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 supercapacitor 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 graphite oxide -- an ionic conducting membrane -- that is useful for applications."
Co-authors of the paper are graduate student Neelam Singh, former postdoctoral researcher Li Song and Lijie Ci, postdoctoral researcher Zheng Liu, research scientist Arava Leela Mohana Reddy and Robert Vajtai, a faculty fellow in mechanical engineering and materials science, all of Rice; and graduate student Qing Zhang and Binngqing Wei, an associate professor of mechanical engineering, both at the University of Delaware.
Nanoholdings LLC funded the research.
Read the abstract at http://www.nature.com/nnano/journal/vaop/ncurrent/abs/nnano.2011.110.html
View a video of the process at http://www.youtube.com/watch?v=3O4YV0mrkfQDownload high-resolution art at
A team of Rice University researchers in the lab of Professor Pulickel Ajayan made supercapacitors by burning patterns into graphite oxide with a laser. From left: graduate student Wei Gao; Robert Vajtai, a faculty fellow in mechanical engineering and materials science; graduate student Neelam Singh and postdoctoral researcher Arava Leela Mohana Reddy. (Credit: Jeff Fitlow/Rice University)
Burning patterns into graphite oxide with a laser turns the thin sheets into fully functional supercapacitors, according to a new paper by Rice University scientists in Nature Nanotechnology. (Credit: Ajayan Lab/Rice University)
Located on a 285-acre forested campus in Houston, Texas, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is known for its "unconventional wisdom." With 3,485 undergraduates and 2,275 graduate students, Rice's undergraduate student-to-faculty ratio is less than 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice has been ranked No. 1 for best quality of life multiple times by the Princeton Review and No. 4 for "best value" among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://futureowls.rice.edu/images/futureowls/Rice_Brag_Sheet.pdf
David | EurekAlert!
Waste from paper and pulp industry supplies raw material for development of new redox flow batteries
12.10.2017 | Johannes Gutenberg-Universität Mainz
Low-cost battery from waste graphite
11.10.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
20.10.2017 | Information Technology
20.10.2017 | Materials Sciences
20.10.2017 | Interdisciplinary Research