The bioinspired optimized structure and working process of the undersea bjTENG. Courtesy of Zhong Lin Wang, Georgia Tech.Inspired by jellyfish, researchers have designed a triboelectric nanogenerator that can harvest energy from waves and power sensors that can detect fluctuations in the water surface [Chen et al., Materials Today (2017), doi: 10.1016/j.mattod.2017.10.006].
The bionic jellyfish triboelectric nanogenerator (bjTENG) could enable the realization of the ‘blue energy dream’, says lead researcher Zhong Lin Wang of Georgia Institute of Technology. Together with colleagues from Beijing Institute of Nanoenergy and Nanosystems and National Center for Nanoscience and Nanotechnology, Wang’s team fabricated the device from polydimethylsiloxane (PDMS) as the hermetic package, a polytetrafluoroethylene (PTFE) thin film as the triboelectric generator, and two metal (Cu and Al) electrodes.
“We took inspiration from the swimming behavior of the jellyfish, a process which is triggered by the fast contraction of the body,” explains Wang. “Our practical bjTENG utilizes a polymeric thin film as the triboelectric material, which is shape-adaptive, with a hermetic package and a unique elastic resilience structure.”
The device shows a sustained performance of 143 V, 11.8 mV/m2 and 22.1 uC/m2 under a low frequency oscillation of 0.75 Hz – sufficient to power numerous light-emitting diodes or a temperature sensor. The potential and current are generated through a charge-separation mechanism. Initially, the PTFE and Al electrode are in contact and there is no potential difference. As the device is squeezed by the waves, the PTFE film/Al electrode moves towards the Cu electrode, inducing charge separation. When it moves back again, charge flows between the electrodes.
“During the wave-induced device’s contraction, the triboelectric materials contact and separate. Based on the coupling of triboelectrification and electrostatic induction, the charge flows back and forth,” explains Wang.
The device could have many potential applications suggest the researchers. It could be attached to the hull of ships to harvest wave energy or used in self-powered liquid-surface fluctuation sensors in the ocean.
“We believe the bjTENG is a priority technology because of its high sensitivity, highly shape-adaptive nature and ability to work in deep water for wave energy harvesting,” says Wang.
Because the device is hermetically sealed, the energy harvester works well in water up to 1 m deep. It also uses conventional materials that are cheap and easy to fabricate.
“However, to apply this technology on a wide scale, some obstacles need to be overcome,” admits Wang. “The main limitation is likely to be the durability of bjTENG. The organic materials used in their manufacture degrade in salty water and sunlight, so new waterproofing materials, such as highly adhesive substances used for underwater cables, might be needed.”
Wang is confident that these limitations can be overcome to realize the ultimate dream of ‘blue-energy’ networks that rival solar or wind power.