells, Journal of Power Sources, 10.1016/j.jpowsour.2015.07.096, 297, 181-187, 2015.08, We have investigated the property of a Fe-Cr-Al-type stainless steel as a porous alloy substrate for metal-supported solid oxide fuel cells (SOFCs) especially on the cathode side. We found that the microstructure and electrical resistance of the surface oxide layer of the alloy changes depending on the heat-treatment conditions. A relatively low electrical resistance was obtained when the porous alloy substrate was coated with La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and heat treated at 700-800 °C in air. The morphology of the surface oxide layer observed by high-resolution transmission electron microscopy was a columnar structure of γ-Al2O3 polycrystal and Sr3Al2O6 growing outward in the same direction. In contrast, the surface oxide layer of the alloy showed a high electrical resistance when the uncoated porous alloy substrate was heat treated. The morphology of the surface oxide layer in that case was a columnar structure consisting of only γ-Al2O3 growing outward in various directions.. |
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Daiki Ishibashi, Shunsuke Taniguchi, Yuko Inoue, Jyh Tyng Chou, Kazunari Sasaki, Deposition, agglomeration and vaporization of chromium oxide by cathode polarization change in SOFC cathodes, Journal of the Electrochemical Society, 10.1149/2.0141607jes, 163, 7, F596-F602, 2016.01, The mechanism of Cr deposition was investigated using NiO/YSZ or NiO/GDC composite cathodes, controlling cathode polarization, and observing the change in Cr distribution. By applying cathode polarization at 200 mV, Cr deposited on the surface of the electrolyte (YSZ or GDC) near the electrode reaction site similarly to the case of typical LSM cathodes. In these cathodes consisting of NiO, the Cr deposition occurred only on the electrolyte surface. After removing the polarization, the deposited Cr partially detached from the electrolyte surface and agglomerated as crystalline Cr2O3 at the interface between NiO and the electrolyte. The deposited Cr may decrease over time by continuous vaporization, and may be agglomerated to form crystalline Cr2O3 transiently. The disappearance of Cr was faster for the NiO/GDC cathode than for the NiO/YSZ cathode. By applying reverse polarization at -200 mV for 1 h, the deposited Cr disappeared from the electrolyte surface for both cathodes. Therefore, the deposition of Cr on the electrolyte seems to be a reversible reaction.. |
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H. C. Pham, S. Taniguchi, Y. Inoue, J. Matsuda, J. T. Chou, Y. Misu, K. Matsuoka, K. Sasaki, Modification of Surface Oxide Layer of Fe-Cr-Al Alloy with Coating Materials for SOFC Applications, Fuel Cells, 10.1002/fuce.201600038, 17, 1, 83-89, 2017.02, We investigated the treatment of Fe-Cr-Al alloy for application in solid oxide fuel cells (SOFCs). The electrical resistance of the Al2O3-based surface oxide layer on the alloy decreased and was stable when La0.6Sr0.4Co0.2Fe0.8O3(LSCF), La0.8Sr0.2MnO3(LSM), LaNi0.6Fe0.4O3(LNF), or Pr0.8Sr0.2MnO3(PrSM) were first coated on the alloy and heat treated at 700 °C in air. The activation energy, calculated from the resistance, also suggested that the surface oxide became more conductive with treatment. The surface oxide layer after treatment had a microstructure of columns growing outward in the same direction, containing small amounts of elements such as Sr, Ni, Fe, La, Mn, and Pr. The microstructure consists of polycrystalline γ-Al2O3and small amounts of Al compounds with these elements. In the case of the LNF coating, the formation of NiAl2O4was observed.The enhanced electrical conductivity may have resulted from the arrangement of the columnar structure, along with the electronic conduction path generated by the reaction of γ-Al2O3with these elements.. |
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Jyh Tyng Chou, Yuko Inoue, Tsutomu Kawabata, Junko Matsuda, Shunsuke Taniguchi, Kazunari Sasaki, Mechanism of SrZrO3 formation at GDC/YSZ interface of SOFC cathode, Journal of the Electrochemical Society, 10.1149/2.0551811jes, 165, 11, F959-F965, 2018.01, SrZrO3 formation at the interface of gadolinia-doped ceria (GDC) interlayer and yttria-stabilized zirconia (YSZ) electrolyte is analyzed using high-resolution electron microscopy. SrZrO3 is dispersed in the inter-diffusion layer on the GDC side from the Ce/Zr border. Zr, which diffuses into the GDC grain, contributes to the formation of SrZrO3. The crystallographic relationship among the SrZrO3 grains and its neighboring GDC grains reveals that SrZrO3 is formed at the surface, at the grain boundary, and inside the grain, while maintaining a highly matched boundary with the adjacent GDC grain. The matching of the interface boundary is confirmed by the O-lattice theory, according to which the threshold Zr/Ce ratio is 13/34. If Zr/Ce ratio in the GDC grain is higher than the threshold, SrZrO3 may significantly grow into the grain. The conduction path for the oxygen ion is retained because the GDC grain containing Zr is split into the SrZrO3 grain and the less-Zr-containing GDC grain. If Zr/Ce ratio is lower than the threshold, SrZrO3 may be formed but will be limited by the amount of Zr diffusing from the adjacent region. Thus, the morphology of SrZrO3 is strongly affected by the state of GDC grains in the inter-diffusion layer.. |
