Breakthrough in Energy Storage Announced by UC Riverside

Mihrimah Ozkan, Cengiz Ozkan and Zachary Favors in the Ozkan's lab. | Photo: UC Riverside

Supercapacitors are one of those "gee whiz" electrical power storage technologies that offer a huge amount of potential for helping make our energy consumption saner and more sustainable... someday. But a team of researchers from UC Riverside has come up with a novel molecular architecture that they say doubles the power storage capacity of commercially available supercapacitors -- today.

Unlike conventional batteries, which store electrical power by converting the electrical energy into chemical energy, supercapacitors essentially hang "extra" electrons on their molecular surface, which allows much faster charging and discharging times. (Imagine a smartphone battery that reached a full charge in a minute or two.)

But because the amount of energy present-day supercapacitors can store -- their "energy density" -- is quite limited, they're basically used mainly for things like current regulation in sensitive electronics. Heavier uses as power supplies for consumer electronics, electric cars, and even to store grid power would require radical improvement in supercapacitor energy density. And UC Riverside engineers say they've taken a potential step in that direction.

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Part of the problem with present-day supercapacitor designs is that since the tecnology involves storing electrons electrostatically on the suurface of electrodes, the amount of charge the devices can store is limited by that surface area. The greater the surface area, the greater amount of power could conceivably be stored.

To that end, researchers have been looking at materials such as graphene, an artificial form of carbon, that has a staggering amount of surface area on the subatomic scale.

As described in an article published earlier this spring in the journal Nature Scientific Reports, a team led by UCR engineering professors Cengiz S. Ozkan and Mihri Ozkan created experimental supercapacitor electrodes covered in a "foam" of graphene and carbon nanotubes, which greatly increased the electrodes' surface area, and studded with nanoparticles of ruthenium oxide. Ruthenium is a very rare metal whose oxide is exceptionally good at accepting and discharging electrical energy.

According to the Nature Scientific reports paper, whose lead author was Ozkan lab graduate student Wei Wang, the graphene-nanotube-ruthenium oxide electrodes were able to store and deliver twice as much power as commercially available supercapacitors, and withstood more than 8,000 charge cycles without physically degrading or declining in performance.

"These promising properties mean that this design could be ideal for future energy storage applications," Wang said in a UC Riverside press release.

One potential hitch: there isn't a whole lot of ruthenium to go around. About 12 metric tons of ruthenium is mined yearly, most of it found as a minor constituent in nickel, copper, or precious metal ores. World reserves are estimated at just 5,000 metric tons. If this electrode technology takes off, it wouldn't take long for ruthenium to get a whole lot more expensive... even if we do use it just a nanoparticle at a time.

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