In response to COVID-19, we have found these nanogenerators to be an inexpensive and engaging at-home science activity.
What if "every breath you take, every move you make" (Sting 1983) could be harnessed to produce renewable energy? Triboelectric nanogenerators (TENGs) are state-of-the-art devices researchers are studying to do just that--convert kinetic energy into electrical energy at the source (Saurabh Rathore 2018). This type of electrical energy is called triboelectricity, commonly experienced as static electricity, and is produced when two materials, such as a rubber balloon and human hair, come into contact, exchanging and separating charges, producing a voltage (Figure 1).
TENGs create triboelectricity through the use of two materials, one that develops a positive charge and one that develops a negative charge. Triboelectricity is produced when the materials within the TENG are repeatedly brought into contact and separated. Typically, the kinetic energy from movement like walking or dancing is dissipated as heat and sound (Corrales, Chartier, and Devanathan 2005), but TENGs convert this kinetic energy into useful electricity that can power small electronics such as cell phones. This article details how students can build a simple, state-of-the-art, renewable energy device; experiment with circuits; and explore how scientists and engineers exploit surface-area-to-volume ratios to achieve desired results.
We begin our discussion with a simple, eye-catching, and familiar demonstration of triboelectricity, i.e., static electricity. Students can rub a balloon with hair or fur and observe how the two objects attract one another. Alternatively, students can run a plastic comb through hair or fur, charging the comb and enabling it to pick up small pieces of plastic or paper in close proximity. Van de Graaff generators produce triboelectricity and allow for exciting demonstrations (please follow all safety considerations with your Van de Graaff generator!). See Online Connections for additional ideas and an excellent PhET simulation that demonstrates how electrical charges are exchanged when two materials come into contact and the effect the charge exchange has on the material's behavior.
Exploring the triboelectric series
Two important concepts of triboelectricity that we want to emphasize are that: (1) when two materials with different charge affinities come into contact with one another, they donate or accept electrons, and (2) some materials are more amenable to accepting electrons, while others are more amenable to donating electrons. To drive these concepts home, students recreated a small section of the triboelectric series (Zou et al. 2019), a ranking of materials' affinity for positive or negative charges.
We gave groups of students six different materials: three rods (wood, glass, PVC) and three cloths (cotton, wool, polyester). Using a DIY electroscope (Figure 2; see Online Connections for original source and our instructions) that we built prior to the activity and that students can build themselves, students tested every combination of rod and cloth in an attempt to create a subsection of the triboelectric series. Rubbing a rod with a cloth separates charges, and then bringing the rod close to the electroscope coil induces a charge gradient in the electroscope,...