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Will you ever again pump a gallon of unleaded that costs less than two dollars? Will your grandchildren drive cars powered entirely by hydrogen fuel cells? Is Progress Energy serious about building a new nuclear power plant in one of the Carolinas?
At two o’clock on this afternoon in June, Jennifer Kelly doesn’t know the answers to these questions. What she does know is that today she will make something new. Darting around a crowded basement lab, she slips on safety goggles and purple latex gloves. She fills a bucket with dry ice then props it beneath a shiny steel reaction vessel about the size of a cocktail shaker. The ice will cool the vessel; Kelly doesn’t want the reaction to heat up until she’s ready.
She carefully syringes her ingredients — two liquid compounds and one gas — into the vessel, heats it up, and turns a valve to add carbon dioxide (CO2 ). As the CO2 flows, she monitors the pressure readout. “If it hits seven thousand, I run,” she says with a laugh. She is mostly kidding; she has done some math to determine the amount of each ingredient to add and to predict what will happen when they combine in CO2. Still, she monitors the pressure, temperature, and ingredient amounts carefully. A small variation could cause a big change in the reaction.
In a few minutes, Kelly turns off the CO2 valve. “That’s it,” she says. “Now, I just let it go for about twelve hours.” The reaction will give Kelly a small vial of oil that she will poke and prod — image with spectroscopy, run through gel chromatograph — to figure out the exact properties of the new polymer she has made.
Polymers are groups of simple molecules linked together like the pearls in a necklace; plastic and rubber, for instance, are polymers. Kelly wants to make one that will conduct protons, even at very high temperatures and low humidity, and never dissolve in water. This polymer could be poured into a mold of any shape imaginable, then hit with UV radiation to turn it into a transparent membrane that would form the heart of a fuel cell. Kelly is part of a group in Joe DeSimone’s chemistry laboratory trying to revolutionize how one type of fuel cell (proton exchange membrane cells) is made.
A fuel cell is portable, like a battery, but it never needs to be recharged or thrown away. It will keep providing power as long as it receives hydrogen, which the cell uses to create energy through a chemical reaction. That reaction (see “How a Fuel Cell Works”) yields only water — and no harmful emissions. So fuel cells have been touted as part of the answer to our dependence on oil and the growing problem of global warming, if they could economically be used in cars.
That’s a big if. Today, fuel cells are too expensive to be practical. And there are some technical problems. A commonly used membrane is Nafion, produced by DuPont. While Nafion membranes were first used in a fuel cell in the Gemini space program, they have been used commercially for the past twenty-five years in making chlorine bleach and other products, so much of their development has been geared to that application. “So DuPont is pretty much locked in to the process that they have, which is great for making chloralkali membranes. But for making fuel-cell membranes, it’s not really as efficient as it might be,” says Everett Baucom, deputy director of Carolina’s National Science Foundation Science and Technology Center and a former head of Nafion and Fluorointermediates Technology at Dupont.
Nafion membranes are very stable, and they conduct protons well, Baucom says. But DeSimone’s group is trying to create a modified membrane that works under a wider range of conditions. DuPont has given DeSimone some funding and access to materials — the secret ingredients they use to make Nafion. And they’re letting DeSimone run with them, no restrictions. But no promises either.
Nafion doesn’t like very high temperatures, and it requires 100 percent relative humidity inside the fuel cell. Otherwise, it can’t conduct current very well. DeSimone’s group is trying to change that by using chemical cross-linking.
A cross-linked polymer’s molecules aren’t connected in a simple row, like pearls on a strand, but in a two- or three-dimensional branching structure, like a spider web, Kelly says. In theory, this more complicated structure will allow the membrane to conduct protons without all that humidity. To conduct, Nafion uses moisture to transport protons between sections of the membrane called acid groups. DeSimone thinks that a cross-linked membrane can handle many more acid groups than Nafion can, so he can create a membrane with a “sea” of acid groups that overlap. Then protons would be able to “hop” from one acid group to the other, no water required. The trick for the chemists is improving the membrane’s conductivity without introducing undesirable side effects. Too many acid groups, for instance, can render a traditional membrane material like Nafion water soluble, and it might dissolve while operating.
They’ve had small victories. Doctoral student Zhillian Zhou has turned her liquid precursors into actual membranes, and in early experiments, the cross-linking method appears to allow these membranes to conduct protons and generate an electrical current at much lower humidity than most membranes. Zhou cautions that these are preliminary results.
DeSimone’s group is also experimenting with making liquid precursors that could be molded into any shape. When a membrane is produced in flat sheets, manufacturers have to build the fuel cell from the inside out, assembling it around the flat membrane, DeSimone says. But if the membrane began as a liquid, like Kelly’s vial of oil, manufacturers could pour it into a mold, creating a membrane with tiny nooks and crannies. This could yield a large surface area to conduct protons and generate a current, but in a tiny space. Reducing size is one of the challenges of making fuel cells marketable, Baucom says. “There’s no question that fuel cells work. But one of the challenges is making them smaller while still being able to generate the amount of power that you need,” he says. “You can’t have the whole back of your S.U.V. taken up with a fuel cell.”
