bluuebunny/crossref_metadata_2025 huggingface dataset:
Long Term (4 Years) Performance of Co/Ce Coated 441 for SOFC Interconnect Applications
Authors: Goebel Claudia , Berger Robert , Lundberg Mats W , Westlinder Jörgen , Svensson Jan-Erik , Froitzheim Jan
Published: February 2020

Ferritic stainless steel interconnectors are widely used in solid oxide fuel cells (SOFC) due to a combination of low cost, compatible thermal expansion properties and ease of manufacturing. However, their viability is hindered by some key technical hurdles. Most stainless steels suggested for SOFC applications rely on the formation of a fairly protective Cr2O3 scale. However, in air side environments Cr species evaporation leads to material failure and insufficient lifetimes. Coatings offer a way to mitigate Cr evaporation and in some cases decrease oxide scale growth. Numerous research papers have investigated different coating compositions and deposition techniques, however, the most commonly suggested material is (Mn,Co)3O4 (MCO). Instead of depositing MCO metallic Co can be applied. During operation Co is converted into Co3O4 and subsequently enriched in Mn from the underlying steel substrate. It has been shown that this type of coating effectively impedes Cr volatilization, even when only very thin layers (600 nm) are applied. Moreover the major advantage of metallic Co coatings are cost savings, since Co can be applied in a large scale roll-to-roll process before stamping the interconnect into its final shape. Furthermore, our previous work has shown that an additional layer of 10 nm Ce in combination with the Co coating results in the aforementioned mitigation of volatilization of Cr species, and also effectively reduces oxide scale growth. Oxide scale growth is detrimental for two reasons. First, a depletion of oxide scale forming element (Cr) can result in the formation of poorly protective iron oxide. Second, even a protective Cr2O3 scale grows with time. Since Cr2O3 is only a moderate electronic conductor this results in an increase of Area Specific Resistance (ASR) as the oxide scale grows in thickness. This eventually creates prohibitively high resistances. Both effects can be mitigated by addition of a thin Ce layer.

In the present work Ce/Co (10/600 nm) coated AISI 441 has been exposed for 4 years (35 000 h) at 800 °C. The mass gain of the samples over the course of exposure has been recorded at selected intervals. After 35 000 h a mass gain of 3.76 mg/cm2 has been measured. Over the entire exposure parabolic mass gain kinetics are observed indicating the absence of a poorly protective iron oxide. After 35 000 h the samples were moved to a different setup to measure Cr(VI) evaporation. It was found that despite the fact that the coating was only 600 nm in thickness, it effectively inhibits volatilization of Cr even after 4 years of exposure. Furthermore, samples were removed at selected intervals to measure ASR.
Thermal Aging Effect on the Joint Strength between an SOFC Glass-Ceramic Sealant and LSM-Coated Metallic Interconnect
Authors: Hou Fan-Lin , Lin Chih-Kuang , Sugeta Atsushi , Akebono Hiroyuki , Wu Si-Han , Yang Peng , Lee Ruey-Yi
Published: February 2020

Fe-based alloys, such as ferritic stainless steels, developed for planar solid oxide fuel cell (pSOFC) interconnect commonly contain Cr and can form a chromia (Cr2O3) scale on the surface. At the high operating temperature of pSOFC, Cr can be oxidized to volatile Cr+6 species which can deposit in the cathode and lead to degradation of cathode performance and limit the lifetime of a pSOFC system. Coating a suitable material, such as lanthanum strontium manganite (LSM), has been practically conducted on the metallic interconnect to prevent such Cr poisoning in the cathode side of pSOFC. In this study, the joint strength between an SOFC glass-ceramic sealant (GC-9) and an interconnect steel (Crofer 22 APU) coated with La0.67Sr0.33MnO3 is investigated at room temperature (RT) and 800 °C in air under both shear and tensile loading modes. In particular, the effect of a long-term thermal aging at 800 °C on the joint strength is characterized. Results indicate that an LSM coating on the metallic interconnect degrades the joint strength between the given GC-9 glass-ceramic sealant and Crofer 22 APU interconnect steel. The shear strength at RT and 800 °C is significantly degraded by 36% and 65%, respectively, and the tensile strength is significantly reduced by 39% and 80% at RT and 800 °C, respectively. It is attributable to the existence of pores around the interface between GC-9 sealant and LSM coating. However, the shear strength of LSM-coated joint specimen is enhanced by 52% at RT and by 200% at 800 °C after 1000-h thermal aging in air. The given thermal aging treatment also improves the tensile strength of LSM-coated joint specimen by 50% at 800 °C. This may be attributed to a self-healing effect of the GC-9 glass-ceramic during thermal aging to reduce the pore size. Fractography analyses reveal that fracture path involving the LSM layer and its adjoining interfaces accompanies a lower joint strength.
Advances in Low Temperature Coatings for Solid Oxide Fuel Cell Components
Authors: Kidner Neil J. , Ibanez Sergio , Seabaugh Matthew Mark , Swartz Scott
Published: February 2020

In the development of solid-oxide fuel cells, coating technologies are essential to successful commercialization. Electrode coating technologies allow the cost-effective deposition of anode and cathodes on cell components at high volumes and high precision. Further, catalytic and corrosion resistant coatings for common steel alloys find application in gas delivery and fuel reforming components of the balance-of-plant. Such corrosion-resistant alloys are also combined with conductive and insulating oxide protective layers to making low-cost steel interconnectors corrosion-resistant at SOFC operating while maintaining low contact resistance and minimizing Cr volatilization.

