Triboelectric nanogenerators are an emerging panacea for sustainable energy generation. They convert random and irregular mechanical energy into usable electrical energy. Triboelectric nanogenerators are offering new solutions to satisfy global energy needs. In fact, large-scale triboelectric nanogenerators in the range of a few km2 have been proposed for large scale harvesting of electricity from random, oscillatory ocean waves at a megawatt scale via the blue energy paradigm. In addition to macroscopic energy production and feasible grid integration at the megawatt scale, scale-scale triboelectric nanogenerators in the range of a few mm2 to cm2 are important for powering LEDs, wearable technologies, transportation monitoring, pressure sensors, and security detection systems.
In the vertical contact mode triboelectric nanogenerators, a force is applied to bring two electrodes separated by insulating spacers into a frictional contact. The electron clouds shared between these electrodes redistributes unevenly consistent with their differences in electronegativity and the contact area when the force is released. This generates an electrical potential that could be harvested in the form of electrical energy implementing an external circuit. For this reason, the overall energy produced by triboelectric nanogenerators is dictated by the contact area between the electrodes and the electro positivity and negativity between the electrodes.
Using electrode materials ranked far apart in the triboelectric series can maximize the potential difference and increasing the contact area via nanopatterning can improve discharge. Researchers at the Clemson Nanomaterials Institute led by graduate student Sai Sunil Mallineni and Prof. Ramakrishna Podila demonstrated a top-down method for fabricating low cost as well as ultra-simple triboelectric nanogenerators implementing off-the-shelf materials for proliferation into the present energy landscape. Their research work is published in Nano Energy.
“To facilitate large-scale production of inexpensive triboelectric generators, we used commercially mature technologies such as indium-tin oxide coated polyethylene terephthalate as the top and bottom electrodes,” explained Sai Sunil Mallineni, first author of the Nano Energy article. The researchers applied four Pyrex insulation spacers to separate the electrodes with an air gap to convert waste mechanical energy into electricity.
The fundamental principle of the study was to come up with a low cost and scalable fabrication of ultra-simple triboelectric nanogenerators implementing commercially available indium-tin oxide coated polyethylene terephthalate as well as Kapton electrodes. Under a vertical pushing force of 50N at 2Hz, the authors recorded a maximum output voltage of 480V and an output power of 1.7mW.
The calculated power density of the developed devices was ~ 0.5 W/cm2 that lasted for over 20,000 cycles and proved sufficient to power red and green LEDs, charge capacitors, and intermittently operated an 8-digit calculator. In addition, the ultra-simple triboelectric nanogenerator was versatile considering that it maintained a steady output voltage of about 480V at temperatures of 60 °C.
“Our triboelectric generator is robust and flexible. We can put it under walkways, and as people walk past, you can harvest energy. You can even integrate this into a T-shirt, so that as you’re walking, it’s rubbing against your skin, there’s wind blowing against you and you can use that energy to light up LEDs,” Prof. Podila said.
The Ultra-simple triboelectric nanogenerator developed in their study was inexpensive to develop and could be scaled up easily for industrial applications in the harvesting of electrical energy from any mechanical motion.
Sai Sunil Kumar Mallineni, Herbert Behlow, Yongchang Dong, Sriparna Bhattacharya, Apparao M. Rao, Ramakrishna Podila. Facile and robust triboelectric nanogenerators assembled using off-the-shelf materials. Nano Energy, volume 35 (2017), pages 263–270.
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