Engineers develop gel-based stretchable triboelectric nanogenerators for wearable technology

From smartwatches, and fitness trackers to medical sensors that can be worn on the body, wearables are transforming the way we interact with technology. As their popularity grows, triboelectric nanogenerators (TENGs) that convert mechanical energy such as body movement to electrical energy offer a solution to power these devices without relying on batteries.

Most TENGs used in wearable applications incorporate a triboelectric material attached to an electrode that conducts current. However, one of the challenges has been finding flexible electrode materials that can move seamlessly with the human body.

To address these challenges, a research team led by Professor Jung Inn Sohn from Dongguk University-Seoul in the Republic of Korea developed a gel polymer electrode-based triboelectric nanogenerator (GPE-TENG). This device is stretchable, semi-transparent, and durable, making it suitable for wearable sensor applications. This paper was published in the Chemical Engineering Journal on 1 Nov 2024.

“We report an in-situ curing strategy to develop a stretchable, semi-transparent, and durable GPE-TENG through enhanced interfacial bonding between the ionic polymer gel and ecoflex layers,” explains Prof. Sohn.

To fabricate the device, the researchers poured a gel mixture of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into an ecoflex mold. The gel is spread evenly and then covered with another ecoflex layer. A copper wire is attached to the gel for electrical connection, and the entire assembly is cured at 70°C for 12 hours, allowing the gel to bond strongly with the ecoflex layers.

The result is a durable, flexible, and semi-transparent device that generates electrical signals when tapped or stretched, delivering a peak power of 0.36 W/m² at a load of 15 MΩ. In tests, the device stretched up to 375% of its original size without damage and could withstand two months of bending, twisting, folding, and stretching without any signs of delamination or loss of electrical performance.

As wearable technology becomes a bigger part of our daily lives, the proposed GPE-TENG could enable wearable devices that track joint activity for rehabilitation purposes or act as a biometric system in clothing, allowing users to unlock smart doors or lockers.

“This work could revolutionize wearable technology by developing sustainable and flexible electronic devices with promising applications in human health care, rehabilitation, security systems, and secure biometric authentication systems,” says Prof. Sohn.