Optimizing GDC electrolytes of FESCs: Insights into microstructure formation and cell processing

Gadolinium doped ceria (GDC) is regarded as a promising alternative to 8YSZ in SOC applications due to its improved ionic conductivity and mixed ionic-electronic conductivity offering potential benefits as fuel electrode material. However, interdiffusion at the active interface between YSZ electrolyte and Ni-GDC electrode results in structural and performance degradation. Thus, implementation of a GDC electrolyte with a Ni-GDC electrode should enhance cell performance, as no interdiffusion zones are formed at the active interface.The incorporation of GDC into a fuel electrode-supported cell poses several challenges. Especially, the appropriate microstructure formation of the electrolyte during the co-sintering of multiple layers requires a fundamental understanding of each processing step. For this reason, cell production, entirely based on screen printing, was systematically investigated with focus on a three-layer GDC/YSZ/GDC electrolyte that can be sintered on a Ni-GDC fuel electrode.Investigations have shown that a pre-treatment of the starting powder can significantly alter the sintered electrolyte structure. Therefore, the influence of powder treatment at various temperatures and the addition of dopants on the sintering behavior was investigated. The powders were characterized by their particle size distribution (PSD), measurements of the specific surface area (SSA) via BET, scanning electron microscopy (SEM) and their sintering behavior via dilatometry measurements. Utilizing rheological measurements, new screen-printing pastes were formulated and optimized regarding their flow behavior. Dispersion stability for non-polar solvents, linear viscoelastic behavior (LVE) and time-dependent structural changes within the pastes after deposition (thixotropy) were evaluated and adjusted. Ultimately, half and full cells were produced. Cell bending after co-sintering of the electrolyte was quantified using white light topography and minimized by adjusting layer thicknesses in the composite. Cross-sections indicate appropriate layer microstructures while performance testing of these three-layer electrolyte cells is currently ongoing.