Triboelectric Nanogenerator

Triboelectricity, more commonly known as static electricity, is a form of contact electrification. When two materials come into contact, they exchange electrical charges such that one material ends up with a net positive charge and the other with a net negative charge. To learn more about triboelectricity, please visit this page. Triboelectric nanogenerators take advantage of this triboelectric effect to create useful electricity to power small circuits and electronics. Scientists and engineers are developing triboelectric nanogenerators for a number of different applications, from energy harvesting floors to wound healing to aiding in weight loss. This activity outlines how to create a triboelectric nanogenerator from inexpensive household materials.

Inclusive Teaching Practices

Inclusive teaching refers to methods that are designed to engage students in learning that is meaningful, relevant, and accessible to all. Equitable learning environments provide supports to address individual student needs and promote learning for all students. Creating an inclusive classroom is a semester long process that should begin before the term with development of your syllabus and lesson plans.

This triboelectric nanogenerator activity contains specific inclusive teaching strategies that align with the learning objectives of the experiment. Creating Learning Objectives makes it clear for all students, regardless of their background, what knowledge or skills you expect them to learn by participating in the activity.

Learning Objectives – Students will:

  1. Be able to explain how kinetic energy is converted into electrical energy.
    • To help students relate the phenomenon to their own lives, have them write about or share in pairs their own experience with static electricity or charge transfer. For example, getting shocked when touching a door knob after walking across carpet with socks, rubbing a balloon on their head and sticking the balloon to a wall, or removing a sock stuck to a shirt after going through the dryer.
  2. Build their own triboelectric nanogenerators.
    • To extend the activity, we let students take the nanogenerators home and remind them that they can fix it since they built it. We ask the students to show it to their friends or family and explain how it works.
  3. Explore simple electrical circuits.
  4. Examine how different materials accept or donate electrons.
    • Have students look at the triboelectric series to predict and select materials to try. Allow students to experiment with materials of their choice in addition to those described here.
  5. Evaluate how different materials and geometries affect the efficiency of their TENG.
    • Allow students to experiment with different containers (e.g., aluminum can, toilet paper roll, whiffle ball) and balls (e.g., marbles, dice, beads) in addition to those described here.

See the Discussion section for more details on some of these learning objectives.

Safety

  • Take caution with sharp objects such as scissors or stripped wires.

Materials

  • Plastic egg (standard Easter eggs are approximately 2.25 inch tall and work well for this activity)
  • Bouncy balls (32 mm diameter, which, IMPORTANTLY, is smaller than the diameter of the egg)
  • Aluminum foil
  • Jumper wires or regular copper wires, stripped
  • Double-sided tape
  • Clear office tape, or FEP (fluorinated ethylene propylene) tape
  • Low amperage green LED, clear lens (green was the easiest to visualize)
  • Black straws (to help visualize the light from the LED) (0.21 or 0.25 inch diameter)
  • Scissors

Procedure

  1. Strip a 1-2 cm section at the end of the jumper wires to expose the metal within. The aluminum foil and metal wires will need to touch in order for current to flow.
  2. Insert one wire into each half of the plastic egg. Using the double-sided tape, secure the wires to the inside of the egg, ensuring that the exposed metal wires are not covered by the tape. Place several more pieces of the double-sided tape on the inside of the plastic egg to hold the aluminum foil in place.
  3. Cut a piece of aluminum foil that is larger than the width of the plastic egg (this was done offscreen of the video above). Push the aluminum foil into and against the sides of the egg. Using scissors, trim the aluminum foil so that no foil sticks out over the edge of the egg. Push the edges of the aluminum foil away from the edges of the egg to ensure that there is a gap between the aluminum foil pieces when the egg is closed. The gap must be around the entire inner circumference of the egg for the nanogenerator to work.
  4. Wrap the bouncy ball with the clear office tape. The ball should be completely covered in clear office tape, using the least amount possible to ensure free movement of the ball inside the egg.
  5. OPTIONAL – If you have a digital voltmeter, measure the voltage output of the nanogenerator by connecting the voltmeter leads to the wires of the nanogenerator.
  6. Insert the LED into the wire jumpers outside the egg. The egg will be shaken, so ensure this connection is secure.
  7. Insert the LED into the black straw (trimmed to size offscreen) just enough to cover the bulb and secure the LED.
  8. Shake the egg back and forth, transferring the ball from one half of the egg to the other. Each time the ball hits one side of the egg, the LED should blink on.

