Tapping 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. Please visit our page on triboelectricity to learn more. Triboelectric nanogenerators take advantage of the 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. For more resources go to our Inclusive Teaching Practices page.

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 shapes and modes of contact in addition to different types of tape, foil, paper, and other materials.

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

• Piece of paper (preferably sturdy paper like an index card)
• Aluminum foil
• Jumper wires or regular copper wires, stripped
• Transparent/Clear office tape
• Low amperage green LED, clear lens (green was the easiest to visualize)
• Scissors
• (Optional) Black straws (to help visualize the light from the LED) (0.21 or 0.25 inch diameter)

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. Cut two strips of paper out of your larger piece. You may find it easiest to cut the strips to about the width of the transparent office tape you are using. The paper strip should be about the same size as each other.
3. Create two aluminum foil strips, each as long as the paper strips, but narrower. The narrower aluminum foil strips will provide the tape access to the paper below, enabling us to connect the paper and aluminum foil with tape.
4. Place one exposed metal end of the wire between the paper and aluminum foil strips. Connect the aluminum foil strip to the paper strip with tape. The narrower aluminum foil should provide a place to tape on both sides so the layers stay together. You can also use a bit of tape to ensure that the wire doesn’t fall out of the device.
5. Repeat Step 4 with the other wire, aluminum foil strip, paper strip, and tape.
6. Slightly crease the two paper strips such that each bends the opposite way from the other. The strips in the device will need to naturally separate for the device to work.
7. With the paper strips in the same orientation as each other, place one on top of the other such that the strips will bend away from each other. Connect the two paper strips at the ends using tape.
8. 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.
9. Insert the LED into the black wire jumper ports.
10. Insert the LED into the black straw (trimmed to size offscreen) just enough to cover the bulb and secure the LED. Alternatively, move to a dark location for testing the device.
11. Tap on the device and release while looking at the top of the LED (the side opposite the LED legs). You should see the LED blink once for each time you do this. Depending on which way you connect your LED, you will either see the LED blink when the strips come together or when they push apart. What happens if you connect your LED the other way?

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 is capable of “stealing” electrons from the paper. When the device is tapped, the tape comes into contact with the paper, taking electrons in the process. When the strips separate, charges flow from one side to the other to achieve electrical equilibrium in the strips. When the strips come back together (from another tap) charges flow in the other direction to achieve electrical equilibrium again. We inserted an LED, so we’ll see a flash of light from one of these!

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

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

LEDs are a diode, which means they only allow electricity to flow in one direction. So, you’ll only see the LED flash once per tap and release, with the timing depending on how you connect your LED. 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. Try different types of paper, or another material to take its place. 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. Can you connect multiple TENGs together? Can you make a TENG that looks more like an accordion? 

The reason that the TENGs produce electricity to light up the LED is because the contact 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.

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.
5. Po-Kang Yang, Zong-Hong Lin, Ken C. Pradel, Long Lin, Xiuhan Li, Xiaonan Wen, Jr-Hau He, and Zhong Lin Wang. (2015). “Paper-Based Origami Triboelectric Nanogenerators and Self-Powered Pressure Sensors.” ACS Nano 9(1), 901-907. DOI: 10.1021/nn506631t