Graphene technique leads to better super-cap
Researchers at Rensselaer Polytechnic Institute are flaking large quantities of graphene from graphite using simple chemistry.
Graphite powder is submerged in a mixture of dilute 1-pyrenecarboxylic acid (PCA), water and methanol; then exposed to ultrasound.
Large quantities of undamaged, high-quality graphene are produced, dispersed in water.
“There are other known techniques for fabricating graphene, but our process is advantageous for mass production as it is low cost, performed at room temperature, devoid of any harsh chemicals, and thus is friendly to a number of technologies where temperature and environmental limitations exist,” said team head Dr Swastik Kar. “The process does not need any controlled environment chambers, which enhances its simplicity without compromising its scalability. This simplicity enabled us to directly demonstrate high-performance applications related to environmental sensing and energy storage, which have become issues of global importance.”
Agitation weakens the already frail molecular bonds that hold together graphene sheets in graphite.
This allows the pyrene part of PCA, which is mostly hydrophobic and clings to the surface of the also-hydrophobic graphite, to work its way between the layers.
“Ultimately, this coordinated attack results in layers of graphene flaking off of the graphite and into the water,” said the Polytechnic. “The PCA also helps ensure the graphene does not clump and remains evenly dispersed in the water.”
The researchers used the graphene to build an thin double-layer capacitor which “demonstrated high specific capacitance, power, and energy density, and performed far superior to similar devices fabricated in the past using graphene,” said Rensselaer, claiming: 120F/g, 105kW/kg, 9.2Wh/kg respectively.
Graphene was first made deliberately in the laboratory by peeling it from graphite using sticky tape.
Since then, faster flaking techniques and ways to build the material from the ground up have been developed, although little of the graphene produced by these methods could match the electrical properties of tape-flaked graphene.
The Rensselaer results are published as a paper: Stable aqueous dispersions of non-covalently functionalized graphene from graphite and their multifunctional high-performance applications, in the journal Nano Letters.