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Graphene and Carbon Nanotubes Join Forces to Tackle Supercapacitors

Combining the two wonder materials could lead to low-cost, high-performance electrodes for supecapacitors

2 min read
Graphene and Carbon Nanotubes Join Forces to Tackle Supercapacitors
Image: Journal of Applied Physics

Graphene and carbon nanotubes have been competing for many of the same applications for years, especially in the broad area of electronics. The jockeying for supremacy between these two carbon materials has been fierce in energy storage applications as well. In fact, both carbon nanotubes and graphene have been proposed as a replacement material for activated carbon on the electrodes of supercapacitors.

Now, following a newly developing trend where graphene and carbon nanotubes join forces to create an even better material than they could on their own, researchers at George Washington University have combined the two materials to create a supercapacitor that is claimed to be both low cost and high performance.

In research published in the Journal of Applied Physics ("Paper-based ultracapacitors with carbon nanotubes-graphene composites"), the GWU researchers mixed graphene flakes with single-walled carbon nanotubes through an arc discharge under various magnetic conditions.

The resulting combination takes advantage of the high-surface area and good in-plane conductivity of graphene flakes while the carbon nanotubes connect all the structures to make a uniform network. The device’s specific capacitance—its ability to store a charge—was reported as 100 Farads per gram (F/g), three times higher than the specific capacitance of a supercapacitor made by carbon nanotubes alone.

“In our lab we developed an approach by which we can obtain both single-walled carbon nanotubes and graphene, so we came up with the idea to take advantage of the two promising carbon nanomaterials together," said Michael Keidar, a professor at GWU and director of the Micro-propulsion and Nanotechnology Laboratory, in a press release.

Supercapacitors, also known as ultracapcitors or electrochemical double-layer capacitors (EDLCs), have held out the promise that they could store as much energy as an electrochemical battery like a lithium-ion battery, but charge up in a matter of seconds and provide quick bursts of a large amount of power as they do now for applications such as powering cranes or buses.

This potential has fueled the hope that supercapacitors could be used to power all-electrical vehicles, providing as much range as a lithium-ion battery does but charge up faster than the time it takes to fill up a car with gasoline. The interest in applying nanomaterials to these devices has become so intense that the lines between batteries and supercapacitors are becoming blurred as new materials are proposed.

In the race to practical—and potentially lucrative—applications, a promising approach in giving supercapacitors the same storage capacity as an electrochemical battery is increasing the surface area of the electrodes. More surface area translates into more ions being stored on the electrodes and the greater specific capacitance. While much is made of graphene’s theoretical surface area of 2630 squared meters per gram, so far the largest surface area anyone has produced with graphene has been 1520 squared meters per gram, which is pretty typically found in today’s activated carbon made from crushed coconuts.

So, the jury is still out on whether graphene or carbon nanotubes are viable alternatives to activated carbon for today's supercapacitor applications, even if you lower the cost of the material (it’s hard to compete with crushed coconuts).

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Two Startups Are Bringing Fiber to the Processor

Avicena’s blue microLEDs are the dark horse in a race with Ayar Labs’ laser-based system

5 min read
Diffuse blue light shines from a patterned surface through a ring. A blue cable leads away from it.

Avicena’s microLED chiplets could one day link all the CPUs in a computer cluster together.

Avicena

If a CPU in Seoul sends a byte of data to a processor in Prague, the information covers most of the distance as light, zipping along with no resistance. But put both those processors on the same motherboard, and they’ll need to communicate over energy-sapping copper, which slow the communication speeds possible within computers. Two Silicon Valley startups, Avicena and Ayar Labs, are doing something about that longstanding limit. If they succeed in their attempts to finally bring optical fiber all the way to the processor, it might not just accelerate computing—it might also remake it.

Both companies are developing fiber-connected chiplets, small chips meant to share a high-bandwidth connection with CPUs and other data-hungry silicon in a shared package. They are each ramping up production in 2023, though it may be a couple of years before we see a computer on the market with either product.

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