A planar solid oxide fuel cell is characterized by a thin ceramic electrolyte sandwiched between porous electrodes, along with seals and current collectors. To perform as a good oxide ion conductor, the electrolyte needs to be very thin. However, a thin electrolyte is highly prone to damage during production, assembly, and subsequent operation. To be both electrochemically efficient and mechanically robust, NexTech Materials Ltd has developed an innovative electrolyte, the FlexCellTM, for use in electrolyte-supported SOFCs. This electrolyte design has a honeycomb structure that supports thin, “active areas” thus providing good electro-chemical efficiency as well as mechanical robustness.
To optimize the FlexCell and understand its mechanical limits, a combination of experiments and finite element modeling are performed. The out-of-plane dimensions are much smaller than the in-plane dimensions, and hence a two-scale approach is required for optimizing the geometrical design of the FlexCell. At the large-scale, the whole electrolytic membrane is modeled with equivalent properties, whereas at the small-scale, the repeating pattern of the honeycomb structure is studied.
Nextech’s goal to commercially produce ultra large FlexCells of the order of 700 to 1200 cm2 depends largely on its mechanical performance. The aim of this work is to suggest ways to geometrically alter the design so that the mechanical membrane performs well under mechanical and thermal loading. By performing finite element simulations on the large area FlexCell, design parameters which influence its mechanical robustness are identified. Results of this analyses show the areas of high stresses. The stresses can be mapped to the small-scale to study small-scale failure. Since it is not known if optimal geometries scale with membrane size, a more methodical approach is undertaken to ensure that the thin active areas have adequate support in thermally varying environments.