Direct internal reforming of methane (steam/carbon=0.031, 850 ℃) is tested using button cells of Ni-YSZ/YSZ/LSM in which the anode layer is supported either on Ni-YSZ or on Ni-CoAl2O4. The Ni-CoAl2O4 supported cell shows little degradation with operating time, as a result of higher resistance against carbon deposition, whereas the Ni-YSZ supported cell deactivates quickly and suffers fracture in 50 h. Upon incorporation of additives such as K, Ce, or Mo into the Ni-CoAl2O4 support, cells with 0.5 wt% CeO2 exhibit the best stable performance as a result of reduced coke formation. Cells with 0.5 wt% Mo exhibit the lowest performance. Although no carbon deposit is detected in the cells with K2CO3 additives, their performance is worse than that in the CeO2 case, and, in constant-current mode, there is a sudden voltage drop to zero after a certain period of time; this time becomes shorter with increasing K content. The injection of potassium into the anode side facilitates the generation of OH. and CO3 2- in the anode and promotes the diffusion of these ions to the cathode. Increased polarization resistance at the cathode and increased electrolyte resistance result in such a sudden failure.