New materials for making high-end electronic components are often expensive and are of high technology. But a team in France recently showed that energy storage components called supercapacitors can be made from a very “dirt” material called grilled seaweed.
Francois Béguin of the Center for CNRS Research on Isolation in the city of Orléans (France) and colleagues say seaweed, when burned into a coal-like form, would become a suitable material to create an electrode in high-performance supercapacitors,works well not lose carbon materials originally used in commercial devices.Mildred Dresselhaus, a carbon materials expert at Massachusetts Institute of Technology (MIT), points out that coconut husks have been used as porous carbon to produce water filters and for other applications. The polymer derived from the seaweed that Béguin produces (called alginate) is non-toxic and has been used as a thickener in food and cosmetics. Each year 20,000 tons of alginate is extracted from seaweed, so the price is very cheap.
Supercapacitors replace batteries in storing power in mobile electronics. It consists of a pair of plates, or electrodes, that carry a charge that can be switched on / off, creating an electric current. Capacitors can provide more power – higher currents or voltages – than batteries, but store less total power. They can be applied as emergency power to computers or auxiliary power in electric vehicles, for example, they can store the energy collected during braking.
The amount of energy stored in a capacitor depends on the charge on the electrodes. Many current supercapacitors have electrodes made from a porous form of graphite-like material, called activated carbon, which is cheap and can store electricity. However, porosity is a disadvantage due to the storage of a large amount of electric charge in a low density material that requires a large amount of material, which is not suitable for applications in small electronic devices.
What Béguin and his colleagues really need is a relatively thick, conductive carbon that is capable of storing large amounts of electricity. Researchers think that cellulose (plant fiber) may be appropriate because it contains a lot of stored oxygen atoms but most of the oxygen is gone when heating cellulose. They then thought of alginate, an excess in brown seaweed, which is chemically similar to cellulose but can hold oxygen when heated.
The French team cooked alginate in an airless enclosure to turn it into black powder. Next, they combined the powder with a polymer to create the hard material they shape into electrodes to use for supercapacitors. The amount of charge and energy these devices can store is relatively equal to those made from activated carbon. However, seaweed capacitors can be charged at twice the voltage without breaking, as the material is twice as thick. Besides, it is also highly durable, and its stored charge decreases by only 15% after every 10,000 charge cycles. Béguin said it will quickly commercialize the material and some companies show interest in the technology.
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