Using a synchronous switch to enhance output performance of triboelectric nanogenerators

Contact-mode triboelectric nanogenerators (TENGs) generally operate as a floating source with its two electrodes connected to an arbitrary external circuit forming a closed loop. In this work, a switch based contact-mode TENG (SW-TENG) is presented, wherein a switch is placed between a TENG electrode and an external circuit. By electrically isolating the TENG from the external circuit when the switch is open, charge leakage is prevented and the output performance of the TENG is enhanced while the transferred tribocharges per cycle remain the same. Effect of different switching frequencies while keeping the contact-separation frequency (fcs) and contact force constant at 1 Hz and 0.5 kgf, respectively, is presented. The versatility of the approach is presented via demonstrating the switching effect in three TENGs fabricated using different types of dielectric films – (a) bare polydimethylsiloxane (PDMS), (b) microdome patterned PDMS, and (c) PDMS-Carbon nanofiber (CNF) composite. When the switching frequency (fsw) is in sync with fcs, the output voltage is increased by a factor of up to 22, 17, and 90, in SW-TENGs made using samples (a), (b), and (c), respectively, compared to that obtained under typical TENG operation. In a 1 μF capacitor charging experiment, it has been shown that synchronous switching can prevent a charge leakage of up to approximately 60%. Further, a maximum area power density of 3.4 W cm−2, 20 W cm−2, and 31.7 W cm−2 is achieved at an external load resistance of 56 Ω, in SW-TENGs made using samples (a), (b), and (c), respectively. Compared with a typical TENG, the optimal load resistance is decreased by six orders of magnitude, from megaohms to ohms. The SW-TENG thus provides a new approach for mechanical energy harvesting.