A group of University of Wisconsin-Madison engineers and a collaborator from China have developed a nanogenerator that harvests energy from a car's rolling tire friction. The technology ultimately could provide automobile manufacturers with a new way to reuse energy and provide greater vehicle efficiency.

The nanogenerator relies on an electrode integrated into a segment of the tire. When the tire's electrode comes into contact with the ground, the friction between the two surfaces ultimately produces an electrical charge-a type of contact electrification known as the triboelectric effect. Energy is harnessed from the changing electric potential between the pavement and the vehicle's wheels.

During initial trials, Xudong Wang, a Harvey D. Spangler fellow and associate professor of materials science and engineering at UW-Madison, and his colleagues used a toy car with LED lights to demonstrate the concept. The team attached an electrode to the wheels of the car; as the vehicle rolled across the ground, the LED lights flashed on and off. The movement of electrons caused by friction was able to generate enough energy to power the lights, demonstrating that energy lost to friction can actually be collected and reused.

The researchers also determined that the amount of energy harnessed is directly related to the weight of a car, as well as its speed.

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