Portable fuel cells powered directly by ethanol could become a viable technology thanks to a new catalyst that has been developed that breaks a strong bond at the heart of ethanol molecules. This frees electrons and generates electricity. These types of fuel cells could replace lithium-ion batteries in laptops and cell phones, and could eventually be used to power electric vehicles.
Ethanol is much easier to transport and store than hydrogen, but up until now researchers have not been able to create a good catalyst for oxidizing ethanol in order to make such fuel cells possible.
Previous catalysts could only release a couple of electrons per ethanol molecule, hence they generated low currents. 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.
The researchers hope that the new catalyst will produce power in the range of hundreds of milliamps per square centimeter. 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.
Radoslav Adzic, the senior chemist at Brookhaven National Laboratory who led the work, deposited tiny clusters of platinum and rhodium on tin oxide nanoparticles. In earlier studies, rhodium had been shown to break bonds between carbon atoms, but only if vaporized at high temperatures in an ultrahigh vacuum. The combination of rhodium with the tin oxide allowed it to break these bonds as a solid and at the relatively low temperatures needed for portable fuel cells. The platinum plays a key role in producing protons and electrons from hydrogen atoms in ethanol.
There are many significant challenges before the catalyst can be commercialized in ethanol fuel cells. In addition to facing the challenges of incorporating it into fuel cells and engineering these to produce electricity efficiently at high currents, the researchers will need to find ways to reduce costs. Rhodium is the most expensive precious metal–it’s even more expensive than platinum–so it will either need to be replaced with another element, or techniques must be developed to reduce the amount of rhodium required.
Still, the new catalyst is a significant improvement over previous attempts. “Breaking the carbon-carbon bond at low temperatures is an extremely hard problem,” Herring says. “The fact that [Adzic] is breaking that bond is pretty exciting.” But he adds that “it’s just one step on the pathway toward this dream of a direct ethanol fuel cell.”