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FP7

METSAPP Report Summary

Project ID: 278257
Funded under: FP7-JTI
Country: Denmark

Final Report Summary - METSAPP (Metal supported SOFC technology for stationary and mobile applications)

Executive Summary:
Most SOFC demonstrations with ceramic cells in real system operation have revealed problems regarding reliability issues. Attention to reliability and robustness has especially been paid for mobile applications. Modelling studies as well as practical experience have shown how up-scaling of cells and stacks to more industrially relevant sizes generally leads to lower reliability in real system operation and intolerance towards system abuse and operation failures. Due to the ductility and mechanical strength of metals, metal supported cells have robustness advantages compared to anode supported cells. Also, the long term durability of anode supported cell and stack components requires a reduction in the operation temperature to ≈ 650 ºC, which is feasible with metal supported SOFCs. Therefore, METSAPP aims at developing novel cells and stacks based on a robust, reliable and up-scale-able metal supported technology for stationary as well as mobile applications.

Prior work demonstrated significant progress towards durability by using unconventional half-cell design, where the major material and durability problems associated by the use of Ni-YSZ anodes are circumvented by alternative anode structure, composed of a FeCr-ceramic porous conductive backbone, into which electro-catalysts are infiltrated. In previous project, oxidation issues of the FeCr metallic phase appeared to be the major durability issues. The METSAPP cell robustness was significantly improved with the LSFNT anode material development and its integration into the cell. The resulting cells with LSFNT based anode designs showed significant improvement in electrochemical stability. In addition, high performance cathodes were also developed and integrated into various sizes of cells successfully. Furthermore, the cell fabrication process was optimised to enhance the cost-efficiency and environmental friendliness by developing the co-casting process using non-toxic materials that enables mass manufacturing. More than 500 good quality cells in different sizes up to 300 cm2 were fabricated during the course of the project.

Several new interconnect coatings were investigated for the anode and cathode sides. The developed coatings result in much lower oxidation rates, inhibition of Cr evaporation and oxide scale resistance reduction. Furthermore, it was demonstrated that the coatings possess a self-healing capability so that even severe deformation damages during shaping of the interconnects can be tolerated. Thus, it is possible to mass produce the interconnect coatings before deformation. The data obtained with respect to oxidation rates and Cr evaporation were used to develop a new lifetime model, expected to describe the situation in a stack more realistically.

Modelling and computer simulations represented some important activities in METSAPP and major progresses were achieved. In particular, in order to assess the degradation failure mode, an oxidation model has been developed and implemented. The model describes the growth of the oxide scale and the change of the pore volume, which in turn influences the gas diffusion in the microstructure. In addition, the extensive electrochemical characterization and stability of the FeCr-LSFNT based cells enabled extraction of the electrochemical parameters for the validation of the developed 2D Finite Element Method (FEM)FEM model for I-V curves. These extracted parameters are in excellent agreement with the simulated I-V curves using 2D FEM model at different temperatures.

ElringKlinger AG took over the stack assembly after TOFC closure at the project end. The welding process parameters were adapted to the METSAPP cell and the stack design was optimised regarding the cell integration into the cell frame, illustrating the flexibility of METSAPP cells for different stack designs (both TOFC and EK designs). The necessary future steps for stack demonstration were defined.

Project Context and Objectives:
State of the art SOFC technology for stationary as well as for transportation application is being demonstrated with either planar or tubular ceramic anode-supported or electrolyte-supported SOFC cells. However, the SOFC technology faces many challenges when it comes to commercialization, since cost reduction, reliability and extended lifetime is required. In order to improve durability and cost efficiency of the cells the stacks and the system much of the development has in the past been focused on lower operation temperature, increased power density and material savings based on reduced cell and stack component thickness. Nevertheless, most of the demonstrations with ceramic cells in real system operation have until now revealed problems regarding these issues in combination with low robustness. Attention to these issues has especially been paid in connection with SOFC technology for mobile application, such as in APUs. Modelling studies as well as recent practical experience has proved how up-scaling of cells and stacks to larger more industrially relevant sizes generally leads to lower reliability in real system operation and intolerance towards system abuse and operation failures. These observations conform to the statistical distribution of mechanical properties governing the probability of failure of cells based on ceramic materials, whether it is for mobile or for stationary applications.

The metal-supported technology has many potential advantages such as cost, good thermal conductivity and ductility of the metallic substrate, which will ensure safe operation including thermal shock resistance and tolerance towards internal temperature gradients and operation cycles. Finally, reduction in the operation temperature to ≈ 650 ºC is feasible with metal supported SOFCs. Therefore, METSAPP aims at developing novel cells and stacks based on a robust, reliable and up-scale-able metal supported technology for stationary as well as mobile applications.

