(Invited) Triboelectric Nanogenerators Harvesting (Bio)Mechanical Energy for Self-Powered Systems

The fundamental science and applicable technologies for harvesting environmental energy are not only essential in realizing the self-powered systems, but also tremendously helpful in meeting the rapid-growing world-wide energy consumptions. Mechanical energy is one of the most universally-existing, diversely-presenting, but usually-wasted energies in the natural environment. The triboelectric effect is a universal phenomenon that can generate electrostatic charges from mechanical contact. Here, a new type of technology—triboelectric nanogenerators (TENGs)—has been developed to efficiently convert mechanical energy into electricity, based on the coupling of triboelectrification and electrostatic induction. In order to develop TENGs of different structural designs for harvesting various types of mechanical energies existing in the natural environment, we established three basic modes/mechanisms of TENGs that serve as the basis for most of the TENG structures: (1) vertical contact-separation mode [1]; (2) lateral sliding mode [2]; (3) freestanding-triboelectric-layer based mode [3]. All of the three modes of TENGs are shown to be effective electrical sources that are capable of generating a voltage over hundreds of volts and a power density larger than 10 W/m2, and also instantaneously driving hundreds of electronic devices (such as LEDs). Based on these fundamental modes, a number of different structural designs for harvesting different types of mechanical energy have been developed. For the storage of the electricity generated by triboelectric nanogenerators, we further developed the self-charging power unit (SCPU) by hybridizing a TENG with a flexible Li-ion-battery into as a single device, which allows a battery to be charged directly by ambient mechanical motion. This physical hybridization enables a new operation mode: the “sustainable mode”, in which the environmental mechanical energy is scavenged to charge the battery while the battery keeps driving an external load. In this mode, the demonstrated SCPU can provide a continuous and sustainable DC current at a stable voltage for as long as there is mechanical motion/agitation. It can be used to continuously drive a UV sensor for extended period of time. Thus, the SCPU can serve as an independent and sustainable power unit, which will meet the general requirement of almost any electronic device. [4] This technology has shown the potential to utilize (bio)mechanical energy to realized self-powered systems. [1] Wang, S. H.; Lin, L.; Wang, Z. L. Nano Lett. 2012, 12, 6339-6346. [2] Wang, S. H.; Wang, Z. L. et al. Nano Lett. 2013, 13, 2226-2233. [3] Wang, S. H.; Wang, Z. L. et al. Adv. Mater. 2014, 26, 2818-2824. [4] Wang, S. H.; Wang, Z. L. et al. ACS Nano 2013, 7, 11263-11271.