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NASA Science News for March 18, 2003

Cool Fuel Cells

Fuel cells promise to be the environmentally-friendly power source of
the future, but some types run too hot to be practical. NASA-funded
research may have a solution. 

March 18, 2003: Astronauts have been using them for power aboard
spacecraft since the 1960s. Soon, perhaps, they'll be just as common
on Earth--powering cars, trucks, laptop computers and cell phones. 

They're called fuel cells.

By combining hydrogen fuel with oxygen, fuel cells can produce plenty
of electric power while emitting only pure water as exhaust. They're
so clean that astronauts actually drink the water produced by fuel
cells on the space shuttle. 

In recent years the interest in bringing this environmentally
friendly technology to market has become intense. But there are
problems: You can't "fill 'er up" with hydrogen at most corner gas
stations. And fuel cell-based cars and computers are still relatively
expensive. These obstacles have relegated fuel cells to a small
number of demo vehicles and some specialty uses, such as power aboard
the space shuttle and back-up power for hospitals and airports. 

Now NASA-sponsored research is helping to tackle some of these
obstacles. By finding a way to build "solid oxide" fuel cells that
operate at half the temperature of current designs--500øC instead of
a blistering 1,000øC--researchers at the Texas Center for
Superconductivity and Advanced Materials (TcSAM) at the University of
Houston hope to make this kind of fuel cell both cheaper to
manufacture and easier to fuel. 


Less is more

"Our key advance was making the heart of the fuel cell--the sheet of
electrolyte that controls the flow of electrically charged ions--out
of a thin film only one micron thick," says Alex Ignatiev, the
director of the NASA-funded TcSAM. 

In contrast, today's off-the-shelf solid-oxide fuel cells have
electrolyte layers 100 microns thick or more (a micron is one
thousandth of a millimeter). Ignatiev explains: "The thinness cuts
down internal resistance to electric current, so we can get
comparable power output at much lower operating temperatures." 

To make this ultra-thin layer, Ignatiev and his colleagues at TcSAM
don't simply shave down a chunk of bulk material until it's thin
enough. Instead, they grow the electrolyte atom by atom, depositing
one layer of atoms at a time in a process called epitaxy. The thin
films in TcSAM fuel cells are about 1000 atoms thick. 

Squeezing out the same power at half the temperature creates a domino
effect of cost savings. For one, cheaper materials can be used to
build them, rather than the expensive heat-tolerant ceramics and
high-strength steels demanded by 1,000-degree fuel cells. And the
automobiles and personal electronics that could use these fuel cells
can also forgo exotic materials and elaborate heat-dissipation
systems, lowering manufacturing costs. All of this tips the scales of
economic feasibility in the right direction. 

Support for fuel cells as the successor to the internal combustion
engine is widespread. All of the major automobile manufacturers are
busily developing fuel-cell vehicles, and President Bush recently
proposed spending US$1.2 billion to help bring the technology to
market. 

The portable electronics industry is also exploring miniature fuel
cells as a more powerful, longer lasting replacement for batteries.
Intel, for example, has funded a start-up company called PolyFuel to
develop such a fuel cell for laptops. 


Fill 'er up with ... take your pick!

Solid-oxide fuel cells are one of six types being developed today.
Each depends on a different chemical trick to combine the hydrogen
fuel with oxygen to produce power. The automotive industry is looking
primarily at proton exchange membrane (PEM) fuel cells to power
tomorrow's cars and trucks, but some companies are also considering
the advantages of the solid-oxide variety. 

Key among these advantages is the ability to run on readily available
fuels, such as methanol or even gasoline, which contain hydrogen
bound to carbon and sometimes oxygen. The other five types of fuel
cell can do this as well, but only with the help of additional
hardware called a "reformer," which extracts pure hydrogen from these
other fuels. These reformers cost extra money, add bulk to the
engine, and sap power, cutting the engine's overall efficiency
roughly in half. 

Solid-oxide fuel cells are able to consume methanol-like fuels
without reformers. 

Most of the environmental benefit of fuel cells is lost when
hydrocarbon fuels are used, because extracting hydrogen from them
leaves behind CO2 and pollutant gases that end up in the exhaust. But
it helps solve the "chicken and egg" problem: Who's going to buy
hydrogen-powered cars until most gas stations have hydrogen pumps?
But what company is going to pay to install hydrogen pumps at
hundreds of gas stations until there are plenty of fuel-cell cars on
the road? Solid-oxide fuel cells can bridge the gap. They can run on
methanol or gasoline now and then switch to pure hydrogen as it
becomes available. 

The thin-film variety being developed at TcSAM improves on this
fueling flexibility. Ignatiev explains: "Normal solid-oxide fuel
cells can use fuels like methanol, but they become impaired over time
as carbon coats the fuel cell's nickel electrode," he says. "This
happens partly because of the cell's 1,000-degree operating
temperature. Research shows that this doesn't happen--at least not to
an appreciable degree--at the lower temperatures at which our cells
operate." 

TcSAM's fuel cells have not yet been tested with fuels other than
pure hydrogen, Ignatiev says, but the scientists plan to perform
tests with methanol-like fuels during the next stage of research. 

There's still much work to be done. If all goes well, though, these
thin films could pave the way to clean-running SUVs and other wonders
of a hydrogen-based economy. 

Credits & Contacts
Author: Patrick L. Barry 
Responsible NASA official: Ron Koczor 
Production Editor: Dr. Tony Phillips 
Curator: Bryan Walls 
Media Relations: Steve Roy

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