A pair of researchers may have brought the affordable fuel cell-powered car a step or two closer to reality.
Gunter Luepke and Erik Spahr are working to perfect their invention, a process designed to reduce the operating temperature of one type of fuel cell. Cooler operating temperatures remove some of the barriers to fuel-cell use.
Fuel cells work by converting chemical energy into electricity. The chemical energy comes from a fuel that could be hydrogen, or hydrocarbons or fossil fuels, said Luepke, professor of applied science at William & Mary. But the most common class of fuel cells, proton-exchange membrane (PEM) cells, run only on hydrogen.
Luepke and Spahr, a Ph.D. student in applied science, are focusing on solid-oxide cells, a less-common technology. When it comes to potential for automobiles or other portable uses, each fuel-cell technology comes with its own set of yet-unsolved problems. Problems with the PEM cells, Luepke said, center around their only fuel: hydrogen. Production costs for hydrogen are high and storage of the gas poses its own set of problems. Not least, he said, is the virtual lack of hydrogen fueling systems.
On the other hand, solid-oxide fuel cells are more versatile, being able to run on hydrogen or just about any hydrocarbon—propane, butane, many biofuels and even gasoline-readily available fuels.
Heat's the problem
The problem is that the solid-oxide fuel cells have to run at very high temperatures—about 600 to 1,000 degrees Celsius, Luepke explained. High operating temperatures requires a long start-up time. You turn them on and it takes an hour for them to reach operating temperature.
The high operating temperature of solid-oxide fuel cells has other implications. Hot-running fuel cells are subject to degradation, he said, which is aggravated by turning the cell off and on.
"In a car, you don't want to have to run the fuel cell all the time, because you will burn up the fuel," he said. "For a car or any portable application, you would like to have short start-up times. You want to turn it on and in a few seconds, have it up and running. That requires that you reduce the operating temperature."
Today's solid-oxide fuel cells run hot to facilitate the chemistry, Spahr said. The anode breaks down the fuel into hydrogen ions and electrons. Then, the ions diffuse through the solid-oxide electrolyte, while the electrons travel around the outside of the cell, and as Luepke says, do all the work, or make electricity.
The electrons can't get to work until the ions pass through the electrolyte, completing the chemical reaction. "How fast the ions can move through the material is a limiting factor," Spahr explained. "Solid-oxide fuel cells must be run at high temperatures in order for the ions to move through the electrolyte with relative ease."
Replacing heat with light
Heat speeds up the ion passage, but Luepke and Spahr have found a way to get the same effect optically. They use infrared light to excite the hydrogen, which then becomes mobile, allowing the hydrogen ions to complete their trip through the electrolyte more easily. In the lab, they've shown the effect of the infrared light to increase the ion conductivity by seven to nine orders of magnitude.
It's a huge effect, Luepke said, and that corresponds to a reduction in operating temperature of 200 to 300 degrees Celsius. Instead of running at 600 to 800 degrees, the enhanced cells could run much cooler.
Their invention could put solid-oxide fuel cells back into consideration for automotive and other portable uses. Cooler operating temperatures would make solid-oxide fuel cells less expensive to manufacture. Luepke explained that their invention would allow cells to be constructed with steel electrodes, rather than using platinum, as required in current solid-oxide cells.
"It would also decrease the startup time, which is a big issue for automotive applications," Spahr said. "If you can make these hydrogen ions mobile optically, startup time will be much quicker. With our invention, startup will probably drop from hours to minutes—possibly seconds."
Luepke likes to compare the process to the operation of a microwave oven. A conventional oven, he explains, heats up the entire oven space, including the food. A microwave, by comparison, heats only the water molecules in the food. "Here, we're using infrared radiation to heat up just the hydrogen," he said.
Spahr and Luepke say their invention also could work the other way, enhancing the efficiency of the production and storage of hydrogen, which can be used in solid-oxide or PEM fuel cells.
"Hydrogen production is just a fuel cell in reverse," Spahr explained. "You apply an electric current to a fuel like methane and the process re-forms it and you get hydrogen out of one end. There's a similar process for making hydrogen from water—water splitting."
Their work has been funded for the past 12 years by the National Science Foundation. Now, Luepke and Spahr are ready to take their work to the next level. They have started a company called Phenom—the name is a kind of acronym for photo-enhanced oxide membrane. Working with Jason McDevitt, the College's director of technology transfer, they've filed for patent protection for their invention.
"This startup company has great potential," McDevitt said. "It's a tremendously innovative approach that could provide a solution to a very important problem. Obviously, development of a commercial product is a long way off, with many challenges to overcome, but we are very excited about the prospects for this technology."
Phenom seeks funding
As Phenom, Luepke and Spahr are seeking support from the U.S. Small Business Administration Office of Technology. They've applied for Small Business Innovation Research (SBIR) funding of $1 million for three years to continue their investigation. They've done their work so far using low-power infrared lasers in their lab in the basement of Small Hall. With the SBIR funding, they will move their investigation to the Free Electron Laser at the Thomas Jefferson National Accelerator Facility (the J-Lab) in Newport News.
"At the J-Lab, we'll be able to use the high-powered laser to sort things out and the project should move along more quickly," Luepke said. "While a commercial product is years away, it is possible that the first fuel-cell car you buy may be based on this technology developed at the College of William and Mary."