Triboelectric Nanogenerator: A Foundation of the Energy for the New Era

Hybrid Energy-Harvesting Systems Based on Triboelectric Nanogenerators

For the development of the internet of things (IoTs), big data, and artificial intelligence, widely distributed sensing network is the most essential element, which has to be driven by the energy storage unit, with a limited lifetime and environmental concerns. Given that the wide distribution and high mobility of these numerous sensors, the success of the IoTs and sustainable development of human society call for renewable distributed energy sources. Since triboelectrification effect is ubiquitous and universal in our living environment, the triboelectric nanogenerator (TENG) for mechanical energy harvesting and self‐powered sensing developed by Wang and co‐workers is one of the best choices for this energy for the new era. In this review, the recent progress of TENGs from fundamental theory to practical applications is systematically summarized. First, the mechanism of contact electrification, first principle theory, working principle, working modes, and figure of merits of the TENG are introduced. Furthermore, recent important progress in four major TENG applications, including micro/nano power sources, active self‐powered sensors, large‐scale blue energy, and direct high‐voltage power sources are reviewed. In the end, some perspectives and challenges for the future development of TENG are also discussed.image

The Beijing Institute of Nanoenergy and Nanosystems (BINN), Chinese Academy of Sciences, was founded in 2012 by Wang. The mission of BINN is to carry out fundamental research related to nanoenergy and nanosensors as well as train future scientists. The two major areas of BINN's research are nanogenerators for self-powered systems and blue energy and piezotronics and piezo-phototronics for third-generation semiconductors. After 7 years of development starting from scratch, BINN now has about 400 members including graduate students. This special issue published in Advanced Functional Materials showcases a group of selected papers submitted by colleagues at the BINN to represent some of the on-going research in the institute. Based on piezoelectric and triboelectric effects, nanogenerators represent a new approach that converts tiny mechanical energy into electric power, which now has attracted worldwide attention, particularly in the era of Internet-of-things, sensor networks, artificial intelligence, and robotics. Piezoelectric nanogenerators (PENGs) were first invented in 2006 using the piezoelectric effect obtained from nanowire materials. The triboelectric nanogenerator (TENG) was first invented in Wang's group in 2012 by using a conjunction of contact-electrification and electrostatic induction effects. TENGs have quickly gained worldwide attention and now comprise a new field of research that involves fundamental physics, chemistry, materials, electric engineering, and mechanical engineering. Nanogenerators have shown very broad applications in different fields. Firstly, they serve as the micro-power source for wireless distributed mobile/wearable electronics, Internet-of-things, sensor networks, and implantable medical electronics, which require a tremendous amount of mobile power sources, and in many cases, the batteries could not completely satisfy the practical requirements in terms of size, capacity, flexibility, or non-replaceable in vivo. Secondly, nanogenerators can serve as a self-powered sensor (or active sensor) for detecting mechanical triggering, pressure fluctuation, and environmental stimulation without requiring external power being supplied to the sensor tip, which thus possesses great potential for human-machine interfacing, security systems, physiological characterization, and infrastructure monitoring. They also have applications in smart skin, robotics, MEMS, and biomedical science among other fields. Lastly, nanogenerators can be a possible approach for harvesting large-scale energy from ocean waves. By constructing units that are the size of a baseball, inside which the TENGs are installed, millions or even billions of such units can be interconnected into a “fishing net,” which can float on the water surface for harvesting the kinetic energy. This technology has the merits of low cost, light weight, high efficiency, high output power density, and easy scaling, leading towards the dream of “blue energy”, the energy from the ocean. Piezotronics is a term coined by Wang in 2007, which involves using the piezoelectric effect to control electronics via mechanical stimuli. For wurtzite structures that have non-central symmetry, such as ZnO, GaN, and InN, piezoelectric polarization charges are created at the interface/surface by applying a strain. The strain created inner-crystal piezopotential can serve as a “gate voltage” that can effectively tune/control the charge transport across an interface/junction. This mechanism is termed the piezotronic effect and the electronics fabricated based on such a mechanism is coined as piezotronics, with applications in force controlled electronic devices, sensors, logic units, memories, and catalysts. Analogically, new electronic components can be fabricated as well by using the electric potential created by contact-electrification as a gating voltage, which is called tribotronics. The presence of polarization charges at a p-n junction can effectively distort the local band structure and consequently affect carrier transport, separation, or recombination. Applying either a compressive or tensile strain depending on the polarization of the piezoelectric material, the efficiency for charge carrier separation or recombination can be effectively enhanced. The combination of photon excitation, coupling among semiconductors, photon excitation, and piezoelectricity represents a new field of research called piezo-phototronics. The piezo-phototronic effect is the tuning and controlling of charge carrier generation, separation or recombination at a heterojunction by the strain induced piezoelectric polarization charge. This effect could lead to tremendous performance gain in LEDs, laser diodes, photodetectors, photovoltatic devices, and catalysis by applying static or quasi-static mechanical strains. The fields of research conducted at BINN can be summarized using a “science tree” (Figure 1) to project its main “trunk”, major fields, and applications. The main trunk is based on functional materials and fundamental physics effects, which leads to new and innovative fields. The major fields of research are self-powered systems, triboelectric nanogenerators, hybridized nanogenerators, blue energy, tribotronics, piezotronics, and piezo-phototronics, which are in the middle of the tree. The small branches are the potential applications, as well as future perspectives. We anticipate this tree will grow fast and expand quickly with abundant fruits in the near future.

