Numerical simulation of a disk-type SOFC for impedance analysis under power generation

To support the impedance analysis in a disk-type SOFC under power generation, a numerical simulation procedure, whose simulation outputs the total impedance of an actual-size disk-type SOFC cell for the input of the local impedance of cell, has been proposed. In the simulation, the quasi-one-dimensional radial flow and mass transport problem with cell reactions is solved. Transient distributions of electromotive force, current and concentrations of chemical species in the cell are calculated to obtain the total cell impedance with parameters, such as local impedance of the cell, ac frequency, fuel utilization, gas flow rate, etc. A parametric simulation study for the simplest case under typical experimental conditions has been carried out. It is found that the Cole-Cole plot for the total cell impedance shows a capacitive semicircle, even if a pure resistance is assumed as the local impedance of the cell. The diameter of the impedance semicircle changes with fuel utilization and supplied gas flow rate, being affected by the diffusion in the flow direction. The characteristic frequency of the impedance semicircle depends on the transit time of the gas through the cell which is also affected by the diffusion in the flow direction. It is also suggested that the total cell impedance appears as a convolution of this capacitive semicircle impedance and local impedance of the cell.