Studies of residual stresses in planar solid oxide fuel cells

Planar solid oxide fuel cells (SOFCs) are composites consisting of porous and dense functional layers as electrodes and electrolyte, respectively. Due to the thermo-elastic mismatch between the individual layers residual stresses develop during manufacturing that result in warping for unconstrained cells. The residual stress of half-cells specimens with oxidized anode has been determined as a function of temperature. Two complementary techniques, X-ray diffraction analyses and measurements of cell curvature were applied. Moreover, changes in electrolyte residual stress associated with cell brazing to a steel interconnect were measured. The joining was carried out with symmetric cell composites having an anode layer sandwiched between two electrolyte layers. In addition to this test the effect of brazing and welding on the stress situation in the electrolyte of a real cell was tested.