A cell which consists of a porous 18 mu m thick Y-doped ZrO2 (YSZ) electrolyte (23 +/- 3 vol % open porosity) on a NiO-YSZ anode substrate and a cathode using (La, Sr)(Co, Fe)O-3 has been investigated in the single-chamber configuration. The cell performance and catalytic activity of the anode was measured in a flowing air-methane gas mixture with various flow rates. The results showed that the open-circuit voltage and the power density increased as the gas flow rate increased. The cell generated an open-circuit voltage of about 0.78 V, which was only about 0.1 V lower than that observed with dense electrolyte specimens. A maximum power density of 660 mW cm(-2) (0.44 V) was obtained at set temperature = 606 degrees C (cell temperature 744 degrees C) in the flow rate of 900 cm 3 min(-1), where the current efficiency was about 5% determined from fuel consumption. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1858811] All rights reserved.