# Triboelectricity: Generating electricity by friction

Friction is a necessary evil. Without friction, we cannot walk, we cannot hold objects in our hands, cannot light matchsticks and cannot even stop fast moving vehicle. But apart from these things there is very useful side of friction which can be utilized to develop clean energy. Triboelectricity can be an answer to the growing energy demand and effective usage of energy. We all have experienced triboelectric effect in our daily lives. Getting a shock when touching a metallic door knob or sticking balloons on wall by rubbing them against hairs. Triboelectricity is defined as an electrical charge produced by friction between two objects that are nonconductive.

When two different materials are rubbed against each other, the surface of one material will steal some electrons from the surface of the other material and will become more negatively charged than the other material, even after the two materials get separated. Because the surface of the material is now electrically charged, either negatively or positively, any contact made up of material having a different charge, may cause an electrical discharge represented by a spark or static electricity. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties. Triboelectricity is not a predictable phenomenon. In order to have a better understanding John Carl Wilcke published the first triboelectric series in a 1757 paper on static charges. The Triboelectric Series is a list of materials, showing which have a greater tendency to become positively charged and which have a greater tendency to become negatively charged [1][2][3].

Harvesting Triboelectricity.

Georgia Tech professor Zhong Lin Wang has created a triboelectric generator that generates small amount of electricity which can be utilized for various purposes. The triboelectric generator uses sheets of two different materials. One of the material is an electron donor while the other is an electron acceptor. When the materials are in contact, electrons gets transmitted from one material to the other. In the event of separation of the two sheets, one of the sheet will hold the electric charge isolated by the gap between them. Connecting an electrical load to the two electrodes placed at the outer edges of the two surfaces will result in a small amount of current that will flow to equalize the charges.By continuously repeating the process, an alternating current can be produced [4].

Researchers at University of Wisconsin–Madison have developed a nano-generator that harvests energy from a car’s rolling tire friction. The nano-generator works on the principle of triboelectric effect and makes use of the changing electric potential between tires and the roads. The friction between tire and the ground, consumes about 10% of vehicles fuel. The nano-generator tries to harness this waste energy that can lead to improvement of fuel economy. The main constituent of the nano-generator is an electrode that is integrated into a segment of the tire. When this part of the tire surface comes into contact with the ground, the friction between the two surfaces produces an electrical charge-a type of contact electrification known as the triboelectric effect. During initial trials, the researchers used a toy car and were successful in illuminating toy car lights via nano-generator [5].

References

1. “Triboelectric Effect.” Wikipedia, Web. 03 Nov. 2016.https://en.wikipedia.org/wiki/Triboelectric_effect
2. “The TriboElectric Series.” AlphaLab, Inc. Web. 03 Nov. 2016. https://www.trifield.com/content/tribo-electric-series/
3. “Triboelectric Effect.” ScienceDaily. Web. 03 Nov. 2016 https://www.sciencedaily.com/terms/triboelectric_effect.htm
4. Toon, John. “Harvesting Electricity: Triboelectric Generators Capture Wasted Power.” N.p., 9 Dec. 2013. Web. 03 Nov. 2016. http://www.news.gatech.edu/2013/12/07/harvesting-electricity-triboelectric-generators-capture-wasted-power
5. Brodt, Lexy. “New Nanogenerator Harvests Power from Rolling Tires.” News. 29 June 2015. Web. 03 Nov. 2016.http://news.wisc.edu/new-nanogenerator-harvests-power-from-rolling-tires/

About HARSHVARDHAN SINGH
Harshvardhan Singh is an Automotive Engineer and has good experience in lubrication science and experimental tribology. He loves to write about tribology and related fields such as coating technology, surface engineering and others.