| 9. |
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.. |
| 10. |
Florian Thaler, David Udomsilp, Wolfgang Schafbauer, Cornelia Bischof, Yosuke Fukuyama, Yohei Miura, Mari Kawabuchi, Shunsuke Taniguchi, Satoshi Takemiya, Andreas Nenning, Alexander Karl Opitz, Martin Bram, Redox stability of metal-supported fuel cells with nickel/gadolinium-doped ceria anode, Journal of Power Sources, 10.1016/j.jpowsour.2019.226751, 434, 2019.09, Metal-supported fuel cells (MSCs) are promising candidates for not only stationary but also mobile applications. Their appeal is in their potential to withstand reoxidation of the anode, which might occur by an interruption of the fuel supply or an emergency shutdown of the fuel cell system. A novel nickel/gadolinium-doped ceria anode (Ni/GDC) was recently introduced in a MSC concept of Plansee, almost doubling power density compared to cells with a nickel/yttria-doped zirconia (Ni/YSZ) anode. In this study, both cell concepts are compared concerning their ability to tolerate harsh redox cycles. Therefore, controlled redox cycles of the anodes were conducted at different temperatures. The response of the cell's power output to the redox cycling experiments was continuously recorded. In the case of MSCs with a Ni/YSZ anode, strong degradation occurs after redox cycling. In contrast, cells with a Ni/GDC anode exhibit significantly improved redox tolerance and cell performance improves with the number of redox cycles. For understanding this behavior, microstructural investigations of the Ni/GDC anode and the adjacent electrolyte were performed by FIB-SEM. The long-term redox behavior of MSCs with a Ni/GDC anode was also investigated by conducting more comprehensive redox cycles at 400 °C, 500 °C, and 600 °C.. |
| 11. |
H. C. Pham, Shunsuke Taniguchi, Y. Inoue, J. T. Chou, Junko Matsuda, Kazunari Sasaki, Investigation of Fe-Cr-Al alloy for metal supported SOFC, 15th International Symposium on Solid Oxide Fuel Cells, SOFC 2017
ECS Transactions, 10.1149/07801.2069ecst, 78, 2069-2075, 2017.05, Porous Fe-Cr-Al alloy was investigated for the support material of solid oxide fuel cells. Interfacial resistance at 700oC in 3% H2O - 97% H2 atmosphere between the porous alloy and Ni coating was stable at around 10 mγcm2. Interfacial resistance at 700oC in air between the porous alloy and LSCF coating was stable at around 20 mγcm2. The surface oxide layer on the Fe-Cr-Al alloy consists of nano-sized γ-Al2O3 columns growing outward in the same direction, containing 4 at.% of Sr, which may contribute electronic conduction. It is expected that the negligible Cr content in the surface oxide layer can solve the Cr contamination problem, generally known in SOFC. We are also developing a cell using the porous Fe-Cr-Al alloy by a co-sintering process.. |
| 12. |
H. C. Pham, Shunsuke Taniguchi, Y. Inoue, Junko Matsuda, J. T. Chou, K. Matsuoka, Kazunari Sasaki, Durability of LSCF-coated Fe-Cr-Al alloy for SOFC applications, Journal of the Electrochemical Society, 10.1149/2.0791803jes, 165, 3, F181-F188, 2018.01, The long-term durability of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-coated Fe-Cr-Al alloy was investigated as a novel current collector material for SOFCs. The LSCF coating and subsequent heat-treatment at 700–900◦C changed the microstructure of the surface oxide layer to a columnar structure of nanosize γ-Al2O3 arranged in the same direction, in which a small amount of Sr3Al2O6 contributes to the electronic conduction. The LSCF coating decreased the alloy oxidation rate by 23% at 700◦C compared to the case without coating, following the parabolic growth law. Raising the temperature from 700◦C to 900◦C increased the oxidation rate of the LSCF-coated alloy by 51 times. The oxidation mechanism at 900◦C was considered to be similar to that at 700◦C, because of the similarity in microstructure, crystal structure, elemental composition and electrical conductivity. It was estimated that the Cr2O3 layer begins to grow on the inner side after roughly 6,000 h at 700◦C, when the thickness of the surface oxide layer exceeds 1 μm. The same γ-Al2O3 columnar microstructure still covered the surface after 12,000 h. However, further improvement in durability and electrical conductivity is needed to meet the requirements for practical application.. |
