MEGO for supercapacitors
10 Jun 2011 by Evoluted New Media
A new form of carbon which could be used in supercapacitors has been discovered by activating expanded graphite oxide – scientists have called it MEGO.
A new form of carbon which could be used in supercapacitors has been discovered by activating expanded graphite oxide – scientists have called it MEGO.
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Atomic resolution electron micrograph of the structure of activated graphene. The image shows that the material is composed of single sheets of crystalline carbon, which are highly curved to form a porous 3D network. Credit Eric A. Stach, Center for Functional Nanomaterials, Brookhaven National Laboratory |
The new carbon is a continuous 3D porous network with single-atom thick walls – a significant fraction of which are negative curvature carbon, similar to inside out buckyballs. It was developed by Rodney Ruoff and colleagues at the University of Texas at Austin, plus colleagues at UT Dallas, Brookhaven National Lab and QuantaChrome Instruments.
Researchers began by converting samples of graphite into graphite oxide, which they expanded using microwaves – dubbing the product microwave expanded graphite oxide, or MEGO. They then treated the MEGO with potassium hydroxide so that the surface becomes decorated with the chemical. After heating for an hour in an inert gas at 800°C, activated MEGO or aMEGO is obtained.
“What was quite surprising was that the potassium hydroxide remarkable restructures the carbon so that a 3D structure is generated with essentially no edge atoms,” said Rouff. “Every wall is one atom thick and all the carbon atoms are sp2-bonded.”
aMEGO has been used as the carbon for electrodes in a supercapacitor. The researchers obtained exceptional gravimetric energy densities that were four times higher than that of state-of-the-art conventional supercapacitors.
It also has a BET – Brunauer-Emmett-Teller – surface area of up to 3100 m2/g, compared to a range of 1000 to 2000 m2/g for other activated carbon. BET aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of a material.
The aMEGO capacitor is also very stable and continues to work as 97% capacitance even after 10,000 constant current charge/discharge cycles.
The team hope to further improve the new carbon and obtain further funding for research into better materials with similar structures. “We also hope to optimise the performance in other electrical energy-storage systems in parallel,” Ruoff said.”
