Researchers suggest that liquid metal has the potential to generate electricity from mechanical motions even underwater.
Researchers at North Carolina State University have developed soft and stretchable devices that convert movement into electricity and can work in wet environments.
“Mechanical energy—such as the kinetic energy of wind, waves, body movement and vibrations from motors—is abundant,” says Michael Dickey, corresponding author of a paper on the work and Camille & Henry Dreyfus Professor of Chemical and Biomolecular Engineering at NC State. “We have created a device that can turn this type of mechanical motion into electricity. And one of its remarkable attributes is that it works perfectly well underwater.”
At the core of this energy harvester is liquid metal alloy of gallium and indium encased in a hydrogel, which is a soft, elastic polymer swollen with water. The water swollen in the hydrogel contains dissolved salts called ions. The ions accumulate at the surface of the metal, inducing charge in the metal. Increasing the area of the metal provides more surface to attract charge. This generates electricity, which is captured by a wire attached to the device.
“Since the device is soft, any mechanical motion can cause it to deform, including squishing, stretching and twisting,” Dickey says. “This makes it versatile for harvesting mechanical energy. For example, the hydrogel is elastic enough to be stretched to five times its original length.”
Researchers observed that deforming the device by only a few millimeters generates a power density of approximately 0.5 mW m^-2.
“However, other technologies don’t work well, if at all, in wet environments,” Dickey says. “This unique feature may enable applications from biomedical settings to athletic wear to marine environments. Plus, the device is simple to make.”
“There is a path to increase the power, so we consider the work we described here a proof-of-concept demonstration.”
The paper describing this work, “A Soft Variable-Area Electrical-Double-Layer Energy Harvester,” is published in the journal Advanced Materials.