June 2008

E-Mail This Article Printer-Friendly Version

St. Louis, MO-based Akermin, Inc. has developed and is offering for testing a biofuel cell prototype that employs a stabilized enzyme as a catalyst instead of the conventional platinum at the cathode. The company says use of the enzyme makes the process inherently more efficient than conventional methods of portable power generation in fuel cells that rely on platinum catalysts, and the immobilization of the enzyme is now measured in years instead of days for other bio fuel cell technology, making this technology truly commercially viable: In a separate late-May release, Akermin said it had achieved a record three years of enzyme stability in an energy-generating biofuel cell electrode. The company also said this long-term test was continuing, with no statistical decay in performance observed so far. Akermin said earlier the enzyme was stabilized in a conductive polymer matrix at the cathode in a system that can be fueled by organic fuels such as methanol in a direct methanol fuel cell (DMFC) Operating on methanol, the prototype delivers longer, though unspecified, run times. At present it delivers 3 V and up to 1W pulse demand capability is roughly the size of two D cell batteries. The company is working on units that it expects will produce 3-5 watts. Benefits of this design are said to include the ability to passively use nearly pure fuel at the stack without the need for complex water recirculation, significantly reducing susceptibility to fuel crossover, the ability to use alternative PEMs and improved system efficiency. The expects that it will be able to double the energy density of conventional DMFCs. Akermin’s release didn’t say what the enzyme consisted of, but a 2007 paper in the “Journal of Power Sources” by four scientists at St. Louis University who were funded by Akermin said the team had immobilized two oxidoreductase enzymes at the surface of a carbon anode - not the cathode - permitting a multi-step oxidation process of glycerol - not methanol - utilizing 86% of the energy density of the fuel. “These glycerol bioanodes were incorporated into a glycerol/oxygen biofuel cell and resulted in power densities up to 1.21Wcm-2 at room temperature,” the team, led by corresponding author and Akermin co-founder Shelley D. Minteer, wrote. Another paper in the “Journal of Membranes” by a second team also headed by Minteer said enzyme immobilization at electrodes can be achieved by hydrophobically modifying chitosan, a polysaccharide made from shrimp shells, and Nafion polymers. However, it’s unclear, to laymen at least, how these findings relate to enzyme stabilization at the cathode, the achievement cited in Akermin’s release as a breakthrough. Other researchers are looking at enzymes as fuel cell catalysts as well: The National Renewable Energy Laboratory is investigating “wiring” together enzymes as catalysts (H&FCL Jan. 08), and in past years General Motors has talked about investigating enzymes as catalysts for automotive fuel cells.

Contacts: Nick Akers, 314/812-8035; media, Julia Bishop-Cross, 314/260-7782, jbishopcross@sbcglobal.net.