Prepartion And Property Characterization Of Layered Cobalt-Based Cathode Material Ca₃Co₄O_9-δ For Solid Oxide Fuel Cell

Solid oxide fuel cells (SOFCs) are considered as one of the most promising power generating technologies in the future. One of the major goals of SOFCs is to reduce the operating temperature to intermediate temperature (600-800℃) range. As operating temperature decreases, the cathode polarization loss will increase, resulted as a severe decline of cell performance, which becomes a major limiting factor of SOFCs’progressing toward intermediate operation temperature. Therefore, it is very important to research and develop cathode materials, which have high catalytic activity and low polarization loss, that are suitable for intermediate temperature operation. This work is focusing on mismatched layer structure Ca3Co4O9-σand its composite material Ca3Co4O9-σ-xSNDC as a study object and systematically characterize and evaluate its properties as SOFC cathode so as to develop cathode materials for intermediate temperature operation.Ca3Co4O9-σ cathode material is synthesized by Sol-gel method in this work. Phase analysis, electroconductivity and electrochemistry properties are characterized, in order to evaluate its suitability of IT-SOFC cathode material. XRD results indicate that sintering after 850℃, the cathode powder formed a mismatched layer structure. DC conductivity test indicate that maximum conductivity is 74.49 S/cm at 550 ℃. EIS tests show that cathode polarization resistance of Ca3Co4O9-σ is 0.236 Ω·cm2. And we prepared an anode-supported single cell which achieves maximum power density of 410.09 mW·cm-2.To improve the properties of Ca3Co4O9-σ cathode material, by adding SNDC electrolyte materials into cathode materials, we made composite cathode material. Adding of SNDC electrolyte expand the triple phase boundary of cathode is expanded. Thus, the cathode catalytic property and electrochemistry properties are obviously improved. Ca3Co4O9-σ cathode and SNDC electrolyte have favorable chemical compatibility. After calcining at 850℃ for 10 hour, there are no chemical reactions occurred between cathode and electrolyte materials. Best electrochemical property appears when SNDC composite content reach 50wt%. Cathode polarization resistance is 0.093 Ω· cm2 at 800 ℃ which decerease by 60.6%, compared with a single phase cathode. It means that, by mixing electrolyte and cathode materials, the electrochemistry properties of cathode can be sufficiently improved. An anode-supported single cell with Ca3Co4O9-σ-SNDC cathode achieves maximum power density of 209.04 mW·cm-2 at 800 ℃. The low power output of single cell with composite material is related to the structure defect as micropore, microcrack at anode side.In conclusion, the cathode and its composite material have favorable SOFC cathode performance. By further process optimization, they can be served as a IT-SOFCs cathode material.