The preceding EU FP7 METSOFC project has been aiming at improved reliability and robustness for mobile applications by the introduction of metal supported cells based on cost effective, industrially relevant manufacturing processes and has shown potential for the use in APU units. Degradation tests have revealed that the novel METSOFC metal supported stack technology has a potential for 5.000-10.000 operation hours at 650-750 oC stack temperature fulfilling the well known requirements for APU applications. However, the knowledge gained from the project as well as from other parallel projects on metal supported cells highlighted the need for further improvements of the cell components in order to fulfil durability requirements in stationary applications (such as: Distributed generation, and CHP) where lifetime of 20.000 to 60.000 hours is mandatory. The objective of the METSAPP project is to improve the lifetime of SOFC stacks based on metal supported technology to beyond 10.000 hours aiming at 40.000 hours for stationary as well as mobile applications with increased power densities. The established experience indicates that long term durability requires a further reduction of the operation temperature to 600 – 700 ºC. METSAPP is targeting at a novel improved cell concept with a cell ASR of 0.5 Ωcm2 at 650 ºC with a degradation rate of less than 0.25% / 1000 h.

For this, the oxidation effects on the metal support and the anode has to be further investigated by combining mathematical oxidation models with testing, characterisation and screening of new materials. This includes further understanding of how microstructural parameters such as porosity or tortuosity change over time with oxidation. It also includes fundamental modelling of physical material parameters such as creep and deformation as a function of mechanical and thermo-mechanical load during operation. Finally, feedback from modelling and testing of cells and stacks are used to improve the materials in the cell and stack development work. Due to the limited project timeframe, this approach has to rely upon development and implementation of accelerated test protocols and extended simulation methods. Key development issues include:
• Metal powder development
• Development of novel anode designs and nano-structured coatings
• Integration of high performance stable cathodes
• Integration of developed components to full cells
• Component and cell manufacturing for testing and stacking
• Development of novel stack concepts
• Development of coatings for ferritic stainless steel interconnects.
• Electrochemical characterization and extraction of parameters for modelling and simulation.
• Development of advanced modelling tools and improved models to investigate the loss and degradation mechanism in cells and stacks
• Models to understand oxidation behaviour

The METSAPP project has the principal objective to improve the robustness and life time of the metal supported SOFC technology to significantly increase its appropriateness for cost effective up-scaling. For commercial breakthrough of the SOFC technology it is vital that the materials cost in case of large scale cell and stack production is reduced. The need for Ni-YSZ materials for the support layer in the current anode-supported cells or YSZ for the electrolyte-supported cells confines the raw material cost to a level of € 50-80 per kg. A metal-based SOFC stack technology has the potential to improve functionality, reliability and reproducibility and reduce the manufacturing cost of SOFC stacks. The objective of METSAPP is to bring the material cost for the major part of the cell and stack down to about € 10-20 per kg in case of stationary as well as mobile systems.

To reach these targets, METSAPP is to focus on improved nano-structured electrodes adapted to the metal-supported cell concept in METSOFC, as well as novel optimized stack designs to be introduced. In one of the work packages (WP2) new sulphur and carbon tolerant anodes based on doped titanates are to be developed, based on collaboration with the SCOTAS-SOFC EU/JTI-FCH project. DTU, USTAN as well as TOFC participated in the SCOTAS-SOFC project. In other cases, the new materials with increased performance are developed and implemented based on close collaboration with parallel national SOFC R&D projects. Furthermore metal supported cells and stacks developed in this project will lead to reliable and cost effective solutions suitable for up-scaling based on optimization in material selection and design. On stack level METSAPP will develop and introduce a new cost effective concept for thin metal interconnects with high oxidation resistance, long lifetime, low Cr evaporation rate and low area specific electrical resistance. The concept relies upon the continuous PVD thin film pre-coating technology for ferritic stainless strip steel developed by Sandvik (SMT) in the METSOFC project. METSAPP takes this breakthrough SOFC interconnect technology a big step further introducing novel in-situ multiple thin film coatings for prolonged life time.

Focusing on the objectives for long-term performance and up-scaling the project includes work on identification of relevant and critical material and design parameters through modelling, characterization, testing and post mortem analysis. An electro-chemical model of the repeatable stack elements will be developed and used for optimizing the cell size and flow patterns of interconnects. CFD & FEM modelling will be used for minimizing pressure drop across the cells and contact resistance between cells and interconnects. The improved understanding and knowledge obtained through modelling and testing will be transferred to other work packages for practical implementation through a close and effective link between the individual work packages and through efficient fast track iterations.
The project consist of a vertically integrated group of partners all supplementing each other and bringing the required competence, and experience into a focused and effective development approach. The project is front end loaded meaning that it first of all has a starting basis in the preceding METSOFC project with the same experienced partners plus two new supplementing partners needed to reach the project objectives. Reference materials whether metal powders for cell support, coatings, interconnects, cell seals or stacks are available for the project already from the starting point. The partners possess the required cross-functional competencies ranging from materials and electrochemical science, physical modelling and testing to materials and component processing and manufacturing. The partners possess all the necessary equipment for all the sequential steps of the whole development course such as: Advanced material characterization, testing stations for cells and stacks laboratory as well as industrial scale manufacturing equipment for powders, strip steels, thin film coatings, powder metallurgical as well as ceramic tape casting, screen printing, spray coating, lamination, powder metallurgical vacuum and hydrogen sintering, brazing, etc. There is a strong focus on industrially relevance by participation of three SOFC experienced industries. Furthermore, these industrial partners have a strong experience in coordinating R&D in collaboration with scientific institutional partners. High probability for success is ensured due to the mutual interest and vertical integration of the project partners avoiding contradictory interest.

