Impact of PVDF and its copolymer-based nanocomposites for flexible and wearable energy harvesters

Encountering the consumption of fossil fuels on a large scale and contamination of the environment due to chemical batteries, along with the rapid growth of various wearable devices and IoT-enabled devices, researchers are urged to discover lightweight, flexible, biocompatible wearables which can be self-powered. Currently, flexible piezoelectric, triboelectric and hybrid nanogenerators are good power sources to integrate into self-powered wearable devices that can even monitor human health conditions. PVDF and its copolymers are widely used materials in self-powering wearable technology, as it is flexible, biocompatible, easily processable and is of low cost. PVDF has five crystalline phases, among them the β phase has strong electroactive and piezoelectric properties. Several attempts have been made to enhance the β phase of PVDF by incorporating different nanofillers for implementation in energy harvesting applications. This review focuses on the recent advancements in energy harvesting by using various additives like Mxene, ZnO, hBN, TMDCs and QDs. Mxene has superb mechanical properties that include good bending stiffness, good Young’s modulus, high thermal conductivity, absorptivity, intrinsic hydrophilicity etc. ZnO is a piezoelectric material with good electrical, chemical, thermal stabilities and optical as well as photocatalytic properties. It is a less toxic material with good resistance against microbes. hBN is an electrical insulator which possess good thermal conductivity, is transparent to visible light and exhibits a high Young’s modulus of ∼1TPa. TMDCs are non-toxic materials with an ultrathin structure and good surface area to mass ratio, exhibiting good mechanical, optical and electronic properties. The current review briefly discusses the deformation sensing mechanism, various methods of β phase enhancement in PVDF, fabrication of PVDF based energy harvesting devices and material selection criteria of nanofillers. A dedicated section is presented for humidity sensors as wearable devices are prone to sweating conditions. The authors hope this review brings a general understanding of PVDF and its copolymer-based nanocomposites for flexible and wearable energy harvesters.