Portable Power Perspectives: Lessons on Reformed MeOH PEMFC
August 28, 2007
While portable fuel cells have shown promise as long-lived replacements to conventional batteries, it's still not clear what will be the fuel of choice. The highest performance, proton exchange membrane fuel cells (or PEMFCs), run from hydrogen. One of the most effective ways to store hydrogen is in the form of a liquid, the simple alcohol methanol. However, the extraction of the hydrogen from the methanol in an energy efficient manner has been a problem, especially at low power scales. One of the biggest problems in is the retaining of heat needed for the process of hydrogen extraction, or reforming, of the methanol. Lost heat equals lost energy that could be used for electricity from the fuel cell.
In his presentation, Besser described a new approach for retaining heat in the fuel processor, by the use of cylindrical symmetry. In this approach, tiny chemical reactors are made as cylindrical layers that slip inside one another. A combustor at the center of the system provides heat, which flows radially outward in the cylindrically-shaped system. A detailed analysis showed that a fuel processor, fuel cell, and fuel integrated together to replace a 20-W battery (typically used in many military systems and in consumer laptops), would have a specific energy density of about 1000 W-hr/kg, while the best batteries have about one-third this value. This battery replacement would provide 20-W at full power for about 50 hours before refueling.