The power of symmetry

In line with the eco-friendly sustainability motivations of developing renewable energy sources, the Clemson researchers were keen to identify a material that was earth-abundant, biodegradable and recyclable. The tribo- or piezoelectric properties of a material are determined by the crystallographic symmetry of the material, and vanish when the crystal lattice has a centre of symmetry. However, the Clemson research team built on previous work by researchers in Japan showing they could remove the centre of symmetry of a biopolymer by adding polarizing molecules to asymmetric carbon atoms in its chemical structure.

Polylactic acid has many of the material attributes the researchers were looking for – it is plant- derived and biodegradable, and contains two asymmetric carbon atoms. However, its electrical resistance is too high for TENG devices, so the researchers used graphene as a filler to produce a nanocomposite that they could combine with the highly electronegative polymer Teflon in 3D-printed wireless TENGs.

We were not surprised by the high voltage generation, but we were awed at the ability to transmit and receive wireless signals without any interference from the surrounding environment, such as WiFi, mobile phones, power outlets, etc,explain Podila and his colleagues. They demonstrated the energy harvesting and transmission capabilities of their device on a range of domestic appliances including smart-tint windows, photoframes, LED displays and a call bell/security alarm.