Portable fuel cells powered directly by ethanol could soon be practical, thanks to a new catalyst that breaks a strong bond at the heart of ethanol molecules, freeing electrons and generating electricity. Such fuel cells could replace batteries in laptops and cell phones, and could eventually be used to power electric vehicles.
Ethanol fuel cells could be far more efficient than conventional ethanol-powered engines. They could also be more practical than hydrogen fuel cells, since ethanol is easier to store and transport than hydrogen. But researchers hadn’t been able to create a good catalyst for oxidizing ethanol in order to make such fuel cells possible.
Previous catalysts converted ethanol into acetic acid and acetaldehyde, a process that releases just a couple of electrons per ethanol molecule, hence generates low currents. Breaking down ethanol molecules further to produce carbon dioxide would release far more electrons (a total of 12 per ethanol molecule) and generate higher currents, but that requires breaking a strong bond between two carbon atoms. To break this bond, researchers had to apply high voltages, making the process inefficient: almost all of the voltage produced by oxidizing the ethanol was used to sustain the reaction, reducing net power output to a trickle, says Manos Mavrikakis, professor of chemical and biological engineering at the University of Wisconsin-Madison.
The new catalyst, developed by researchers at Brookhaven National Laboratory, breaks the carbon bonds without high voltages, efficiently releasing enough electrons to produce electrical currents 100 times higher than those produced with other catalysts. The next step is to incorporate the catalyst into a fuel cell, so that its performance can be compared with those of other catalysts in fuel cells, says Brian Pivovar, a scientist at the National Renewable Energy Laboratory, in Golden, CO, who was not involved in the research.
In initial tests outside of a fuel cell, the catalyst efficiently produced currents of 7.5 milliamps per square centimeter. Radoslav Adzic, the senior chemist at Brookhaven National Laboratory who led the work, says that he is “almost positive” that the catalyst, once built into a fuel cell, will produce electrical currents in the range of hundreds of milliamps per square centimeter. Pivovar says that estimate seems reasonable. This level of current, multiplied by the anticipated voltage produced by the cell, would put ethanol fuel cells in the same range as methanol-powered fuel cells, producing enough power for portable electronics. Ethanol is preferable to methanol in several ways: it stores more energy, is less toxic, and is easier to make from renewable sources. For powering vehicles, and competing with the performance of hydrogen fuel cells, the catalyst and fuel cell would need to be improved. The currents would need to be well above 1,000 milliamps per square centimeter, says Andy Herring, a professor of chemical engineering at the Colorado School of Mines, in Golden, CO.