Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Packing the ions

Computational modeling of carbon supercapacitors with the effects of surface curvature included. (Image credit: Jingsong Huang, ORNL)
Computational modeling of carbon supercapacitors with the effects of surface curvature included. (Image credit: Jingsong Huang, ORNL)

Abstract:
Discovery boosts supercapacitor energy storage

Packing the ions

Oak Ridge, TN | Posted on June 17th, 2011

Flat is in the eye of the beholder.

When you're talking about nanomaterials, however, that eye is pretty much useless unless it's looking through an electron microscope or at a computer visualization. Yet the pits and ridges on a seemingly flat surface—so small they are invisible without such tools—can give the material astonishing abilities. The trick for researchers interested in taking advantage of these abilities lies in understanding and, eventually, predicting how the microscopic topography of a surface can translate into transformative technologies.

Drexel University's Yury Gogotsi and colleagues recently needed an atom's-eye view of a promising supercapacitor material to sort out experimental results that were exciting but appeared illogical. That view was provided by a research team led by Oak Ridge National Laboratory (ORNL) computational chemists Bobby Sumpter and Jingsong Huang and computational physicist Vincent Meunier.

Gogotsi's team discovered you can increase the energy stored in a carbon supercapacitor dramatically by shrinking pores in the material to a seemingly impossible size—seemingly impossible because the pores were smaller than the solvent-covered electric charge-carriers that were supposed to fit within them. The team published its findings in the journal Science.

The mystery was not simply academic. Capacitors are an important technology that provides energy by holding an electrical charge. They have several advantages over traditional batteries—charging and discharging nearly instantaneously and recharging over and over again, almost indefinitely, without wearing out—but they also have drawbacks—most importantly, they hold far less energy.

An electric double-layer capacitor, or supercapacitor, represents an advance on the technology that allows for far greater energy density. While in traditional capacitors two metallic plates are separated by a nonconducting material known as a dielectric, in a supercapacitor an electrolyte is able to form an electric double layer with electrode materials that have very high surface areas.

As such, supercapacitors are able to achieve the same effect within a single material, as properties of the material divide it into separate layers with a very thin, nonconducting boundary. Because they can both forgo a bulky dielectric layer and make use of the carbon's nanoscale pores, supercapacitors are able to store far more energy than their traditional counterparts in a given volume. This technology could help increase the value of energy sources that are clean, but sporadic, meting out stored energy during downtimes such as night for a solar cell or calm days for a wind turbine.

So Gogotsi's discovery was potentially ground breaking. The energy was stored in the form of ions within an electrolyte, with the ions surrounded by shells of solvent molecules and packed on the surfaces of nanoporous carbons. The researchers were able to control the size of pores in the carbon material, making them 0.7 to 2.7 nanometers. What they found was that the energy stored in the material shot up dramatically as the pores became smaller than a nanometer, even though the ions in their solvation shells could not fit into spaces that small.

"It was a mystery," Sumpter said. "Many people questioned the result at the time. Yet the experimental data was showing an incredible increase in capacitance."

Fortunately, it was a mystery that the ORNL team could unravel.

"We thought this was a perfect case for computational modeling because we could certainly simulate nanometer-sized pores," Sumpter said. "We had electronic-structure capabilities that could treat it well, so it was a very good problem for us to explore."

Using ORNL's Jaguar and Eugene supercomputers, Sumpter and his team were able to take a nanoscale look at the interaction between ion and carbon surface. A computational technique known as density functional theory allowed them to show that the phenomenon observed by Gogotsi was far from impossible. In fact, they found that the ion fairly easily pops out of its solvation shell and fits into the nanoscale pore.

"It goes in such a way that it desolvates in the bulk to get inside because there's electrostatic potential and van der Waals forces that pull it in," Sumpter explained. "There are a whole lot of different forces involved, but in fact it's very easy for it to get in."

The ORNL team and colleagues at Clemson University, Drexel University, and Georgia Tech detailed their findings in a series of publications, including Angewandte Chemie, Chemistry-A European Journal, ACS Nano, Journal of Chemical Physics C, Physical Chemistry Chemical Physics, Journal of Materials Research, and Nano Letters.

"In addition," Sumpter noted, "the microscopic bumps and divots on a carbon plate make a dramatic difference in the amount of energy that can be stored on or in it.

"When you get to the nanoscale, the surface area is huge, and the curvature, both concave and convex, can be very large. This makes a large difference in the capacitance. We derived a model that explained all the experimental data. You can back out the pieces of the model from the electronic structure calculations, and from that model you can predict capacitance for different types of curved shapes and pore sizes."

For example, he said, the calculations showed that the charge-carrying ions are stored not only by slipping into pores but also attaching to mounds in the material.

"It's a positive curvature instead of a negative curvature," Sumpter said, "and they can store and release energy even faster. So you can store ions inside a hole or you can store ions outside."

