The program objective is to identify the poisoning mechanism(s) responsible for performance losses of molten carbonate fuel cells (MCFC) when operating on sulfur-containing gases. The mechanisms will be identified by focusing out-of-cell and in-cell experiments on single mechanistic issues, followed by incorporating the results into a model that correlates cell potential decline to contaminant(s) concentration. When coupled with gas cleanup cost projections, the model can be used to conduct trade-off studies leading to the selection of optimum feed-gas compositions for MCFC power plants. During the first quarter we began a literature survey of catalysis work and prior fuel cell work to establish a basis for determining the extent of poisoning of the electrochemical oxidation of hydrogen by sulfur species. Experimentally, we began assembling the test apparatus for studying these effects on single-wire electrodes, and we operated two 4-in. x 4-in. (94 cm/sup 2/) bench-scale cells on a 10% hydrogen/90% helium fuel mixture. This fuel mixture was chosen to mitigate the impact of the water gas shift reaction on cell performance. The results from the two bench-scale tests indicate a strong poisoning effect when hydrogen sulfide contaminates the fuel. This poisoning, which is manifested by high polarization losses, is not reversible when clean uncontaminated hydrogen/helium fuel is reintroduced into the cell under the conditions tested. (WHK)