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Wind And Rain Power Smart Windows

Electrochromic Materials: Triboelectric nanogenerator harvests energy from motion to drive color-changing redox reactions in windows

by Bethany Halford
April 20, 2015 | A version of this story appeared in Volume 93, Issue 16

So-called smart windows, which use redox chemistry to darken with the flip of a switch, have been a reality for several years. But efficiently powering them has been problematic. Using batteries for every window is impractical, and integrating them with solar cells inevitably obscures some of the window. Researchers at Georgia Tech, led by Zhong Lin Wang, believe they have a solution to this power problem. Wang’s group has been working on triboelectric nanogenerators, or TENGs, which are devices that convert motion into electricity. To make a self-powered smart window, they coupled a device that darkens as a result of redox chemistry to two types of TENGs (ACS Nano 2015, DOI: 10.1021/acsnano.5b00706). One of the TENGs sits atop the device and harvests electrostatic energy from falling raindrops. The other gathers energy when blowing wind moves two of the device’s layers, which are separated by tiny springs, across one another. Prussian blue nanoparticles, which can be reduced by the TENGS to colorless Prussian white nanoparticles, make up the color-changing layer of the window, and ZnHCF nanocubes constitute the device’s ion storage material. The researchers say they think TENGs will find use in other self-powered systems such as flexible displays, wearable electronics, and energy-efficient buildings.

Smart Schematic
This is a schematic of the components of a self-powered smart window and that device in its darkened and bleached states.
Credit: ACS Nano
This prototype window incorporates two types of triboelectric nanogenerator (TENG); PMMA = poly(methyl methacrylate), FTO = fluorine-doped tin oxide, ITO = indium tin oxide, PET = polyethylene terephthalate, and PDMS = polydimethylsiloxane.


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