These are just two of the possibilities raised by a novel supercapacitor design invented by material scientists at Vanderbilt University that is described in a paper published in the Oct. 22 issue of the journal Scientific Reports.
It is the first supercapacitor that is made out of silicon so it can be built into a silicon chip along with the microelectronic circuitry that it powers. In fact, it should be possible to construct these power cells out of the excess silicon that exists in the current generation of solar cells, sensors, mobile phones and a variety of other electromechanical devices, providing a considerable cost savings.
“If you ask experts about making a supercapacitor out of silicon, they will tell you it is a crazy idea,” said Cary Pint, the assistant professor of mechanical engineering who headed the development. “But we’ve found an easy way to do it.”
Instead of storing energy in chemical reactions the way batteries do, “supercaps” store electricity by assembling ions on the surface of a porous material. As a result, they tend to charge and discharge in minutes, instead of hours, and operate for a few million cycles, instead of a few thousand cycles like batteries.
These properties have allowed commercial supercapacitors, which are made out of activated carbon, to capture a few niche markets, such as storing energy captured by regenerative braking systems on buses and electric vehicles and to provide the bursts of power required to adjust of the blades of giant wind turbines to changing wind conditions. Supercapacitors still lag behind the electrical energy storage capability of lithium-ion batteries, so they are too bulky to power most consumer devices. However, they have been catching up rapidly.
Research to improve the energy density of supercapacitors has focused on carbon-based nanomaterials like graphene and nanotubes. Because these devices store electrical charge on the surface of their electrodes, the way to increase their energy density is to increase the electrodes’ surface area, which means making surfaces filled with nanoscale ridges and pores.
“The big challenge for this approach is assembling the materials,” said Pint. “Constructing high-performance, functional devices out of nanoscale building blocks with any level of control has proven to be quite challenging, and when it is achieved it is difficult to repeat.”
So Pint and his research team – graduate students Landon Oakes, Andrew Westover and post-doctoral fellow Shahana Chatterjee – decided to take a radically different approach: using porous silicon, a material with a controllable and well-defined nanostructure made by electrochemically etching the surface of a silicon wafer.
This allowed them to create surfaces with optimal nanostructures for supercapacitor electrodes, but it left them with a major problem. Silicon is generally considered unsuitable for use in supercapacitors because it reacts readily with some of chemicals in the electrolytes that provide the ions that store the electrical charge.
With experience in growing carbon nanostructures, Pint’s group decided to try to coat the porous silicon surface with carbon. “We had no idea what would happen,” said Pint. “Typically, researchers grow graphene from silicon-carbide materials at temperatures in excess of 1400 degrees Celsius. But at lower temperatures – 600 to 700 degrees Celsius – we certainly didn’t expect graphene-like material growth."
When the researchers pulled the porous silicon out of the furnace, they found that it had turned from orange to purple or black. When they inspected it under a powerful scanning electron microscope they found that it looked nearly identical to the original material but it was coated by a layer of graphene a few nanometers thick.
When the researchers tested the coated material they found that it had chemically stabilized the silicon surface. When they used it to make supercapacitors, they found that the graphene coating improved energy densities by over two orders of magnitude compared to those made from uncoated porous silicon and significantly better than commercial supercapacitors.
The graphene layer acts as an atomically thin protective coating. Pint and his group argue that this approach isn’t limited to graphene. “The ability to engineer surfaces with atomically thin layers of materials combined with the control achieved in designing porous materials opens opportunities for a number of different applications beyond energy storage,” he said.
“Despite the excellent device performance we achieved, our goal wasn’t to create devices with record performance,” said Pint. “It was to develop a road map for integrated energy storage. Silicon is an ideal material to focus on because it is the basis of so much of our modern technology and applications. In addition, most of the silicon in existing devices remains unused since it is very expensive and wasteful to produce thin silicon wafers.”
Pint’s group is currently using this approach to develop energy storage that can be formed in the excess materials or on the unused back sides of solar cells and sensors. The supercapacitors would store excess the electricity that the cells generate at midday and release it when the demand peaks in the afternoon.“All the things that define us in a modern environment require electricity,” said Pint. “The more that we can integrate power storage into existing materials and devices, the more compact and efficient they will become.”
Research associate Jeremy Mares, graduate student William Erwin, Assistant Professor of Chemical and Biomolecular Engineering Rizia Bardhan and Associate Professor of Electrical Engineering and Computer Science Sharon Weiss also contributed to the research, which was funded by National Science Foundation grants CMMI 1334269 and EPS 1004083 and Army Research Office grant W911BF-09-1-0101.
Visit Research News @ Vanderbilt for more research news from Vanderbilt. [Media Note: Vanderbilt has a 24/7 TV and radio studio with a dedicated fiber optic line and ISDN line. Use of the TV studio with Vanderbilt experts is free, except for reserving fiber time.]
David F. Salisbury | Vanderbilt University
Multiregional brain on a chip
16.01.2017 | Harvard John A. Paulson School of Engineering and Applied Sciences
Researchers develop environmentally friendly soy air filter
16.01.2017 | Washington State University
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
16.01.2017 | Power and Electrical Engineering
16.01.2017 | Information Technology
16.01.2017 | Power and Electrical Engineering