Fuel cells in your future
Posted: Wednesday, August 22, 2007 8:03 PM by Alan Boyle
Does the future of energy lie in fuel cells? You might think so, based on what chemists have cooked up for this week’s annual meeting of the American Chemical Society. One team has come out with a pellet system that could open the way for safe and easy hydrogen-based fuel, while another has developed a battery-scale fuel-cell system that capitalizes on, um, the microbes in a cow’s guts. Such technologies could provide less smelly alternatives to the poop-fueled systems that are already belching out power today.
Pellets are often proposed as the best way to distribute hydrogen for use in next-generation fuel-cell cars like the ones being developed by GM. The hydrogen isn't an energy source per se, but rather a carrier of energy generated from other sources, ranging from natural gas (not so good) to wind (better) to microbial waste processing (best).
When it comes to distribution, the trick is to come up with pellets that can pack a lot of hydrogen inside. Purdue researchers recently unveiled a system that could extract hydrogen from water using aluminum pellets, but they acknowledged that the raw materials for the system were too expensive to compete in today's economy.
Researchers from the Pacific Northwest National Laboratory are pursuing a different approach, with compressed pellets of ammonia borane that are about the size of aspirin tablets. It would take just two pellets to store the equivalent of a liter (61 cubic inches) of hydrogen gas - and after the hydrogen is released in a fuel-cell system, the pellets can be reprocessed for reuse.
The lab says the pellet fuel system could take up less space and weigh less than systems using pressurized hydrogen gas - potentially resulting in fuel-cell cars that are comparable to today's gasoline-powered cars in room, range and performance. Now the researchers are working on ways to regulate the release of hydrogen from the pellets, so that accelerating would be as easy as stepping on a gas pedal.
"With this new understanding and our improved methods in working with ammonia borane, we're making positive strides in developing a viable storage medium to provide reliable, environmentally friendly hydrogen power generation for future transportation needs," Dave Heldenbrant, a researcher at Pacific Northwest National Laboratory, said in Tuesday's news release.
Hydrogen storage is just one challenge facing future fuel cells. The cost of the materials that go into building the cells themselves is another. Today's fuel-cell engines require expensive catalysts that often incorporate platinum, one of the world's priciest metals. However, researchers at Argonne National Laboratory are experimenting with less expensive ruthenium-based catalysts. As noted in this week's news release, ruthenium costs just 1 percent as much as platinum.
Now, about those cows: The idea of generating electricity from the methane in cow manure isn't exactly new, and some farmers have even experimented with extracting hydrogen from the methane for fuel cells.
Researchers at Ohio State University have been experimenting with a different kind of cow power for fuel cells: microbe-rich fluid extracted from the largest chamber of a cow's stomach, known as the rumen. The microbes in the fluid can be harnessed to produce an electric current as they break down cellulose in a specially designed biofuel cell.
The scientists collected the fluid from a living cow's stomach via a surgically implanted tube. The fluid was then mixed with cellulose in one chamber of the cell, and an oxidizing agent called potassium ferricyanide was put in the other chamber. As the cellulose was digested, the microbial brew released electrons that flowed from one chamber to the other, setting up a circuit.
The system generates a tiny amount of power - enough to put the shine into a miniature light bulb on a Christmas tree, said Ann Christy, an associate professor of food, agricultural and biological engineering at Ohio State. The key is to make the system smaller and more efficient, so that tiny fuel cells can take on bigger and bigger jobs.
Ohio State's researchers have already come a long way: The latest biofuel cells are only about a fourth the size of the cells developed two years ago, but generate three times the power, said researcher Hamid Rismani-Yazdi. Each cell measures about 2 inches wide and 3 inches in height and length - somewhere between the size of a D-cell battery and a 6-volt lantern battery. Two of the cells are enough to recharge one AA-size battery, the research team reported.
Rismani-Yazdi said he adds fresh cellulose to the cells every two days or so. The amount varies, depending on how quickly power is drained from the cells.
"But the power output of these fuel cells is sustainable indefinitely as long as we keep feeding the bacteria with cellulose," Christy said in Tuesday's news release. "We ran these cells for three months."
And the kind of cellulose digested by the bacteria can be harvested from crop waste, wastepaper or wood - the sorts of things that even cows leave behind.
Will Ohio State's biofuel cells - plus other renewable-energy technologies ranging from cellulosic ethanol to microbial fuel factories - add up to enough to avert a future energy crisis? Or does the energy frontier offer more hype than hope? Feel free to weigh in with your comments below.
