Electrochemical characteristics of tubular flat-plate-SOFCs fabricated by co-firing cathode substrate and electrolyte

Tubular flat-plate (TFP)-solid oxide fuel cells (SOFCs) supported by cathodes with gas flow channels were fabricated by co-firing the cathodes and electrolytes. The size of a single cell is 43 mm×4.5 mm×100 mm, and the maximum power density of 0.83 W/cm2 was achieved at a current density of 1.6 A/cm2 at 1000 °C. We studied the electrochemical characteristics of the anode and the cathode by the ac impedance method. The resistance corresponding to the reaction around the three-phase boundaries of the anode/electrolyte interface increases with decreasing temperature from 1000 to 800 °C in the Ni–Y2O3 stabilized ZrO2 (YSZ) anode of the TFP cell. From ac impedance measurements made at various oxygen partial pressures PO2, we found that under high PO2 (log PO2>−0.77) surface diffusion of adsorbed oxygen atoms was the dominant step, but under low PO2 (log PO2<−0.77) the diffusion of oxygen gas was the rate-determining step in the cathode reaction in this TFP cell.