First-Principles Models of Triboelectrification.

Environmental degradation and the depletion of fossil fuels have emerged as pressing issues that must be addressed for progressing sustainable life. Reducing the usage of the fossil fuels and exploring different eco-friendly resources and energy are in highly valued. The abundant mechanical energy is the most promising source of accessible alternative energy in our daily lives. Harvesting energy from bodily movements such as running, jogging, shaking, and so on enabled to power low-power electronics using nanogenerators (NGs) and has recently emerged as an important area of study due to their diverse applicability in practical scenarios. To obtain highest mechanical energy optimization and greater voltage outputs from NGs, scientists all over the globe have put forward potential options of hybrid NGs with numerous and unique designs utilizing a combination of more than one of the following pyroelectric, triboelectric, piezoelectric, thermoelectric, and other NGs. In large-scale operations, hybridization of NGs has proven to be an effective approach for mechanical energy harvesting and sensing applications. This book chapter focuses on major types of NGs for energy harvesting, such as piezoelectric NG (PENG), triboelectric NG (TENG), and hybrid NGs. The emphasis is primarily on the fundamental working mechanisms of three types of NGs, newly developed materials, and typical applications for energy harvesting in fields such as wearable and human monitoring, implementable devices, and artificial intelligence. Finally, we summarize recent advancements in this field and describe future opportunities for improving energy harvester performance.

With the rapid development of the Internet of Things (IoT), the number of sensors utilized for the IoT is expected to exceed 200 billion by 2025. Thus, sustainable energy supplies without the recharging and replacement of the charge storage device have become increasingly important. Among various energy harvesters, the triboelectric nanogenerator (TENG) has attracted considerable attention due to its high instantaneous output power, broad selection of available materials, eco-friendly and inexpensive fabrication process, and various working modes customized for target applications. The TENG harvests electrical energy from wasted mechanical energy in the ambient environment. Three types of operational modes based on contact-separation, sliding, and freestanding are reviewed for two different configurations with a double-electrode and a single-electrode structure in the TENGs. Various charge transfer mechanisms to explain the operational principles of TENGs during triboelectrification are also reviewed for electron, ion, and material transfers. Thereafter, diverse methodologies to enhance the output power considering the energy harvesting efficiency and energy transferring efficiency are surveyed. Moreover, approaches involving not only energy harvesting by a TENG but also energy storage by a charge storage device are also reviewed. Finally, a variety of applications with TENGs are introduced. This review can help to advance TENGs for use in self-powered sensors, energy harvesters, and other systems. It can also contribute to assisting with more comprehensive and rational designs of TENGs for various applications.

Performance of piezoelectric and triboelectric transducers under gait loading for energy harvesting and load monitoring in total knee replacements.

With the growing demand for sustainable energy solutions and self-powered sensing devices, triboelectric nanogenerators (TENGs) have gained considerable attention due to their ability to efficiently convert mechanical energy into electricity with the advantages of simple structure and cost-effectiveness. Among several key factors affecting the performance of TENGs, interfacial polarization has emerged as a promising route to enhance surface charge density and triboelectric output. This perspective discusses the principles of interfacial polarization in dielectric-based TENGs and explores four key strategies for leveraging interfacial polarization to improve triboelectric device efficiency. First, we examine how controlled polymer chain alignment and dipole orientation at material interfaces create optimized pathways for charge transfer. Second, we introduce engineered nanostructures and strategic material compositions that amplify local electric fields through enhanced interfacial polarization effects. Third, we highlight the impact of layered architectures with precisely controlled phase boundaries, enabling superior charge accumulation at interfaces. Fourth, we discuss how systematic optimization of bulk material properties and device geometries contributes to improved overall device efficiency. By integrating these approaches, we establish comprehensive design principles for maximizing interfacial polarization in triboelectric devices. Additionally, we highlight emerging applications enabled by controlled polarization, including self-powered sensors, wearable electronics, and energy harvesting systems. Finally, we address key challenges in understanding and controlling interfacial phenomena, and propose future research directions for next-generation TENGs through interfacial engineering.

Highly electronegative borophene/PVDF composite hybrid nanofibers based triboelectric nanogenerator for self-powered sensor for human motion monitoring and energy harvesting from rain