Primary objectives:
● Robust metal-supported cell design, ASRcell < 0.5 Ωcm2, 650 oC
● Cell optimized and fabrication upscaled for various sizes
● Improved durability for stationary applications, degradation < 0.25% / 1000 h
● Modular, up-scaled stack design, stack ASRstack < 0.6 Ωcm2, 650 oC
● Robustness of 1-3 kW stack verified
● Cost effectiveness, industrially relevance, up-scale-ability illustrated

The work is organised in eight work packages. Three of which are related to overall management and dissemination across the whole project. The other five work packages deal with the five major technological areas to focus on. The work package interaction/interdependence is based on a LEAN spiral concept, with effective short cuts, avoiding sub-optimization and increasing speed of development.

Project Results:
The METSAPP project scientific and technical main results for the development and integration of metal supported cells (MS-SOFCs) and stacks are covering mainly five areas. A lot of focus was put on the development and characterisation of novel MS-SOFCs, including in particular the development of new robust anode material and their integration, as well as manufacturing of cells for demonstration and detailled electrochemical characterisation. The project also addressed the development of robust stack components, as well as robust stack designs and building of stacks by two consecutive partners, first Topsoe Fuel Cells and then ElringKlinger. This work was supported by development of characterization tools and numerical models. Details on the S&T results obtained can be found in the attached pdf file.

Potential Impact:
Metal-supported SOFC is clearly better suited for the use in mobile applications, for instance for APU and electric vehicles, than state-of-the-art ceramic based anode-supported or electrolyte-supported SOFC. The use of MS-SOFCs for µ-CHP has also clear potentials. The METSAPP project demonstrated the feasibility of a stable metal supported cell, based on a FeCr-LSFNT anode backbone infiltrated with Ni-GDC electrocatalyst. This cell design showed significantly improved oxidation resistance and electrocatalytic stability, with potential for further improvement of the stability and initial performance. The current stability level reached makes the cell usable for mobile applications. Further development would be needed for stationary applications. Hundreds of cells were produced using relevant industrial techniques. However, the cell manufacturability has to be further improved with focus on the electrocatalyst integration process. This, in addition with further understanding of the backbone/electrocatalyst interaction is expected to result in superior stability as well as improved initial performance. New highly performant coatings that can be mass produced on thin interconnects can be exploited for the METSAPP based stack concept, as well as for any SOFC stack concept using thin metallic interconnects. The extensive electrochemical characterization and stability of the FeCr-LSFNT based cells enabled extraction of the electrochemical parameters for the validation of the developed 2D FEM model for I-V curves. These extracted parameters are in excellent agreement with the simulated I-V curves using 2D FEM model at different temperatures. The advanced models for flow-homogenization optimization, developed at TOFC, partly under METSAPP, are in used for SOEC (HTAS) and SOFC (Resolvent I/S) applications. The project also demonstrated the use of THDA device to assist the development process of SOFC stacks for the first time, using anode supported SOFC stacks with great success. This method can be exploited further for all types of SOFC stacks and is expected useful also on the cell level. The project demonstrated that the METSAPP cells can be used for different stack designs, though demonstration potential for stacking with ElringKlinger’s design was shown and the necessary knowledge was obtained to promote MS-SOFC development even further. The main industrialisation is foreseen on special markets, which are mobile home, a houseboat, a yacht, etc.. The advantages of a SOFC APU, like silent and efficient power generation, and potentially of a combined production of heat and power are highly desirable and valuable. Furthermore, these markets are open to new technologies and customers are willing to spend more on technologically advanced products. For the special markets, ElringKlinger assumes a volume of 5000 units for the year 2030. Following these special markets, the larger markets for APUs in the transport sector and micro-CHPs become accessible and the upscaling into the new markets will help to reduce cost even further. Even an assumed small percentage of 1% of the total amount of boilers sold in Europe each year (approximatively 5 million) will increase stack sales up to 50.000 units per year. This is equivalent to over 1.5 million cells. This method should help to establish the SOFC technology in the European market and will help to achieve the goals for 2020 (20% cut in greenhouse gases, 20% increase in energy efficiency and 20% energy from renewable sources). More details on the advantages and use of metallic supported based stack are given in the attached pdf file.

List of Websites:
www.metsapp.eu
Contact details are provided in the attached final report as a pdf file

Related information

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Soren Dahlkilde, (Project Controller)
Tel.: +45 5180 1579
Fax: +45 4677 5858
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