Language：English   Publishing type：Research paper (scientific journal)  

The long-term durability of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (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.

DOI： 10.1149/2.0791803jes

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.2069ecst

Language：English   Publishing type：Research paper (scientific journal)  

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 La_0.6Sr_0.4Co_0.2Fe_0.8O₃(LSCF), La_0.8Sr_0.2MnO₃(LSM), LaNi_0.6Fe_0.4O₃(LNF), or Pr_0.8Sr_0.2MnO₃(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.

DOI： 10.1002/fuce.201600038

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/2.0141607jes

Language：English   Publishing type：Research paper (scientific journal)  

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 La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (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.

DOI： 10.1016/j.jpowsour.2015.07.096

Language：English   Publishing type：Research paper (scientific journal)  

Chromium poisoning phenomena of solid oxide fuel cells (SOFCs) were investigated using (La_0.8Sr_0.2)_0.98MnO ₃ (LSM), Pr_0.8Sr_0.2MnO₃ (PrSM), Nd_0.8Sr_0.2MnO₃ (NdSM), and Br _0.5Sr_0.5Co_0.8Fe_0.2O₃ (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.

DOI： 10.1016/j.ssi.2014.01.047

Language：English   Publishing type：Research paper (scientific journal)  

Chromium poisoning phenomena were compared among three SOFC cathodes using (La_0.8Sr_0.2)_0.98MnO₃ (LSM), La _0.6Sr_0.4Fe_0.8Co_0.2O₃ (LSCF) and LaNi_0.6Fe_0.4O₃ (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.

DOI： 10.1016/j.ijhydene.2013.11.030

Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Steam oxidation behavior of four general-purpose stainless steels, SUS430, SUS430LX, SUS430J1L, and SUS445J1, under humidified H2 was investigated for application in solid oxide fuel cells (SOFCs). A Cr-rich surface oxide layer, preliminarily formed via pre-oxidation, effectively mitigated steam oxidation and suppressed elemental diffusion and oxide growth. After pre-oxidation at 900 °C for 2 h in air, the oxidation rate was less dependent on the gas composition, which was varied from 10%H2O-90%H2 to 50%H2O-50%H2, whereas it was strongly dependent on temperature. The structure of the surface oxide layer and direction of oxide growth differed depending on the alloy composition. The oxidation rate of SUS430J1L was similar to that of ZMG232G10 and relatively lower than those of three other stainless steels The Cr-rich oxide layer contained few defects, and its structure suppressed the diffusion of metal ions. Although a Si-rich oxide layer grew on the alloy side during the durability test performed at 727 °C for 1500 h, it had a lesser impact on the area specific resistance than that in SUS430. The microstructure of the Si-rich oxide layer, which featured other elements such as Cr, Mn, and Fe, maintained the electrical conduction path.

DOI： 10.1149/1945-7111/adc5a7

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：International Journal of Hydrogen Energy  

Automotive Solid oxide fuel cells (SOFCs) require improvements in mechanical robustness, power generation at low temperatures, and system compactness. To address these issues, we attempt to improve the internal reformation of metal-supported SOFCs (MS-SOFCs) via catalyst infiltration. After introducing nickel/gadolinium-doped ceria (Ni/GDC) nanoparticles, power densities of 1.16 Wcm−2 with hydrogen (3%H2O) and 0.85 Wcm−2 with methane (Steam-to-Carbon ratio, S/C = 1.0) are obtained at 600 °C, 0.7 V. This is the highest performance achieved in previous studies on MS-SOFCs. Internal reforming with various hydrocarbon is also demonstrated. In particular 0.64 Wcm−2 at 600 °C, 0.7 V is obtained when the fuel is iso-octane. We develop a numerical model to separately analyze reforming and electrochemical reaction. Catalyst infiltration dramatically increases the number of active sites for steam reforming. In addition, ruthenium/gadolinium-doped ceria (Ru/GDC) should be suitable as a catalyst metal at low temperatures because of the lower activation energy of steam reforming.

DOI： 10.1016/j.ijhydene.2023.03.195

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Language：Japanese  

Language：Others   Publishing type：Research paper (other academic)  

Stability of nickel/scandia-doped-stabilized-zirconia (Ni/ScSZ) composite anode under high pH2O condition was investigated. Electrolyte supported cell with ScSZ electrolyte and Ni/ScSZ anode was operated at 700oC for 500 h by feeding mixture of H2/H2O/N2as a fuel. Under 10%H2-40%H2O-50%N2, Sc diffused out of the ScSZ grain and dissolved into the adjacent Ni phase. Condensation of Sc in the Ni grain was enhanced by the application of current density of 0.5 A/cm2

DOI： 10.1149/10301.1879ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/10301.0375ecst

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.jpowsour.2019.227459

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ijhydene.2019.12.089

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.jpowsour.2019.227459

Language：Others   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ijhydene.2019.12.089

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/1945-7111/ab904f

Language：English   Publishing type：Research paper (scientific journal)  

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 BaZr_0.8Y_0.2O_3-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.

DOI： 10.1149/1945-7111/ab904f

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/1945-7111/abac87

Language：English   Publishing type：Research paper (scientific journal)  

The surface oxide layer of Fe-Cr-Al alloy was modified for use as the metal support of SOFCs. The Fe-Cr-Al alloy was firstly coated with LSCF and pre-heat-treated in a vacuum at 1000 °C for 1 h. In comparison with heat treatment at 700 °C, in which the surface oxide was identified as columnar γ-Al2O3/Sr3Al2O6, durability was greatly improved while maintaining electric conductivity at the same level. High-resolution STEM/TEM analysis revealed that the morphology was a similar columnar structure arranged in the same direction. The primary component was -Al2O3 polycrystal (>80%) and the secondary component was Sr3Al2O6 (∼15%). After the formation of columnar γ-Al2O3/Sr3Al2O6 in the low temperature range (<800 °C), γ-Al2O3 was transformed to a more stable -Al2O3 by increasing the temperature to 1000 °C. Ionic diffusion paths, which cause growth of the oxide during operation, were reduced in the columnar structure. Electronic conduction similarly occurred for both γ-Al2O3/Sr3Al2O6 and -Al2O3/Sr3Al2O6, which was enhanced along the interface between Al2O3 and Sr3Al2O6. Thus, we obtained a stable semiconductive Al2O-based surface oxide layer with a columnar -Al2O3/Sr3Al2O6 structure.

