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Small interconnects and gas-tight seals are required when micro-scale cells or stacks are accumulated for the construction of micro-SOFC. We have developed gas-tight sealing devices embedded electrical conduction paths for electrode-supported micro-SOFCs. The sealing devices were prepared by combining insulating glass precursor sealing materials and conductive Ag-Si-Ge alloy. The glass precursor material was prepared with two kinds of spherical particles. The alloy sealing material was prepared by metal rolling various Ag-Si-Ge alloys in order to attain oxidation resistance at 650oC in air. The bi-layer seals composed of the glass precursor seals and the Ag-Si-Ge alloy seals were arranged between porous electrodes and firing the seals at 850oC in air resulted in crack-free interfaces of alloy seals/glass seals, alloy seals/electrode, and glass seals/electrodes. The arrangement of both the seals would lead to be the interface containing adequate electric conduction paths for high-performance micro SOFCs.

SOFC anode requires long three phase boundaries (TPBs) and appropriate gas diffusion passes for the fast transport of both fuel and exhaust gases, but the area where gas diffusion passes are especially required would be different from the area suitable for electrochemical reaction in the anode. Then gradient porous structures of SOFC anodes have been proposed to fulfill the anodic functions in adequate anodic areas. Ni- YSZ anodes with various gradient pore-distributions were then prepared using pore-formers by screen-printing method. The relationship between maximum power densities and the pore size and porosity distributions was investigated to identify an effective gradient porous structure that can improve anode performance. The gradient porous structure improved anodic polarization. Pore structure contains two factors of pore size and porosity but the gradient in pore size was more effective in improving anode performance.

Micro-SOFCs require precise control of conduction paths among small cells or stacks. We have developed both insulating and highly conductive gas-tight seals in order to arrange both the seals and to fabricate the gas-tight sealing interface that has various electric conduction paths. The insulating seals were prepared with amorphous Na2O-SiO2 spherical particles and amorphous SiO2 particles. Porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) ceramics were used as a porous cathode to investigate sealing behavior. Firing the insulating sheet at 800oC resulted in gas-tight melt sealing. Penetration of viscous fused glasses into porous LSCF was controlled by changing the particle ratios. On the other hand, the highly conductive seals were prepared with various Ag-Si-Ge alloys by metal rolling. The alloys was melted at 850oC in air and led to highly conduction paths. The bi-layer sheets composed of the insulating and the conductive sheets was also resulted in gas- tight sealing at 850oC in air.

Gas-tight seals are also indispensable for fabricating high-performance portable SOFC as well as other cell components because gas sealing leakage causes severe damage to integrated cells or stacks. We investigated glass/ceramic composite materials to apply to gas-tight seals for portable SOFC. The composite seals with glass precursor particles and ceramic precursor showed relatively high reliable gas sealing properties under some SOFC working conditions. The composite seals showed sufficient high gas sealing properties in humidified hydrogen gas as well as air, and humidified hydrogen gas would be little impact on fusible conditions. The seals can be used in hydrogen as well as air. The composites also exhibited high durability against the thermal cycle between 650oC and 250oC, and they kept gas-tight sealing and no leakage was observed under raid heating conditions at the rate more than 200oC/min.

Determines pore-size distribution of ceramic green bodies through mercury intrusion porosimetry. Influence of mercury intrusion on the original pore structure; Relationship of organic ingredients included in green bodies; Application of measurement method to ceramic green bodies from various forming methods.