The anode materials that have been developed for solid oxide fuel cells (SOFCs) are vulnerable to deactivation by carbon buildup (coking) from hydrocarbon fuels or by sulfur contamination (poisoning). We report on a mixed ion conductor, BaZr(0.1)Ce(0.7)Y(0.2-)(x)Yb(x)O(3-delta), that allows rapid transport of both protons and oxide ion vacancies. It exhibits high ionic conductivity at relatively low temperatures (500 degrees to 700 degrees C). Its ability to resist deactivation by sulfur and coking appears linked to the mixed conductor's enhanced catalytic activity for sulfur oxidation and hydrocarbon cracking and reforming, as well as enhanced water adsorption capability.

The effect of hydrogen sulfide ͑H 2 S͒ on the performance of nickel/yttria-stabilized zirconia ͑YSZ͒ cermet anode for solid oxide fuel cells has been studied under various operating conditions. In all cases, a small amount of H 2 S ͑ppm level͒ causes a sharp drop in cell performance within the first few minutes of exposure, followed by a gradual but persistent deterioration in performance for several days. The extent of anode degradation caused by sulfur poisoning increases with increasing H 2 S concentration, increasing cell voltage ͑i.e., closer to open-circuit voltage or decreasing cell current density͒, or decreasing cell operating temperature. The initial sharp degradation in performance is attributed to rapid adsorption of sulfur onto the Ni surface, which blocks the active sites for hydrogen adsorption and oxidation. However, the mechanism for the subsequent slow degradation is still not clear. Upon removal of H 2 S from the fuel stream, the anode performance can be recovered fully or partially, depending on operating conditions and duration of H 2 S exposure. The rate of the recovery process increases with operating temperature and cell current density.

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