Triboelectric generators, powered by your pants

It’s sounds like a utopian idea – walk around, dance, or simply convert the mechanical action of rainfall into electric current. A Phys.org article asks the question: Tribo-electric, the buzzword of the future?

It is an alluring goal of clean, reliable power free from geo-political risks—and scientists in the United States said Tuesday it lies within reach, thanks to a smart way to harvest energy called tribo-electricity.

What is triboelectricity? (We’re going with the unhyphenated version of this word – like piezoelectric.) Science Daily has a good description:

In its simplest form, the triboelectric generator uses two sheets of dissimilar materials, one an electron donor, the other an electron acceptor. When the materials are in contact, electrons flow from one material to the other. If the sheets are then separated, one sheet holds an electrical charge isolated by the gap between them. If an electrical load is then connected to two electrodes placed at the outer edges of the two surfaces, a small current will flow to equalize the charges. By continuously repeating the process, an alternating current can be produced.

It sounds simple enough, but the energy source is unpredictable, and scientists have found it difficult to harness the sporadic bursts of energy.

Zhong Lin Wang, a professor of materials science and engineering, has a new invention he describes as breakthrough. Wang and his team have built a small, prototype device about 10 cm (four inches) wide that captures ambient energy:

Inside are two circular sheets of material, one an electron “donor” and the other an electron “receiver,” brought together through rotary movement. If the sheets are separated, one then holds an electrical charge isolated by the gap between them. Sandwiched between the two discs is a third disc with electrodes, which bridges the gap and helps a small current to flow. At a top speed of 3,000 revolutions per minute, the device generated 1.5 watts. 

Energy efficiency of the triboelectric device was about 24 percent, which makes it as efficient as magnetic-induction turbine generators, and more than three times greater than piezoelectric generators.

Wang and his team actually discovered the principle of their device by accident. After noticing that the output from one piezoelectric device was much greater than expected, they realized the cause was a loose assembly that let two polymer surfaces rub together. Six months later (in 2012), they published their first journal paper on their triboelectric generator.

Everybody has seen this effect, but we have been able to find practical applications for it, said Wang. It’s very simple, and there is much more we can do with this. (Science Daily)

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