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Boron boosts capacity of graphene micro-supercapacitor

19 May 2015

A laser-induced graphene micro-supercapacitor developed by researchers at Rice University benefits greatly when boron becomes part of the mix.

A laser-induced graphene micro-supercapacitor treated with boron has five to ten times the energy density of boron-free versions (image courtesy of Professor Tour's group at Rice University)

The Rice lab of chemist, Professor James Tour uses commercial lasers to create thin, flexible supercapacitors by burning patterns into common polymers. The laser burns away everything but the carbon to a depth of 20 microns on the top layer, which becomes a foam-like matrix of interconnected graphene flakes.

By first infusing the polymer with boric acid, the researchers quadrupled the supercapacitor’s ability to store an electrical charge while greatly boosting its energy density.

In earlier work, the team led by Rice graduate student Zhiwei Peng tried many polymers and discovered a commercial polyimide was the best for the process. For the new work, the lab dissolved boric acid into polyamic acid and condensed it into a boron-infused polyimide sheet, which was then exposed to the laser.

Photo courtesy of Professor Tour's group at Rice University)

The two-step process produces micro-supercapacitors with four times the ability to store an electrical charge and five to ten times the energy density of the earlier, boron-free version. 

The new devices proved highly stable over 12,000 charge-discharge cycles, retaining 90 percent of their capacitance. In stress tests, they handled 8,000 bending cycles with no loss of performance.

Tour says the technique lends itself to industrial-scale, roll-to-roll production of microsupercapacitors. “What we’ve done shows that huge modulations and enhancements can be made by adding other elements and performing other chemistries within the polymer film prior to exposure to the laser. Once the laser exposes it, those other elements perform new chemistries that really increase the supercapacitor’s performance. This is a step in making these even more amenable for industrial applications.”

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