 Gold: Powering The Future
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Sept. 30, 2003 — Tiny sponges made from pure gold hold promise for extending and boosting the power of batteries used in computers and mobile phones.
Professor Michael Cortie from the University of Technology, Sydney and Elma van der Lingen, from Mintek in Johannesburg will present their research this week in Vancouver at the international conference, Gold 2003.
The researchers replaced carbon with gold in ultra-capacitors, the tiny devices that boost battery output during peak demand. By switching to gold, researchers found the ultra-capacitors didn't overheat and could store up to six times the energy of standard capacitors.
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Chemical batteries are great at storing electrical energy but poor at delivering it rapidly. Ultra-capacitors (also called ultra-caps and super-capacitors) have an incredible capacity to absorb or deliver electrical power and can extend the life of conventional batteries by increasing the output of the batteries when extra power is needed, such as starting up a computer.
Ultra-capacitors currently in use store charge in a double layer of porous carbon. Unfortunately, while these ultra-caps can absorb and deliver electrical charge very quickly, they don't store it very well. They also tend to generate significant amounts of internal heat due to a high internal resistance, limiting their performance and use.
But this dark cloud may have a golden lining. Gold could prove to be a perfect material to get around these limitations, according to Cortie.
"Gold seems rather an improbable choice compared to carbon as it's a precious metal that comes at a considerable price," Cortie told ABC Science Online. "But it turns out that gold, being an excellent electrical conductor, doesn't suffer the high internal resistance that limits carbon-based ultra-capacitors.
"And expense isn't really a major concern because carbon-based ultra-capacitors aren't all that cheap anyway. Including a fraction of a gram of gold won't add too much to its cost."
In developing the ultra-capacitor prototype, the researchers first used an intermetallic compound of gold and aluminum known as purple glory. As its name suggests, the metal has a rich purple hue and is sometimes used in exotic jewelry. The aluminum is chemically removed leaving a sponge of pure gold. This porous form of gold is rich in tiny holes as small as 10 nanometers in diameter. The result is a small amount of gold with an enormous surface area, perfect for the rapid exchange of electrical charge.
These ultra-caps could provide extra power, for example, for portable computers on initial power-up and during the operation of hard-drives. This might allow manufacturers to use smaller batteries for the less demanding energy requirements of a computer. Ultra-caps may even help make electrical cars more of a reality by enabling them to accelerate as quickly as conventional automobiles by providing a surge of electrical power.
"It's still very early days," Cortie said. "Right now we're just exploring the behavior of these new gold-based ultra-caps in order to identify what their competitive advantages might be. However, given how new this approach is and the potential of ultra-capacitors in today's electrical devices, I think it'd be safe to say this is truly a golden opportunity."
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