Scientists find new way to generate electricity

Coated carbon nanotubes could replace combustion engines and turbines

Researchers have found a way to produce large amounts of electricity from tiny cylinders made from carbon atoms.

The achievement could replace decades-old methods of generating electricity, such as combustion engines and turbines, the researchers say.

In the future, coated carbon nanotubes crafted from individual atoms could power everything from cell phones to hybrid-electric vehicles. The team envisions such nanotube-based power being available to consumers in the next five years.

Carbon nanotubes are thin sheets of carbon rolled up into teensy tubes each with a diameter about 30,000 times smaller than a strand of hair.

When carbon — one of the most abundant elements on Earth — is rolled up into tubes, it exhibits some extraordinary properties such as high heat conduction, which the team exploited in the new study.

A carbon firecrackerThe researchers coated the nanotubes with a fuel, such as gasoline or ethanol, and applied heat to one end. The result:  The fuel reacts and produces more heat, which ignites more fuel to create even more heat.

The process creates “a wave that travels like dominoes falling in a line [down the length of the nanotube],” said study team member Michael Strano, a chemical engineer at the Massachusetts Institute of Technology (MIT).

The resulting heat wave, it turns out, also creates a wave of electrons moving in one direction — aka electricity.

“The thermal wave squeezes electrons out of the nanotubes like a tube of toothpaste,” Strano explained.

The devices built in the MIT lab produced 10 times more power than a lithium-ion battery of equivalent mass.

“What's intriguing about these waves is that we haven’t really done any engineering to make them efficient yet and already they’re ten times [more powerful than] a lithium-ion battery,” Strano told TechNewsDaily. “We may be able to make very very small power sources out of them."

Cell phone battery replacementThe fuel-coated nanotubes could replace batteries for cell phones and other devices. Strano imagines a device with a button that you would push to create heat from friction, triggering the electricity-generating reaction inside the microscopic tubes.

These power devices could be made 10 times smaller than today’s cell-phone batteries but still hold the same amount of power. Furthermore, unlike today’s batteries, the carbon nanotube variety would not contain any toxic metals.

With some tweaking, the carbon nanotubes could even power a car, Strano said. But instead of coating the carbon cylinders with fuel, a liquid fuel could be stored in the car's gas tank and get injected onto the carbon nanotube battery when needed.

Strano said he was confident his team's discovery could be translated into commercial batteries within a few years.

 

Solar cells made through oil-and-water 'self-assembly'

Researchers have demonstrated a simple, cheap way to create self-assembling electronic devices using a property crucial to salad dressings.

It uses the fact that oil- and water-based liquids do not mix, forming devices from components that align along the boundary between the two.

The idea joins a raft of approaches toward self-assembly, but lends itself particularly well to small components.

The work is reported in Proceedings of the National Academy of Sciences.

Crucially, it could allow the large-scale assembly of high-quality electronic components on materials of just about any type, in contrast to "inkjet printed" electronics or some previous self-assembly techniques.

Specific gravity

Such efforts have until now exploited the effect of gravity, assembling devices through so-called "sedimentation".

In this approach, "blank" devices are etched with depressions to match precisely-shaped components. Simply dumped into a liquid, the components should settle down into the blank device like sand onto a riverbed, in just the right places.

"That's what we tried for at least two years and we were never able to assemble these components with high yield - gravity wasn't working," said Heiko Jacobs of the University of Minnesota, who led the research.

SELF-ASSEMBLY EXPLAINED The oil/water mix contains a number of individual solar cell elements Each is coated with a "water-loving" molecule on the bottom and a "water-hating" one on top The elements align neatly at the oil/water boundary in a two-dimensional sheet The "blank" solar cell has pre-cut places for the elements and is dipped through the boundary As it is slowly drawn upwards, the elements pop into place

"Then we thought if we could concentrate them into a two-dimensional sheet and then have some kind of conveyor belt-like system we could assemble them with high yields and high speed," he told BBC News.

To do that, the team borrowed an idea familiar to fans of vinaigrette: they built their two-dimensional sheets at the border between oil and water.

They first built a device blank as before, with depressions lined with low-temperature solder, designed for individual solar cell elements.

They then prepared the elements - each a silicon and gold stack a few tens of millionths of a metre across - and put different coatings on each side.

On the silicon side, they put a hydrophobic molecule, one that has a strong tendency to evade contact with water. On the gold side, they put a hydrophilic molecule, which has the converse tendency to seek out water.

By getting the densities of the oil- and water-based parts of the experiment just right, a "sheet" of the elements could be made to "float" between the two, pointing in the right direction thanks to their coatings.

The conveyor belt process is to simply dunk the device blank through the boundary and draw it back slowly; the sheet of elements rides up along behind it, each one popping neatly into place as the solder attracts its gold contact.

The team made a working device comprising 64,000 elements in just three minutes.

Bendy future

Having proved that the concept works, the team is now investigating just how small they can go in terms of individual elements, or how large they can go in finished devices.

The approach should also work for almost any material, stiff or flexible, plastic, metal or semiconductor - a promising fact for future display and imaging applications.

Babak Parviz, a nano-engineering professor at the University of Washington in Seattle, said the technique is a "clear demonstration that self-assembly is applicable across size scales".

"Self-assembly is probably the best method for integrating high-performance materials onto unconventional substrates," he told BBC News.

The method tackles what Dr Parviz said is the most challenging problem - the proper alignment of thousands of parts, each thinner than a human hair. But it also works with the highest-performance materials, he said.

"For example, this method allows one to use single-crystal silicon, which is far superior to other types of silicon for making solar cells."