Mechanical Characterization and Modeling of Solid Oxide Fuel Cell Electrolytes with Honeycomb Support

Planar solid oxide fuel cells (SOFCs) are made up of repeating sequences of electrolytes, electrodes, seals, interconnects, and current collectors. For electro-chemical reasons it is best to keep the electrolyte as thin as possible. However, for electrolyte-supported cells, the thin electrolytes are susceptible to damage during production, assembly, and operation. To produce cells with sufficient mechanical robustness, electrolytes can be made with a co-sintered honeycomb structure that supports the thin, electro-chemically efficient electrolyte membranes.;The proposed electrolyte is characterized mechanically using various experimental and computational techniques. Elastic properties for the electrolyte materials are obtained at temperatures ranging from room temperature to 800°C using a sonic resonance technique. The electrolyte geometry is characterized at various length scales using a two-scale finite element model. The smaller, meso-scale model is used to obtain homogenized equivalent properties which are used as material inputs for the macro-scale. Stresses at the two scales are related via a scalar magnification factor. The equivalent stiffness and magnification factor are computed for a variety of meso-scale and macro-scale geometries and validated experimentally using four-point bending and tension experiments on representative samples. Using the results of the macro-scale simulations, design recommendations are made concerning how to reduce stress in the electrolyte in response to both thermal and pressure loading while being mindful of electro-chemical performance.;The electrolytes are further modeled in the context of an SOFC stack assembly with thermal and pressure loading. Current-collecting metal foams which neighbor the electrolyte are characterized using inverse finite element analysis, through which material properties are determined iteratively until the loads and displacements reported via simulation best match those measured experimentally. Coefficients of friction for the inverse model are obtained experimentally between the foams and various surfaces. The inverse method is validated by subjecting samples of the same material and geometry to compression between plates having different coefficients of friction. The stack model is then used to evaluate the loads imposed on the electrolyte by the surrounding assembly during operation. Based on the results of the stack model, it is found that the stresses imposed on the electrolyte due to thermal loading are significantly higher than those imposed due to pressure. The design recommendations from the macro-scale electrolyte model are revisited and updated to reflect stack operating conditions. Using the design recommendations, SOFCs having electrolytes with honeycomb support can be produced with sufficient mechanical robustness without sacrificing electro-chemical performance.