Many of the first generation coating technologies that have found commercial implementation were designed for cell and stack operating temperatures of 750°C and higher. By design, conductive coatings for steels provide low contributions to the overall stack resistance (ASR < 0.05 ohm-cm2) at these operating temperatures. However, as stack operating temperatures push to the 600°C range, new protective coatings are required that achieve similar resistances at lower temperatures. In this paper, Nexceris will report on the development of new formulations designed to meet these needs, based on our patented approaches.

To complement these protective coatings, Nexceris has developed a suite of contact paste, insulating layer coatings and catalytic materials for SOFC stacks and balance of plant, all designed with the end-user needs in mind. Leveraging aerosol spray deposition approaches that have been scaled to commercial requirements, Nexceris can interleave these coatings to create uniquely functional interconnects, cells and reformer components. Examples of the flexibility of these coating approaches will be provided, with performance data.
Towards Solid Oxide Fuel Cells (SOFCs) with Proton Conducting Electrolytes Operating at Low Temperature: Is the Scale-up Feasible?
Authors: Traversa Enrico
Published: February 2020

Solid oxide fuel cells (SOFCs) are an efficient and environmental-friendly alternative to combustion engines for supplying power. There is at present a keen interest on SOFCs in China with the government supporting a number of commercialization initiatives with large grants. However, their high operating temperatures and cost hampers their broad use and causes long-term stability problems. A step forward towards reducing the SOFC working temperature at 600°C or below can be the use of high temperature proton conductor (HTPC) oxides as electrolytes, due to their lower activation energy for proton conduction (0.3-0.6 eV), with respect to oxygen-ion conducting electrolytes. We have recently made significant progresses in the development of chemically-stable HTPC electrolytes and cathode materials associated, by using Y-doped barium zirconate (BZY). In this talk, after an introduction reporting an overview of the state-of-the-art of SOFC research in China, the recent work performed in our group toward the prospective commercialization of SOFC based on chemically stable proton conducting electrolyte will be presented.
Evaluation of Mechanical Damages in SOFCs during Start/Stop Operation by Using Acoustic Emission Technique
Authors: Kumada Keigo , Sato Kazuhisa , Hashida Toshiyuki
Published: February 2020

The mechanical durability and reliability of solid oxide fuel cells (SOFCs) are one of the critical issues for their realizations and engineering applications. To achieve the goal, extensive and detailed investigations into the mechanical damage process are needed. This paper presents an acoustic emission (AE) method for detecting the mechanical damage in anode-supported cells (ASCs). Start/Stop cycle tests (between RT and 800°C) were carried out using single cells. The cells with a configuration of NiO-YSZ/YSZ/GDC/LSCF-GDC/LSCF of 20 mm in diameter were prepared and sealed on an alumina tube with a borosilicate glass ring only in the cathode side. After 2 cycle start/stop cycles, no damage was induced in the cells and their electrical performances were maintained without degradation. The experimental results indicated that the AE technique employed in this study allowed us to distinguish the damages in the cells from the cracking in the glass seals. Based on the result, the mechanical damages during redox treatments were evaluated using the AE technique. The electrochemical evaluation performed concurrently with the redox treatments demonstrated the validity and significance of AE monitoring for detecting mechanical damages in SOFCs.
Mechanical Investigation of Various Stack Designs for Solid Oxide Cells
Authors: Molla Tesfaye T , Kwok Kawai , Frandsen Henrik Lund
Published: February 2020

Stress development in metallic interconnects during operational cycles of solid oxide cells (SOCs) could create permanent plastic deformations, which can cause contact losses in the interface between the interconnect and cells. The magnitude of these stresses and their distribution within the SOC stack are dependent on the overall design of the stack and its operational parameters/conditions. In this study, analysis of stress generation in metallic interconnects due to temperature and stack assembly loadings for different types of generic SOC stack designs operated under the same operational cycles is performed. The analysis includes stack design concepts with and without contact layers having cross-shaped and/or corrugated metallic interconnect. To consider the effect of thermal gradient over the surface of the stacks (due to electro-chemical reaction), stacks with two types of temperature profiles are studied. The analysis is performed numerically using finite element modeling of a standard repeating unit of SOC stack. Special focus is given to stresses that can cause possible delamination of the interconnect from the cell that subsequently leads to loss of electrical contact. Comparison of stress for different types of stack design concepts are presented. An effective way to minimize stresses in the interconnect is found to be through designing the micro-architectures of the interconnect and us eof contact layers materials.

Key words: Solid oxide fuel cells, Metalic interconnect, Creep, finite element modeling
Experimental Characterization of Low Temperature Solid Oxide Cell Stack
Authors: Tallgren Johan , Himanen Olli , Noponen Matti
Published: February 2020

Reversible solid oxide cell (rSOC) and solid oxide electrolysis (SOE) are gaining growing interest because they can convert both electricity into a chemical fuel and fuel back to electricity with high efficiency. This work summarizes for the first time the electrochemical performance characterization of Elcogen E350 stack both in fuel cell and electrolysis modes. Elcogen E350 stack is composed of 15 unit layers all having an 121 cm2 active electrode area. The electrochemical characterization is conducted in temperature region 650 – 700 °C and with varying current densities, multiple steam-to-hydrogen ratios, reactant utilizations and air flow rates. Results indicate that the stack can be used not only as a fuel cell but also in electrolysis mode and it is capable to be operated up to 1 A/cm2current density already at 650 °C and can be operated also with high reactant utilization even in electrolysis mode.

