Vapor Phase Silica Transport During SOFC Operation at 1000°C

During the operation of tubular solid oxide fuel cells (SOFC) at 1000°C in CH 4 -H 2 O fuel, we observed silica deposit formation on the fuel electrode (Ni-YSZ cermet), nickel felt contacts and reforming catalyst surfaces.Silica deposition on the fuel electrode resulted in the electrical performance degradation, coverage of the catalyst surface and breakdown of the zirconia skeleton present on the fuel electrode. Sources of silica were identified. A thermochemical model relating to the formation and transport of vapor phase silica species, deposition on the catalytically active surface and interaction with the anode was developed. Vapor transport of silica is considered to take place at the quartz surface in the presence of water vapor. Silica deposition and deactivation of the catalyst is postulated to be due to the dissociation of gaseous hydrated silicious species on the active nickel surface during the reformation of hydrocarbon. Experiments were designed and conducted to validate the mechanism. It is concluded from these experiments that the presence of silica in the solid oxide fuel cell generator and the catalyst support should be eliminated for long term stable operation of cells and generator.