Energy harvesting technologies, which scavenge and capture various types of abandoned energies from an ambient environment, have grown more comprehensive and crucial as they play a role to power the emerging mobile electronic systems and micro devices. Lots of energy harvesting technologies have been successfully demonstrated and explored based on photovoltaic effect, piezoelectric effect, electromagnetic effect and so forth. Recently, the eminent concept of the triboelectric nanogenerator (TENG), where operation mechanism is coupling of triboelectricity and electrostatic induction, has been proposed. The TENG is mainly composed of 1) the contact layer, where the triboelectric effect occurs, and 2) the electrode layer inducing movement of the electrical charges to generate electric current and power. Since its first demonstration, the TENG has been proven as one of the promising energy harvesting platforms due to its high accessibility, low manufacturing cost and high energy conversion efficiency compared with the other existing energy harvesting platforms. With those advantageous aspects, so far, the TENG has been widely applied to versatile applications such as biomedical monitoring system, self-powered sensor and portable power supply to drive wearable electronics. As above mentioned, although lots of potential applications of TENGs have been successfully demonstrated, for their reliable utilization as a practical power source, the electrical output performance of TENGs still needs to be further increased. From this point of view, enhancing the electrical output performance of the TENG has been one of the important issues in research fields from its first proposal to present. The simplest and most powerful way to enhance the electrical output performance of the TENG is based on formation of micro/nanoscale surface topographies on its contact layer inducing localized concentration of contact forces, which generates higher electrical charge amounts on its surface. As well as formation of topographies on its external surface, recently, the concept of modifying internal molecular arrangement has been suggested. For example, the synthesis of material where important derivatives are carbon increased the interface for charge storage by acting charge trapping sites. On top of that, the alignment of positive and negative charges referred to as poling process has been reported. During this poling or dipolar alignment, a large electric potential is applied across the material which induces the alignment of dipole and production of net positive charge. To be detailed, the maximized surface charge and charge difference between upper and bottom surface of material can produce the developed electrical energy compared with that of non-aligned material. In this respect, it has been considered as a potent strategy to increase the energy output of the TENG. Previously, we reported the one-step simple method to fabricate the advanced energy output TENG by using nanoimprinting process. Through thermal nanoimprint process, there are obvious advantages in terms of increasing energy output of the TENG, and practical commercialization. Firstly, the energy output of the TENG can be enhanced due to the formation of nano topographies on the contact layer of thermoplastic fluoropolymer. Secondly, in viewpoint of commercialization, the thermal nanoimprint is one-step fabrication, with coincidently replication of nano structure and integration of contact later with the electrode layer which are essential prerequisite components of TENG. Besides these merits, low cost and mass producible nanofabrication process present the application of practical commercialization. In this study, we first introduced the innovative strategy which is coupling process between nano imprint and poling process to maximize the electrical energy output performance of TENG based on the formation of nano-topographical surface on contact layer and modulation of the internal dipole moments of ferroelectric thermoplastic polymer. The most remarkable novelties are shown that energy output of TENG can be enhanced by achieving the alignment of dipole moments of polymer while taking advantages of fabricating the TENG by using the nanoimprint process. In aspects of the modulation of internal moments, the degree of alignment dipole moments is higher than when the conventional poling method is used. Compared with the conventional poling process, the method we suggested has distinct advantages. Given that the flexibility of thermoplastic polymer increased due to the elevated temperature, the alignment of dipole moments can be achieved more effectively. In addition, the electric field concentrated on each nano structure contributes to obtain the high portion of dipole moments alignment due to their higher electric field in comparison with when the electrode which has no nano-topograpies on surface is used to poling process. Lastly, based on these effects, the overall poling period is much shorter than that of conventional poling. Figure 1

Effect of humidity and pressure on the triboelectric nanogenerator

Hydrogel-based triboelectric devices for energy-harvesting and wearable sensing applications

A self-powered mechanical energy harvesting system consists of the storage system and the energy scavenging TENG. Triboelectric nanogenerator includes a system which integrates a self-powered sensor and the power generator, this triboelectric nanogenerator has the potential to be used in a modern wearable electronic TENG. It has been reported that triboelectric nanogenerator working under complicated deformation like bending, stretching and twisting brings the main problem. Here we have fabricated the shape adaptive Triboelectric nanogenerator which solves all the deformation issues and can harvest the mechanical energy through human body motion in any deformation, the fabricated TENG is a self-powered sensor which can sense the different human activities and can monitor the health issues, the TENG stores the energy directly to the capacitor for powering the wearable electronics. A human skin based triboelectric nanogenerator was designed from the silicon rubber and the copper acetate-II used as the electrode, which makes the TENG flexible self-powered sensor, it can be stretched up to 200%. The stretchable nature and the flexibility of the human skin based silicon rubber triboelectric nanogenerator makes it the promising flexible and shape-adaptive energy harvesting TENG. The fabricated TENG generated the open circuit voltage 70 V and the short circuit current 11 μA and delivered the power 55 μW at the load of 80 MΩ. 42 LEDs were powered directly from the TENG. The fabricated TENG has human skin tactile property which does not harm the human skin while using it multiple times. The layer of copper acetate is completely coated with silicone rubber. The fabricated TENG is flexible, biocompatible and cost effective.