Figure 1. (left) Elcogen E350 polarization at conditions: T[furnace] = 650°C, T[air,inlet] = T[fuel,inlet] = 640 °C, V[steam] = 21.1 Nl/min, V[H2] = 2.24 Nl/min, V[air] = 67 Nl/min. (right) Elcogen E350 polarization at conditions: T[furnace] = 650°C, T[air,inlet] = T[fuel,inlet] = 640 °C, V[steam] = 7.76 Nl/min, V[H2] = 7.76 Nl/min, V[air] = 33 Nl/min.

Figure 1
Ceria/Bismuth Oxide Bilayer Electrolyte based Low-Temperature SOFCs with Stable Electrochemical Performance
Authors: Jaiswal Abhishek , Pesaran Alireza , Omar Shobit , Wachsman Eric D.
Published: February 2020

SOFCs are electrochemical devices that directly convert the electrochemical energy of a fuel into electricity. One common approach to lower the operating temperature of the SOFC is to replace the widely used yttria – stabilized zirconia (YSZ) with higher conductivity materials such as doped ceria. Doped-ceria materials such as GDC, are mixed ionic electronic conductors (MIECs) that are reduced from Ce4+ to Ce3+ in a fuel atmosphere, resulting in electronic conduction in the electrolyte by small-polaron hopping mechanism. In order to block the electronic leakage current through the electrolyte that induces lower OCV and power dissipation, we are developing advanced SOFCs based on ceria/bismuth oxide bilayer electrolyte, which can operate at low temperatures (450-650 °C). Stabilized-Bi2O3 has been reported to be an ionic conductor under oxidizing conditions that can effectively suppress the leakage current through GDC. Recently developed stabilized bismuth oxide (SBO) electrolyte material, which showed stable conductivity at lower temperatures was used to block the electronic leakage current. In this work, the effect of SBO/GDC thickness ratio and overall thickness of the electrolyte on the OCV of the cell was studied. Thickness of GDC and SBO layers was varied. The results showed the addition of SBO layer was effective in blocking electronic conduction and increased the OCV compared to the baseline single layer GDC cell. Further, the relative and total thickness of the two layers had a significant impact on the OCV of the cell at different temperatures with best performance obtained with cells with lower GDC thickness and higher SBO thickness. Lastly, long-term stability tests showed exceptional low degradation rates for both OCV and power density of the bilayer SBO/GDC cells.
Reaction Mechanism and Rate-Determining Step Speculation of Reversible CO/CO2 Electrochemical Conversion on the Nickel Patterned Electrodes
Authors: Luo Yu , Li Wenying , Shi Yixiang , Cai Ningsheng
Published: February 2020

The nickel(Ni)-patterned electrode enables researchers to quantify the triple-phase boundary (TPB) length and Ni surface area, exclude the influence of bulk gas diffusion and clearly separate the active regions of the chemical/electrochemical reactions. This tool has been studied for identifying the reaction mechanism in SOFC but rarely in SOEC. In this study, the Ni-patterned electrodes with the stripe width of 100 μm were tested in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes at the atmosphere of H2O/H2 and further H2O/CO2/H2/CO. The experimental test shows the stability of the Ni-patterned electrode in the H2O/H2 atmosphere was much poorer than that in the CO/CO2 atmosphere due to the nickel reacting with steam. Thus, the Ni-patterned electrode needed to operate at a temperature of ≤700oC with the inlet H2/H2O molar ratio of >7 and the current-applied time shouldn’t be over 5 h to keep the accuracy of the TPB length and Ni surface area. The effects of the temperature, partial pressure of H2O and H2 are investigated. The activation energy of the Ni-patterned electrodes was 0.386 eV. The electrochemical performance had a positive correlation with both the partial pressure of H2 and H2O, especially showed higher sensitivity to the partial pressure of H2O. Further, a possible mechanism of the H2O/H2 electrochemical conversion was proposed according to the experimental data and existing literature, which contains two-step charge-transfer reaction: H(Ni)+O2-(YSZ)OH-(YSZ)+(Ni)+e- and H(Ni)+OH-(YSZ)H2O(YSZ)+(Ni)+e-. Based on the experiments, an analytical calculation was performed to investigate the rate-determining steps in the Ni-patterned electrodes by bridging the connection between the kinetic parameters and operating conditions. The results indicate the rate-limiting steps may be different for the SOFC and SOEC modes. In SOFC mode, the H2 electrochemical oxidation could depend more on the charge-transfer reaction H(Ni)+O2-(YSZ)→OH-(YSZ)+(Ni)+e-, however in SOEC mode, the rate-determining step of the H2O electrochemical reduction should be H2O(YSZ)+(Ni)+e-→OH-(YSZ)+H(Ni). In this way, a reversible mechanism could be applied for reversible SOFC (RSOFC) to describe the conversion between hydrogen and steam by different charge-transfer-reaction domination in the SOFC and SOEC mode.

