Hydrogen
chip to fuel handhelds
By
Kimberly Patch,
Technology Research NewsAs 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, said Kothare.
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 cell reaction.
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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September 12, 2001
Page One
Internet stays small world
Tools automate computer sharing
Nanotube kinks control current
Hydrogen chip to fuel handhelds
Scheme harnesses Internet handshakes
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