The use of freeze casting is suggested as a solution to significantly increase the volumetric power density of Tubular SOFCs (T-SOFCs) by enhancing gas diffusivity and triple phase boundary reactions. This paper reports the fabrication and characterization of freeze cast tubular anode supports for SOFCs. Tubular anode supports were fabricated using three methods: gelation casting, center pin method, and a freeze and drain method. 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.

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Tubular solid-oxide fuel cells (t-SOFCs) fed directly with biogas, an equiproportioned mixture of CH 4 and CO 2 produced by fermentation of organic waste, are subject to nonuniform thermal stresses due to internal dry reforming in the anode entrance region coupled with structure exfoliation due to coking, resulting eventually in cell rupture. The integral t-SOFC is of practical interest, although many laboratory studies are conducted in differential button cells. Guided by mechanistic understanding and a robust thermodynamic model, the operating temperature and biogas feed composition were explored experimentally in order to enhance durability and performance of the t-SOFC. Thus, a temperature of 900 °C, a feed CH 4 /CO 2 ratio of 45/55, and a fuel utilization ≥25% were found to be optimal. The cell durability, performance, efficiency, and outlet gas composition at open-circuit voltage (OCV) as well as at different loads were found to be in accord with a thermodynamic analysis and mechanistic understanding based on a set of four independent overall reactions (ORs). It is shown that the OCV is independent of the chosen electrodic OR. In addition to single-tube experiments, a 5-tube SOFC pilot-unit was preliminarily tested as a step toward scale-up of this promising renewable energy technology.