DOI： 10.1149/1945-7111/ababd8

Language：Others   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/1945-7111/abac87

Language：Others   Publishing type：Research paper (scientific journal)  

The surface oxide layer of Fe-Cr-Al alloy was modified for use as the metal support of SOFCs. The Fe-Cr-Al alloy was firstly coated with LSCF and pre-heat-treated in a vacuum at 1000 °C for 1 h. In comparison with heat treatment at 700 °C, in which the surface oxide was identified as columnar γ-Al2O3/Sr3Al2O6, durability was greatly improved while maintaining electric conductivity at the same level. High-resolution STEM/TEM analysis revealed that the morphology was a similar columnar structure arranged in the same direction. The primary component was -Al2O3 polycrystal (>80&#37;) and the secondary component was Sr3Al2O6 (∼15&#37;). After the formation of columnar γ-Al2O3/Sr3Al2O6 in the low temperature range (<800 °C), γ-Al2O3 was transformed to a more stable -Al2O3 by increasing the temperature to 1000 °C. Ionic diffusion paths, which cause growth of the oxide during operation, were reduced in the columnar structure. Electronic conduction similarly occurred for both γ-Al2O3/Sr3Al2O6 and -Al2O3/Sr3Al2O6, which was enhanced along the interface between Al2O3 and Sr3Al2O6. Thus, we obtained a stable semiconductive Al2O-based surface oxide layer with a columnar -Al2O3/Sr3Al2O6 structure.

DOI： 10.1149/1945-7111/ababd8

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/09101.2299ecst

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.jpowsour.2019.226751

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/09101.1889ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/09101.0847ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/09101.1009ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/09101.1905ecst

Language：Others   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1002/fuce.201800181

Language：Others   Publishing type：Research paper (scientific journal)  

Achievements of NEDO durability projects on SOFC mode are summarized with a focus on the physicochemical mechanisms characterized by diffusion properties of cell components and chemical reactions of cell components with gaseous impurities. Ni sintering and depletion including impurity (P, B, S) effects have been examined in terms of the surface/interface energies of Ni/oxide cermet anodes. The conductivity degradation due to the transformation of the cubic YSZ electrolyte was found to be characterized in terms of two time constants for the reductive and the oxidative regions to be determined by the Y-diffusivity and its enhancement on NiO internal reduction in YSZ, while observed gaps in conductivity degradation behavior between stacks and button cells were ascribed to differences in those physicochemical properties involved, namely cation diffusion and kinetics associated with NiO internal reduction. The cathode performance degradation due to sulfur poisoning exhibits a variety of dependences on the microstructure (dense or porous) of doped-ceria interlayers, the thickness of YSZ electrolyte and the humidity in the anode atmosphere, suggesting effects of protons in the cathode vicinity and the SrO activity changes during fabrication the LSCF/GDC/YSZ multilayers. Some defect chemical considerations were made on how such defects are affected by fabrication processes.

DOI： 10.1002/fuce.201800187

Language：English   Publishing type：Research paper (scientific journal)  

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&#37;, 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&#37;, 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.

DOI： 10.1016/j.ijhydene.2019.02.136

Language：Others   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ijhydene.2019.01.223

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ijhydene.2019.01.223

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1002/fuce.201800181

Language：English   Publishing type：Research paper (scientific journal)  

Achievements of NEDO durability projects on SOFC mode are summarized with a focus on the physicochemical mechanisms characterized by diffusion properties of cell components and chemical reactions of cell components with gaseous impurities. Ni sintering and depletion including impurity (P, B, S) effects have been examined in terms of the surface/interface energies of Ni/oxide cermet anodes. The conductivity degradation due to the transformation of the cubic YSZ electrolyte was found to be characterized in terms of two time constants for the reductive and the oxidative regions to be determined by the Y-diffusivity and its enhancement on NiO internal reduction in YSZ, while observed gaps in conductivity degradation behavior between stacks and button cells were ascribed to differences in those physicochemical properties involved, namely cation diffusion and kinetics associated with NiO internal reduction. The cathode performance degradation due to sulfur poisoning exhibits a variety of dependences on the microstructure (dense or porous) of doped-ceria interlayers, the thickness of YSZ electrolyte and the humidity in the anode atmosphere, suggesting effects of protons in the cathode vicinity and the SrO activity changes during fabrication the LSCF/GDC/YSZ multilayers. Some defect chemical considerations were made on how such defects are affected by fabrication processes.

DOI： 10.1002/fuce.201800187

Language：English   Publishing type：Research paper (scientific journal)  

In situ transmission electron microscopy (TEM) observations of a Ni(O)-Sc2O3-stabilized ZrO2 (ScSZ; 10 mol&#37; Sc2O3, 1 mol&#37; CeO2, 89mol&#37; ZrO2) anode in a solid oxide fuel cell (SOFC) have been performed at high temperatures under a hydrogen/oxygen gas atmosphere using an environmental transmission electron microscope (ETEM); the specimens were removed from cross-sections of the real SOFC by focused ion beam milling and lifting. When heating the NiO-ScSZ anode under a hydrogen atmosphere of 3mbar in ETEM, nano-pores were formed at the grain boundaries and on the surface of NiO particles at around 400°C due to the volume shrinkage accompanying the reduction of NiO to Ni. Moreover, densification of Ni occurred when increasing the temperature from 600 to 700°C. High-magnification TEM images obtained in the early stages of NiO reduction revealed that the (111) planes of Ni grew almost parallel to the (111) planes of NiO. In the case of heating Ni-ScSZ under an oxygen atmosphere of 3mbar in ETEM, oxidation of Ni starting from the surface of the particles occurred above 300°C. All Ni particles became polycrystalline NiO after the temperature was increased to 800°C. Volume expansion/contraction by mass transfer to the outside/inside of the Ni particles in the anode during repeated oxidation/reduction seems to result in the agglomeration of Ni catalysts during long-term SOFC operation. We emphasize that our in situ TEM observations will be applied to observe electrochemical reactions in SOFCs under applied electric fields.

