A Review on the Development of Biopolymer Nanocomposite-Based Triboelectric Nanogenerators (Bio-TENGs)

Triboelectric nanogenerators (TENGs) are electronic devices capable of harvesting low-frequency mechanical motions to produce electrical energy through the triboelectrification effect. A great number of electronic devices, such as wearable devices, implantable medical devices, and monitoring sensors, among others, use conventional power sources such as batteries and capacitors. They are usually toxic, nondegradable, and hard to recycle, representing human and environmental hazards. In addition, conventional batteries and capacitors are usually rigid, heavy, and not suitable for the fabrication of portable and flexible devices. TENGs appear as a promising option to be used in the development of light, portable, and self-powered electronic devices. TENGs were first developed using synthetic polymers such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), polydimethylsiloxane (PDMS), and polyimide (Kapton) for the fabrication of the active surfaces that store charge. Bio-TENGs have been fabricated using biopolymers such as cellulose, silk, and chitosan. These Bio-TENGs take advantage of the inherent biodegradability and biocompatibility of biopolymers. In order to improve the capability of biopolymer-based surfaces to store electrostatic charge, several treatments are reported, including the incorporation of nanoparticles and surface treatments. These biopolymer-based active surfaces with improved properties allow Bio-TENGs to achieve output performances similar to those reported for synthetic TENGs. Bio-TENGs have been used in a wide range of applications, such as human monitoring systems, tissue engineering, electronic devices, and industrial-level flooring, among others. This review is focused on the development of Bio-TENGs. The different types of biopolymers used for the fabrication of active surfaces are described and classified as protein-based, polysaccharide-based, and synthetic-based biopolymers. The different strategies used for improving the triboelectric properties of biopolymer-based surfaces are presented, along with the resulting output performance of Bio-TENGs. The reported applications for these Bio-TENGs are also discussed.