Researchers use leaves as inspiration for graphene micro supercapacitor

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An international team of researchers, including scientists from Sungkyunkwan University in South Korea, has devised a technique for creating an micro supercapacitor (MSC) that delivers high electrochemical performance.

The team modelled the film structure of its MSC on natural vein-textured leaves in order to take advantage of the natural transport pathways which enable efficient ion diffusion parallel to the graphene planes found within them.

To create this shape, the team layered a graphene-hybrid film with copper hydroxide nanowires. Once the desired thickness was attained, an acid solution was used to dissolve the nanowires, leaving a thin film with nano-impressions.

This film was applied to a plastic layer with long parallel gold strips placed on top. Material not covered by the gold strips was etched away so that only the gold strips on top of a layer of film were left. Gold contact pads were added and the remaining space filled with a conductive gel. Once peeled from the plastic layer, the MSCs is said to resemble clear tape with gold electrical leads on opposite sides.

In addition to superior energy density, the film is not only said to be highly flexible but also to increase its capacitance after initial use. Volumetric energy density was found to be 10 times higher than currently available commercial supercapacitors and better than the results of other recent research.

The MSCs are displaying electrical properties about five orders of magnitude higher than similar lithium batteries and are comparable to existing, larger supercapacitors. Team leader Young Hee Lee noted: "To our knowledge, the volumetric energy density and the maximum volumetric power density in our work are the highest values among all carbon based solid state MSCs reported to date."

The researchers anticipate the technology being applied where light, reliable energy storage, combined with a long lifespan and fast charge/discharge time, is required. The team also said the MSCs could be used in implantable medical devices, active RFID tags and micro robots, as well as in portable, stretchable and wearable devices.