Storage boost

Energy storage devices called ultracapacitors can be recharged many more times than batteries, but the total amount of energy they can store is limited. Now researchers at Drexel University in Philadelphia have successfully made thin-film carbon ultracapacitors that store three times as much energy by volume as conventional ultracapacitor materials. Still not the same as batteries, the thin-film ultracapacitors could operate without ever being replaced. Unlike batteries they have almost unlimited lifetimes.

While batteries store and release energy in the form of chemical reactions, which cause them to degrade over time, ultracapacitors work by transferring surface charges. This means they can charge and discharge rapidly. The difficulty so far has been in fabrication methods.

The team used chemical vapor deposition to create thin films of metal carbides such as titanium carbide on the surface of a silicon wafer. The films are then chlorinated to remove the titanium, leaving behind a porous film of carbon. In each place where a titanium atom was, a small pore is left behind.This matching means that when used as the charge-storage material in an ultracapacitor, the carbon films can accumulate a large amount of total surface charge.

The material was developed some years ago but the demonstration was only done now.In theory, there is no limit to the size of the films that could be made using these methods, the team claimed.

Ultracapacitors have been banked heavily by the renewable energy industry where storing power is very important, given its intermittent nature. This demo shows we are heading in the right direction to clean energy.