The solid oxide fuel cell (SOFC) can operate effectively on a variety of fuels, such as coal-syngas and hydrogen. A Ni-based cermet is a cost-effective anode material for these fuels; however, H 2 S in the fuel can degrade cell performance by poisoning the Ni-based anode. In this research, nickel-gadolinium doped ceria (Ni-GDC) hybrid anodes were exposed to synthesized coal-syngas and H 2 fuels with various concentrations of H 2 S at 800 • C under constant current conditions. Some SOFC prototypes contained a ∼5 μm thick GDC barrier layer inserted between the Ni-GDC hybrid anode and the YSZ electrolyte. A reference electrode was incorporated in the cell to monitor changes in the anode and cathode polarization resistances. The tests showed that the cells with a GDC barrier layer were resistant to H 2 S at levels up to 1000 ppm in wet H 2 and 100 ppm in syngas during long-term tests. Cells without the barrier layer had a significantly lower tolerance for the H 2 S impurity. This result, along with post-mortem analyses of the poisoned anode, lead to the hypothesis that the GDC barrier layer assists in the prevention of nickel oxidation at the anode/electrolyte interface by acting as an oxidation catalyst for the H 2 S.Coal-derived syngas is a potential fuel source for the SOFC. However, the presence of volatile contamination containing H 2 S, PH 3 , HCl, AsH 3 , Sb, and Hg species in warm syngas can cause degradation of the SOFC performance. 1 Sulfur is one of the most abundant impurities in coal and most of the sulfur appears as H 2 S in the gasified syngas. The concentration could range from 0.1 to 1.6% by volume H 2 S in raw coal syngas derived from typical gasification systems. 2, 3 Although commercial desulfurization techniques, such as adsorption and wet absorption at ambient temperature, could remove H 2 S down to 1 ppm, a level which may not lead to SOFC degradation, the hot syngas from the gasifier has to be cooled, thereby reducing the overall thermal efficiency of the system. Some transition metal oxide desulfurization sorbents, such as Cu 2 O, ZnO, NiO, CoO and MnO, have been reported to yield as high as 99% H 2 S removal efficiency at temperatures over 600 • C. 3 However, the warm gas cleanup technique would leave some level of H 2 S in the syngas, possibily down to levels of 50 ppm. 4 Therefore, developing H 2 S resistance in the Ni-based anode is still a meaningful target for a highly efficient SOFC energy system fueled by coal-derived syngas.The poisoning mechanisms of H 2 S on the Ni-based anode have been discussed and reported in literature. There are two steps of H 2 S poisoning on Ni-based anodes that have been identified; the first step is an initial rapid degradation which is reversible, followed by a slow nonstop degradation step which is irreversible. The initial H 2 S poisoning mechanism is attributed to the adsorption of sulfur on the nickel which blocks the hydrogen reaction sites. 5-7 For the second degradation step, there has been a discrepancy in the literature. Dong et al. reported that...