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Powerful Storage

Researchers have discovered a new material that could improve digital storage in the future.

by Gurpreet Syan

Courtesy of Bettina Loycke, Wiley-VCH

The structure of the new material combines an outer shell of vanadium oxide and an inner core of vanadium nitride.

Thanks to advancements in technology, people can now do more and more with their gadgets. Mobile phones, for example, are no longer just for talking - they can be used to listen to music, take photos and soon even to watch movies. But this also means that new sources of power will be required to accommodate the technology - and at Carnegie Mellon University in Pittsburgh, Pennsylvania, a team of researchers led by Prof. Prashant Kumta has recently synthesised a new material that can store more energy than the supercapacitors used today.

Unlike a battery where energy is stored in a chemical form, a supercapacitor is an electrical device that stores energy in an electric field. This field is generated by negative and positive plates in the capacitor - and their "super" status comes from their ability to hold four times as much charge as a normal capacitor.

Currently, supercapacitors are made from ruthenium oxide but the high price of this compound limits their use in a wide range of technologies. They are most useful in applications like hybrid cars and robotics where a large, fast pulse of energy is required. Compared to a normal battery, a supercapacitor can also last much longer.

The new material - called nanocrystalline vanadium nitride - could be a viable alternative to ruthenium oxide. It has a capacitance that is almost two times greater and can also store energy for longer. The structure of the material has two layers: it has an outer shell of vanadium oxide and an inner core of vanadium nitride. This set-up enables energy storage because of electrochemical reactions that occur on the vanadium oxide surface - which generate an electric charge. The vanadium nitride interior stores the charge generated.

Courtesy of Bettina Loycke, Wiley-VCH

Micrograph of vanadium nitride nanocrystals synthesised at 400°C.

To create this new material, nanocrystals were made by a method described by Kumta as "simple and novel", where vanadium chloride is reacted with ammonia, at 400 degrees C, in an environment without water. The final product is a material made up of tiny nanocrystals six nanometers wide, and is particularly interesting because it combines the good electric conductivity of vanadium nitride with vanadium's many oxidation states in vanadium oxide.

But the main advantage of vanadium nitride is its price. According to Prof. Ian Boyd, Executive Director at the London Center for Nanotechnology, although ruthenium oxide exhibits some of the most desirable properties for supercapacitors, such as constant capacitance, reversibility, and cycle times running into the hundreds and thousands cycles, the main problem is that it is very expensive. Ruthenium oxide costs $100 per gram whereas vanadium nitride is priced at $50 per gram.

The researchers are confident that this new material will be cheaper, more stable and a higher quality material for energy storage in the future. Prof. Kumta says that this nanomaterial is key to creating the next generation of supercapacitors, and will be used in everything from cars, camcorders and lawn mowers to industrial backup power systems at hospitals and airports.

For more information:

Nanotechwire.com - Carnegie Mellon University Researcher discovers new materials

Post-gazette.com - Power Up: CMU team develops technology to make the energized bunny run farther


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First Science 2014