Discussion

What is powering the LED? Where does the energy that produces the light come from?

Triboelectric nanogenerators take advantage of the triboelectric effect to produce useful electricity. In this device, the tape covering the ball is capable of “stealing” electrons from the aluminum foil on the inside of the egg. When the egg is shaken, the tape-covered-ball takes electrons from one side of the egg and brings them to the other side, creating a charge imbalance between the two halves, which we call a voltage. This voltage is applied to a small circuit (the wires and LED), causing the LED to blink on.

The energy that produces the light comes from you, the user! Shaking the egg requires kinetic energy, which this devices converts into electrical energy that flows through the LED, producing light.

Observe the brightness of the LED when shaking the egg in different orientations and movements. Are there any differences between methods of shaking? Do you observe any differences when you switch the leads connected to the LED?

The side of the egg that causes the LED to blink will depend on the orientation of the LED, such that reversing the leads of the LED will cause the opposite side of the egg to turn the LED on. Drawing a diagram of the nanogenerator can help clarify how the device works.

Make multiple TENGs with different combinations of materials. Try using copper or nickel foil instead of aluminum. Try FEP (fluorinated ethylene propylene) or PTFE (polytetrafluoroethylene) or any other household tape instead of the clear office tape. Which combinations of materials work, and how well? Can you use the triboelectric series to predict the effectiveness of different materials?

Make TENGs of other shapes and sizes. Look around for other hollow objects to use instead of an egg, such as a wiffle ball. Try using different sizes of bouncy ball, or even multiple balls. Can you find any relation between shell-to-ball size and effectiveness? Are there any shapes of outer shell that work better or worse than the egg shape? 

The reason that the TENGs produce electricity to light up the LED is because the friction between the two materials produces a charge separation (tribo is a prefix meaning friction or rubbing). The extent of charge separation is based on the materials chosen. Clear office tape (Scotch brand has a polyvinylchloride derived backing) and aluminum, for example, are far apart on the triboelectric series. As more surface area of the materials come into contact, there is more opportunity for charge separation, which means more triboelectricity. Therefore, for this geometry for TENG, the largest possible ball that can still move freely within the shell maximizes the electricity production.

Scientists and engineers are using these concepts for real world applications of TENGs. Since maximizing surface area is key, increasing the surface area to volume ratio will maximize electricity production efficiency. The smaller the TENGs are, the more efficient they are for their size. One day these energy harvesters could be used to power your phone from the movement of your body, or used in implanted medical devices to eliminate the need for batteries and subsequent replacement. What uses can you think of for these devices?

References

  1. Saurabh Rathore, S. S., Bibhu P Swain, Ranjan Kr Ghadai. (2018). “A Critical Review on Triboelectric Nanogenerator.” IOP Conference Series: Materials Science and Engineering, 377(012186).
  2. Yao, C., Hernandez, A., Yu, Y., Cai, Z., and Wang, X. (2016). “Triboelectric nanogenerators and power-boards from cellulose nanofibrils and recycled materials.” Nano Energy, 30, 103-108.
  3. Zhang, X.-S., Su, M., Brugger, J., and Kim, B. (2017). “Penciling a triboelectric nanogenerator on paper for autonomous power MEMS applications.” Nano Energy, 33, 393-401.
  4. Long, Y., Wei, H., Li, J., Yao, G., Yu, B., Ni, D., Gibson, A. L. F., Lan, X., Jiang, Y., Cai, W., and Wang, X. (2018). “Effective Wound Healing Enabled by Discrete Alternative Electric Fields from Wearable Nanogenerators.” ACS Nano, 12(12), 12533-12540.