Project aims to mass-produce 'nanopetals' for sensors, batteries

These color-enhanced scanning electron microscope images
show nanosheets resembling tiny rose petals.
The nanosheets are key components of a new type
of biosensor that can detect minute concentrations
of glucose in saliva, tears and urine. The technology
might eventually help to eliminate or reduce
the frequency of using pinpricks for diabetes testing.
(Purdue University photo/Jeff Goecker)

Researchers at Purdue University are developing a method to mass-produce a new type of nanomaterial for advanced sensors and batteries, with an eye toward manufacturing in the Midwest.

Research findings indicate the material shows promise as a sensor for detecting glucose in the saliva or tears and for "supercapacitors" that could make possible fast-charging, high-performance batteries.

However, for the material to be commercialized researchers must find a way to mass-produce it at low cost.

"It's one thing to say you've got a new wonder material, but can you prove that it can be made on a commercial scale?" said Arvind Raman, Robert V. Adams Professor of Mechanical Engineering. "In many cases we find that fundamental research needs to be done for scaling up. You want to be able to produce large quantities of the material at 50 cents per square meter."

Now, a team of Purdue researchers will aim to do just that. The project, funded with a $1.5 million grant from the National Science Foundation, focuses on creating a nanomanufacturing method that is "scalable," or capable of mass production at low cost.

The underlying technology was developed by a research group led by Timothy Fisher, the James G. Dwyer Professor in Mechanical Engineering. It consists of vertical nanostructures resembling tiny rose petals made of a material called graphene, which is a single-atom-thick film of carbon.

"Using these graphene nanopetals we have realized exceptional performance in a wide range of devices at laboratory scales," Fisher said.

The researchers hope to boost the production speed of nanopetal-coated surfaces to 10 square meters per hour, representing a dramatic increase over the laboratory-scale production rate.

Raman has expertise in roll-to-roll manufacturing, a mainstay of many industrial operations including paper and sheet-metal production. He models the mechanics of the process of creating flexible materials in sheets at high speed and under tension.

"A key factor is going to be industry partners," he said. "There are many industries that have roll-to-roll operations. So focusing on roll-to-roll as a platform for doing nanomaterials production is very strategic for the Midwest."

He also has expertise in precision measurement using an atomic force microscope. 

"You have to be able to measure the material while it is being manufactured, and this is a challenge because of the nanometer scale of the petals," he said.

The graphene nanopetals also have shown promise as a "thermal-interface" material to keep computer chips from overheating. 

"A slew of new device and material concepts based on graphene nanopetals are emerging in applications as diverse as carbon fiber composites and new thermal-interface materials," Raman said. "Commercial interest is extremely high for this recent carbon nanomaterial. "

Other key researchers in the project are Alina Alexeenko, an associate professor of aeronautics and astronautics; Alexander Wei, a professor in the Department of Chemistry; Ernesto E. Marinero, a professor of engineering practice in the schools of Chemical Engineering and Materials Engineering; and Euiwon Bae, a research professor of mechanical engineering.

The nanopetals are created in a vacuum by exposing a cloth of carbon fiber to high-energy plasma that contains hydrogen ions and other ingredients, a process known as plasma-enhanced chemical vapor deposition. Alexeenko will lead work to model the plasma reactor and to optimize its conditions for fast and environmentally friendly conversion of raw materials, such as methane and hydrogen, into carbon nanopetals. 

Wei will functionalize petals with metal nanoparticles and enzymes that recognize glucose or other target molecules for biosensing. Marinero will focus on reliability of devices made using the nanomaterial, and Bae will work to ensure proper petal size by analyzing patterns of light scattering from the material's surface.

Most of the research will be based at the Birck Nanotechnology Center in Purdue's Discovery Park.

"Scale-up production is a key challenge facing nanotechnology," said Ali Shakouri, the Mary Jo and Robert L. Kirk Director of the Birck Nanotechnology Center and a professor of electrical and computer engineering. "This NSF project is part of a broader nanomanufacturing initiative at the Birck Nanotechnology Center where we focus on roll-to-roll production of smart thin films for applications in pharmacy and food packaging."

Wei said, "The project represents the front edge of a much larger movement at Purdue to synergize core research expertise in science and engineering in a way that provides graduate students with opportunities to overcome the challenges of converting exciting research discoveries into products that can be commercialized."

Technologies developed in the project might be commercialized through collaboration with a local start-up company, Folium Nanotechnologies LLC, co-founded by Fisher and Marinero, as well as Roche Diagnostics and the Battery Innovation Center. The center was launched this year to leverage Indiana's public- and private-sector assets in advanced battery technologies to facilitate research and development, rapid prototyping and contract manufacturing for industry, academic and military customers.

"A regional workshop series on roll-to-roll nanomanufacturing will be organized to serve as a catalyst to innovation in the Midwest by bringing together interested small, medium and large enterprises together with original equipment manufacturers and university researchers," Raman said.

The new technology could be of particular interest to battery makers in Indiana.

