Friday, May 11, 2012

"Laser writer makes graphene supercapacitors."


"Laser writer makes graphene supercapacitors."

Researchers in the US have employed a routine laser-writing technique to create sheets of graphene on the surface of a DVD. The graphene sheets can then be joined together to make electrochemical capacitors (or supercapacitors) that are able to store as much energy as a conventional battery but that can be charged 100–1000 times faster. The capacitors are completely flexible and robust, which makes them ideal energy-storage systems for next-generation flexible and portable electronics.
Capacitors are devices that store electric charge. Electrochemical capacitors – also known as supercapacitors or electric double-layer capacitors – can store much more charge thanks to the double layer formed at an electrolyte-electrode interface when voltage is applied. Although promising energy-storage materials, they still lag behind traditional batteries (which store energy through electrochemical reactions) in terms of energy densities: just 4 to 5 Wh/kg as opposed to 10 to 150 Wh/kg. They do, however, have a much longer shelf- and cycle life than batteries and can deliver large amounts of power much more quickly.
Now, a research team led by Richard Kaner and Maher El-Kady at the University of California, Los Angeles, say they have developed a graphene-based device that combines both the power performance of capacitors with the high energy density of batteries. The researchers have come up with a new process that involves coating an ordinary DVD disc with a film of graphite oxide supported on a sheet of plastic.

Kaner and colleagues begin by reducing the graphite oxide to graphene using a standard “LightScribe” DVD drive head – usually used to optically etch labels and images on DVD media discs. The process can easily be monitored as the golden-brown-coloured graphite oxide turns into black-coloured graphene. The plastic (now coated with graphene) is subsequently peeled off and cut with scissors to make different devices.
Electrochemical capacitors are made by simply “gluing” together two identical pieces of graphene sheet (which can be used as electrodes without the need for any additional binders or additives) with a little polymer gel electrolyte that is placed between them. “We also tested a variety of other electrolytes confirming that the material can be used in a number of device systems for different applications,” said Kaner.

More information:
Laser writer makes graphene supercapacitors.
Maher F. El-Kady Veronica Strong,  Sergey Dubin,  Richard B. Kaner.
Science 16 March 2012:  Vol. 335 no. 6074 pp. 1326-1330
DOI: 10.1126/science.1216744


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