For years, engineers have been trying to reduce the cost of €ultracapacitors,€ devices that store more energy than batteries and discharge it in an instant. That kind of capability is the ultimate power source for advanced electric cars, trains or airplanes.

Now, a team of researchers at George Washington University says they've figured out how to build a low-cost ultracapacitor by combining carbon nanotubes and graphene.

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Because of the quick-discharge and big capacity, electric car owners could charge in minutes instead of plugging in overnight, according to Shashurin.

€It's very fast,€ said Alexey Shashurin, a research scientist in mechanical and aerospace engineering at GWU.

Single-walled carbon nanotubes and graphene both have electronic, thermal and mechanical properties that make them good materials for new ultracapacitors, said Jian Li, first author on the paper, which appears in the Journal of Applied Physics.

Many groups have explored the use of the two materials separately, but few had looked at combining them, Li said.

Pairing these materials into a hybrid ultracapacitor turned out to be a good thing.

The graphene flakes provided high surface area and good electrical conductivity, while the carbon nanotubes connected all of the structures to form a uniform network.

To combine them, the GWU researchers heated the graphene flakes and nanotubes and then mixed the two nanostructures together to form an ink that they rolled onto paper -- a common separator for current commercial capacitors.

In tests, the scientists demonstrated that they were able to boost the power storage by three-fold over existing ultracapacitors that use nanotubes alone, said Shashurin.

The team says their hybrid mixture of carbon would be 5 to 10 times cheaper than existing ultracapacitors.

The next big challenge is scaling up the lab prototype to a working device. Shashurin says that some private firms are interested in developing the project further, but MIT electrical engineering professor Joel Schindall says it's still tricky to jump from lab to factory.

€Intuitively, a nanotube-graphene mix sounds promising, and these results will help to move in this direction,€ said Schindall said in an e-mail to Discovery News. €As research and development, I am glad to see this achievement. It looks like they are getting some encouraging results. However, the path to commercialization and at a competitive price might be uncertain.€