DOI： 10.1093/jmicro/dfy025

Language：English   Publishing type：Research paper (scientific journal)  

In situ transmission electron microscopy (TEM) observations of a Ni(O)-Sc₂O₃-stabilized ZrO₂ (ScSZ; 10 mol% Sc₂O₃, 1 mol% CeO₂, 89mol% ZrO₂) anode in a solid oxide fuel cell (SOFC) have been performed at high temperatures under a hydrogen/oxygen gas atmosphere using an environmental transmission electron microscope (ETEM); the specimens were removed from cross-sections of the real SOFC by focused ion beam milling and lifting. When heating the NiO-ScSZ anode under a hydrogen atmosphere of 3mbar in ETEM, nano-pores were formed at the grain boundaries and on the surface of NiO particles at around 400°C due to the volume shrinkage accompanying the reduction of NiO to Ni. Moreover, densification of Ni occurred when increasing the temperature from 600 to 700°C. High-magnification TEM images obtained in the early stages of NiO reduction revealed that the (111) planes of Ni grew almost parallel to the (111) planes of NiO. In the case of heating Ni-ScSZ under an oxygen atmosphere of 3mbar in ETEM, oxidation of Ni starting from the surface of the particles occurred above 300°C. All Ni particles became polycrystalline NiO after the temperature was increased to 800°C. Volume expansion/contraction by mass transfer to the outside/inside of the Ni particles in the anode during repeated oxidation/reduction seems to result in the agglomeration of Ni catalysts during long-term SOFC operation. We emphasize that our in situ TEM observations will be applied to observe electrochemical reactions in SOFCs under applied electric fields.

DOI： 10.1093/jmicro/dfy025

Language：Others   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/2.0551811jes

Language：Others   Publishing type：Research paper (scientific journal)  

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&#37; 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.

DOI： 10.1149/2.0791803jes

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ijhydene.2017.10.122

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ijhydene.2017.10.122

Language：Others   Publishing type：Research paper (scientific journal)  

Long-term performance testes by CRIEPI (Central Research Institute for Electric Power Industry) on six industrial stacks have revealed an interesting correlation between cathode polarization loss and ohmic loss. To make clear the physicochemical meaning of this correlation, detailed analyses were made on the conductivity degradation of YSZ electrolyte in button cells and then on the ohmic losses in the industrial cells in terms of time constants which are determined from speed of the tetragonal transformation through the Y diffusion from the cubic phase to the tetragonal phase. In some cases, shorter time constants (faster degradations) were detected than those expected from the two-time-constant (with and without NiO reduction effects) model, suggesting that additional ohmic losses after subtracting the contribution from the tetragonal transformation must be caused from other sources such as cathode-degradation inducing effects. Main cathode degradations can be ascribed to sulfur poisoning due to contamination in air in the CRIEPI test site. An important feature was extracted as this cathode degradations became more severe when the gadolinium-doped ceria (GDC) interlayers were fabricated into dense film. Plausible mechanisms for cathode degradations were proposed based on the Sr/Co depletion on surface of lanthanum strontium cobalt ferrite (LSFC) in the active area. Peculiar cathode degradations found in stacks are interpreted in term of changes in surface concentration by reactions with sulfur oxide, electrochemical side reactions for water vapor emission or Sr volatilization, and diffusion of Sr/Co from inside LSCF.

DOI： 10.1002/fuce.201600186

Language：English   Publishing type：Research paper (scientific journal)  

Long-term performance testes by CRIEPI (Central Research Institute for Electric Power Industry) on six industrial stacks have revealed an interesting correlation between cathode polarization loss and ohmic loss. To make clear the physicochemical meaning of this correlation, detailed analyses were made on the conductivity degradation of YSZ electrolyte in button cells and then on the ohmic losses in the industrial cells in terms of time constants which are determined from speed of the tetragonal transformation through the Y diffusion from the cubic phase to the tetragonal phase. In some cases, shorter time constants (faster degradations) were detected than those expected from the two-time-constant (with and without NiO reduction effects) model, suggesting that additional ohmic losses after subtracting the contribution from the tetragonal transformation must be caused from other sources such as cathode-degradation inducing effects. Main cathode degradations can be ascribed to sulfur poisoning due to contamination in air in the CRIEPI test site. An important feature was extracted as this cathode degradations became more severe when the gadolinium-doped ceria (GDC) interlayers were fabricated into dense film. Plausible mechanisms for cathode degradations were proposed based on the Sr/Co depletion on surface of lanthanum strontium cobalt ferrite (LSFC) in the active area. Peculiar cathode degradations found in stacks are interpreted in term of changes in surface concentration by reactions with sulfur oxide, electrochemical side reactions for water vapor emission or Sr volatilization, and diffusion of Sr/Co from inside LSCF.

DOI： 10.1002/fuce.201600186

Language：Others   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/2.0071710jes

Language：English   Publishing type：Research paper (scientific journal)  

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(Zr_0.1Ce_0.7Y_0.1X_0.1)O_3-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.

DOI： 10.1016/j.ijhydene.2017.04.267

Language：English   Publishing type：Research paper (scientific journal)  

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&#37; 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.

DOI： 10.1016/j.ijhydene.2017.04.267

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.0993ecst

Language：English   Publishing type：Research paper (other academic)  

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, Ce_0.9Gd_0.1O₂) is utilized as a mixed ionic electronic conductor (MIEC), and combined with lanthanum-doped strontium titanate (LST, Sr_0.9La_0.1TiO₃) 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.

DOI： 10.1149/07801.1179ecst

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.1253ecst

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.2563ecst

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.1523ecst

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.2497ecst

Language：English   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.0197ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.1179ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.1253ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.2563ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.1523ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.2497ecst

Language：Others   Publishing type：Research paper (other academic)  

Porous Fe-Cr-Al alloy was investigated for the support material of solid oxide fuel cells. Interfacial resistance at 700oC in 3&#37; H2O - 97&#37; 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.&#37; 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.

