High Performance Single Step Co-Fired Solid Oxide Fuel Cells
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0972-AA10-02
High Performance Single Step Co-Fired Solid Oxide Fuel Cells Kyung Joong Yoon, Srikanth Gopalan, and Uday B. Pal Department of Manufacturing Engineering, Boston University, 15 St.Mary's Street, Brookline, MA, 02446
ABSTRACT Anode-supported planar solid oxide fuel cell (SOFC) was successfully fabricated by a single step co-firing process. The cell comprised of a Ni + yittria-stabilized zirconia (YSZ) anode, a YSZ electrolyte, a Ca-doped LaMnO3 (LCM) + YSZ cathode active layer, and an LCM cathode current collector layer. The fabrication process involved tape casting of the anode, screen printing of the electrolyte and the cathode, and single step co-firing of the green-state cells at 1300°C for 2 hours. The maximum power densities were 1.50W/cm2 at 800oC, and 0.87W/cm2 at 700oC with humidified hydrogen (97% H2-3% H2O) as fuel and air as oxidant. The experimentally measured I-V curves were fitted into a polarization model to obtain cell parameters including the area specific ohmic resistance, exchange current density, effective binary diffusivity of hydrogen and water vapor in the anode, and that of oxygen and nitrogen in the cathode. The cell was also tested at 800oC with various compositions of humidified hydrogen to evaluate the cell performance at high fuel utilization, and the maximum power densities were 1.30W/cm2 with 75.7% H2-24.3% H2O, 0.94W/cm2 with 49.4% H2-50.6% H2O, and 0.49W/cm2 with 27.3% H2-70.7% H2O.
INTRODUCTION Solid oxide fuel cells (SOFCs) have gained significant interest due to their high energy conversion efficiency, low pollution emission, and flexibility with various fuels. Among the basic designs of SOFCs, the anode-supported SOFCs are extensively investigated because they exhibit higher cell performance compared to either the electrolyte-supported or cathodesupported designs. Maximum power density of as high as 1.8-1.9 W cm2 at 800oC has been reported using an anode-supported design [1-3]. The major challenge for the commercialization of SOFCs is reducing the high manufacturing costs. Currently, the production cost of batch-processed SOFCs is significantly higher than that of conventional power generation systems. Conventional SOFC fabrication technologies involve multiple sintering steps for a single cell fabrication, and the sintering step is one of the most expensive processes during cell fabrication. Therefore, the manufacturing costs of SOFC can be greatly lowered by employing single step co-firing technique. To realize the successful single step co-firing of SOFCs, it is critical to lower the sintering temperature of the electrolyte and to minimize the thermal expansion mismatch between the components. In the present work, anode-supported planar SOFC was fabricated by a single step co-firing process. The fabricated cell was tested in the temperature range between 700~800°C with humidified hydrogen as fuel and air as oxidant to evaluate the cell performance under various fuel utilization conditions. Experimentally measured voltage versus current density traces were fitted
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