Contaminant effects in solid oxide fuel cells

Two full scale (50-cm length) SOFCS, each representative of generator cells in the field, were electrically connected in series; then operated at 1000{degrees}C and 350 mA/cm{sup 2}. An initial run of approximately 150 hours served to establish baseline performance in 89% H{sub 2}, 11% H{sub 2}0 fuel at 85% fuel utilization and 4 stoichs, air. Then, for approximately 200 hours, a similar base-line was established for operation in simulated coal gas fuel. Finally, the fuel impurity components were sequentially added. The cumulative effect on performance as shown in Table 3. These data reveal no strong association of cell resistance with cell performance change in the cases of NH{sub 3} and HCI. When H{sub 2}S is added, resistance increases account for a minor part of the 0.06V decline observed for each cell over the first 24 hours. However, cell resistances thereafter change linearly, along with linearly declining voltages. In this latter phase, resistance accounts for a major part of each observed cell voltage decline. The same two SOFCs were subsequently continued in operation, but at a moderately higher temperature, 1025{degrees}C. As Figure 2 demonstrates, No. 1 cell tended to decline more slowly, and No. 2 cell continued to decline at themore » same rate as before, when it was operating at 1OOO{degrees}C. Later operation, without impurities, at 1025{degrees}C for 450 hours served to improve performance and stabilize the cells. When operation at 1000{degrees}C resumed, the cell resistance trend lines returned to approximately the original R vs. t slopes observed during 0-500 hours on test, signifying cessation of impurity-related voltage degradation.« less