The MCFCs are an emerging promising technology for military applications, primarily for natural gas and coal-based power plants. These high-temperature fuel cells use an electrolyte that represents a molten carbonate salt mixture, suspended in a porous, chemically inert ceramic lithium aluminum oxide matrix. Operating at the temperature of about 650°C (~1200°F), MCFCs can use non-precious metals as catalysts at both the anode and cathode; hence, much lower costs are associated with them.
One of the major advantages of MCFCs is that they have increased efficiencies: when used with a turbine, fuel cell efficiencies reach 65%, significantly higher than the 37%-42% efficiencies seen in phosphoric acid fuel cell plants. When waste heat is harnessed and converted into total fuel efficiencies, values can top 85%.
Among other variants of fuel cells, such as alkaline, phosphoric acid, and PEM, MCFCs do not require any external reformer for fuels like natural gas and biogas to be converted into hydrogen. Because of their high operating temperature, internal reforming can be achieved in MCFCs, a process whereby methane and other light hydrocarbons are converted into hydrogen within the cell, further reducing the cost.
However, the major challenge with MCFC technology at the moment is durability. High operating temperatures and the corrosive nature of the electrolyte increase the deterioration and corrosion rates of the components and hence cell life. Corruption-resistant material and fuel cell design are under active investigation and may give further potential for doubling cell life up to 40,000 hours at approximately 5 years without any performance loss.
In a development that may be considered parallel, chemical engineers at MIT have harnessed an effective method for turning carbon dioxide into carbon monoxide, a precursor for the manufacture of useful compounds such as ethanol and other fuels. If scaled up industrially, it could greatly reduce greenhouse gas emissions coming from power plants and other sources.
Ariel Furst, the Paul M. Cook Career Development Assistant Professor of Chemical Engineering at MIT, emphasized the decarbonization opportunity that this technology presents. “This would allow you to take carbon dioxide from emissions or dissolve in the ocean, and convert it into profitable chemicals,” she said. Electricity drives the chemical reaction in the new process, with a catalyst tethered to the electrode surface using strands of DNA. The DNA acts like a type of Velcro, keeping all reaction components nearby, hence making the reaction far more efficient.
Details of the approach, led by the MIT research team and including former MIT postdoc Gang Fan and other collaborators, have been published in the Journal of the American Chemical Society Au. The technique dissolves carbon dioxide in water inside an electrochemical device that contains an electrode driving the reaction. The catalysts, suspended in solution, interact with carbon dioxide at the surface of the electrode, boosting the rate of the electrochemical conversion.
They attached single strands of DNA to a carbon electrode and designed the system so that the catalyst reversibly binds to the DNA on the electrode, which enables the conversion of carbon dioxide to carbon monoxide. This method realized a Faradaic efficiency of 100%, which means that all the electrical energy input directly goes into the chemical reaction, with no waste of energy.
If carbon electrodes and non-expensive catalysts can easily scale the technology for industrial purposes, this technology may soon be useful in military applications. To this effect, the research was funded by the U.S. Army Research Office, among others, because of its significance in military and industrial decarbonization efforts.