DeSimone, and UNC-Chapel Hill for that matter, is a newcomer to fuel cells. But DeSimone’s group has a track record in finding better ways to make polymers. They did it years ago when they showed that DuPont’s Teflon, the stuff that coats your pots and pans, could be manufactured using carbon dioxide instead of a more harmful chemical solvent, making the manufacturing process both friendlier to the environment and less expensive. In 2002, the DuPont plant in Fayetteville, North Carolina, began using the new process to manufacture Teflon for use in specialty products such as wire and cable insulation.
Even if Kelly, Zhou, and DeSimone have similar success with creating a better fuel-cell membrane, a lot of road has to be laid before fuel-cell cars routinely roam North Carolina or any state. Such a car would still need to fuel up, but with hydrogen, not petroleum. So a system of hydrogen fueling stations will have to be set up across the country.
And one of the big questions — where will we get the hydrogen? It doesn’t exist by itself in nature; we must extract it from some other product, such as oil, natural gas, or water. That process requires electricity, which pollutes the air with greenhouse gases and also uses fossil fuel. Critics say that, by using fuel-cell cars, we would be merely polluting the environment and using up fuel earlier, when we extract the hydrogen, rather than when we drive the car.
DeSimone, for one, says that fuel cells are really just devices for storing and transporting electricity, in the form of hydrogen. They are not a way of avoiding using up that electricity in the first place. Their immediate use will be as a longer-lasting power source for laptops, cell phones, and other mobile devices.
But fuel-cell cars can help reduce pollution, DeSimone says, if the hydrogen fuel is derived using renewable energy sources or nuclear power. Tom Meyer, professor of chemistry at Carolina and former associate director for strategic research at Los Alamos National Laboratory, says that hydrogen-based energies such as fuel cells are exciting because water becomes a potential fuel. “But you’ve got to have an energy source to pull the hydrogen out of the water,” he says.
Fuel cells and hydrogen are one part of a broad energy plan that will have to be implemented over time, Meyer says. The first step is using the fossil fuel we do have more efficiently. The issue of supply of oil and natural gas are “going to come up faster than people think,” he says. According to petroleum company data, our petroleum reserves will hit their peak in as little as ten to fifteen years. And demand is increasing, not just from the United States, but from increasingly industrialized countries such as China. “The prices we pay now for gasoline are not accidental,” Meyer says. “They’re a reflection of that demand.”
We will have cars that get sixty-five miles to the gallon,” Meyer says. “We will have very energy-efficient houses. And this will be driven by the marketplace, as these prices go up and up and up.”
The rising levels of CO2 and other greenhouse gases in the air are also driving the need to use energy more efficiently and find alternatives to fossil fuels. “Most everybody in the scientific community who knows something about this area would say that greenhouse gases are increasing the average temperature of the earth with potentially important consequences for the environment,” Meyer says. In the short term, he suggests, scientists will have to work on various methods to handle those emissions — carbon sequestration, for example, which involves capturing the carbon dioxide and storing it underground or in oceans.
Another part of the plan includes using energy sources that are proven to work, such as nuclear power, while developing new technologies to replace petroleum, Meyer says. “It’s important to hold on to nuclear power, but there are some real technical problems to overcome, and they are not trivial.” Other energy sources, such as hydropower (using moving water to make electricity) and wind power, may provide small amounts of our total energy budget. But when combined, they may add up to 20 percent, which could help, he says.
Then there’s hydrogen. Scientists will have to work quickly to solve the technical problems involved in using hydrogen and other renewable energy sources. The Department of Energy’s plan calls for all utility vehicles (mass transit such as trains and buses) to run on hydrogen by 2020. Just fifteen years from now.
So DeSimone, Kelly, and Zhou keep working on their small part of the picture. On that June afternoon, Kelly’s reaction turned out fine. The next day, she slowly vented the reaction vessel, then poured out a vial of liquid. But her work was just beginning. She might heat up the liquid or hit it with UV light, to cross-link it and make a membrane. Or she might find that she must mix another compound with it to form a membrane. Her mind will focus on these details, on her little vial of oil. Not on global warming predictions or timelines on an energy plan. But those issues loom.
“You have to face up to where we are now,” Meyer says. “You’ve got a little bit of a time window to go out and explore hydrogen and fuel cells.”
But it’s not guaranteed that Kelly, Zhou, DeSimone, or anyone trying to perfect fuel cells and hydrogen will succeed.
“If that doesn’t work, you better go to plan C,” Meyer says.
And what is Plan C?
“Good question.”
