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Water Droplets On A Slide

Electricity from water drops project published in prestigious journal

College of Engineering Associate Dean David Ma‘s project that generates electricity from water drops was recently published in Nano Energy — one of the top journals in energy, electrical engineering and renewable energy & sustainability.

The method he and research associate Dr. Jian Yu used in the project 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 the article, 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. 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 LEDs.

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.

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