The secret ingredient for ultra-capacitors: Flowers

http://www.tgdaily.com/content/view/39367/113/
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By Rick C. Hodgin
Thursday, September 18, 2008 09:23
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Beijing (China) - Hao Zhang, of the Research Institute of Chemical Defence in Beijing, has discovered an interesting mix which effectively doubles the energy storage ability of ultra-capacitors. He's constructed tiny little "flowers" of manganese oxide (MnO) and "grass" out of carbon nanotubes all atop a field of tantium metal foil, literal creating vast (nearly blinding) nanoscopic meadows which help overcome one of the limiting factors in using MnO in ultra-capacitors; namely their high resistance to receiving a charge. His discovery has created an ultra-capacitor with double the energy storage and ten times the charging performance of carbon based solutions, making it the front-runner for continued research.

Ultra-capacitors can be thought of as a hybrid between batteries and capacitors. Whereas batteries are slow to charge as they store their electricity chemically, capacitors store energy in ion form in vast little "holes" or "reservoirs" where the ions can accumulate, traditionally in a carbon-based solution. Because capacitors store their energy that way, they can charge and discharge almost instantly. This has given them their current role in electronics, a type of "noise dampening" line filter for electrical signals.

Batteries, on the other hand, can store much greater quantities of energy through chemical reactions. The downside of their storage mechanism is that it's slow to charge and relatively slow to discharge. What would be needed is a hybrid solution - the ultra-capacitor.

Researchers began discovering ways to construct capacitor electrolytes (the materials inside the capacitor), which increase their energy storage potential and life expectancy before being completely discharged, some time ago. However, the dominant ultra-capacitor designs up until Zhang's model were based on activated carbon, which provided lots of reservoirs to store ions. And essentially Zhang's model isn't any different in approach, he just figured out a way to create more reservoirs by increasing the surface area and delivery mechanisms for migrating electrons to and from the inner substrate.

Ultra-capacitors offer the promise of powering clean, carbon-free automobiles with energy storage solutions that could be recharged at an "electric gas station" along the highway as quickly as we fill our tanks today with petroleum, making them a real alternative in future cars.

There have been cars announced using ultra-capacitor technology already, such as ZENN's EEstor car due out in Fall 2009 (which looks a lot like the Smart Car), capable of driving 80 mph and 250 miles per charge, sufficient enough to call it a real replacement technology. Toyota also introduced a hybrid racing model using ultra-capacitors, the Toyota Supra HV-R. In 2007, it won the 24-hour endurance race in Japan, completing 616 laps of the 3-mile course. There are also many "garage mechanics" who converting their old jalopies into ultra-capacitor powered test vehicles, mostly to show the neighbors that they've got some game.

Ultra-capacitors suffer from similar problems of other energy storage solutions, namely that they lose their ability to hold and release a charge as effectively after repeated charge/discharge cycles. For example, even Zhang's solution loses 3% of its energy output every 20,000 cycles. And while that may not seem like a lot, regenerative braking solutions in cars may cause five limited recharges per minute while driving around town. Over time it begins to add up, making the life expectancy of ultra-capacitors much, much lower than internal combustion engines.

Still, future technologies like ultra-capacitors are gaining momentum. Even today, they offer real alternative solutions to the growing problems of high energy costs and concerns over our environment through carbon emissions.

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