In his mind’s eye, Dr. Raymond J. Gorte, the Carl V.S. Patterson Professor of Chemical Engineering and chair of the department, sees a fuel cell in your basement. He can see one in your car, too, though that image is a little farther off. And he sees both of them using natural gas or some other hydrocarbon to create electricity—not by burning it but by drawing electrical current from a chemical reaction between the fuel and oxygen in the air.
In some ways, Gorte’s vision may not strike the cognoscenti as entirely unique. Chemical engineers have been designing fuel cells for some years now—both the solid-oxide fuel cells (SOFCs) that Gorte and his Penn colleagues have been using and the better-known polymer electrolyte membrane fuel cells (PEMs). Both kinds operate rather like batteries that never need recharging, though they do require a steady supply of fuel to operate. They also have the potential to be significantly cleaner and more efficient than, say, the internal-combustion engine.
But until now, fuel cells were, pretty much by necessity, designed to run on hydrogen. And hydrogen—which is usually made by “reforming” hydrocarbons (reacting them with steam over a catalyst)—is expensive to buy and problematic to produce and store.
Now Gorte and two colleagues at Penn—Dr. John M. Vohs, professor of chemical engineering, and Dr. Seungdoo Park, a post-doctoral associate—have designed a fuel cell that runs directly on hydrocarbons, bypassing the hydrogen phase.
“What’s unique about our system is that we wouldn’t have to have the reformer in front of it to take the hydrocarbon and make it into hydrogen,” says Gorte. “You’d have natural gas or butane or whatever fuel you want to use being fed directly into the fuel cell. The fuel cell would electrochemically oxidize the hydrocarbon, making electricity.”
While there is a certain elegant simplicity to the notion, the devil was in the details. The fuel cell works by having a cathode, or negative terminal, combine oxygen from the air with electrons to form oxygen ions, while the anode, or positive terminal, attracts the oxygen ions and combines them with fuel—thus freeing electrons from the fuel and producing electricity. The oxygen ions flow through the electrolyte —a thin ceramic core between the anode and the cathode.
Earlier efforts to use hydrocarbons in fuel cells had failed, since soot, in the form of graphite, would quickly build up on the nickel-based anode, breaking the circuit. Gorte’s team decided to replace the nickel with a porous copper material. While the details of that process are perhaps better left to the article they wrote for the March 16 issue of Nature, Gorte acknowledges that “coming up with a way to get a porous material that we could heat to high temperatures and would stay porous” was a tricky and time-consuming process—and one that they’re still refining.
Heat has also been a challenging factor for the electrolyte, says Gorte. “The copper system doesn’t allow us to use the same methods that people have developed for making these thin electrolyte films. You need not only to make a thin film—that’s easy—but also to make a thin film that can be heated to 1,000 degrees Centigrade and stay dense and not break and crack.”
The fact that, in an SOFC, oxygen ions will only flow through the electrolyte at temperatures approaching 600 degrees explains why PEMs (which operate at temperatures of approximately ~70 degrees Centigrade) have been the fuel cell of choice among those seeking to put them in cars. In 1997, Chrysler and the industrial-consulting firm of Arthur D. Little announced that they had built a gasoline-powered PEM that would power a car, Gorte notes. “What they were going to do was actually reform gasoline on board, and make hydrogen from the gasoline in what amounts to a little refinery in your trunk, and then use the hydrogen as the primary source for running the car.” But the hydrogen-making process, says Gorte, “takes up a lot of space; it’s inefficient; it’s difficult.”
While numerical estimates of efficiency are notoriously unreliable, Gorte says, fuel cells will be much more efficient than the internal-combustion engine. And by several important measures—including the amount of carbon dioxide produced—they will be cleaner. “Because efficiency is just the amount of energy you get out of burning a given amount of fuel, if you can get twice as much energy from a given amount of fuel, then you don’t have to burn as much fuel—and you make less CO2.”
Through the University’s Center for Technology Transfer, Gorte’s team and the Gas Research Institute (which provided funding for their work) have applied for a joint patent on their fuel cell.
“I don’t think there will be any problem getting approval at some level,” he says. “I certainly think that the work is novel.”
Though he notes that the Office of Naval Research is interested in exploring their possibilities as portable generators for the battlefield, Gorte has no idea how long it might be before these fuel cells are commercially available. “We’re not involved in manufacturing, and I have no real idea of how long it takes to develop this. The system that you would have in a house, I think, would be relatively simple. For cars, it’s going to be a very long time. There are an awful lot of issues that need to be confronted.”