Figure 1
Half-Cell Study of La and Ca Doped Strontium Titanates Anode for Direct Methane Solid Oxide Fuel Cell
Authors: Tiwari Pankaj Kr , Irvine John T. S. , Basu Suddhasatwa
Published: February 2020

Solid oxide fuel cell (SOFC) has been providing high conversion efficiency of chemical energy to electricity without any pollution. One of the major advantages of SOFC over other fuel cell is use of direct natural gas at high temperature without any external reformer. Conventional Ni-yttria stabilized zirconia (YSZ) composite anode provides excellent catalytic property, current collection and stability for H2 oxidation but it is not tolerant towards sulphur poisoning and also accelerates coke deposition in presence of hydrocarbon fuels. It necessitates the use of alternate anode for direct hydrocarbon SOFC. In the present work, attempts have been made to apply A-site deficient La and Ca doped SrTiO3 (LSCTA-) as potential anode for direct methane SOFC. Electrolyte supported half-cells with LSCTA- anode backbone have been tested in H2 and humidified CH4 fuel. Low catalytic activity of LSCTA- towards electro oxidation of fuel is significantly improves in presence of metallic catalyst. 6% CeO2 loading in LSCTA- backbone improves the performance of the cell in H2 as well as in humidified CH4 at 800 °C. It has been observed that coke deposition did not degrade the anode active surface even after 6 h of exposure of CH4 at the elevated temperature of 800 °C. 4% Ni infiltration in 6%CeO2-LSCTA- enhances the performance from 131 mW cm-2 to 200 mw cm-2 at 800 °C in H2. In humidified CH4 environment, cell having 4% Ni-6% CeO2-LSCTA- anode shows lesser performance (140 mw cm-2 Power density) due to sluggish methane oxidation reaction but provided enhanced power density (216 mw cm-2) once H2 is again fed after 6 h cell operation in humidified CH4. i-V/ i-P analysis of half-cell shown in fig. 1 explains the performance in H2 as well as in CH4 at 800 °C. Maximum power density of cell is 200 mW cm-2 (554 mA cm-2) at 1 h of operation in H2, which increases up to 216 mW cm-2 (578 mA cm-2) in H2 after 6h of cell operation in humidified CH4. In humidified CH4 exposure, maximum power density of cell is 89 mW cm-2 (285 mA cm-2) at 1 h of operation, which increases up to 140 mW cm-2 (409 mA cm-2) at 6 h of operation. The performance of the cell is reasonably good as results presented here correspond to a cell having thick electrolyte (300 μm). The cells are found to be structurally robust even after 12 h of accelerated testing. LSCTA-is a potential anode backbone material for direct methane SOFC and could be an excellent anode for other hydrocarbons.

Key Words: A-site deficient SrTiO3, Direct Methane SOFC, LSCTA- anode, half-cell study.

Figure 1
Current Status of National SOFC Projects in Japan
Authors: Nirasawa Hitoshi
Published: February 2020

The New Energy and Industrial Technology Development Organization (NEDO) has been conducting technology development and demonstrative research programs related to SOFC, as one of the most important and promising technologies for CO2 reduction and realizing dispersed power sources. One of their achievements was the-first-in-the-world commercialization of SOFC-based combined heat and power (CHP) system “ENE-FARM type S” in 2011.

In June 2014, the Ministry of Economy, Trade and Industry (METI) has compiled a Strategic Road Map for Hydrogen and Fuel Cells. It was established, releasing fuel cells for commercial and industrial use onto the market in 2017 as one of the processes of expanding the use of fuel cell technology. NEDO’s activities and recent trends on SOFC, including a program “Technology development for promoting SOFC commercialization” , will be overviewed.
Network Analysis of Fuel Cell Heat Engine Distributed Energy Systems
Authors: Williams Mark C , Gemmen Randall
Published: February 2020

A thermodynamic and electrochemical framework transformed into an electrical network is used to analyze the power output and efficiency of high-temperature, ceramic fuel cell heat engine systems for the hydrogen oxidation reaction. It is interesting that the heat engine combustor subsystem performance was able to be recast in electrochemical and electrical network terms. The analysis includes the effect of temperature on the operation and performance of these ceramic, high-temperature systems. The power and efficiency responses of a distributed energy system operated at constant voltage to protect the fuel cell, using supplemental firing of the heat engine, and subjected to a cyclic load demand is presented. These systems are of interest to the emerging renewable energy grid. While the perfect fuel cell would undergo no degradation, practical fuel cells will degrade. The partition of power in a degrading distributed energy system is examined.
Gradual Conductivity Degradation of Nickel Doped Yttria Stabilized Zirconia by Phase Transformation at Operating Temperature
Authors: Ishiyama Tomohiro , Kishimoto Haruo , Bagarinao Katherine Develos- , Yamaji Katsuhiko , Horita Teruhisa , Yokokawa Harumi
Published: February 2020

The conductivity degradation of yttria stabilized zirconia(YSZ) due to the phase transformation from cubic phase to tetragonal phase is one of the issue in solid oxide fuel cells [1,2]. The phase transformation is enhanced by the reduction of nickel oxide which dissolved into YSZ electrolyte when making an anode-support-type-cells. The correlation of conductivity degradation and phase transformation ratio and dependence on oxygen profile in electrolyte for the area of tetragonal formation region about the 1 mol % nickel doped 8mol% yttria stabilized zirconia (Ni-YSZ) at 1173K were reported in our previous studies [2,3,4]. In this study, in order to investigate the factor of temperature for this phase transformation phenomena in nickel doped YSZ electrolyte, conductivity degradation behaviors were measured at various conditions. Even at around 750oC which similar to operating temperature of industrial SOFCs, the tetragonal formation was slightly observed at the area where the reduction of nickel oxide was occurred after over 500h measurement. The time constant for the conductivity degradation due to the tetragonal formation is well fitted on the Arrhenius type plot. This results show the strong temperature dependence for phase transformation. This is an important factor for rapid evaluation of durability of SOFCs.

