The chemical and electrochemical stabilities of some sulfur-tolerant materials have been studied for use as cathodes in an electrochemical membrane system that removes H,S from hot fuel gas streams. The typical fuel stream inlet composition at 650-750degreesC and 1 atm was 34% CO, 22% CO2, 35% H-2, 8% H2O, and 0.2-2% (molar) H2S. Among the compounds studied, Gd2TiMoO7 and La0.7Sr0.3VO3 exhibited the best stability when exposed to fuel streams containing high concentrations of H2S, CO2, and H2O. The electrical conductivities of Gd2TiMoO7 and La0.7Sr0.3VO3 were 6 and 30 S cm(-1), respectively, as measured at 650degreesC in 4% H-2 balanced with argon. They also showed adequate microstructural stability at temperatures up to 750degreesC. However, Gd2TiMoO7 had better stability with molten electrolyte (Li0.62K0.38CO3) present, whereas La0.7Sr0.3VO3 had better stability in the sour gas stream without molten electrolyte present. Accordingly, a layered electrode that could help preserve a stable environment for each of these compounds is a promising candidate electrode for the application. (C) 2004 The Electrochemical Society.