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Abstract:

At present, one of the major obstacles for the commercialization of solid oxide fuel cell (SOFC) power systems is high cost per unit power ($/kW).
In this work, anode-supported planar SOFCs were fabricated by a cost-competitive single step co-firing process. The cells comprised of a porous Ni + yittria-stabilized zirconia (YSZ) anode support, a porous-fine-grained Ni + YSZ anode active layer, a dense YSZ electrolyte, a porous-fine-grained Ca-doped LaMnO3 (LCM) + YSZ cathode active layer, and a porous LCM cathode current collector layer. The fabrication process involved tape casting or high shear compaction (HSC) of the anode support followed by screen printing of the remaining component layers. The cells were then co-fired at 1300~1340°C for 2 hours.

The performance of the cell was improved by minimizing various polarization losses through experimental and theoretical modeling approaches, and the maximum power density of 1.5 W/cm2 was obtained at 800oC with humidified hydrogen (3% H2O) and air. The cells were also tested with various compositions of humidified hydrogen (3~70% H2O) to simulate the effect of practical fuel utilization on the cell performance. Based on these measurements, an analytical model describing anodic reactions was developed to understand reaction kinetics and rate limiting steps. The cell performance at high fuel utilization was significantly improved by increasing the number of the reaction sites near the anode-electrolyte interface.

Lowering the operating temperature of the SOFC will enable the use of less expensive metallic interconnects and more effective sealing materials, and thus lower the overall cost of the SOFC system. However, to lower the operating temperature better cathode materials with high catalytic activity are required. Lanthanum ferrite based cathode materials are considered to be good candidates for lower temperature operation due to its high catalytic activity and mixed electronic and oxygen ion conductivity. The defect chemistry and electrical properties of (La0.8Ca0.2)0.95FeO3-δ were studied through thermogravimetry and electrical conductivity measurements between 550-850oC under various oxygen partial pressures. Comprehensive defect model was developed to interpret experimental data and elucidate equilibrium defect concentrations, oxygen non-stoichiometry, and electronic conduction mechanisms. Future experiments will incorporate these cathode materials in single-step co-fired cells and their performance at lower temperatures (600-700 C) will be analyzed.

Biography:

Professor Pal has six years of industrial and eighteen years of academic research experience in high temperature chemical and electrochemical processes, including fuel cells, sensors, membrane separation, batteries, and green processing. He has received several professional awards, authored/co-authored over 100 publications and has 21 patents. He serves on the editorial board of the Journal of Materials Research and Metallurgical and Materials Transactions.