DOI： 10.1149/07801.2069ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.0197ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/07801.0441ecst

Language：English   Publishing type：Research paper (scientific journal)  

Ru-based solid oxide fuel cell (SOFC) cermet anodes are presented. The preparation conditions of the Ru-based anodes are adjusted by preventing the sublimation of Ru-oxides at elevated temperatures by using an oxidizing atmosphere. SOFC single cells with zirconia-electrolyte and cathode are prepared, and the electrochemical performance is examined using realistic fuels containing low concentrations of higher hydrocarbons and trace sulfur impurities. The degradation rate is relatively high under simulated high fuel utilization operating conditions. However, under the operational condition near the fuel inlet of SOFC systems, the Ru-based anode satisfies 5000-h durability by using hydrocarbon-containing fuels. While a much higher durability is needed for stationary applications, the cells with the Ru-based anode may be applicable to e.g. automobile applications with hydrocarbon-containing fuels as high internal reforming activity, carbon deposition tolerance, and sulfur impurity tolerance have been verified.

DOI： 10.1016/j.ijhydene.2017.01.028

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Ru-based solid oxide fuel cell (SOFC) cermet anodes are presented. The preparation conditions of the Ru-based anodes are adjusted by preventing the sublimation of Ru-oxides at elevated temperatures by using an oxidizing atmosphere. SOFC single cells with zirconia-electrolyte and cathode are prepared, and the electrochemical performance is examined using realistic fuels containing low concentrations of higher hydrocarbons and trace sulfur impurities. The degradation rate is relatively high under simulated high fuel utilization operating conditions. However, under the operational condition near the fuel inlet of SOFC systems, the Ru-based anode satisfies 5000-h durability by using hydrocarbon-containing fuels. While a much higher durability is needed for stationary applications, the cells with the Ru-based anode may be applicable to e.g. automobile applications with hydrocarbon-containing fuels as high internal reforming activity, carbon deposition tolerance, and sulfur impurity tolerance have been verified.

DOI： 10.1016/j.ijhydene.2017.01.028

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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.

DOI： 10.1002/fuce.201600038

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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&#37;. The results revealed that the thickness of the solid solution decreased with increasing dopant concentration up to 20 mol&#37; 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&#37; 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&#37; is optimal to minimize the internal resistance of SOFCs when YDC is used as the interlayer material.

DOI： 10.1007/s11581-016-1816-9

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/2.0071710jes

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1007/s11581-016-1816-9

Language：English   Publishing type：Research paper (scientific journal)  

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&#37; and 9.7&#37; 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.

DOI： 10.1016/j.ijhydene.2016.07.265

Language：English   Publishing type：Research paper (scientific journal)  

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(Zr_0.1Ce_0.7Y_0.1Yb_0.1)O_3−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.

DOI： 10.1016/j.ijhydene.2016.07.265

Language：Others  

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.

DOI： 10.1002/9781119234531.ch4

Language：English  

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.

DOI： 10.1002/9781119234531.ch4

Language：Others   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/2.0141607jes

Language：Others   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ssi.2015.09.005

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.ssi.2015.09.005

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1016/j.jpowsour.2015.07.096

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/06801.0171ecst

Language：English   Publishing type：Research paper (scientific journal)  

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).

DOI： 10.1038/srep12640

Language：English   Publishing type：Research paper (scientific journal)  

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&#37; 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&#37; (LHV) corresponds to a net AC efficiency of approximately 76&#37; (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).

DOI： 10.1038/srep12640

Language：Others   Publishing type：Research paper (other academic)  

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, Uf<inf>M</inf>, is expressed as a function of number of stacks, n, and total fuel utilization, Uf<inf>T</inf>. When n = 10 and Uf<inf>T</inf> = 85&#37;, Uf<inf>M</inf> is calculated to be 36&#37;, which is much smaller than Uf<inf>T</inf>. Therefore, if the most downstream stack has high robustness against lean fuel gas, Uf<inf>T</inf> could be set to higher values without serious degradation by using this flow system.

DOI： 10.1149/06801.1961ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/06801.2209ecst

Language：Others   Publishing type：Research paper (other academic)  

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 La<inf>0.6</inf>Sr<inf>0.4</inf>Co<inf>0.2</inf>Fe<inf>0.8</inf>O<inf>3</inf> (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.

DOI： 10.1149/06801.1715ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/06801.1031ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/06801.2463ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/06801.1345ecst

Language：Others   Publishing type：Research paper (other academic)  

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.

DOI： 10.1149/06801.3107ecst

Language：English   Publishing type：Research paper (scientific journal)  

The influence of operating temperature and fuel/air utilization on long-term chemical stability and cell performance degradation is comprehensively investigated and reported for a segmented-in-series tubular solid oxide fuel cell (SOFC), with a (La0.5Sr0.25Ca0.25)MnO 3 (LSCM) cathode and a (Ce0.8Sm0.2)O 2 (SDC) cathode interlayer, under development for large-scale power plants combined with SOFCs. During three kinds of durability tests for 5000 hours, the average degradation rates of the cell-stacks were around zero, well meeting a tolerant cell voltage degradation rate target of 0.25&#37; per 1000 hours, corresponding to the 10&#37; cell voltage degradation for 40,000 hours. The electrochemical performance was stable at high operating temperature, although the porosity of the SDC cathode-interlayer decreased due to Mn and Ca diffusion from the LSCM cathode. On the other hand, the cell voltage noticeably decreased at lower operating temperature, below 800°C. Detailed observation of the microstructure and elemental distribution after durability testing revealed that a dense layer formed between the LSCM cathode and the SDC interlayer at low temperature, consisting of La, Ca, and Mn. The degradation in cell performance is attributed to the formation of this dense layer, preventing oxygen supply to the electrode reaction sites. © 2013 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.027403jes

Language：English   Publishing type：Research paper (scientific journal)  

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. © 2014 Elsevier B.V.

DOI： 10.1016/j.ssi.2014.01.047

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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. © The Author(s) 2014. Published by ECS. All rights reserved. Published by ECS. All rights reserved.

