Ruoff Group produces a new carbon material for electrical energy storage
AUSTIN, TEXAS—May 18, 2011
Professor of Materials Science in the Department of Mechanical Engineering at The University of Texas at Austin Rodney S. Ruoff and three researchers in The Ruoff Group Nanoscience and Technology Lab, post-doc Dr. Yanwu Zhu and Ph.D. students Shanthi Murali and Meryl Stoller published a paper on May 12, 2011 describing their discovery of a new carbon material. The new material is a highly porous 3-dimensional carbon that has atom-thick walls.
This new carbon, under high magnification, is shown to be comprised of many tunnels all with a wall structure one atom thick. Because of the exceptionally high surface area per weight, this new carbon shows enhanced electrical storage in supercapacitors (also known as ultracapacitors or electrochemical capacitors), which store electrical charge and are used either individually or in conjunction with batteries.
How supercapacitors differ from rechargeable batteries
Supercapacitors store an electrical charge on high surface-area conducting materials, similar to rechargeable batteries. You may have used them in items such as hand crank flashlights. They have much higher power density than a battery, but the electrical energy stored is less than that of a battery. If a battery were a marathon runner, a supercapacitor could be described as a sprinter that can respond much faster than a battery, and do so for many more cycles efficiently, but that cannot store as much charge per unit weight as batteries. Another difference between supercapacitors and batteries is that supercapacitors will still work after hundreds of thousands or millions of charge-discharge cycles, unlike current lead or lithium ion batteries. Imagine never having to replace your car’s battery and rarely, if ever, recharging your laptop’s or cell phone’s battery. This research has the potential to make these things a reality, and significantly enhance today’s consumer electronics.
How it's different and why it's so exciting
This new carbon material is exciting for a number of reasons. First of all, the carbon material is made by a process that should be scalable to industrial levels. It shouldn't prove prohibitively expensive or extremely difficult to produce, either.
The enhanced surface area of the material is attributed to its unusual atomic structure. The interior surfaces (the walls of the nanopores) is highly curved, because the hexagonal "honeycomb" structure has some heptagons and octagons that introduce 'negative curvature.' The geometric surface area of the material is greater than the value, e.g., of graphene. Ph.D. student and one of the paper's authors, Meryl Stoller explains why in the short video (above) using a model of the material.
"The sponge-like carbon has a surface area of up to 3,100 square meters per gram (two grams has a surface area roughly equivalent to that of a football field). It also has much higher electrical conductivity and, when further optimized, will be superb for thermal management as well," Ruoff said.
The process used by team members Zhu, Murali, Stoller and Ruoff to synthesize the carbon material involved using microwaves to exfoliate graphite oxide, followed by treatment with potassium hydroxide, which created a carbon full of tiny tunnels— essentially a sponge that, when combined with an electrolyte, can store a giant electrical charge. The team of coauthors and collaborators at Brookhaven then analyzed the atomic structure of the carbon material at the nanoscale using very high-resolution electron microscopes. Their observations confirmed Ruoff's hypothesis that the carbon was a new three-dimensional material having highly curved, single-atom-thick walls that form tiny pores.
Making the leap from research to industry
This research at UT Austin is funded by the National Science Foundation, the Department of Energy, and the Institute for Advanced Technology at The University of Texas at Austin. The University of Texas at Austin's Office of Technology Commercialization has filed a patent with the U.S. Patent Office on behalf of the inventors.
"Rod and his team define what we mean when we talk about innovation to address grand challenges," said Gregory L. Fenves, dean of the Cockrell School of Engineering.
The Ruoff Group and other collaborators
Ruoff's research team of about 40 people, including five undergraduate researchers, collaborated with faculty and students from The University of Texas at Dallas, scientific staff at Brookhaven National Laboratory in New York and staff members at QuantaChrome Instruments in Florida. Three other department researchers, Dr. Paulo Ferreira, graduate student K.J. Ganesh and post-doc Weiwei Cai (now a professor at Xiamen University) also contributed to this research.