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

Triboelectric nanogenerators (TENGs) are electronic devicescapableof harvesting low-frequency mechanical motions to produce electricalenergy through the triboelectrification effect. A great number ofelectronic devices, such as wearable devices, implantable medicaldevices, and monitoring sensors, among others, use conventional powersources such as batteries and capacitors. They are usually toxic,nondegradable, and hard to recycle, representing human and environmentalhazards. In addition, conventional batteries and capacitors are usuallyrigid, heavy, and not suitable for the fabrication of portable andflexible devices. TENGs appear as a promising option to be used inthe 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 surfacesthat store charge. Bio-TENGs have been fabricated using biopolymerssuch as cellulose, silk, and chitosan. These Bio-TENGs take advantageof the inherent biodegradability and biocompatibility of biopolymers.In order to improve the capability of biopolymer-based surfaces tostore electrostatic charge, several treatments are reported, includingthe incorporation of nanoparticles and surface treatments. These biopolymer-basedactive surfaces with improved properties allow Bio-TENGs to achieveoutput performances similar to those reported for synthetic TENGs.Bio-TENGs have been used in a wide range of applications, such ashuman monitoring systems, tissue engineering, electronic devices,and industrial-level flooring, among others. This review is focusedon the development of Bio-TENGs. The different types of biopolymersused for the fabrication of active surfaces are described and classifiedas protein-based, polysaccharide-based, and synthetic-based biopolymers.The different strategies used for improving the triboelectric propertiesof biopolymer-based surfaces are presented, along with the resultingoutput performance of Bio-TENGs. The reported applications for theseBio-TENGs are also discussed.