chip to fuel handhelds
Technology Research News
As the field of portable electronics matures,
producing increasingly complicated handheld devices, there is a growing
need for more efficient ways to power them. One alternative is to use
tiny versions of fuel cells, which create power by making hydrogen and
oxygen react chemically rather than burning them like an engine does.
Two groups of scientists have made separate advances toward this goal.
A group of researchers at Lehigh University has worked out a way to fuel
a chip-sized fuel cell. Another group at NEC Corporation has used a type
of carbon nanotube to make the fuel cell reaction more efficient.
The methods could eventually be used in chip-sized fuel cells to power
devices that require small, rechargeable power sources, like laptop computers
and cellular phones.
A major challenge in producing a practical chip-sized fuel cell is providing
the cell with a source of hydrogen. This usually involves a bulky storage
device because hydrogen stored as gas or metal hydrides does not provide
as much energy by volume as a liquid hydrocarbon fuel, according to Mayuresh
Kothare, an assistant professor of chemical engineering at Lehigh.
One way to sidestep the storage problem is to extract hydrogen as it is
needed from liquids that contain it at room temperature. The Lehigh researchers
have found a way to do this by mixing methanol and water in the presence
of a catalyst, said Kothare.
The Lehigh device uses tiny capillaries etched into a silicon chip to
act as fuel lines to mix and carry the raw materials of the reaction --
methanol and water -- to channels coated with a catalyst layer of copper,
said Kothare. “The channels… provide a closed path for flow of fluids.
The inside of the channels will be coated with a catalyst. The reaction
will take place on the surface of the catalyst.”
When the mix of methanol, which contains one carbon, one oxygen and four
hydrogen molecules, and water, which contains one oxygen and two hydrogen
molecules, reaches the coated channels, it reacts to form hydrogen, said
Kothare. "The hydrogen and unreacted methanol [and] water will flow out
of the channel. [The] hydrogen will then be purified and sent to the fuel
cell to produce power," he said.
The key to efficiently extracting hydrogen is controlling the size and
location of the microfluidic channels as well as the environment within
them in order to prevent leaks and bypasses and make the reaction efficient,
The channels of the device are 1 to 2 centimeters long and half a millimeter
deep. The copper coating is about 33 nanometers thick. A nanometer is
one millionth of a millimeter
In order to carry out and control fluid delivery at such a small scale,
the temperature of the microreactors that produce the hydrogen must be
finely controlled via tiny sensors and heaters, said Kothare. The researchers
are also working on optimizing the dimensions and geometry of the microreactors
in order to maximize the amount of hydrogen they can extract in the reaction,
he said. They are also working on ways to connect the hydrogen generator
to a microfuel cell that would use the hydrogen to produce power, he said.
The Lehigh prototype has "excellent potential for mass production", said
Lois Anne Zook, an assistant professor of analytical and environmental
chemistry at Delta State University. "Fuel cells have the potential to
be one of the most commercially viable renewable energy technologies for
the electronics industry [and] the [Lehigh] hydrogen power chip work...
proposes an approach to solving one of the main limitations of the hydrogen
oxygen fuel cell system -- the fuel supply," she said.
Although the Lehigh prototype is a good proof of concept, there are still
technical challenges to address in order for the technology to become
practical, she said. "The reformer is not as fuel-efficient as using pure
hydrogen gas, and byproducts of the reformer reaction poison the fuel
cell catalysts, degrading performance over time," she said. The biggest
technical hurdle to making the extraction approach commercially viable
is addressing this fuel cleanup, she said.
The Lehigh researchers' goal is to build and demonstrate the hydrogen
generator portion of the microfuel plant, said Kothare. Microfuel plants
that use such generators could be ready for commercial use in about five
years, he said.
Meanwhile, the NEC scientists found that a type of carbon nanotube dubbed
nanohorns can be used to make more efficient catalyst for a chemical reaction
in the fuel cell that extracts energy from the hydrogen. The scientists
found that they could coat the carbon nanohorns, which are sheets of carbon
molecules rolled up in a horn shape, with a coating of platinum catalyst
particles that were less than half the size supported by ordinary activated
carbon. The finer grain of the platinum makes for a more efficient fuel
Although using nanotubes in fuel cells is not new, the nanohorn shape
may make for more efficient cells, said Zook. "Typically, the higher the
surface area to volume ratio of the platinum catalyst, the better it works,
so putting platinum on these high-surface-area carbon tubes reduces the
amount of platinum used while keeping the surface area for the reaction
high," she said.
Kothare's research colleagues were Ashish V. Pattekar, Sooraj V. Karnik
and Miltiadis K. Hatalis. They published the research in the proceedings
of the 5th International Conference on Microreactors Technology, which
was held in Strasbourg, France, in May. The research was funded by the
National Science Foundation (NSF), the Pittsburgh Digital Greenhouse,
and Sandia National Laboratories.
The NEC team of scientists was led by NEC research fellow Sumio Iijima.
Timeline: 5 years
Funding: Corporate; Government
TRN Categories: Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "A Microreactor for in-situ
Hydrogen Production by Catalytic Methanol Reforming," proceedings of the
5th International Conference on Microreaction Technology held in Strasbourg,
France, May 27-30, 2001.
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