Solid Oxide Fuel Cells (SOFCs) are currently being demonstrated in sizes from 1kW up to 250-kW plants, with plans to reach the multi-MW range. SOFCs utilize a non-porous metal oxide (usually yttria-stabilized zirconia, Y2O3-stabilized ZrO2) electrolyte material. SOFCs operate between 650 and 1000°C, where ionic conduction is accomplished by oxygen ions (O=). Typically the anode of an SOFC is cobalt or nickel zirconia (Co-ZrO2 or Ni-ZrO2) and the cathode is strontium-doped lanthanum manganite (Sr-doped LaMnO3) (Singhal, 1997; Minh, 1993).
SOFCs offer the stability and reliability of
all-solid-state ceramic construction. High-temperature operation, up to 1,000°C,
allows more flexibility in the choice of fuels and can produce very good
performance in combined-cycleapplications. SOFCs approach 60 percent electrical
efficiency in the simple cycle system, and 85 percent total thermal efficiency
in co-generation applications (Singhal, 1997).The flat plate and monolithic
designs are at a much earlier stage of development typified by sub-scale, single
cell and short stack development (kW scale). At this juncture, tubular SOFC
designs are closer to commercialization.