One of the advantages of internal reforming is improved thermal management by directly coupling the exothermic electrochemical oxidation with the endothermic steam reforming of hydrocarbons. Significant differences in the rates of oxidation and reforming can lead to the development of thermal gradients across the anode plate that can compromise the physical integrity of the cell. The purpose of this study is to directly measure the thermal gradient created during internal reforming of methane with relation to the inherent activity and deactivation behavior of NiYSZ anodes. The current study shows that the endotherm will migrate down the anode plate until a stable thermal profile is achieved. This migration can be related to the sintering behavior of both bulk-Ni and Ni crystallites (evolved from the YSZ). During testing of an anode plate, steam and hydrogen treatments are not sufficient to fully stabilize the activity of the NiYSZ by sintering. Evidence from thermal profiles, activity testing, Ni surface area analysis, and TEM imaging suggests that methane reforming may have a significant role in the evolution and subsequent sintering of Ni crystallites leading to a stable structure.