Direct Ethanol Fuel Cells (DEFC)

Direct Ethanol Fuel Cells work much like methanol fuel cells. Ethanol has the advantage of being less toxic than methanol and because there is a supply chain in place, delivery of fuel is less of a concern.

Function and Reactions of DEFCs

Ethanol is oxidized at the anode, in the presence of steam and a platinum catalyst, to produce hydrogen, carbon dioxide, and electrons. Because ethanol is hydrogen-rich, it produces more energy per kilogram than do fuels like methanol or pure hydrogen. The result is more energy per volume of fuel.

Benefits of DEFCs

The two biggest advantages of direct ethanol fuel cells are the fact that a supply chain is already available and that ethanol can be generated from a number of sources, particularly biomass like sugar cane, wheat, and corn. The benefit of using biological sources to produce ethanol is that it can reduce the overall amount of carbon dioxide released by a fuel given that plants absorb carbon dioxide.

The infrastructure for both producing and distributing ethanol is already in place, making these fuel cells an ideal candidate for replacing internal combustion engines in the near future.

Because ethanol is a larger molecule than methanol, these fuel cells do not suffer from cross over current to the degree that methanol fuel cells do. The result is that higher voltages and more power can be obtained from DEFCs.

Drawbacks of DEFCs

Like many fuel cells, the major downside to DEFCs is the cost related to catalysts and the risk of catalyst poisoning by carbon monoxide. There has been less research invested into DEFCs, so they tend to be behind the curve in terms of technology. Advances using platinum-tin hybrid catalysts have show promise in research conducted in France. The hybrid catalyst is less susceptible to carbon monoxide poisoning.

Ethanol fuel cells do have some potential as power for vehicles, but little has been invested in this area because hydrogen fuel cells have been the focus. Part of the reason that ethanol is not more popular as a vehicle fuel, both for conventional engines and fuel cells, is that fact that to produce enough to meet current demand petroleum would have to be reformed, which means the ecological advantages are greatly diminished. The reason for this has to do with scale.

To produce enough ethanol to meet current demands would require that every field, the world over, be planted in corn or sugar cane, all of which would be converted to ethanol. This leaves no land for farming for nutritional needs. As discussed above, petroleum could be reformed to produce ethanol, but that creates other problems. There is currently research into algae and other methods by which ethanol might be produced on a large scale without jeopardizing the food chain.