Frustrated trying to charge your phone on the go? A newly developed energy harvesting method may soon lead to technologies that will allow you to keep your phone charged, without external chargers.

A University of Hawaiʻi at Mānoa research team led by Tianwei “David” Ma, interim associate dean and professor in civil engineering in the College of Engineering, has developed a new method of generating electricity from water drops moving on hydrophobic (water resistant) surfaces.

This method is based on electrostatic induction (the process by which an electrical conductor becomes electrified when near a charged body) and contact electrification, or charging by friction. In a paper published in Scientific Reports, Ma’s group demonstrated that motions of a water drop on a dielectric hydrophobic (electric insulator surface that resists water) cause the surface to be charged. Moreover, when the surface is composed of two different materials, the level of charging can be significantly different for the surface areas associated with the materials. Such a difference, along with the electrostatic effect, can be tapped into for electricity generation.

Ma’s group fabricated a prototype device, which consists simply of a silicon substrate, covered with hydrophobic (water resistant) coatings of Cytop and PTFE (the material used in nonstick pans) and a water drop. A very low-level mechanical excitation will drive the water drop to move across the non-sticking surfaces and generate electricity because of the electrostatic induction effect in the water drop. Although some similar devices have been developed, the new prototype can increase the efficiency of former devices by almost 100 times. Under a low level vibration, such as that induced from human walking, one water drop can generate 42V, enough to illuminate 15 green LED s.

The team is working toward replacing the rigid silicon substrate with soft materials, such as grapheme to develop flexible, encapsulated devices, which can be incorporated as a mini-generator into everyday clothing. They are also looking into extending the same theory to harvesting energy from ocean waves and falling raindrops.