DOI： 10.1149/2.0421409jes

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/2.0421409jes

Language：Others   Publishing type：Research paper (scientific journal)  

Niobium-doped SnO2 is selected as an alternative carbon-free support material to negate carbon corrosion in polymer electrolyte fuel cells (PEFCs) electrocatalysts. The durability is measured using a membrane electrode assembly (MEA) over 60,000 start-stop cycles at high potential, equating to the lifetime of fuel cell vehicles. Using the Nb-doped SnO2 support results in retention of 99&#37; of the initial cell voltage. The current-voltage characteristics are improved by adding carbon nanofibers as fillers in the Nb-doped SnO2, indicating that electronic conduction in the electrocatalyst layer is critical in the application ofmetal oxide-supported electrocatalysts. © 2014 The Electrochemical Society.

DOI： 10.1149/2.005404eel

Language：English   Publishing type：Research paper (scientific journal)  

The influence of operating temperature and fuel/air utilization on long-term chemical stability and cell performance degradation is comprehensively investigated and reported for a segmented-in-series tubular solid oxide fuel cell (SOFC), with a (La_0.5Sr_0.25Ca_0.25)MnO ₃ (LSCM) cathode and a (Ce_0.8Sm_0.2)O ₂ (SDC) cathode interlayer, under development for large-scale power plants combined with SOFCs. During three kinds of durability tests for 5000 hours, the average degradation rates of the cell-stacks were around zero, well meeting a tolerant cell voltage degradation rate target of 0.25% per 1000 hours, corresponding to the 10% cell voltage degradation for 40,000 hours. The electrochemical performance was stable at high operating temperature, although the porosity of the SDC cathode-interlayer decreased due to Mn and Ca diffusion from the LSCM cathode. On the other hand, the cell voltage noticeably decreased at lower operating temperature, below 800°C. Detailed observation of the microstructure and elemental distribution after durability testing revealed that a dense layer formed between the LSCM cathode and the SDC interlayer at low temperature, consisting of La, Ca, and Mn. The degradation in cell performance is attributed to the formation of this dense layer, preventing oxygen supply to the electrode reaction sites.

DOI： 10.1149/2.027403jes

Language：English   Publishing type：Research paper (scientific journal)  

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. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2013.11.030

Language：English   Publishing type：Research paper (scientific journal)  

Niobium-doped SnO₂ is selected as an alternative carbon-free support material to negate carbon corrosion in polymer electrolyte fuel cells (PEFCs) electrocatalysts. The durability is measured using a membrane electrode assembly (MEA) over 60,000 start-stop cycles at high potential, equating to the lifetime of fuel cell vehicles. Using the Nb-doped SnO₂ support results in retention of 99% of the initial cell voltage. The current-voltage characteristics are improved by adding carbon nanofibers as fillers in the Nb-doped SnO₂, indicating that electronic conduction in the electrocatalyst layer is critical in the application ofmetal oxide-supported electrocatalysts.

DOI： 10.1149/2.005404eel

Language：Others   Publishing type：Research paper (other academic)  

The durability and reliability of segmented-in-series (SIS) type cellsstack was investigated by multimodal assessment in which Tokyo Gas collaborated with research institutes under NEDO project, "Development of system and elemental technology on SOFCs". The SIS cells-stack, developed by Tokyo Gas in cooperation with Kyocera, has many advantages such as reduced temperature operation, highvoltage / low-current power generation, and lower in material cost of electrical insulating substrate compared to Ni based substrates for anode-supported cells. Another key advantage is that there is no need for alloy interconnects. This would make the cell-stack more durable than other types of cell-stacks having metallic interconnects. Durability of the stacks was investigated by the operations in electric furnaces at Tokyo Gas, Central Research Institute of Electric Power Industry (CRIEPI), and Kyushu University. After the operations post analyses were conducted by the research institutes, such as National Institute of Advanced Industrial Science and Technology (AIST), Tohoku University, Kyoto University, The University Tokyo, and Kyushu University. Through the multimodal assessment durability and reliability of the SIS stacks for long-term operation and thermal cycles have been shown to be high enough for 40,000 h life and more. © The Electrochemical Society.

DOI： 10.1149/05701.0325ecst

Language：English   Publishing type：Research paper (scientific journal)  

In SOFCs, a wide range of fuel gases can be applied, but fuel impurity tolerance may be desired. By applying gadolinia-doped ceria (GDC) anode material, we analyzed power generation characteristics and internal reforming followed by high-resolution electron microscopy in order to moderate sulfur poisoning. Effect of ceria addition into the anodes layers on sulfur poisoning is systematically analyzed and discussed.

DOI： 10.1149/05701.1395ecst

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/05701.1593ecst

Language：English   Publishing type：Research paper (scientific journal)  

We already clarified that chromium deposition near the cathode/electrolyte interface was predominantly affected by the cathode polarization and the chromium deposition occurred not only on the cathode materials (LSM, LSCF etc.) but also on the electrolyte material, which seems to be involved in the electrode reaction sites. In this study, influence of cathode polarization change on the distribution of the deposited chromium was investigated by using LSM cathode. Microstructure at the cathode/electrolyte interface seems to change by cathode polarization and the microscopic distribution of the deposited chromium can be affected by the change in the microstructure.

DOI： 10.1149/05701.1859ecst

Language：English   Publishing type：Research paper (scientific journal)  

The durability and reliability of segmented-in-series (SIS) type cellsstack was investigated by multimodal assessment in which Tokyo Gas collaborated with research institutes under NEDO project, "Development of system and elemental technology on SOFCs". The SIS cells-stack, developed by Tokyo Gas in cooperation with Kyocera, has many advantages such as reduced temperature operation, highvoltage / low-current power generation, and lower in material cost of electrical insulating substrate compared to Ni based substrates for anode-supported cells. Another key advantage is that there is no need for alloy interconnects. This would make the cell-stack more durable than other types of cell-stacks having metallic interconnects. Durability of the stacks was investigated by the operations in electric furnaces at Tokyo Gas, Central Research Institute of Electric Power Industry (CRIEPI), and Kyushu University. After the operations post analyses were conducted by the research institutes, such as National Institute of Advanced Industrial Science and Technology (AIST), Tohoku University, Kyoto University, The University Tokyo, and Kyushu University. Through the multimodal assessment durability and reliability of the SIS stacks for long-term operation and thermal cycles have been shown to be high enough for 40,000 h life and more.