Using these and other insights gained through supercomputer simulation, the ORNL team partnered with colleagues at Rice University to develop a working supercapacitor that uses atom-thick sheets of carbon materials.

"It uses graphene on a substrate and a polymer-gel electrolyte," Sumpter explained, "so that you produce a device that is fully transparent and flexible. You can wrap it around your finger, but it's still an energy storage device. So we've gone all the way from modeling electrons to making a functional device that you can hold in your hand."— Leo Williams, June 16, 2011

####

For more information, please click here

Contacts:
Oak Ridge National Laboratory
P.O. Box 2008
Oak Ridge, TN 37831
(+1) 865.574.4160

Copyright © Oak Ridge National Laboratory

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

Drexel University's Yury Gogotsi

Related News Press

News and information

Pixelligent Launches New PixClear® Light Extraction Materials for OLED Lighting August 4th, 2015

The annual meeting on High Power Diode Lasers & Systems will be held as part of the Enlighten Conference, October 14th & 15th August 4th, 2015

Atomic view of microtubules: Berkeley Lab researchers achieve record 3.5 angstroms resolution and visualize action of a major microtubule-regulating protein August 4th, 2015

World's quietest gas lets physicists hear faint quantum effects August 4th, 2015

Graphene

Better together: Graphene-nanotube hybrid switches August 3rd, 2015

This could replace your silicon computer chips: A new semiconductor material made from black phosphorus may be a candidate to replace silicon in future tech July 30th, 2015

March 2016; 6th Int'l Conference on Nanostructures in Iran July 29th, 2015

Stretching the limits on conducting wires July 25th, 2015

Academic/Education

Pakistani Students Who Survived Terror Attack to Attend Weeklong “NanoDiscovery Institute” at SUNY Poly CNSE in Albany July 29th, 2015

Deben reports on the use of their CT500 in the X-ray microtomography laboratory at La Trobe University, Melbourne, Australia July 22nd, 2015

JPK reports on the use of SPM in the Messersmith Group at UC Berkeley looking at biologically inspired polymer adhesives. July 21st, 2015

Renishaw adds Raman analysis to Scanning Electron Microscopy at the University of Sydney, Australia July 9th, 2015

Discoveries

Atomic view of microtubules: Berkeley Lab researchers achieve record 3.5 angstroms resolution and visualize action of a major microtubule-regulating protein August 4th, 2015

World's quietest gas lets physicists hear faint quantum effects August 4th, 2015

Artificial blood vessels become resistant to thrombosis August 4th, 2015

Engineering a better 'Do: Purdue researchers are learning how August 4th, 2015

Materials/Metamaterials

Engineering a better 'Do: Purdue researchers are learning how August 4th, 2015

Thin films offer promise for ferroelectric devices: Researchers at Tokyo Institute of Technology demystify the ferroelectric properties observed in hafnium-oxide-based thin films, revealing a potentially useful device material August 3rd, 2015

Self-assembling, biomimetic membranes may aid water filtration August 1st, 2015

Transparent, electrically conductive network of encapsulated silver nanowires: A novel electrode for optoelectronics August 1st, 2015

Announcements

Artificial blood vessels become resistant to thrombosis August 4th, 2015

Engineering a better 'Do: Purdue researchers are learning how August 4th, 2015

Proving nanoparticles in sunscreen products August 4th, 2015

Global Carbon Nanotubes Industry 2015: Acute Market Reports August 4th, 2015

Tools

University of Puerto Rico announces August 11th as the launch date for their NASA mission to look for life in space – XEI reports August 3rd, 2015

Thin films offer promise for ferroelectric devices: Researchers at Tokyo Institute of Technology demystify the ferroelectric properties observed in hafnium-oxide-based thin films, revealing a potentially useful device material August 3rd, 2015

Heating and cooling with light leads to ultrafast DNA diagnostics July 31st, 2015

Take a trip through the brain July 30th, 2015

Energy

Transparent, electrically conductive network of encapsulated silver nanowires: A novel electrode for optoelectronics August 1st, 2015

Springer and Tsinghua University Press present the second Nano Research Award: Paul Alivisatos of the University of California Berkeley receives the honor for outstanding contributions in nanoscience July 30th, 2015

Controlling Dynamic Behavior of Carbon Nanosheets in Structures Made Possible July 30th, 2015

March 2016; 6th Int'l Conference on Nanostructures in Iran July 29th, 2015

Battery Technology/Capacitors/Generators/Piezoelectrics/Thermoelectrics/Energy storage

Sol-gel capacitor dielectric offers record-high energy storage July 30th, 2015

Stretching the limits on conducting wires July 25th, 2015

BESSTECH’s Innovative Battery Technology is Highlighted During Featured Presentations at SEMICON West 2015: CEO Fernando Gómez-Baquero delivers invited remarks at the event’s Silicon Innovation Forum and Semiconductor Technology Symposium July 16th, 2015

Molecular fuel cell catalysts hold promise for efficient energy storage July 16th, 2015

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project