Scaling up aqueous processing of A-site deficient strontium titanate for SOFC anode supports

The authors gratefully acknowledge funding from the Fuel Cells and Hydrogen Joint Undertaking under grant agreement n° 256730.All ceramic anode supported half cells of technically relevant scale were fabricated in this study, using a novel strontium titanate anode material. The use of this material would be highly advantageous in solid oxide fuel cells due to its redox tolerance and resistance to coking and sulphur poisoning. Successful fabrication was possible through aqueous tape casting of both anode support and electrolyte layers and subsequent lamination. Screen printing of electrolyte layers onto green anode tapes was also attempted but resulted in cracked electrolyte layers upon firing. Microstructural, electrical and mechanical properties of anode supports and half cells will be discussed. The use of two different commercial titanate powders with nominal identical, but in reality different stoichiometries, strongly affect electrical and mechanical properties. Careful consideration of such variations between powder suppliers, and batches of the same supplier, is critical for the successful implementation of ceramic anode supported solid oxide fuel cells.PostprintPeer reviewe

Curvature and stresses for bi-layer functional ceramic materials

The technical application of layered functional ceramic components is challenged by curvature effects and residual stresses originating mostly from the thermal mismatch or chemical strains of the joined materials. Based on the general solution for elastic deformation of monolithic and multilayered materials the determination of curvature and residual stress for linear elastic bi-material specimens with chemical strains, chemical reduction in stiffness, shape variations, gradients in elastic modulus or thermal expansion is outlined. The use of the relationships is exemplified for ceramic solid oxide fuel cell (SOFC) and ceramic membrane materials. For SOFCs curvature changes are considered resulting from the reduction of the anode and crystallization of a glass–ceramic sealant with semi-spherical shape. For gas separation membranes which currently under development for fossil power plants the effect of chemical strains is assessed. The limits of using analytical relationships are addressed for the warpage of thin, rectangular SOFCs

Steady State Creep of Ni-8YSZ Subsrates for Application in Solid Oxide Fuel and Electrolyser Cells

Steady state creep was characterized for Ni-8YSZ solid oxide fuel/electrolysis cell (SOFC/SOEC) substrate material. Intrinsic and extrinsic factors affecting creep behavior were assessed, such as compositional ratio, porosity and mechanical loading configuration. Mechanical tests were supported by analytical and numerical calculations. The results indicated a diffusion-dominated creep mechanism under both compressive and tensile creep conditions. Creep appeared to be dominated by the ceramic phase. Porosity significantly reduced creep resistance. The activation energy was discussed based on loading configuration, temperature and porosity

The Effect of an Oxygen Particle Pressure Gradient on the Mechanical Behavior of Perovskite Membrane Materials

In application of perovskite as oxygen conducting materials the membrane is operated at elevated temperatures under an oxygen gradient. The effect of the partial pressure difference on the mechanical properties is reported in the current work. Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) samples were annealed under an oxygen gradient. The mechanical properties of cross-sections were characterized using indentation testing. Chemical strains for BSCF and LSCF were too small to detect them after cooling to RT by XRD; however, the results suggest that the indentation crack length is affected by chemical strains for LSCF, but not for BSCF. An anisotropy of the indentation crack length and corresponding apparent fracture toughness is related with the interaction of domain switching and residual strain that is probably also associated with the observation that vacuum (10−5 mbar) annealed LSCF showed surface cracking on heating in air, whereas for BSCF such fracture features were not observed