References: [1] H. Yokokawa, ECS Trans. 68 (2015) 1827–1836. [2] H. Yokokawa, H. Kishimoto, T. Shimonosono, K. Yamaji, M. Muramatsu, K. Terada, K. Yashiro, T. Kawada, J. Electrochem. En. Conv. Stor.
in press (Paper No: JEECS-16-1083). [3] T. Shimonosono, H. Kishimoto, M.E. Brito, K. Yamaji, T. Horita, H. Yokokawa, Solid State Ionics.
225(2012) 69–72. [4] H. Kishimoto, K. Yashiro, T. Shimonosono, M.E. Brito, K. Yamaji, T. Horita, H. Yokokawa, J. Mizusaki, Electrochim. Acta.
82 (2012) 263–267.
Spatial Distribution of Oxygen Chemical Potential Profile across Zr0.84Y0.16O1.92 / Ce0.9Gd0.1O1.95 Bilayer Electrolyte under SOFC Operating Conditions
Authors: Kim In-Ho , Bae Hohan , Hong Jae-Woon , Lim Ji-Won , Song Sun-Ju
Published: February 2020

Partial electronic conductivity and total conductivity of Zr0.84Y0.16O1.92 and Ce0.9Gd0.1O1.95 have been measured by Hebb-Wagner polarization method and D.C. 4-probe conductivity measurements, respectively as a function of temperature and oxygen partial pressure. (600 ≤ temp/˚C ≤ 900, 10-18 ≤ PO
2/atm ≤ 0.21) Theoretical current-voltage characteristics and power density were calculated by integrating partial conductivities of charge carriers under various DC bias condition at fixed oxygen chemical potential gradient at both sides of the electrolyte (YSZ side: PO
2=10-22 GDC side: PO
2=0.21). The spatial distribution of oxygen partial pressure across the bilayer electrolyte with various thickness ratio was calculated based on Choudhury and Patterson’s model by considering zero electrode polarization. From the spatial distribution, oxygen partial pressures of interface were calculated with various operating condition. Interfacial oxygen chemical potential with various thickness ratio (YSZ/GDC) shows strong dependence upon cell operating potential.
Linking Initial Microstructure to Microstructure Evolution and Conductivity Change in SOFC Electrodes: A Phase Field Simulation
Authors: Lei Yinkai , Cheng Tian-Le , Wen Youhai
Published: February 2020

Microstructure evolution driven by thermal coarsening is an important factor for degradation of SOFC electrode. In this work, the effect of the initial microstructure on the microstructure evolution in SOFC electrode is investigated using a recently developed phase field model. Specifically, we tune the average grain size, broadening of the grain size distribution and the shape of the grains in the initial microstructure, and explore the evolution of the grain size, the specific surface area and the density of triple phase boundary in Ni-YSZ anode and LSM-YSZ cathode. And the conductivity change due to the microstructure evolution in both electrodes is studied as well. A map between the properties of the initial microstructure and the evolution rate of the properties in SOFC has been established, and an optimal initial microstructure is identified and discussed.
Multi-Scale, Multi-Physics Approach for Solid Oxide Fuel Cell Anode Reaction
Authors: Liu Shixue , Liu Shusheng , Saha Leton Chandra , Iskandarov Albert M , Jiao Zhenjun , Hara Shotaro , Ishimoto Takayoshi , Tada Tomofumi , Umeno Yoshitaka , Shikazono Naoki , Matsumura Syo , Koyama Michihisa
Published: February 2020

Electrode processes in solid oxide fuel cells are intensively studied to increase the system efficiency to compete with that of the state-of-the-art LNG-fueled combined cycle thermal power plant. Because the electrode performance depends both on electrode materials and microstructure, we are obliged to breakdown the complexity of phenomena in the porous electrode into elementary processes by best utilizing both the advanced measurement and the simulation techniques. Closely examining the efforts in literature [1-7], we have taken the combined top-down and bottom-up approach.

The most difficult issue has lied on the meso-scale modeling, which typically is based on microkinetic modeling [5-8]. To guarantee the predictivity of the modeling, it is inevitable to realize the simulation without arbitrary fitting parameters that are not necessarily based on realistic physics. For this purpose, we first exhaustively summarized literature data followed by the careful examinations. Next, we have made exhaustive simulations assuming different combinations of parameters in literature.

Finally, we obtained a set of parameters that matches with experimental observations within reasonable differences.

The details together with the results of top-down and bottom up simulations will be introduced together with future perspectives.

Acknowledgements

The activities of INAMORI Frontier Research Center is supported by Kyocera Co. Ltd. The activities of Advanced Automotive Research Collaborative Laboratory in Hiroshima University are supported by Mazda Corporation. The part of the research is supported by CREST, Japan Science and Technology Agency.

