Energy Harvesting Based on TPU-Ecoflex/ZnO/MWCNT Triboelectric Nanogenerator

The triboelectric nanogenerator (TENG) is a device that converts mechanical energy into electricity using triboelectrification and electrostatic induction. TENGs use two different types of polymers, i.e., positive and negative triboelectric polymers. When these two polymers make physical contact, electrons transfer from the positive layer to the negative layer due to triboelectrification. Positive charges accumulate on the opposite side of the negative triboelectric layer, while negative charges accumulate on the opposite side of the positive layer. This accumulation of opposite charges creates a high potential difference between the triboelectric layers when they separate. To compensate for the triboelectric charges and maintain electrical equilibrium, electrons flow through an external circuit, generating electricity. TENG collects energy based on contact electrification at diverse interfaces, including solid-solid, liquid-solid, gas-solid, and gas-liquid. The charge transfer mechanism between interfaces can be explained by electron cloud potential model and electron double model. TENG harvests energy from sources such as human motion (stepping, running, elbow bending, and stretching), water, wind, and sound. The application of TENG focuses on energy harvesting and self-power touching sensors. Recently, its applications are expanding into wider research areas including biomedical to robotics.
For practical applications, TENGs must withstand environmental factors such as humidity, temperature, chemical exposure, and charge retention, etc. Besides, TENGs must have mechanical robustness after thousands of contact-separations cyclic loading without compromising their performances. To address these challenges, several steps have been taken into consideration including selecting triboelectric pairs having higher electron affinity difference, physical and chemical modifications, adding nanofiller and dielectric materials, and structural changes of TENGs, etc. Of them, adding nanofillers and dielectric materials are more interesting methods for fabricating TENG devices.
In this work, a tribo-pair, thermoplastic polyurethane (TPU) as positive layer and ecoflex 00-30 as negative layer have been chosen for the TENG fabrication. TPU has high tensile strength, durability, and self-healing ability in lower crystalline state at room temperature. In contrast, ecoflex 00-30 is a highly stretchable, flexible, and biocompatible polymer. Nanofillers such as ZnO, ZnTiO₃, and MWCNT will be added to increase the charges in the ecoflex 00-30 polymer. Adding nanofillers and dielectric materials to the tribo-layers will solve one of the key issues of charge retention in tribo-layers as well as enhance the output performance. The fabricated TENG will be tested for output performance for various loads/pressures. The effect of temperature and humidity on the TENG’s output will also be investigated. The generated electricity will be used to power up small electronic devices such LED bulbs, watches, and calculators. The application of TENG is diverse including energy generator to power up small portable device to health monitoring devices. Successfully fabricated and tuned TENG devices will open a door for high output performance towards harvesting mechanical energy.