DOI： 10.1149/05701.0325ecst

Language：English   Publishing type：Research paper (scientific journal)  

Durability of SOFCs is one of the most important requirements for commercialization. In this paper, we analyze chemical degradation phenomena caused by both extrinsic and intrinsic origins besides by thermal/redox cycling. As external degradation, impurity (sulfur, phosphorus etc.) poisoning has been systematically analyzed and classified based on both thermochemical and kinetic consideration. We present typical intrinsic chemical degradation phenomena observed, mainly diffusion-related processes (interdiffusion, grain boundary diffusion, dopant dissolution, phase transformation etc.) around interfaces between the electrolyte and the electrode, which has been revealed through high-resolution STEM-EDX analysis of cells after long-term operation. Degradation mechanisms have been classified.

DOI： 10.1149/05701.0315ecst

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1149/05701.2841ecst

Language：English   Publishing type：Research paper (scientific journal)  

Metal supported cells with porous metallic substrates made of stainless steels are expected to drastically improve remaining issues of durability and cost for solid oxide fuel cells (SOFCs). In this study, we succeeded in fabricating a porous alloy substrate for SOFC using a Fe-Cr-Al type stainless steel, which showed excellent heat resistance. We investigated the application of the alloy substrate for the cathode side and good heat resistance and relatively low contact resistance between the alloy substrate and La _0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) was obtained at 700°C in air.

DOI： 10.1149/05701.2289ecst

Language：English   Publishing type：Research paper (scientific journal)  

Durability of cells and stacks against thermal cycling and redox cycling is essential for practical SOFCs, in which the system experiences various kinds of cycling conditions, including the shutoff of fuel supply. In this study, we have investigated the influence of thermal cycling conditions, such as hot-standby, cold-standby, and shut-down, on the cell performance degradation.

DOI： 10.1149/05701.0691ecst

Language：English   Publishing type：Research paper (scientific journal)  

For the further commercialization of SOFCs, the cost reduction for materials is one of the most important technological issues. Currently, Y or Sc is widely used as a dopant of zirconia-based electrolytes, but these rare-earth elements are relatively expensive. In this study, we have examined the possibility to use Ca as an alternative dopant since it is abundant in the earth and inexpensive. We have experimentally found that Ca diffusion is relatively fast, causing cell performance degradation. Even so, such fast diffusion could be depressed by decreasing the concentration gradient of Ca dopant, leading to an improvement in the durability.

DOI： 10.1149/05701.0807ecst

Language：Others   Publishing type：Research paper (other academic)  

Durability of SOFCs is one of the most important requirements for commercialization. In this paper, we analyze chemical degradation phenomena caused by both extrinsic and intrinsic origins besides by thermal/redox cycling. As external degradation, impurity (sulfur, phosphorus etc.) poisoning has been systematically analyzed and classified based on both thermochemical and kinetic consideration. We present typical intrinsic chemical degradation phenomena observed, mainly diffusion-related processes (interdiffusion, grain boundary diffusion, dopant dissolution, phase transformation etc.) around interfaces between the electrolyte and the electrode, which has been revealed through high-resolution STEM-EDX analysis of cells after long-term operation. Degradation mechanisms have been classified. © The Electrochemical Society.

DOI： 10.1149/05701.0315ecst

Language：Others   Publishing type：Research paper (other academic)  

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. © The Electrochemical Society.

DOI： 10.1149/05701.2841ecst

Language：Others   Publishing type：Research paper (other academic)  

Metal supported cells with porous metallic substrates made of stainless steels are expected to drastically improve remaining issues of durability and cost for solid oxide fuel cells (SOFCs). In this study, we succeeded in fabricating a porous alloy substrate for SOFC using a Fe-Cr-Al type stainless steel, which showed excellent heat resistance. We investigated the application of the alloy substrate for the cathode side and good heat resistance and relatively low contact resistance between the alloy substrate and La 0.6Sr0.4Co0.2Fe0.8O3 (LSCF) was obtained at 700°C in air. © The Electrochemical Society.

DOI： 10.1149/05701.2289ecst

Language：Others   Publishing type：Research paper (other academic)  

Durability of cells and stacks against thermal cycling and redox cycling is essential for practical SOFCs, in which the system experiences various kinds of cycling conditions, including the shutoff of fuel supply. In this study, we have investigated the influence of thermal cycling conditions, such as hot-standby, cold-standby, and shut-down, on the cell performance degradation. © The Electrochemical Society.

DOI： 10.1149/05701.0691ecst

Language：Others   Publishing type：Research paper (other academic)  

For the further commercialization of SOFCs, the cost reduction for materials is one of the most important technological issues. Currently, Y or Sc is widely used as a dopant of zirconia-based electrolytes, but these rare-earth elements are relatively expensive. In this study, we have examined the possibility to use Ca as an alternative dopant since it is abundant in the earth and inexpensive. We have experimentally found that Ca diffusion is relatively fast, causing cell performance degradation. Even so, such fast diffusion could be depressed by decreasing the concentration gradient of Ca dopant, leading to an improvement in the durability. © The Electrochemical Society.

DOI： 10.1149/05701.0807ecst

Language：Others   Publishing type：Research paper (other academic)  

In SOFCs, a wide range of fuel gases can be applied, but fuel impurity tolerance may be desired. By applying gadolinia-doped ceria (GDC) anode material, we analyzed power generation characteristics and internal reforming followed by high-resolution electron microscopy in order to moderate sulfur poisoning. Effect of ceria addition into the anodes layers on sulfur poisoning is systematically analyzed and discussed. © The Electrochemical Society.

DOI： 10.1149/05701.1395ecst

Language：Others   Publishing type：Research paper (other academic)  

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. © The Electrochemical Society.

DOI： 10.1149/05701.1593ecst

Language：English   Publishing type：Research paper (other academic)  

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. © The Electrochemical Society.

