Characterization of copper-ceria-samarium(0.2)cerium(0.8)oxide(1.9) anodes for direct utilization of dry hydrocarbon fuels
Copper-ceria-SDC anodes have been developed and characterized for direct utilization of dry hydrocarbon fuels at low temperatures (600°C to 700°C). The functions of Cu and ceria in the anodes are examined. It is found that copper provides electronic conductivity in the anodes and its catalytic activity toward hydrocarbon (e.g. C4H10) oxidation is negligible. Ceria serves as a catalyst to enhance the anode performance with dry hydrocarbon fuels. A theory is developed to explain Cu percolation behavior in the anodes, and suggests that Cu percolation threshold increases with anode pore size, porosity, and the average thickness of Cu particles. Conductivity-measurement results of various porous SDC samples indeed support theoretical analysis. The cell performance increases gradually when Cu loading is below the percolation threshold, and exhibits a huge leap in an anode-composition range over which Cu accomplishes percolation. This strongly indicates the importance of forming a percolated Cu structure in the anodes to conduct electrons sufficiently for achieving good cell performance. Porous anodes with distinguishable microstructure are formed with the application of different pore formers, and the effect of anode microstructure on the cell performance is studied. At 700°C increasing anode pore size and porosity has insignificant impact on the cell performance with either H2 or C4H10. Thus, the anode performance is unlikely limited by the absolute area of a reaction zone along an electrolyte-anode interface. It is found that impregnated copper particles in the porous Cu-ceria-SDC anodes sinter at 700°C, based on single-cell characterization, conductivity measurement and microscopic observation. The long-term stability of a SOFC with a Cu25%-ceria16%-SDC anode is studied in H2. The cell conductance and cell performance decrease with time due to the Cu sintering. A technical approach to impede the copper sintering is proposed, in which a barrier phase is built in the Cu-ceria-SDC anodes to cover the Cu particles. The experimental results corroborate the effectiveness of the proposed approach in suppressing the Cu sintering in the anodes.
Lu, Chun, "Characterization of copper-ceria-samarium(0.2)cerium(0.8)oxide(1.9) anodes for direct utilization of dry hydrocarbon fuels" (2004). Dissertations available from ProQuest. AAI3125863.