Triboelectric nanogenerators (TENGs) play a crucial role in attaining sustainable energy for various wearable devices. Polymer materials are essential components of TENGs. Biopolymers are suitable materials for TENGs because of their degradability, natural sourcing, and cost-effectiveness. Herein, the latest progress in commonly used biopolymers and well-designed biomimetic techniques for TENG is summarized. The applications of natural rubber, polysaccharides, protein-based biopolymers, and other common synthetic biopolymers in TENG technology are summarized in detail. Each biopolymer is discussed based on its electrification capability, polarity variations, and specific functionalities as active and functional layers of TENGs. Important biomimetic strategies and related applications of specific biopolymers are also summarized to guide the structural and functional design of TENG. In the future, the study of triboelectric biopolymers may focus on exploring alternative candidates, enhancing charge density, and expanding functionality. Various possible applications of biopolymer-based TENGs are proposed in this review. By applying biopolymers and related biomimetic methods to TENG devices, the applications of TENG in the fields of healthcare, environmental monitoring, and wearable/implantable electronics can be further promoted.

Triboelectric nanogenerators (TENGs) have been gaining significant attention owing to their excellent energy conversion efficiency and their integration towards a large number of practical applications in energy harvesting, wearables, and self-powered sensing. In recent advancements, the utilization of flexible triboelectric composite films can help to enhance the TENG's electrical output performance, as they possess excellent mechanical and dielectric properties and tunable surface characteristics. Moreover, by combining flexible active layers with triboelectric nanogenerators, the advantages of each component result in sensor devices which offer superior characteristics, including high sensitivity, biocompatibility, less weight, and mechanical flexibility. This review mainly focuses on the applications of TENGs in mechanical energy harvesting, self-powered wearable sensor systems, as well as the latest research progress in the TENG field. The working principles of TENG will be first explained in detail, including four basic operational modes of TENG, simulation results, and the working mechanism of the contact-separation mode TENGs. The fabrication techniques of triboelectric flexible films, along with TENG construction, will then be introduced. Common applications of TENGs are based on mechanical energy harvesting and powering portable electronic devices, which will subsequently be classified and summarized. Additionally, the applications of various wearable and self-powered sensor applications are elucidated. Finally, the current limitations and future directions of the TENG will be explained in detail and proposed. By exploring these innovations, the review underscores the importance of triboelectric flexible film-based TENGs in driving the future of energy harvesting and sensor technologies.