DOI： 10.1149/05030.0021ecst

Language：English   Publishing type：Research paper (other academic)  

We already clarified that chromium deposition near the cathode/electrolyte interface was predominantly affected by the cathode polarization and the chromium deposition occurred not only on the cathode materials (LSM, LSCF etc.) but also on the electrolyte material, which seems to be involved in the electrode reaction sites. In this study, influence of cathode polarization change on the distribution of the deposited chromium was investigated by using LSM cathode. Microstructure at the cathode/electrolyte interface seems to change by cathode polarization and the microscopic distribution of the deposited chromium can be affected by the change in the microstructure. ©The Electrochemical Society.

DOI： 10.1149/05701.1859ecst

Language：English   Publishing type：Research paper (scientific journal)  

Sulfur is one of the major contaminants for SOFC anodes, and can cause performance degradation of SOFC systems. In the present study, H2S poisoning phenomena are analyzed at around 800°C, using electrolyte-supported single cells to understand Ni anode degradation mechanisms, especially under relatively oxidizing conditions. Anode performance degradation caused by sulfur in partially or fully pre-reformed CH₄-based fuels has been evaluated as a function of various operational parameters, including; operational temperature, pre-reforming ratio, steam-to-carbon ratio, fuel utilization, and current density, for different fuel compositions. Besides the well-known change in cell voltage by the reversible surface adsorption/desorption mechanism, sulfur poisoning phenomena associated with voltage oscillation and Ni oxidation are newly found at high fuel utilizations and at high current densities, respectively. Such degradation is associated with the increase in the O/Ni ratio, and grain growth of Ni-based particles in the anodes.

DOI： 10.1149/2.032211jes

Language：English   Publishing type：Research paper (other academic)  

Chromium poisoning phenomena were compared among three SOFC cathodes consisting of Lai_0.8Sr0.2MnO₃ (LSM), Lai _0.06Sri_0.4Fei_0.8Co_0.2O₃ (LSCF) and LaNii_0.06Fei_0.4O₃ (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.

DOI： 10.1149/05030.0021ecst

Language：Others   Publishing type：Research paper (scientific journal)  

Hydrogen purity sensor cells were newly developed with the principle of PEFC. By using the phenomena of PEFC's voltage drop seen in the presence of impurities and further minimizing the amount of Pt to make the cells more sensitive to impurities, the sensor cells were prepared. This unique sensing principle was applied to typical impurities in practical hydrogen gases, including CO, H2S, and NH3. Sensor responses were derived by analyzing various kinds of dependency on Pt loading, current density, impurity concentration, and operational temperature. Possibility of recovery from impurity poisoning was also studied by varying impurities' supply and potential charge. Consequently, our simple PEFC-type hydrogen purity sensors were verified to have ability to sense ppm-level impurities within 10 min. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2012.08.062

Language：English   Publishing type：Research paper (scientific journal)  

Hydrogen purity sensor cells were newly developed with the principle of PEFC. By using the phenomena of PEFC's voltage drop seen in the presence of impurities and further minimizing the amount of Pt to make the cells more sensitive to impurities, the sensor cells were prepared. This unique sensing principle was applied to typical impurities in practical hydrogen gases, including CO, H₂S, and NH₃. Sensor responses were derived by analyzing various kinds of dependency on Pt loading, current density, impurity concentration, and operational temperature. Possibility of recovery from impurity poisoning was also studied by varying impurities' supply and potential charge. Consequently, our simple PEFC-type hydrogen purity sensors were verified to have ability to sense ppm-level impurities within 10 min.

DOI： 10.1016/j.ijhydene.2012.08.062

Language：Others   Publishing type：Research paper (other academic)  

Sulfur is one of the major contaminants for SOFC anodes, and can cause performance degradation of SOFC systems. In the present study, H2S poisoning phenomena are analyzed at around 800°C, using electrolyte-supported single cells to understand Ni anode degradation mechanisms, especially under relatively oxidizing conditions. Anode performance degradation caused by sulfur in partially or fully pre-reformed CH4-based fuels has been evaluated as a function of various operational parameters, including; operational temperature, pre-reforming ratio, steam-to-carbon ratio, fuel utilization, and current density, for different fuel compositions. Besides the well-known change in cell voltage by the reversible surface adsorption/desorption mechanism, sulfur poisoning phenomena associated with voltage oscillation and Ni oxidation are newly found at high fuel utilizations and at high current densities, respectively. Such degradation is associated with the increase in the O/Ni ratio, and grain growth of Ni-based particles in the anodes. Copyright © 2012 The Electrochemical Society.

DOI： 10.1149/2.032211jes

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.5796/electrochemistry.80.150

Language：English   Publishing type：Research paper (other academic)  

Sulfur poisoning effect on the electrochemical performance and long-term durability of SOFC cathodes has been investigated for (La _0.8Sr _0.2) _0.98MnO ₃ (LSM) and La _0.6Sr _0.4Co _0.2Fe _0.8O ₃ (LSCF) up to 1000 hours. Gradual degradation of performance occurred, associated with the formation of strontium sulfate, which depended on SO ₂ concentration.

DOI： 10.1149/1.3570221

Language：English   Publishing type：Research paper (other academic)  

Carbon black is commonly used as an electrocatalyst support material in polymer electrolyte fuel cells (PEFCs). However, during the fuel cell start-stop cycles, carbon is known to be oxidized electrochemically. In the present study, SnO ₂ has been selected as a candidate for the support material, and the relation between SnO ₂ preparation conditions and electrochemical properties is analyzed.

DOI： 10.1149/1.3635766

Language：English   Publishing type：Research paper (other academic)  

Long-term durability is one of the most important technological issues for SOFC system development. Life time of SOFCs can be critically affected by foreign species, including impurities and minor constituents in fuels and oxidants, from the raw materials of cell components, and from system components. This paper summarizes an effort to understand the impurity poisoning analyzed by adding specific impurity species into fuels under various operational conditions to clarify poisoning mechanisms and their concentration threshold. Possible acceleration procedures for poisoning phenomena have also been discussed.

