The “triboelectric effect” is a phenomenon that scientists from the USA and China harnessed in 2012 to create the triboelectric nanogenerator (TENG), which transforms unwanted mechanical energy into useable electrical energy. Their system consisted of two metallic electrode-equipped triboelectric polymer films that, when brought together and apart, caused charge separation and the production of an electric voltage strong enough to power small electronic devices.
It has been attempted to increase the power output of TENGs by injecting charges onto the surface of triboelectric films, which are thought of being possible sustainable energy harvesters. They are unable to achieve high surface charge densities due to charge recombination in the electrode and charge repulsion on the material’s surface.
In light of this, a group of scientists from the Gwangju Institute of Science and Technology (GIST) in South Korea, led by Professor Chanho Pak, created a charge-confinement layer in a recent study. This layer controls the transfer of injected charges between the triboelectric film and the electrode to increase the charge density on the surface of the triboelectric film.
“In the design of high-performance TENGs, it is critical to transport the charge on the surface to a deep position while reducing charge recombination,” says Prof. Pak. To make the layers, the researchers used electrospun mesoporous carbon spheres together with layers of polyvinylidene fluoride (PVDF) and nylon. The carbon spheres, which trap charges on the surface, were arranged in ascending order of their specific surface areas, making for a gradient charge-confinement layer. As a result of this gradient arrangement, the injected charges could drift towards the electrode but were confined just before reaching it. “The layers transport as well as confine the charges,” explains Prof. Pak.
The layers enable the triboelectric material to maintain more charge by transferring the injected charges away from the surface where they would build up and reject one another. A triboelectric surface with a higher charge density is produced by confining the charges close to the electrodes since doing so prevents charge loss due to recombination.
The researchers increased the output voltage and current of the TENG by 40 and 7 times, respectively, with the inclusion of charge-confining layers. Additionally, they managed to dramatically increase output current by a factor of 1300 by combining a cylindrical TENG and an electromagnetic generator.
“With these promising results, TENGs could one day be powerful enough to serve as sustainable energy harvesters as well as power wearable devices of the future,” says Prof. Pak.
