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Working towards Mass Manufactured, Low Cost and Robust SOFC stacks

Final Report Summary - MMLRC=SOFC (Working towards Mass Manufactured, Low Cost and Robust SOFC stacks)

Executive Summary:
Lightweight SOFC stacks are currently being developed for automotive applications such as APU, for portable devices and possibly in the near future also vehicle propulsion. They supply electrical efficiencies of up to 60% and offer high fuel flexibility. SOFC are able to operate on a variety of fuels relevant for mobile and portable devices, such as syn-gas from Diesel reforming, LPG, alcohols or propane/butane, or directly on methane, ammonium or hydrogen.
The requirements for thermal cycling in lightweight stacks are high, since start-up times for vehicles of most kinds (road and rail vehicles, even aircraft and ships) are short compared to those for power generation. The same applies to portable devices which are expected to be operational within very short time intervals. But also for stationary applications rapid start-up will be an advantage since the SOFC system can be operated more closely in accordance with the electrical and thermal loads of the customer. It is therefore essential that lightweight stacks have excellent thermo-mechanical properties. This requires a specific stack design that compensates mechanical stresses from temperature gradients in space and time.
The cost pressure on mobile and portable applications is high and the requirements for (mechanical) robustness challenging. It is therefore important to manufacture stacks to high quality standards and implement as many automated precision assembly processes as possible in an approach of parallel improvement of quality and lowering of manufacturing cost.
The MMLCR=SOFC project addressed a specific design solution that uses thin sheet metal formed in such a way that the coupling of mechanical stress between the SOFC cell and the metal interconnect frames is minimised. Furthermore, the cost of materials is reduced. The design allows for low-cost mass manufacturing of stack components, and automated quality assurance and assembly.

Project Context and Objectives:
The project targeted:
(1) further developing and qualifying the JÜLICH lightweight SOFC stack with flexible integration of the SOFC cells in the stack and separate contacting and sealing force with respect to design, sealing materials and protective coatings; evaluation of the environmental impact of the SOFC stack product and environmental optimisation
(2) setting up industrial mass manufacturing processes and equipment for repeating unit manufacturing, including low-cost produced cells
(3) setting up automated industrial mass manufacturing processes and equipment for stack assembly and joining
(4) performing tests under relevant application operating conditions for steady state and transient operation
(5) verifying the industrialisability and market relevance of the project results with the perspective of adequate valorisation after project termination

Project Results:
During the first (2012) and second (Jan to June 2013) reporting period extensive design simulations were performed in order to optimise the thermo-mechanical bahaviour of the cassette type stacks. It was decided to use the JUELICH CSIV design as the starting point as design D1.0 and further develop this into the design 2.0 (alias CSV) in the course of the project. Therefore BORIT could immediately start with manufacturing samples that could be built into cassettes at JUELICH and subsequently tested. During the second reporting period the design simulations were concluded and the final Design 2.0 further detailed. Elements of the Design 2.0 were implemented and tested on shaping samples. Partner BORIT then proceeded to manufacture the required amount of parts and further refine the manufacturing process by simplifying the spacer parts.
Sample parts became available from March and April 2014, and were built into cassettes at JUELICH and subsequently tested.
Improved glass samples were extensively characterised thermomechanically. Solder glasses with properties superior to previously used glasses were introduced for component testing towards the end of the project but not used for the proof-of-concept testing for lack of time and resources. Laser supported glass welding was considered an important element of automated manufacturing. The first basic tests were accomplished with good success and work further evolved towards the milestone in 2013. Although the milestone requirements were not fully met, it was decided to continue work with the hope to acquire essential knowledge on the methodology. In practical welding tests, though, it was finally shown that the required balance between laser beam power to melt the glass sealant and avoidance of melting the steel coupons to be joined was not possible.
The automated manufacturing line was already fully designed according to the requirements derived from the design process in WP 1, manufacturing experience and manufacturability and cost considerations during Period 1 of the project. Following the ‘freeze’ od Design D2.0 this planning was further detailed. Unfortunately an update of the costings revealed that the project budget was not capable of accommodating the cost and it was decided to reduce actual building of the assembly line to one or two key components.

Potential Impact:
The project results are immediately commercialisable for the industry project partners (BORIT, SOLIDpower, Turbocoating). BORIT is already going ahead with a variety of projects it is applying the hydroforming technology in for manufacturing bipolar plates and interconnects. Likewise, Turbocoating is involved in a number of projects and developments to deliver coated steel parts. SOLIDpower is developing its SOFC stack and system projects with direct use of the foreground gained in this project for future APU projects.
The research partners have made good use of the project results by submitting a large number of conference congributions (22) and scientific papers (8).
The final issue to be solved is the full commercialisation of the stack technology developed in this project (D2.x). Talks with investment companies following a first contact with the EIB resulted in a lack of interest on the side of potential investors in the technology. Apparently it is essential to first find an industrial partner to transfer the full technology to, establish technology demonstrators and then create business cases finance institutions can get interested in. This is a weak spot of the FCH JU technology development chain where the 'valley of death' between technology development and product development is still not addressed and prevents valorisation of technology developed with FCH JU funding.

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