References

[1] J. Mizusaki, H. Tagawa, T. Saito, T. Yamamura, K. Kamitani, K. Hirano, S. Ehara, T. Takagi, T. Hikita, M. Ippommatsu, S. Nakagawa, K. Hashimoto, Solid State Ionics, 70/71, 52 (1994)

[2] W. Yao and E. Croiset, Can. J. Chem. Eng., 93, 2157 (2015)

[3] A. Bieberle, L. P. Meier, L. J. Gauckler, J. Electrochem. Soc., 148, A646 (2001)

[4] A. Utz, H. Störmer, A. Leonide, A. Weber, E. Ivers-Tiffée, J. Electrochem. Soc., 157 B920 (2010)

[5] W. G. Bessler, S. Gewies, M. Vogler, Electrochim. Acta, 53, 1782 (2007)

[6] W. G. Bessler, Solid State Ionics, 176, 997 (2005)

[7] M. Vogler, A. Bieberle-Hütter, L. Gauckler, J. Warnatz, and W. G. Bessler, J.

Electrochem. Soc., 156, B663 (2009)

[8] H. Kohno, S. Liu, T. Ogura, T. Ishimoto, D. S. Monder, K. Karan, M. Koyama, ECS Trans., 57(1), 2821 (2013)
Hybrid Approach to Remaining Useful Life Prediction of Solid Oxide Fuel Cell Stack
Authors: Dolenc Boštjan , Boškoski Pavle , Pohjoranta Antti , Noponen Matti , Juričić Đani
Published: February 2020

Improvement in efficiency and reliability are essential for more intensive deployment and exploitation of solid oxide fuel cell (SOFC) systems in modern society. Having the information about current health, degradation rate, and estimated remaining useful life (RUL) of the stack, at all times during operation, can greatly benefit the control system performance. Such information can be beneficial also for the service providers and end-users as the maintenance needs, including stack replacements, can be planned in advance. The control system can be able to optimize performance through a trade-off between maximal life span and best efficiency of power conversion. The knowledge on health status and its anticipated evolution assures easy and cost-effective maintainability. However, works that address issue of RUL prediction for SOFC are scant. On top of that, most of authors define voltage as health index and predict RUL accordingly. Such a selection of health index becomes inappropriate when SOFC is working under varying load conditions. In such a case stack voltage becomes affected by the changes in operating conditions and it is difficult to correlate drop in voltage with degradation rate. In this paper, we propose a novel hybrid approach to RUL prediction of SOFC systems, which overcomes the limitations of the known approaches and allows for reliable RUL prediction in non-stationary operating conditions. The approach consists of three main modules: (i.) estimation of area specific resistance (ASR) of the stack, (ii.) prediction of its future progress based on collected data, and (iii.) prediction of RUL. The methodology is evaluated on a 6 kW SOFC system.

Figure 1
Design of Leakage Gas Induction Channels for Reliable Planar-Type Solid Oxide Fuel Cell Stacks
Authors: Yoon Heesung , Jang Inyoung , Kim Chanho , Kim Sungmin , Paik Ungyu
Published: February 2020

Managing the leakage gas in a planar solid oxide fuel cell (SOFC) stack is one of the important factors associated with stack degradation. When the fuel leaks to the air electrode, the catalytic property of the cathode deteriorates. Further, when air leaks to the anode using Ni metal, the electrolyte thin film is peeled from the anode surface by reoxidizing Ni with NiO. Therefore, one of the ways to prevent deterioration characteristics of the SOFC stack is to effectively manage the sealing method to shut off the leaking gases. However, when the SOFC stack is used over a long period of time, gas leakage may occur due to degradation of the sealing material. In this study, we developed a stack of specially designed channels in a sealing gasket to prevent gas leakage to the fuel and air electrodes for the stability of the SOFC stack. The stack was evaluated using 10 x 10 cm2 anode support cells. This stack design can be operated for thermal cycling from operating temperature to room temperature, and ensuring the reliability of the stack even in the event of momentary interruption of air or fuel.
High Efficiency Direct Ammonia Type Fuel Cells based on BaZr
x
Ce0.8-X
Y0.2O3/Pd Oxide-Metal Junctions
Authors: Aoki Yoshitaka , Yamaguchi Tomoyuki , Kobayashi S , Zhu Chunyu , Habazaki Hiroki
Published: February 2020

Recently, ammonia has attracted a considerable interest as a prospective carbon-free fuel source for fuel cells due to the low cost, ease in liquefaction and transportation at ambient temperatures, and high volumetric energy density. The proton conducting ceramic fuel cells (PCFCs) using proton-conducting oxides, such as BaZr
x
Ce0.8-x
Y0.2O3-

d

, as an electrolyte is promising as a direct ammonia type fuel cells. The water formation in PCFCs is mainly progressive at the cathode side, unlike solid oxide fuel cells (SOFCs), and therefore, the contamination of the ammonia fuels into the exhaust water is precluded, thereby eliminating re-purification of water exhaust and simplifying total systems. Hydrogen membrane fuel cell (HMFC), which was firstly proposed by Ito et al., consists of an ultrathin proton conducting ceramic electrolyte supported on a dense hydrogen permeable metal anode. The cell facilitates efficient power generation, giving 900 mW cm-2 at 400°C, since reduced electrolyte thickness can significantly decreases the ohmic loss at lower temperatures. This unique cell configuration could be advantageous for ammonia fuel cells because 1) the NO
x
formation at the anode is perfectly prevented because NH3 gases are isolated from the oxide electrolytes by Pd solid anode and 2) Pd is expected to capture efficiently the hydrogen gases produced by the pyrolysis of ammonia due to the large ahydrogen sorption ability. Herein, we demonstrated the high efficiency power generation of the direct ammonia type HMFC due to the hydrogen pumping effects realized by BaZr0.1Ce0.7Y0.2O3-

