NASA and others have shown improved power density of planar solid oxide fuel cells (P-SOFCs) fabricated via the freeze casting technique. As a manufacturing process, freeze casting is capable of producing ceramic, metal, and cermet components with unique and tailorable microstructural features that enhance SOFC performance. Low thermo-cyclic durability and slow startup times are common problems for P-SOFCs and have similarly limited the development of freeze cast P-SOFCs. Tubular SOFCs (T-SOFCs) have demonstrated superior thermal cycling capability and relatively fast startup times but have been reported to have lower volumetric power density compared to P-SOFCs. The utilization of freeze casting for fabrication of tubular geometries is suggested as a solution to significantly increase the volumetric power density of T-SOFCs by enhancing gas diffusivity and triple phase boundary reactions and to be at par or better than the power densities of state-of-art P-SOFCs.

This paper reports the fabrication and characterization of freeze cast tubular anode supports for SOFCs. NiO-8YSZ (nickel oxide yttria-stabilized zirconia) anode supports were fabricated using three methods: gelation casting, center pin method, and a freeze and drain method. Slurry rheology was modified for vertical dip coating, and a dual purpose freezing and drying chamber was designed and manufactured. The effects of slurry properties and process parameters were studied with respect to the resulting microstructures. The freeze and drain method was determined to be optimum for producing highly porous tubular anode supports with hierarchical, acicular or dendritic micro-pore channels. With an optimized freeze-drying cycle, drying time was reduced significantly with minimal residual moisture in the green bodies. Additionally, the electrochemical performance of the T-SOFCs with freeze cast anode was evaluated.