The MCFC is often referred to as a second generation fuel cell because it is expected to reach commercialization after PAFCs have reached the marketplace. These fuel cells operate at relatively high temperatures (600-650°C) allowing them to operate with unreformed fuels. They require a significant time to reach operating temperature and, therefore, are best suited for the provision of power in utility applications. Programs are underway in Japan, the U.S., and Europe to develop large scale systems. A schematic description of the components in an MCFC is shown here:
As illustrated in this figure, the operation of a MCFC is based on the shuttle action provided by carbonate ions. The carbonate ions also serve as an acidic electrolyte. The CO2 rich gas product gas of the anode is fed to the cathode where CO2 is transformed into carbonate ions during the reduction of oxygen. The higher operating temperature of MCFCs provides an opportunity for achieving higher overall system efficiencies and greater flexibility in the use of available fuels. On the other hand, the higher operating temperature places severe demands on the corrosion stability and life of cell components. The electrolyte in this fuel cell is usually a combination of alkali (Na, K, Li) carbonates retained in a ceramic matrix made of LiAlO2. At the high operating temperature of this fuel cell Ni and nickel are respectively adequate electrocatalysts for the anode and cathode.
MCFCs, which operate at a higher temperature and are more efficient than PAFCs, are expected to fit best in larger (1 - 20 MW) baseload distributed power applications, particularly in certain industrial markets where cogeneration opportunities exist. If built in low numbers, MCFCs are likely to cost around $3000/kW. If costs can be reduced to $1500/kW, which would require order commitments to support high-volume manufacturing, these systems could find significant utility markets for distributed generation in grid-support applications. In a demonstration project cosponsored by EPRI and a number of utilities, a 2-MW MCFC pilot unit in Santa Clara, California, recently completed 4000 hours of successful test operation.