Molten Carbonate Fuel Cells (MCFC)

Molten Carbonate Fuel Cells are high temperature fuel cells that can use natural gas, biogas, and coal as fuels. They are currently being developed for industrial and military uses. There is a great deal of interest in using MCFCs to produce electricity in place of current coal-fired power plants.

There are currently over 50 commercial installations worldwide of MCFCs. Most of these are capable of producing 250 kW though combination installations can produce electricity in the megawatt range. In the state of Washington, a 1 megawatt power plant is operating at the King County wastewater treatment facility where it is fueled by gas produced from wastewater.

Function and Reaction of MCFCs

The electrolyte in MCFCs is a molten salt mixture suspended in a ceramic matrix of beta-alumina solid electrolyte, which is permeable only to carbonate. At the cathode, carbon dioxide and oxygen are combined with electrons to produce carbonate. Carbonate diffuses through the electrolyte layer to the anode where it combines with hydrogen to produce water and electrons. The electrons are siphoned off to an external channel and returned to the cathode. The carbon dioxide is also returned to the cathode where it can participate in the reaction again.

Benefits of MCFCs

Because molten carbonate fuel cells must operate at temperatures of 650° C, there is no need for precious metals to be used as catalysts. This has tremendous cost saving benefits. Also as a result of their high operating temperatures, MFCFs do not require the fuel be reformed prior to entering the fuel cell. This dramatically reduces the number of parts, which increases reliability and reduces maintenance costs.

MCFCs are also highly efficient, achieving approximately 50% efficiency where waste heat is not captured and 85% efficiency when it is.

Because they do not contain platinum catalysts they are not susceptible to carbon monoxide or carbon dioxide poisoning. In fact, they can use carbon dioxide as fuel. This fact makes them very attractive for energy production in countries like the United States that have large natural reserves of coal.

Drawbacks of MCFCs

Like other high temperature fuel cells, MCFCs derived both benefits and drawbacks from their high operating temperatures. The primary disadvantage of MFCFs is that their high temperatures decrease cell life. There is currently research underway to find corrosion resistant materials for use at high temperatures.

The other drawback to MFCFs is their susceptibility to poisoning by sulfur, which is found at high concentration in many types of coal. This problem is currently addressed with the use of sulfur absorption, which requires frequent changing of components.

The other major drawback to MCFCs is that they use hydrocarbon fuels. While this may be seen as an advantage in terms of supply and production over hydrogen, it is a tremendous disadvantage in terms of greenhouse gas emissions and, in the case of coal, acid rain producing sulfur emissions.