DOI： 10.1149/1.3570280

Language：Others   Publishing type：Research paper (other academic)  

The influence of water vapor in the air on the performance and durability of solid oxide fuel cell (SOFC) has been investigated for the-state-of-the-art cathodes, (La0.8Sr0.2)0.98MnO3 (LSM) and La0.6Sr0.4Co0.2Fe0.8O 3 (LSCF). Durability experiments were carried out at 800 °C up to 1000 h with various water vapor containing-air fed to the cathode side. Both types of cathode materials were basically stable under typical water vapor concentrations in the ambient air. Degradations could be accelerated at much higher water vapor concentrations, which could be associated with the decomposition of the cathode materials. Temperature dependence of this degradation was analyzed between 700 °C and 900 °C under 10 vol&#37; water vapor concentration, which showed that the effect of water vapor depends strongly on the temperature and led to a severe degradation at 700 °C within a short time period for both cathode materials. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2010.08.014

Language：English   Publishing type：Research paper (scientific journal)  

The influence of water vapor in the air on the performance and durability of solid oxide fuel cell (SOFC) has been investigated for the-state-of-the-art cathodes, (La_0.8Sr_0.2)_0.98MnO₃ (LSM) and La_0.6Sr_0.4Co_0.2Fe_0.8O ₃ (LSCF). Durability experiments were carried out at 800 °C up to 1000 h with various water vapor containing-air fed to the cathode side. Both types of cathode materials were basically stable under typical water vapor concentrations in the ambient air. Degradations could be accelerated at much higher water vapor concentrations, which could be associated with the decomposition of the cathode materials. Temperature dependence of this degradation was analyzed between 700 °C and 900 °C under 10 vol% water vapor concentration, which showed that the effect of water vapor depends strongly on the temperature and led to a severe degradation at 700 °C within a short time period for both cathode materials.

DOI： 10.1016/j.jpowsour.2010.08.014

Language：Others   Publishing type：Research paper (other academic)  

Sulfur poisoning effect on the electrochemical performance and long-term durability of SOFC cathodes has been investigated for (La 0.8Sr 0.2) 0.98MnO 3 (LSM) and La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) up to 1000 hours. Gradual degradation of performance occurred, associated with the formation of strontium sulfate, which depended on SO 2 concentration. ©The Electrochemical Society.

DOI： 10.1149/1.3570221

Language：Others   Publishing type：Research paper (other academic)  

Carbon black is commonly used as an electrocatalyst support material in polymer electrolyte fuel cells (PEFCs). However, during the fuel cell start-stop cycles, carbon is known to be oxidized electrochemically. In the present study, SnO 2 has been selected as a candidate for the support material, and the relation between SnO 2 preparation conditions and electrochemical properties is analyzed. © 2011 ECS - The Electrochemical Society.

DOI： 10.1149/1.3635766

Language：Others   Publishing type：Research paper (other academic)  

Long-term durability is one of the most important technological issues for SOFC system development. Life time of SOFCs can be critically affected by foreign species, including impurities and minor constituents in fuels and oxidants, from the raw materials of cell components, and from system components. This paper summarizes an effort to understand the impurity poisoning analyzed by adding specific impurity species into fuels under various operational conditions to clarify poisoning mechanisms and their concentration threshold. Possible acceleration procedures for poisoning phenomena have also been discussed. ©The Electrochemical Society.

DOI： 10.1149/1.3570280

Event date： 2024.12

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2024.5 - 2024.6

Language：English   Presentation type：Oral presentation (general)  

Venue：ボストン   Country：United States  

Event date： 2023.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神奈川大学   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.7

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2019.9

Language：English  

Venue：Kyoto   Country：Japan  

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 La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (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 1000^oC for 1 h. Stability of mass gain and electrical resistance in air at 700^oC was significantly improved. The morphology of the surface oxide layer was a complex structure consisting of α-Al₂O₃/Sr₃Al₂O₆.

Event date： 2019.9

Language：English  

Venue：Kyoto   Country：Japan  

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.

Event date： 2019.9

Language：English  

Venue：Kyoto   Country：Japan  

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 (LaNi_0.6Fe_0.4O₃) 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.

Event date： 2019.9

Language：English  

Venue：Kyoto   Country：Japan  

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 BaZr_0.8Y_0.2O_3-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.

Event date： 2019.9

Language：English  

Venue：Kyoto   Country：Japan  

In order to improve the stability under high fuel utilization, alternative anodes are fabricated with ionic (mixed) conducting GDC (Ce_0.9Gd_0.1O₂) and electronic conducting LST (Sr_0.9La_0.1TiO₃), 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.

Event date： 2017.7

Language：English  

Venue：Hollywood   Country：United States  

Transmission electron microscopic (TEM) studies have revealed SrZrO₃ formation and growth at La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF)/Ce_0.9Gd_0.1O₂ (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.

Event date： 2017.7

Language：English  

Venue：Hollywood   Country：United States  

The electrochemical properties of the proton-conducting ceramic fuel cells (PCFCs) with BaZr_0.1Ce_0.7Y_0.1X_0.1O_3-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.

Event date： 2015.7

Language：English  

Venue：Glasgow   Country：United Kingdom  

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.

Event date： 2015.7

Language：English  

Venue：Glasgow   Country：United Kingdom  

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.

Event date： 2015.7

Language：English  

Venue：Glasgow   Country：United Kingdom  

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.

Event date： 2015.7

Language：English  

Venue：Glasgow   Country：United Kingdom  

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.

Event date： 2015.7

Language：English  

Venue：Glasgow   Country：United Kingdom  

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 La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (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.

Event date： 2015.7

Language：English  

Venue：Glasgow   Country：United Kingdom  

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.

Event date： 2015.7

Language：English  

Venue：Glasgow   Country：United Kingdom  

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, Uf_M, is expressed as a function of number of stacks, n, and total fuel utilization, Uf_T. When n = 10 and Uf_T = 85%, Uf_M is calculated to be 36%, which is much smaller than Uf_T. Therefore, if the most downstream stack has high robustness against lean fuel gas, Uf_T could be set to higher values without serious degradation by using this flow system.

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：5

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc.