Green tea laced capacitor may power gen-next wearable devices

New Delhi, February 21

Scientists have used green tea compounds to develop a new flexible and compact rechargeable energy storage device which may power more comfortable wearable electronics such as heart rate monitors.

The most prominent versions of wearable electronics are sold in the form of watches or sports bands.

More comfortable products could become available in softer materials made in part with an unexpected ingredient - green tea, researchers said.

Powering soft wearable electronics with a long-lasting source of energy remains a big challenge.

However, most supercapacitors are rigid, and the compressible supercapacitors developed so far have run into roadblocks.

"Our objective is to fabricate wearable electronic devices. Compressible energy storage devices are the first step towards achieving that objective," Kothandam Krishnamoorthy, from the CSIR-Network of Institutes for Solar Energy told PTI.

Supercapacitors have been made with carbon-coated polymer sponges, but the coating material tends to bunch up and compromise performance.

Researchers including those from CSIR-National Chemical Laboratory in Pune and Academy of Scientific and Innovative Research (AcSIR) in New Delhi wanted to take a different approach.

The researchers prepared polymer gels in green tea extract, which infuses the gel with polyphenols.

The polyphenols converted a silver nitrate solution into a uniform coating of silver nanoparticles.

Thin layers of conducting gold and poly(3,4-ethylenedioxythiophene) were then applied.

The resulting supercapacitor demonstrated power and energy densities of 2,715 watts per kilogramme and 22 watt-hours per kilogramme - enough to operate a heart rate monitor, LEDs or a Bluetooth module.

"If you brew green tea and leave it for a while in a glass, you will see a coating. The coating comprises polyphenols, which are the antioxidants in green tea. They are capable of reducing metal ions such as silver," said Krishnamoorthy.

"We could use polyphenols in green tea to prepare metal coated sponges that are essential for the fabrication of compressible supercapacitors," he said.

The researchers tested the device's durability and found that it performed well even after being compressed more than 100 times.

The study was published in The Journal of Physical Chemistry C. — PTI