Development and Applications of Hydrogel-Based Triboelectric Nanogenerators: A Mini-Review

Abstract

In recent years, with the appearance of the triboelectric nanogenerator (TENG), there has been a wave of research on small energy harvesting devices and self-powered wearable electronics. Hydrogels—as conductive materials with excellent tensile properties—have been widely focused on by researchers, which encouraged the development of the hydrogel-based TENGs (H-TENGs) that use the hydrogel as an electrode. Due to the great feasibility of adjusting the conductivity and mechanical property as well as the microstructure of the hydrogels, many H-TENGs with excellent performance have emerged, some of which are capable of excellent outputting ability with an output voltage of 992 V, and self-healing performance which can spontaneously heal within 1 min without any external stimuli. Although there are numerous studies on H-TENGs with excellent performance, a comprehensive review paper that systematically correlates hydrogels’ properties to TENGs is still absent. Therefore, in this review, we aim to provide a panoramic overview of the working principle as well as the preparation strategies that significantly affect the properties of H-TENGs. We review hydrogel classification categories such as their network composition and their potential applications on sensing and energy harvesting, and in biomedical fields. Moreover, the challenges faced by the H-TENGs are also discussed, and relative future development of the H-TENGs are also provided to address them. The booming growth of H-TENGs not only broadens the applications of hydrogels into new areas, but also provides a novel alternative for the sustainable power sources.

Boosting Contact Electrification by Amorphous Polyvinyl Alcohol Endowing Improved Contact Adhesion and Electrochemical Capacitance

“…It is shown that when film made from hydrogels are used as active tribomaterial, their triboelectrification efficiency increases upon ionic doping. [16,[30][31][32][33] Ionic conductive hydrogels encased into an impermeable tribomaterial scaffold as Ecoflex, [34][35][36] silicone (Si)-rubber, [37] or even scotch tape, [38,39] allow to fabricate transparent and flexible TENGs with improved time-stability. [40,41] In this device configuration, the hydrogel's ions migration toward the electrode is triggered by the contact electrification occurring at the elastomer external surface, and is responsible for the increased electrical double layer capacitance (EDLC) of the TENG's electrodes.…”

“…It is shown that when film made from hydrogels are used as active tribomaterial, their triboelectrification efficiency increases upon ionic doping. [ 16,30–33 ]…”

A “Square Box”-Structured Triboelectric Nanogenerator for Road Transportation Monitoring

“…Since it was first reported in 2012, the triboelectric nanogenerator (TENG) that can collect energy from the ambient mechanical energy has attracted widespread attention in the self-powered equipment field [1][2][3][4], owing to its unique advantages, such as simple design, Polymers 2022, 14, 2695 2 of 10 excellent output performance, and high integration [5,6]. The TENG can be broadly divided into four types: the vertical contact-separation mode [7][8][9][10], the sliding mode [11,12], the single electrode mode [13][14][15], and the freestanding triboelectric-layer mode [16,17], and the working principle of the TENG is a coupling of the triboelectric effect and electrostatic induction [18].…”