d
(BZCY) and Pd heterointerface. Ohmic characteristics of the heterojunctions, altogether with hydrogen solubility of Pd, can facilitate the hole proton exchange between Pd and BZCY regardless of the lowered hydrogen concnetartion in NH3-fed anodes. The cell gained the maximum power density of 0.52 W cm-2 at 600°C, which was much higher than the champion data of ammonia PCFCs.
The Correlation of Sulfur Distribution in LSCF and Performance Degradation under Different Operation Temperatures
Authors: Wang Fangfang , Yan Kang , Budiman Riyan Achmad , Kishimoto Haruo , Ishiyama Tomohiro , Bagarinao Katherine Develos- , Yamaji Katsuhiko , Horita Teruhisa , Yokokawa Harumi
Published: February 2020

The investigation on the durability of solid oxide fuel cell (SOFC) stacks in real operation environments has revealed that the cathode is contaminated with sulfur during SOFC operation, although the sulfur dioxide concentration is very low in air (in ppb level). In this work, the effect of low concentration SO2 (0.01ppm) in air on the degradation of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF6428) cathode was investigated with different operation temperature of 650 oC, 700 oC, and 800 oC for 300 h. The performance degradation of LSCF6428 cathode is most serious at 700 oC due to both of ohmic and polarization resistance increase. The sulfur distribution and the SrSO4 formation concentrate near TPB at T ≤ 700 oC, but are near cathode surface at 800 oC. These different morphology changes of cathode near TPB are the main reason for the different performance degradation of the LSCF6428 cathode at different temperature.
In Operando Electrochemical High-Temperature X-Ray Diffraction Study of Ni-Ce0.9 Gd0.1O2-δ Redox Properties
Authors: Korjus Ove , Aruväli Jaan , Kirsimäe Kalle , Kivi Indrek , Nurk Gunnar
Published: February 2020

Typical anode materials for solid oxide fuel cells (SOFC) are Ni-cermets, either Ni/yttria stabilized zirconia (Ni-YSZ) or Ni/gadolinia doped ceria (Ni-GDC) [1]. In the case of Ni-cermet materials before the anode is ready for work NiO is reduced to Ni. During reduction process the solid phase volume of an anode decreases approximately 40%. Due to either system malfunction or contamination, air (oxygen) might diffuse into anode compartment, which causes Ni reoxidation to NiO. During this process the solid phase volume of an anode increases 66% [1,2]. Reoxidation of Ni might take place if after cell operation fuel gas flow is stopped in order to decrease fuel cell upkeep costs [3]. Reoxidation of Ni might also occur if electric load for the cell is too high and oxide ion flux through the membrane creates too oxidative environment at Ni catalyst.

In order to understand the dynamics of redox processes and to design the Ni-GDC electrodes with optimal microstructure the information related to simultaneous structural and electrochemical changes during SOFC operation would be very useful. In this work a novel approach for simultaneous monitoring of electrochemical (EC) properties and crystallographic structure in operating SOFC i.e. in operando SOFC EC-XRD measurement cell has been proposed and applied to understand the redox dynamics in Ni-GDC anode.

The impact of polarization on structure of Ce0.9 Gd0.1O2-d (GDC) in Ni-GDC cermet anode as well as impact of NiO ⇌ Ni redox cycles on the size and structure of Ni particles and electrical contact between particles has been studied with the in house developed in operando EC-HTXRD cell. Changes in the lattice parameters of Ni and GDC as well as electrochemical properties of Pt|Ni-GDC|ScCeSZ|GDC|LSC were monitored as a function of temperature (T), electrode polarization (E) and oxygen partial pressure (pO2). Influence of temperature, pO2 and polarization on GDC lattice parameters was observed. O2- current through the membrane lead to decrease of unit cell volume of GDC lattice. The observed change in lattice parameter upon polarization change from open circuit voltage (OCV) (depending on temperature, about 1.1 V) to 0.9V (potential of 3-electrode setup) was equal to 50 degree temperature change.

[1] A. Faes, A. Hessler-Wyser, A. Zryd, J. Van Herle, A review of RedOx cycling of solid oxide fuel cells anode, Membranes (Basel). 2 (2012) 585–664. doi:10.3390/membranes2030585.

[2] T. Klemenso̸, C. Chung, P.H. Larsen, M. Mogensen, The Mechanism Behind Redox Instability of Anodes in High-Temperature SOFCs, J. Electrochem. Soc. 152 (2005) A2186. doi:10.1149/1.2048228.

[3] D. Waldbillig, A. Wood, D.G. Ivey, Thermal analysis of the cyclic reduction and oxidation behaviour of SOFC anodes, Solid State Ionics. 176 (2005) 847–859. doi:10.1016/j.ssi.2004.12.002.

