The Promise and Challenges of Intermediate Temperature Fuel Cells

Fuel cell systems span a wide range of temperatures, materials, and type of ionic transport. An intermediate temperature range of 200 to 500 degrees Celsius has received less attention than higher and lower temperature fuel cell systems due to the relatively few number of electrolytes that operate in this range. However materials research over the past 15 years has resulted in new electrolytes with sufficiently high ionic conductivity to enable intermediate temperature fuel cells (ITFCs). The focus of the Reliable Electricity Based on ELectrochemical Systems (REBELS) program at the U.S. Department of Energy Advanced Research Projects Agency-Energy (ARPA-E) is to create ITFCs with the potential for drastically reduced system costs, as well as enhanced electrochemical functionality such as rapid response to transients and electrochemical production of liquid fuels. Compared to lower temperature polymer electrolyte membrane (PEM) fuel cells, little or no precious metal catalysts are required for sufficient electrode kinetics. The higher temperatures also increase fuel flexibility and tolerance to impurities. Compared to higher temperature solid oxide fuel cells (SOFCs), a range of less expensive interconnects and seals are available and the system can be operated in more of a load-following manner. In addition to these ITFC benefits, challenges will be identified and discussed particularly with respect to higher temperature SOFCs. These challenges include methane reforming, ohmic resistance of the electrolyte, and electrode overpotentials at reduced temperatures. Potential pathways to overcome these challenges will be proposed and examples of the new concepts under development in the REBELS program will be highlighted.