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Integration techniques for up-scaled SOFC modules (SOFC integration)

Objective

In 1987, SOFC (Solid Oxide Fuel Cells) R&D began in the CEC JOULE programme, with the development of small SOFC cells. This research has now reached a stage where kW-size SOFC systems are constructed according to different concepts. The Dornier concept aims at development of flatplate SOFC with ceramic bipolar plates. The development of stacks and suitable scaling between the cells are key problems.
The objectives of this project are:
- The development and optimization of materials, components and techniques for sealing and joining purposes needed for the stacking of up-scaled planar SOFC components (minimum size 100x100 mm2) and the integration of stacks and manifolds.

- The evaluation of factors limiting electrode performance The expected deliverables are:
- Improved materials and components for sealing purposes in planar SOFC units
- Optimized processes for the stacking of up-scaled planar sofc components and the joining of stacks and manifolds
- Verification of integration procedures by test results
- Modeling and experimental results as a basis for further electrode improvement

The project is in parallel with a German R&D programme in which substantial basic development has already been carried out.
The project dealt with an important step in the development of large planar SOFC units. The research was focused on the development and optimization of the techniques for the stacking and joining of up-scaled planar SOFC components and on the materials and components necessary for the
gastight sealing of stacks. Moreover detailed investigations of the CH4 steam reforming reaction kinetics and its effects on the anode/electrolyte interface were carried out (ICE/HT, Patras).

Research at Daimler-Benx/Dornier focused on the development of the stacking and joining techniques. The principal stacking techniques, that have been developed for a small cell size of 5 x 5 cm{2} in a previous project, were transferred to the up-scaled cell size. In the first stage of the
development the electrode joining layers and the sealing pastes were optimized with respect to their composition and adapted to the processing properties. After establishing the integration techniques for the up-scaled stack size, automation of the stacking process was introduced. This led to a significantly improved reproducibility and yield of the stack manufacturing.

As a result of the optimization of the stacking techniques and fine tuning of the joining materials important and promising test results were achieved with up-scaled SOFC stacks. High reproducibility and uniformity in the cell and stack performances could be demonstrated with a significant number of stacks. In particular a 1 kW unit was successfully operated under realistic operating conditions. Excellent long-term behaviour was achieved with a 10-cell stack operated for more than 6000 hours with only 0.7% power loss per 1000 hours. Moreover the possibility of a high fuel utilization of up to 80% resulting in a high electrical efficiency could be proven with a 300 W SOFC module.

In parallel Cookson was developing new non-alkali glass ceramics suitable for use as sealing in the Dornier SOFC. The system studied was based on the region of the calcia-alumina-magnesia-silica where diopside, enstatite and wollastonite are expected to form. Trends in the flow properties and thermal expansion coefficient have been related to the composition and the crystalline phases present. The most promising material was tested in the Dornier stacking processes. The results suggested that reasonable sealing could be achieved but further refinement of the glass ceramic properties is necessary.
The roles of the three partners are: Dornier (Friedrichshafen, Germany) acts as coordinator and is technically responsible for the specification of seal requirements, electrical long term investigation of sealing materials, stacking and manifolding processes, manufacture and experimental investigation of test modules.

Cookson Technology Centre (Oxford, England) is responsible for developing and testing materials for sealing planar stacks and stack/manifold interfaces and supplying sealing materials and components.

Institute of Chemical Engineering and High Temperature Chemical Processes (University of Patras, Greece) will carry out research into the factors limiting electrode performance which is of interest for the optimization of general operating characteristics.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Dornier Luftfahrt GmbH
Address
An Der Bundesstraße 31
88039 Friedrichshafen
Germany

Participants (2)

Cookson Group plc
United Kingdom
Address
Sandy Lane Yarnton
OX5 1PF Kidlington
Foundation for Research and Technology-Hellas
Greece
Address
Stadiou 18, Platani
26500 Patras