Mechanical energy — such as the kinetic energy of wind, waves, body movement, and vibrations from motors — is abundant. Researchers have created a device that can turn this type of mechanical motion into electricity. One of the device’s attributes is that it works well underwater.
The heart of the energy harvester is a liquid metal alloy of gallium and indium. The alloy is encased in a hydrogel, a soft, elastic polymer swollen with water. The water in the hydrogel contains dissolved salts called ions. The ions assemble 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. This makes the device versatile for harvesting mechanical energy. The hydrogel is elastic enough to be stretched to five times its original length.
In experiments, researchers found that deforming the device by only a few millimeters generates a power density of about 0.5 mW m2. This amount of electricity is comparable to several popular classes of energy harvesting technologies. Other technologies, however, do not work well, or at all, in wet environments. This feature may enable applications from biomedical settings to athletic wear to marine environments.
The researchers already have two related projects underway. One is aimed at using the technology to power wearable devices by increasing the harvester’s power output. The second project evaluates how this technology could be used to harvest wave power from the ocean.