dinsdag 16 september 2008

Nanoflowers Improve Ultracapacitors

Nanoflower power: A transmission electron microscope image shows a flowerlike manganese oxide nanoparticle deposited at the junction of crossed carbon nanotubes. Used as an electrode material, this nanotube-manganese-oxide composite could improve the energy-storage ability of ultracapacitors, which show promise as powerful, long-lasting replacements for batteries. Credit: American Chemical Society Technology Review, Sept 16, 2008

A novel design could boost energy storage.
Imagine a cell-phone battery that recharges in a few seconds and that you would never have to replace. That's the promise of energy-storage devices known as ultracapacitors, but at present, they can store only about 5 percent as much energy as lithium-ion batteries. An advance by researchers at the Research Institute of Chemical Defense, in China, could boost ultracapacitors' ability to store energy.
A capacitor consists of two electrodes with opposite charges, often separated by an insulator that keeps electrons from jumping directly between them. The researchers have developed an electrode that can store twice as much charge as the activated-carbon electrodes used in current ultracapacitors. The new electrode contains flower-shaped manganese oxide nanoparticles deposited on vertically grown carbon nanotubes.
The electrode design promises to deliver more power, says Hao Zhang, lead author of the Nano Letters paper describing the new work. The electrode's longevity also compares with that of activated-carbon electrodes, Zhang says: discharging and recharging the electrodes 20,000 times reduced the capacitor's energy-storage capacity by only 3 percent.

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