Figure 1
Synthesis of Ru-doped Double Perovskite Anode for SOFC
Authors: Monteiro Natalia K , Candido Gabriel Alves Silva , Fonseca Fabio C.
Published: February 2020

One of the great current needs for anode material in solid oxide fuel cells is to combine in one redox-resistant compound an efficient multifunctionality, that is, that the same material must exhibit both good catalytic activity and mixed ionic-electronic conductivity. Such a material should ideally be active towards different fuels allowing fuel-flex SOFCs capable to operate using the most convenient fuel available in various situations. Ceramics with perovskite structure are, from this point of view, are promising candidates. Different compounds such as (La,Sr)(Mn,Cr)O and SrMoMgO have been investigated, but more efficient anodes are still required. In this study, the Pr0.5Ba0.5MnO3 was used as the precursor phase of the double perovskite PrBaMn2O5+δ (PBMO), obtained at reducing conditions. The transport and catalytic properties were studied in the pristine compound and in Ru-doped samples Pr0.5Ba0.5Mn1-xRuxO3 (Ru-PBMO). Ru substitution at the B-site is expected to enhance the catalytic properties of the ceramic toward ethanol or methane fuels. Ceramic powders were synthesized by the polymeric precursor method and characterized by thermogravimetric analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrical properties of sintered samples were evaluated by dc 4-probe technique, in the 25 - 800 °C temperature range in both air and reducing conditions. The TG/DTA and XRD data show mass loss stabilization and crystalline phase formation occurring at ~800 °C. The evolution of the XRD pattern upon calcining temperature indicated the formation of single phase of Ru-PBMO samples at ~1100 °C. The initial results suggest that PBMO and PBMO-Ru compounds are promising SOFC anodes.
Improving Operation of a 2.5kW SOFC Power System with Supervisory Control
Authors: Vrecko Darko , Nerat Marko , Vrancic Damir , Dolanc Gregor , Dolenc Boštjan , Pregelj Bostjan , Meyer Fabien , Au Siu Fai , Makkus Robert , Juričić Đani
Published: February 2020

Operation of the SOFC power system can be improved by upgrading the low-level controllers with a supervisory controller (see Figure 1). In this work a simple, model-free supervisory optimizer that adjusts references for the low level controllers is proposed. The optimization problem for the SOFC power system is formulated with the cost function depending on the electrical efficiency of the system and deviations of the system temperatures from their limits. Electrical efficiency is calculated as the ratio of the net electrical power to the total power obtained by burning the fuel. The dominant parasitic losses of the system are assumed to be mainly related to the air blower consumption. Based on efficiency analysis, which demands a number of simulations on SOFC power system model, the references for the burner lambda and stack outlet and inlet air temperatures are selected as optimization variables. The optimization problem is solved by using the extremum-seeking approach where optimum is sought directly on the process. An advantage of this approach is that it does not need a model of the system and exceeds the weakness of model-based optimizers, which assume nominal process condition all the time and do not take into account the degradation processes in fuel cells. Its disadvantage is it needs to probe the system at all time by imposing small variations on manipulated variables and delivers a convergence speed which is somewhat slower compared to the model based approach. A simple algorithm is designed to perform the model-free optimization. The algorithm is additionally augmented to incorporate changes in the current load in order to increase the convergence speed of the optimization at large load changes. The efficiency of the optimizer is governed by properly tuned parameters of the optimization algorithm. Proposed supervisory optimizer is assessed on a simulated detailed physical model of a 2.5 kW SOFC power system by applying large step current load changes. Simulation results indicate that the optimizer improves efficiency of the system by approximately 10 % compared to the low-level controllers and keeps the system temperatures within the safe ranges (see Figure 2). Due to its simplicity the optimizer appears appropriate for practical applications.

Figure 1
A Dual Functional Solid Oxide Fuel Cell for Power Generation and Energy Storage
Authors: Zhang Cuijuan , Huang Kevin
Published: February 2020

Large-scale, cost-effective energy storage is highly desirable for balancing utility grid and renewable energy production. However, commercial scale demonstration of grid energy storage is generally lacking. Recently, we demonstrated a new bifunctional fuel-cell/battery hybrid system suited for stationary grid-scale energy storage. The new system is comprised of a reversible SOFC as the electrical charger/discharger and a redox-active metal/metal-oxide chemical bed as the energy store. During operation, the cathode of the system is constantly open to air, whereas the anode configuration defines the functionality of the system: power generation when the anode chamber is open to a fuel, and energy storage when the anode chamber is closed next to a neighboring metal/metal-oxide chemical bed.

The presentation highlights recent progress in performance evaluation and computational analysis of the fuel-cell/battery hybrid. These highlights include cycling performance in a temperature range of 500-600 oC and computational analysis of performance limiting factors. Strategies to achieve efficient and reversible hybrid system for simultaneous power generation and energy storage are proposed.
Failure Statistics for Commercial Lithium Ion Batteries
Authors: Harris Stephen J
Published: February 2020

There are relatively few publications that assess capacity decline in enough commercial cells to quantify

cell-to-cell variation, but those that do show a surprisingly wide variability. Capacity curves cross each

other often, a challenge for efforts to measure the state of health and predict the remaining useful life

(RUL) of individual cells. We analyze capacity fade statistics for 24 commercial pouch cells, providing an

estimate for the time to 5% failure. Our data indicate that RUL predictions based on remaining capacity or

internal resistance are accurate only once the cells have already sorted themselves into “better” and

“worse” ones. Analysis of our failure data, using maximum likelihood techniques, provide uniformly good

fits for a variety of definitions of failure with normal and with 2- and 3-parameter Weibull probability

density functions, but we argue against using a 3-parameter Weibull function for our data. pdf fitting

parameters appear to converge after about 15 failures, although business objectives should ultimately

determine whether data from a given number of batteries provides sufficient confidence to end lifecycle

testing. Increased efforts to make batteries with more consistent lifetimes should lead to improvements

in battery cost and safety.