SOFC stack development
La(Sr)TiO3 has been developed as a potential current collector for thin anode structures. The state-of-the-art Ni-anode is dimensionally unstable during redox due to the volume expansion associated with oxidation of Ni. The new material proved very useful with respect to stability, conductivity and thermal expansion, but showed an unexpected volume decrease during reduction, which may introduce contact problems during service.
Objective: Further development of the Danish SOFT technology aiming at a stack price of about 4000 DKK/kW-electricity production capacity in case of mass production. Work programme: 1) Anode for internal reforming. 2) Lower polarization resistance of cathode. 3) A thin electrolyte. 4) Cheap ceramic shaping methods. 5) Efficient contacting of interfaces. 6) Cell testing. 7) Economic analysis. 8) Post mortem of a 0.5 kW stack. Target for cell performance: 0.3 OMEGA cm2 at 950 deg. C using an internal reforming anode
An earlier economical optimisatin project (EFP94) focused upon the cost of the thick, profiled ceramic interconnect component as the largest contribution to overall stack cost. The concept has been changed and patenting of the new concept is considered. As part of the new concept a non-sintered, porous element containing gas channels and forming the electrical contact between a gas tight membrane and the cell has been developed. Test of the element in a single cell stack during 800 hours of operation minimizing the number of cell cracks and resulted in optimal stack element performance including absence of ageing. The optimisation project also showed than reduction of materials purity could be a valuable tool for cost reduction. Consequently materials based on high purity lanthanum has been attempted repalaced by materials base on lanthanides (La contaminated with other rare earth elements) enabling a cost reduction factor of 2-3 for the materials. Performance changes car still investigated in several projects, however it may be concluded that major cost reduction without consequences may be realised. A patent has been obtained by HTAS. Electrical contact problems between ceramic surfaces has received new attention as a major source for stack internal resistance. Equipment has been designed and fabricated for analyses of electrical resistances simultaneously with dimensional changes during component assembly at high temperature with controlled contact pressure. Measurements will be made in the context of the EFP98 and EFP99 SOFC project. A study has been made of the improtance of grading materials compositions in interconencts, electrodes and electrolyts supports as a basis for development of new electrodes and electrode supported thin electrolyte cells. Since June 1997 development of an anode supported thin electrolyte call has been carried out in the EFP96, EFP97 and EFP98 SOFC projects. The development is therefore described in all the projects. This development reached the first primary target at the end of 1998 by the demonstration of an internal resistance of 0.4OMEGA.cm2 at 850 deg. C for 5x5 cm cells. Simultateously the cost of production has been minimized further by enabling contiuous wet ceramic processing of the combined anode and electrolyte element with a single cofiring operation. Patenting is attemptes in 1999
Key figures
Category
Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| HALDOR TOPSØE A/S | ||
| IRD Fuel Cells A/S | ||
| Syddansk Universitet | ||
| Danmarks Tekniske Universitet (DTU) |
Contact
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