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Carbon power: Twenty layers of carbon nanotubes are assembled on a polymer backing.

Nanotube Super-capacitors
A method for making electrodes doubles electrical storage capacity

Source: “Layer-by-Layer Assembly of All Carbon Nanotube Ultrathin Films for Electrochemical Applications”
Paula Hammond et al.
Journal of the American Chemical Society
131: 671-679

Results: MIT researchers have developed a new technique for making thin films of multi­walled carbon nanotubes. The materials have low electrical resistance and can store about 160 farads of electrical charge per gram–a capacitance more than twice that of other carbon nanotube films and an order of magnitude higher than that of conventional carbon materials.

Why it matters: Since the films can store large amounts of electrical charge and discharge it rapidly, they are promising materials for supercapacitors, long-lasting batterylike devices that charge up quickly. The way they’re made gives the researchers a great deal of control over their thickness and porosity, and thus over their electrical properties. That means the materials could be useful in diverse applications, including microbatteries for medical implants and flexible electrodes for electronics.

Methods: The researchers treated carbon nanotubes with either positively or negatively charged surface molecules, then put them into separate water suspensions. They dipped a substrate, such as a silicon wafer, alternately in the positive and negative nanotube solutions; the difference in charge created electrostatic attraction, causing the nanotubes to cling to one another without the need for chemical binders. (Previous nanotube films, which required such binders, did not have electrical properties as impressive as those displayed by a pure mat of nanotubes.) The researchers have now made nanotube films of varying thicknesses, released them from their substrates, and tested their electrical properties.

Next steps: The researchers will modify the nanotubes so that the materials can store even more charge. They are also developing faster assembly methods based on spraying rather than dipping.

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Credit: Seung Woo Lee/ Journal of the American Chemical Society

Tagged: Energy, Materials

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