| 초록 |
The direction of ionic / electronic current and the corresponding internal oxygen chemical potential profile through the electrolyte can have a profound effect on its stability. If cell imbalance exists in a series-connected fuel cell stack, a “bad” cell characterized by a higher resistance can be operated under a negative voltage. In our previous study, yttira stabilized zirconia (YSZ; predominantly oxygen ionic conductor) electrolyte cells were tested with an applied DC bias in order to investigate the SOFC stack failure mechanism by simulating abnormal behavior in a single cell test. Rapid degradation occurred characterized by an increased cell resistance with delamination developed along the anode interface during the abnormal operation. This was attributed to the high internal oxygen chemical potential formed just under the anode interface in the predominantly oxygen ionic conducting electrolyte, YSZ. In the present study, anode-supported cells were made of two different electrolyte compositions: 8 mol% yttria doped zirconia (8YSZ) and 92 mol% 8YSZ and 8 mol% CeO2 (8CYSZ), and both cells were operated under a negative voltage. It was observed that no degradation in the performance and delamination occurred in the cell with 8CYSZ, contrarily to the cell with 8YSZ. Based on the local equilibrium criteria, a solid electrolyte with the increased electronic conduction releases the internal oxygen chemical potential due to the electronic leakage. That is the reason why the 8CYSZ cell was not delaminated and degraded. Thus, the electronic conduction determined by the composition in a solid electrolyte plays an important role in its thermodynamic stability. |
