Rice University's Professor Pulickel Ajayan, along with his research team, have discovered a new property of graphite oxide (GO). Simply "drawing" a pattern on a sheet of GO will turn it into a supercapacitor that can be cycled thousands of times.
The teams main discovery that lead to the supercap was how when hydrated GO can hold ions and become a solid electrolyte and an electrically insulating separator. "All you need are a pattern and the electrodes, and you have a device. Of course the devices also perform in the presence of external electrolytes, which is even better," said Professor Ajayan.
Heating GO with a laser will turn it into conducting reduced graphite oxide (RGO). The team would draw the design into a sheet of GO, creating a mixture of GO and RGO. This created the conducting and insolating sections of the cap. When RGO patterns are separated by soaked and ion rich GO, a energy storage device is made. Lead author Wei Gao explained, "To build a fully functional supercapacitor, conducting electrode materials need to be separated by an insulator that contains the electrolyte. When laser-written patterns of conducting RGO are separated by GO, the material becomes an energy storage device."
As an experiment, the sheet was vacuumed dry, losing all its storage properties. After exposing the sheet to the atmosphere, within 3 hours its properties returned. Also, laser heat was used to suck oxygen out of the surface to create dark, porous RGO. This provided resistance and contained the ions in the GO portion until the planned release of the energy. The material exhibited proton exchange characteristics similar to that of Nafion.
Although this capacitor will never reach the market, Aiayan said that these finding should open up further possibilities in fuel cell and battery technology.
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