The researchers also will make available advanced simulation tools for vacuum-based roll-to-roll processes. The tools will be available to companies through the cyberinfrastructure of the manufacturing HUB and nanoHUB, an interactive website that makes available scientific simulations, seminars, interactive courses and other specialized nanotech-related materials.

"We will educate the U.S. workforce through an innovative online class on nanomanufacturing offered as part of the nanoHUB U initative," Raman said.

The research has potential for broad impact. 

"Many results from this research are not just applicable to graphene nanopetal technology, but rather to a wide variety of nanomaterials manufactured in low-pressure and ambient roll-to-roll nanomanufacturing processes," he said. 

Source: http://www.purdue.edu/newsroom/releases/2013/Q4/project-aims-to-mass-produce-nanopetals-for-sensors,-batteries.html

Clay key to high-temperature supercapacitors

Rice University lab creates energy storage that may find use in oil discovery, space, military applications 

Clay, an abundant and cheap natural material, is a key ingredient in a supercapacitor that can operate at very high temperatures, according to Rice University researchers who have developed such a device.

The Rice group of materials scientist Pulickel Ajayan reported in Nature’s online journal, Scientific Reports, that the supercapacitor is reliable at temperatures of up to 200 degrees Celsius (392 degrees Fahrenheit) and possibly beyond. It could be useful for powering devices for use in extreme environments, such as oil drilling, the military and space.

A composite of clay and an electrolyte allowed Rice University researchers to make sheets of material that can serve as both electrolyte and a separator in a new kind of high-temperature supercapacitor. Images courtesy of the Ajayan Group

“Our intention is to completely move away from conventional liquid or gel-type electrolytes, which have been limited to low-temperature operation of electrochemical devices,” said Arava Leela Mohana Reddy, lead author and a former research scientist at Rice.

“We found that a clay-based membrane electrolyte is a game-changing breakthrough that overcomes one of the key limitations of high-temperature operation of electrochemical energy devices,” Reddy said. “By allowing safe operation over a wide range of temperatures without compromising on high energy, power and cycle life, we believe we can dramatically enhance or even eliminate the need for expensive thermal management systems.”

A supercapacitor combines the best qualities of capacitors that charge in seconds and discharge energy in a burst and rechargeable batteries that charge slowly but release energy on demand over time. The ideal supercapacitor would charge quickly, store energy and release it as needed.

“Researchers have been trying for years to make energy storage devices like batteries and supercapacitors that work reliably in high-temperature environments, but this has been challenging, given the traditional materials used to build these devices,” Ajayan said.

In particular, researchers have struggled to find an electrolyte, which conducts ions between a battery’s electrodes, that won’t break down when the heat is on. Another issue has been finding a separator that won’t shrink at high temperatures and lead to short circuits. (The separator keeps the electrolyte on the anode and cathode sides of a traditional battery apart while allowing ions to pass through).

“Our innovation has been to identify an unconventional electrolyte/separator system that remains stable at high temperatures,” Ajayan said.

The Rice researchers led by Reddy and Rachel Borges solved both problems at once. First, they investigated using room-temperature ionic liquids (RTILs) developed in 2009 by European and Australian researchers. RTILs show low conductivity at room temperature but become less viscous and more conductive when heated.

Clay has high thermal stability, high sorption capacity, a large active surface area and high permeability, Reddy said, and is commonly used in muds for oil drilling, in modern construction, in medical applications and as a binder by iron and steel foundries.

After combining equal amounts of RTIL and naturally occurring Bentonite clay into a composite paste, the researchers sandwiched it between layers of reduced graphene oxide and two current collectors to form a supercapacitor. Tests and subsequent electron microscope images of the device showed no change in the materials after heating it to 200 degrees Celsius. In fact, Reddy said, there was very little change in the material up to 300 degrees Celsius.

“The ionic conductivity increases almost linearly until the material reaches 180 degrees, and then saturates at 200,” he said.

Despite a slight drop in capacity observed in the initial charge/discharge cycles, the supercapacitors were stable through 10,000 test cycles. Both energy and power density improved by two orders of magnitude as the operating temperature increased from room temperature to 200 degrees Celsius, the researchers found.

The team took its discovery a step further and combined the RTIL/clay with a small amount of thermoplastic polyurethane to form a membrane sheet that can be cut into various shapes and sizes, which allows design flexibility for devices.

Co-authors of the paper are graduate students Marco-Tulio Rodrigues and Hemtej Gullapalli and former postdoctoral researcher Kaushik Balakrishnan, all of Rice; and Glaura Silva, an associate professor at the Federal University of Minas Gerais, Belo Horizonte, Brazil. Ajayan is the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry at Rice. Borges is a visiting student from the Federal University of Minas Gerais. Reddy is now an assistant professor at Wayne State University in Detroit.

The Advanced Energy Consortium supported the research.

http://news.rice.edu/2013/09/03/clay-key-to-high-temperature-supercapacitors-2/