A simple slice of energy storage

August 1, 2011
A simple slice of energy storage
Rice University graduate student Neelam Singh holds a supercapacitor made from a single sheet of graphite oxide. The heat from writing a pattern in the material with a laser turns it into electrically conducting reduced graphite oxide. (Credit: Jeff Fitlow/Rice University)

Turning graphite oxide (GO) into full-fledged supercapacitors turns out to be simple. But until a laboratory at Rice University figured out how, it was anything but obvious.

Rice Professor Pulickel Ajayan and his team discovered they could transform a sheet of GO into a functional by writing patterns into it with a laser. Scientists already knew that the heat of a laser could convert GO -- the oxidized form of graphite, or carbon-based pencil lead -- into electrically conducting reduced graphite oxide (RGO). By writing patterns of RGO into thin sheets of GO, the Rice researchers effectively turned them into free-standing supercapacitors with the ability to store and release energy over thousands of cycles.

The discovery was reported this week in the online edition of Nature Nanotechnology.

The surprising find was that GO, when hydrated, can hold ions and serve as a solid electrolyte and an electrically insulating separator. "This is quite easy, as GO soaks up water like a sponge and can hold up to 16 percent of its weight," said Wei Gao, lead author of the paper and a graduate student in the Ajayan Lab.

"The fundamental breakthrough here is that GO, when it contains water, acts as an ionic conductor," said Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry. "So we're able to convert a sheet of GO into a supercapacitor without adding anything. All you need are a pattern and the electrodes, and you have a device. Of course the devices also perform in the presence of external electrolytes, which is even better.

"I think you're going to see a lot of tiny devices that need smaller power sources. Intermediate-sized devices might also be powered by this material; it's very scalable."

As a control experiment, the team sucked all the water out of an RGO-GO-RGO device in a vacuum to kill its ionic conductivity. Exposing it to air for three hours completely restored its supercapacitor function, another potentially handy characteristic.

To build a fully functional supercapacitor, conducting electrode materials need to be separated by an insulator that contains the electrolyte. When laser-written patterns of conducting RGO are separated by GO, the material becomes an energy storage device, Gao said. The patterns can be layered top and bottom or on the same plane.

In their experiments, heat from a laser at Rice's Oshman Engineering Design Kitchen sucked oxygen out of the surface to create the dark, porous RGO, which provided a level of resistance and restrained the GO-contained ions until their controlled release. Patterns were written in the GO with nearly one-micron accuracy.

Essentially, the devices exhibited good electrochemical performance -- without the chemicals.

Testing of the devices at Rice and by colleagues at the University of Delaware showed their performance compares favorably with existing thin-film micro-supercapacitors. They exhibit proton transport characteristics similar to that of Nafion, a commercial electrolyte membrane discovered in the 1960s, Ajayan said.

While the lab won't make flat supercapacitors in bulk anytime soon, Ajayan said the research opens the way to interesting possibilities, including devices for use in fuel cells and lithium batteries.

He said the discovery is surprising "because a lot of people have been looking at graphite oxide for five or 10 years now, and nobody has seen what we see here. We've discovered a fundamental mechanism of -- an ionic conducting membrane -- that is useful for applications."

Explore further: Batteries get a (nano)boost

More information: Nature Nanotechnology (2011) doi:10.1038/nnano.2011.110

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5 / 5 (2) Aug 01, 2011
not rated yet Aug 01, 2011
This is just the ticket for building cheaper appliances and cheaper automobiles.If it can be scaled up,it might also provide current for evening periods when maintaining a greatly reduced load occurs.
not rated yet Aug 01, 2011
Maybe, but I agree with Dirk. To many articles have promised much and delivered little. Without numbers, it is hype, not science.
1.5 / 5 (2) Aug 01, 2011
"a supercapacitor made from a single sheet of graphite oxide"

Isn't this graphene?
5 / 5 (1) Aug 01, 2011
"a supercapacitor made from a single sheet of graphite oxide"

Isn't this graphene?

not necessarily. graphene is a 1-atom thick sheet, graphite can be many atomic layers, but still a single sheet. It's like saying 'single graphite tube' and *not* talking about a carbon nanotube.
not rated yet Aug 01, 2011
Make this at home, use simple laser cnc setup, oxidize some pencil lead. on a thin sheet of the resulting Graphite Oxide use laser to etch pattern onto your GO , who knows if its humid theres prob. enough oxygen and hydrogen in the air to form the conductive lattice.

seems to me like all you are doing is re-arranging an amorphous composite (GO) into a higher energy state lattice structure which has different electromagnetic properties.

Gets me thinking about how they will discover fusion, I wonder if they have tried to synthesize a very heavy unstable element and try adding a much lighter element like Hydrogen using a low energy charge.

Seems like we are always smashing hydrogen and hydrogen or hydrogen and anti-hydrogen lets mix it up with some americium 243.
not rated yet Aug 02, 2011
Um. Yes! A thousand times yes! Somebody notify the Nobel committee...
5 / 5 (1) Aug 02, 2011

Click on the link at the bottom of the article, it has a lot more information.
1 / 5 (3) Aug 02, 2011
"Isn't this graphene?" - Capitalism fails

Graphene is pure carbon while GO contains oxygen.

That is what the "O" tells you.
1 / 5 (2) Aug 04, 2011
Low leakage caps for DRAM.
not rated yet Aug 09, 2011
Keep up the experimentation. Build a Beveled Box with a wind rotating mirror deflector to capture ions. See how much power you could aachieve with a array of 32 rotating units as one unit.

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