Why is the performance different between small- and large-scale SOFCs?

Small-scale planar solid oxide fuel cells (SOFCs) with several centimeters in diameter called "button cells" or "coin cells" are widely used for fundamental research. Although the performance of large-scale cells is inferior to that of button cells, the precise reason is unclear. In the present work, electrochemical impedance spectroscopy (EIS) are performed for button cells with different cathode areas under different fuel utilization, and distribution of relaxation times analysis was conducted to deconvolute the EIS. The power density decreased with increasing cathode diameter for the button cells. The polarization resistances associated with the gas diffusion process at low frequencies increased for a cell with a large cathode area, when the gas flow path is different between the inner and outer electrode areas for the button cells. The polarization resistance related to the gas diffusion process also increases with increasing fuel utilization. As a result of simple simulation considering the Nernst loss, the power density at 0.75 V was estimated to be 0.169 W/cm2 at Uf = 0.8 for a large-scall cell with di-mensions of 10 x 10 cm2, which is smaller than that for a button cell with a cathode diameter of 6 mm (0.730 W/ cm2 at Uf = 0.04).