IMPROVEMENT IN INTERFACE RESISTANCE OF CONDUCTIVE GAS-TIGHT SEALING MATERIALS FOR STACKING MICRO-SOFC

摘要

Micro-sized SOFCs are required small and correctly positioned interconnects, which work as gas-tight sealing and simultaneous electrical connection between cathodes and anodes in order to minimize electrochemical stacking losses and fabricate compact SOFC systems. We have developed highly conductive gas-tight seals that melt at lower than 850℃ in air and maintain electrical conductive connection between both electrodes at 650℃ in air. The addition of Si into Ag-Ge alloy much improved oxidation resistance and Ag-Si-Ge alloy resulted in highly conductive gas-tight seals after melting at 850℃ when the alloy was fused on dense ceramics or metal manifolds. Ag-Si-Ge alloy had eutectic structure, which was composed two regions; one region contained silver and the other was composed of Si-Ge alloy. Ag region in the alloy would play a role in high electrical conduction, whereas Si-Ge region would improve oxidation resistance. Adsorbed or residual oxygen in the alloy would be trapped in the Si-Ge region, and this oxygen getting region would prevent highly conductive Ag region from oxidation or degradation of electrical properties. However, the fusion of Ag-Si-Ge alloy on LSCF porous cathode materials partly led to form thin glassy interfacial phase that showed relatively high resistance. Ag-containing paste was then developed to decrease the interfacial resistance. The coating with the Ag paste on Ag-Si alloys much reduced the interfacial resistance. Ag-Si alloy coating with Ag paste would be suitable for the highly conductive gas-tight sealing devices applicable for stacking micro-sized SOFCs.