A research program to investigate fuel cell performance effects and other implications due to soot formation, particulate deposition, and the effect of ammonia, arsenic, trace metal contaminants, and hydrocarbons is under way. Soot formation caused by simulated fuel under atmospheric operating conditions at 650/sup 0/C was studied both in-cell and out-of-cell. These experiments have shown that molten carbonate wetted surface (e.g., the nickel anode) tend to suppress the Boudouard soot forming reaction as contrasted with non-wetted surfaces. A 0.6% concentration of acetylene contaminant in borderline stable fuel gas was also observed to increase the tendency to soot formation. This indicates that even small amounts of unsaturated hydrocarbon contaminants may be detrimental and steps must be taken to adjust overall fuel gas composition to remain stable for long-term operation. The effect of particulates (using zinc oxide dust) in coal gas was also studied in a bench-scale cell. Even though only 1% of the total zinc passing through the cell was chemically absorbed, this zinc dissolved as Zn-ions in the electrolyte and migrated to the wet seal regions. This may have contributed to some decrease in cell performance. A 1 ppm arsenic concentration in fuel was also fed to another bench-scale cell and this was experimentally identified as the ''safe''limit of exposure for the MCFC without causing any immediate detrimental effects. Other contaminants such as volatile trace metals (which include zinc vapor present in coal-gas from a ZnFe/sub 2/O/sub 4/ desulfurizer), have also been surveyed and are being screened by out-of-cell testing.