Residual stresses and strength of multilayer tape cast solid oxide fuel and electrolysis half-cells

The cost-effectiveness of Solid Oxide Cells production can be improved by introducing "multilayer-tape-casting" (MTC: sequential casting of the layers) and co-sintering of the half-cells. MTC additionally results in more homogeneous layers with strong interfaces. However, the thermal expansion coefficient (TEC) mismatch between the layers, cumulated from high temperature, induces significant residual stresses in the half-cells. Furthermore, it has been observed that MTC half-cells with 4 layers (MTC4: support, fuel electrode, electrolyte and barrier layer) are sometimes more fragile to handle than those with 3 layers (MTC3: without barrier layer). The bending strength of MTC3 and MTC4 under various loading orientations (electrolyte on the tensile or compressive side of the loading) is compared. The analysis, by taking residual stresses into account, shows that the strength of the half-cells with the electrolyte on the compressive side corresponds to the strength of the support. With the loading in the other direction (electrolyte on the tensile side), the origin of the failure is in a different layer for MTC3 (fuel electrode) and for MTC4 (barrier layer). In order to decrease the tensile residual stresses, especially in the outer barrier-layer, possible changes to the layer properties are discussed and some optimization guidelines proposed.