OPTIMIZED SOFC ELECTRODE MICROSTRUCTURE

Recent SOFC electrode investigations indicate that the Triple Phase Bo undary reaction and the Internal Diffusion reaction should be regarded as occurring over different zones of the electrolyte surface. Under t hese conditions, an optimization consists of giving the faster process a reaction zone as large as possible. A duplex electrode microstructu re composed of an ultra-thin layer of a mixed conductor covered by a p orous current-collecting layer made of coarse grains is analyzed in te rms of in-plane ohmic drop and diffusion overpotential. Relationships can be defined to optimize this microstructure. With currently availab le materials, excellent performances can be projected for the medium-t emperature SOFC electrodes. A critical parameter for the mixed conduct ing layer is its electronic conductivity which should be higher than 1 S/cm. Solutions to improve a possibly slow surface oxygen exchange pr ocess are also examined.