Sharing their results in the Nature Communications journal under the title “A bionic stretchable nanogenerator for underwater sensing and energy harvesting”, the researchers describe what they call a bionic stretchable nanogenerator (BSNG) that mimicks the ion channels structure of an electric eel’s electrocyte cytomembrane.
Built out of polydimethylsiloxane (PDMS) and silicone, the layered construction consists of an electrification layer and an induction layer. The electrification layer contains a series of controllable channels which connect to a fluid chamber filled with deionized water. Those channels open or close upon stretching or release of the whole elastic construction. Underneath is the induction layer containing two ionic solution (NaCl) electrodes under the channels and chamber of the first layer.
In the experiments, the whole stretchable nanogenerator measured 10×6cm and was 8mm thick.
Upon stretching, the channels in the electrification layer open and draw-in deionized water, coming in contact with the silicone substrate onto which surface negative ions are selectively absorbed (creating an accumulation of negative triboelectric charges).
The liquid in the BSNG is positively charged and the silicone near to the liquid is negatively charged by triboelectrification through the iterative liquid-silicone contact. In the meantime, the induction layer underneath the channels induces electric charges that accumulate on the bottom of upper layer through electrostatic induction.
This asymmetric accumulation of electric charges between the two liquid electrodes form the potential difference that drives electrons to flow from one electrode to the other through an external circuit. By exerting an alternate mechanical traction repeatedly, the back and forth movement of the electrification liquid induces a continuous alternating electric signal between the two ionic solution electrodes, generating a continuous alternating current through an external circuit.
Experiment showed that such a BSNG could achieve an open-circuit voltage over 170V in dry conditions and over 10V in a liquid environment. Next, the researchers used the current signal from several BSNGs affixed to a wet suit to monitor a swimmer’s strokes in water. Recording the signals from BSNGs at elbow and knee joints, the authors were able to reliably detect different swimming strokes. They conclude such stretchable underwater bio-inspired nanogenerators could offer a sustainable power source for soft wearable electronics used underwater. Integrated in wet suits, the devices could also be used as sensors, to detect motion or tapping for the design of simple interfaces.