Triboelectric nanogenerator module for circuit design and simulation

The major aim of this study is to provide a broad review of the fundamental ideas, progress, and utilization of triboelectric nanogenerators (TENGs). The modes and operations of numerous triboelectric nanogenerator configurations along with applications and materials are also discussed. Triboelectric nanogenerators, a ground-breaking power production technology, were unveiled in 2012 and classified as one of the most effective generators to convert unused mechanical energy into electrical energy to run a wide range of devices. Triboelectric nanogenerators have made significant progress since the creation of this novel power-generation technology. The operating principles of various modes, such as freestanding triboelectric-layer, single-electrode, lateral sliding, and vertical contact-separation have also been carefully investigated in order to give readers a deeper understanding of the technology. The key applications of TENGs, such as high voltage power supply, blue energy, self-power sensors, and micro/nano-energy, are also described in this work along with concepts for further research. As a result, triboelectric nanogenerators are very important and attractive technology with advantages of low cost, straightforward construction, simple fabrication, high efficiency, and relatively high output performance. Wide range of material choice allows researchers to use the technology in many configurations with multiple applications. Numerous scientific modeling and analysis are also reviewed for a more solid understanding of this revolutionary and unique technology.

Triboelectric nanogenerators (TENGs) are a kind of mechanical energy harvester with a larger force sensing range and good energy conversion, which is often applied to human kinetic energy collection and motion sensing devices. Polymer materials are the most commonly used materials in TENGs’ triboelectric layers due to their high plasticity and good performance. Regarding the application of TENGs in insoles, research has often used brittle Teflon for high output performance together with hard materials, such as springs, for the mechanism to maintain its stability. However, these combined materials increase the weight and hardness of the insoles. Here, we propose a polyethylene terephthalate (PET)-based TENG with a micro-needle polydimethylsiloxane (PDMS) elastomer, referred to as MN-PDMS-TENG, to enhance performance and maintain comfort flexibility, and structural stability. Compared with a flat PDMS, the TENG with a microstructure enhances the output open-circuit voltage (Voc) from 54.6 V to 129.2 V, short-circuit current (Isc) from 26.16 μA to 64.00 μA, power from 684 µW to 4.1 mW, and ability to light up from 70 to 120 LEDs. A special three-layer TENG insole mechanism fabricated with the MN-PDMS-TENG and elastic materials gives the TENG insole high stability and the ability to maintain sufficient flexibility to fit in a shoe. The three-layer TENG insole transforms human stepping force into electric energy of 87.2 V, which is used as a self-powered force sensor. Moreover, with the calibration curve between voltage and force, it has a sensitivity of 0.07734 V/N with a coefficient of determination of R2 = 0.91 and the function between force and output voltage is derived as F = 12.93 V − 92.10 under human stepping force (300~550 N). Combined with a micro-control unit (MCU), the three-layer TENG insole distinguishes the user’s motion force at different parts of the foot and triggers a corresponding device, which can potentially be applied in sports and on rehabilitation fields to record information or prevent injury.

Penciling a triboelectric nanogenerator on paper for autonomous power MEMS applications

Development of Triboelectric Sensors for IoT and Wearable Applications

Based on the conjunction of contact electrification and electrostatic induction, triboelectric nanogenerators (TENGs) can harvest mechanical energy dispersed in our environment. With the characteristics of simple structure, light weight, broad material availability, low cost, and high efficiency even at low operation frequency, TENG can serve as a promising alternative strategy for meeting the needs of distributed energy for the internet of things and network. The major potential applications of TENG can be summarized as four fields containing micro/nano power sources, self-powered sensors, large-scale blue energy, and direct high-voltage power sources. In this paper, the fundamental physics, output performance enhancement, and applications of TENGs are reviewed to timely summarize the development of TENGs and provide a guideline for future research.

Rolling friction contact-separation mode hybrid triboelectric nanogenerator for mechanical energy harvesting and self-powered multifunctional sensors

High-performance triboelectric nanogenerator with enhanced energy density based on single-step fluorocarbon plasma treatment

Triboelectric nanogenerators (TENGs) have been utilized in a wide range of applications, including smart wearable devices, self-powered sensors, energy harvesting, and high-voltage power sources. The surface morphology and structure of TENGs play a critical role in their output performance. In this review, we analyze the working mechanism of TENGs with the aim to improve their output performance and systematically summarize the morphological engineering and structural design strategies for TENGs. Additionally, we present the emerging applications of TENGs with specific structures and surfaces. Finally, we discuss the potential future development and industrial application of TENGs. By deeply exploring the surface and structural design strategy of high-performance TENGs, it is conducive to further promote the application of TENGs in actual production. We hope that this review provides insights and guidance for the morphological and structural design of TENGs in the future.

Electrochemical triboelectricity: A comprehensive survey of current research and future prospects