If you want to take an electric car on a long drive, you need a gas-powered generator, like the one in the Chevrolet Volt, to extend its range. The problem is that when it's running on the generator, it's no more efficient than a conventional car. In fact, it's even less efficient, because it has a heavy battery pack to lug around.
Gas guzzler: The fuel cell developed at the University of Maryland.
Now researchers at the University of Maryland have made a fuel cell that could provide a far more efficient alternative to a gasoline generator. Like all fuel cells, it generates electricity through a chemical reaction, rather than by burning fuel, and can be twice as efficient at generating electricity as a generator that uses combustion.
The researchers' fuel cell is a greatly improved version of a type that has a solid ceramic electrolyte, and is known as a solid-oxide fuel cell. Unlike the hydrogen fuel cells typically used in cars, solid-oxide fuel cells can run on a variety of readily available fuels, including diesel, gasoline, and natural gas. They've been used for generating power for buildings, but they've been considered impractical for use in cars because they're far too big and because they operate at very high temperatures—typically at about 900 ⁰C.
By developing new electrolyte materials and changing the cell's design, the researchers made a fuel cell that is much more compact. It can produce 10 times as much power, for its size, as a conventional one, and could be smaller than a gasoline engine while producing as much power.
The researchers have also lowered the temperature at which the fuel cell operates by hundreds of degrees, which will allow them to use cheaper materials. "It's a huge difference in cost," says Eric Wachsman, director of the University of Maryland Energy Research Center, who led the research. He says the researchers have identified simple ways to improve the power output and reduce the temperature further still, using methods that are already showing promising results it the lab. These advances could bring costs to a point that they are competitive with gasoline engines. Wachsman says he's in the early stages of starting a company to commercialize the technology.
Wachsman's fuel cells currently operate at 650 ⁰C, and his goal is to bring that down to 350 ⁰C for use in cars. Insulating the fuel cells isn't difficult since they're small—a fuel cell stack big enough to power a car would only need to be 10 centimeters on a side. High temperatures are a bigger problem because they make it necessary to use expensive, heat-resistant materials within the device, and because heating the cell to operating temperatures takes a long time. By bringing the temperatures down, Wachsman can use cheaper materials and decrease the amount of time it takes the cell to start.
Even with these advances, the fuel cell wouldn't come on instantly, and turning it on and off with every short trip in the car would cause a lot of wear and tear, reducing its lifetime. Instead, it would be paired with a battery pack, as a combustion engine is in the Volt, Wachsman says. The fuel cell could then run more steadily, serving to keep the battery topped without providing bursts of acceleration.
The researchers achieved their result largely by modifying the solid electrolyte material at the core of a solid-oxide fuel cell. In fuel cells on the market, such as one made by Bloom Energy, the electrolyte has to be made thick enough to provide structural support. But the thickness of the electrolyte limits power generation. Over the last several years, researchers have been developing designs that don't require the electrolyte to support the cell so they can make the electrolyte thinner and achieve high power output at lower temperatures. The University of Maryland researchers took this a step further by developing new multilayered electrolytes that increase the power output still more.
The work is part of a larger U.S. Department of Energy effort, over the past decade, to make solid-oxide fuel cells practical. The first fruits of that effort likely won't be fuel cells in cars—so far, Wachsman has only made relatively small fuel cells, and significant engineering work remains to be done. The first applications of solid oxide fuels in vehicles may be on long-haul trucks with sleeper cabs.
Equipment suppliers such as Delphi and Cummins are developing fuel cells that can power the air conditioners, TVs, and microwaves inside the cabs, potentially cutting fuel consumption by 85 percent compared to idling the truck's engine. The Delphi system also uses a design that allows for a thinner electrolyte, but it operates at higher temperatures than Wachsman's fuel cell. The fuel cell could be turned on Monday, and left to run at low rates all week and still get the 85 percent reduction. Delphi has built a prototype and plans to demonstrate its system on a truck next year.
By Kevin Bullis
From Technology Review