Electrochemical full cell evaluation of a Versa Power Systems TSC-2 solid oxide fuel cell was conducted in 1 ppmv hydrogen sulfide (H2S) at 750 degrees C with 25%,35% and 50% levels of direct internal reforming (DIR) of methane. It is shown that the addition of H2S significantly degrades both the cell voltage as well as the DIR activity of the cell, as evidenced by gas chromatographic analysis of the cell exhaust gas. With the removal of H2S, the cell voltage recovers, but not to pre-H2S exposure levels. The onset of degradation of electrochemical activity commences before the onset of DIR activity degradation, indicating that H2S penetrates to the Ni-containing anode functional layer before Saturation coverage of Ni with sulfur in the support layer. Secondary ion mass spectrometric post-analysis indicated that, while adsorbed sulfur remains on the surface of Ni after recovery for similar to 200 h in H2S-free gas, there remains sufficient active Ni surface area in the anode substrate to continue to catalyze the DIR reactions. (C) 2008 Elsevier B.V. All rights reserved.