Poisoning effects by various fuel impurities, including H2S, CH3SH, COS, Cl-2, and siloxane, to Ni-ScSZ cermet anodes have been analyzed and compared. Degradation of cell performance caused by these impurities was characterized by measuring cell voltage and anode polarization at a constant current density of 0.2 Acm(-2) for humidified H-2 and CH4 fuels. Poisoning for hydrogen-based fuels containing 5 ppm sulfur compounds, H2S, CH3SH, and COS, caused an initial cell voltage drop of about 15 mV at 1000 degrees C. The initial voltage drop was independent of the kind of sulfur compounds, whereas in the case of poisoning by CH3SH, an additional gradual decrease in cell voltage was clearly detected after the initial voltage drop. Thermochemical calculation and FESEM-EDX analysis also indicated that the poisoning by Cl-2 caused the fon-nation of nickel nano-particles on zirconia grains via NiCl2 (g), while the poisoning by siloxane formed segregated silica (SiO2) in porous cermet anodes. (C) 2008 Elsevier B.V. All rights reserved.