A one-structure-layer PDMS/Mxenes based stretchable triboelectric nanogenerator for simultaneously harvesting mechanical and light energy

Energy harvesting and power generation technologies hold significant potential for meeting future energy demands and improving environmental sustainability. A triboelectric nanogenerator (TENG), which harnesses energy from the surrounding environment, has garnered significant attention as a promising and sustainable power source applicable in various fields. In this study, we present a technique to improve the triboelectric performance of a PDMS-based TENG by incorporating nanostructured cadmium sulfide (N-CdS). This study investigates the utilization of CdS nanomaterials in TENG production, where mechanical energy is converted into electrical energy. We conducted a comparative analysis of TENGs utilizing N-CdS/PDMS, commercial CdS/PDMS (C-CdS/PDMS), and pure PDMS substrates. The N-CdS/PDMS substrates demonstrated superior triboelectric performance compared to TENG devices based on pure PDMS and C-CdS/PDMS. The triboelectric open-circuit voltage (Voc) and short-circuit current (Isc) of the N-CdS/PDMS-based TENG device were approximately 236 V and 17.4 µA, respectively, when operated at a 2 Hz frequency. These values were approximately 3 times and 2.5 times higher, respectively, compared to the pure PDMS-based TENGs. They were further studied in detail to understand the effect of different parameters such as contact-separation frequency and contact force on the TENGs' operation. The stability of the TENG devices was studied, and their potential to be integrated into self-powered smart textiles as power sources was demonstrated.

Hybrid harvesting of wind and wave energy based on triboelectric-piezoelectric nanogenerators

Electric-field energy harvesters (EFEHs) have emerged as a promising technology for harnessing the electric field surrounding energized environments. Current research indicates that EFEHs are closely associated with Tribo-Electric Nano-Generators (TENGs). However, the performance of TENGs in energized environments remains unclear. This work aims to evaluate the performance of TENGs in electric-field energy harvesting applications. For this purpose, TENGs of different sizes, operating in single-electrode mode were conceptualized, assembled, and experimentally tested. Each TENG was mounted on a 1.5 HP single-phase induction motor, operating at nominal parameters of 8 A, 230 V, and 50 Hz. In addition, the contact layer was mounted on a linear motor to control kinematic stimuli. The TENGs successfully induced electric fields and provided satisfactory performance to collect electrostatic charges in fairly variable electric fields. Experimental findings disclosed an approximate increase in energy collection ranging from 1.51% to 10.49% when utilizing TENGs compared to simple EFEHs. The observed correlation between power density and electric field highlights TENGs as a more efficient energy source in electrified environments compared to EFEHs, thereby contributing to the ongoing research objectives of the authors.

A high-performance triboelectric nanogenerator (TENG) has been developed for breath sensing applications, utilizing tribopositive electrospun nylon-6 nanofibers and tribonegative fluorinated ethylene propylene (FEP). The optimization toward the development of electrospun nylon-6-based TENG includes a range of factors such as the applied force and frequency on tribo responses, the thickness of the fiber mat, the concentration of nylon-6 in the fiber mats, and the selection of the tribonegative material for pairing with nylon-6 nanofiber. Among these parameters, the nanofiber prepared with 18 wt% nylon-6, characterized by a uniform fiber distribution, the highest surface area of 55.69 m2 g−1, and an optimal thickness of 0.169 mm, demonstrated excellent TENG performance, among others. The TENG module constructed using nanofiber in a 4 cm2 area showed the TENG responses of more than 30 μA short-circuit current, 200 V open-circuit voltage, and 90 nC charge when hand-pressed. It achieved a substantial power density of 890 mW m−2 at 20 MΩ by applying a constant force of 10 N at a 10 Hz frequency. Charging a 1 μF capacitor to approximately 30.1 V in just 30 s highlights the potential of electrospun nylon-6 as a promising material for nanogenerator energy harvesting and sensing applications. The TENG device was found to be sufficient to power small, portable electronics such as LEDs and digital watch displays. A wearable belt was fabricated to showcase its breath-sensing capabilities by pairing it with FEP. The microcontroller connected to the TENG in the wearable belt is used to analyze the output produced through breathing patterns, subsequently activating a buzzer and LED by the nature of the breathing.

The developments of natural biomaterials‐based triboelectric nanogenerators (TENGs) have been emerged with the extensive and promising requirements in biomedical and biowearable fields due to the properties of renewability, cost‐effectivity, biocompatibility, and biodegradability. In this work, a flexible, recyclable, and high‐performance pullulan‐based TENG, fabricated with pullulan and other additives, is developed. Based on the open‐circuit voltage, the thickness and the additives of pullulan‐based TENGs are optimized. The maximum open‐circuit voltage, 79 V, under 10 Hz motion frequency and 10 W loading power is obtained in the NaF‐pullulan TENG. And the optimal output power density is 41.7 mW m−2 under 7 MΩ loading resistance. Then, practical applications of the as‐fabricated pullulan‐based TENGs on lighting LED arrays and monitoring hand bending movements are successfully investigated, presenting the feasibility of powering electric devices and acting as wearable devices. Finally, the excellent recyclability of the P‐P film is illustrated by the excellent TENG performance within five‐times recycles. Thus, the recyclability and facile fabrication procedures of the pullulan‐based TENGs could provide a potential prospect in the next‐generation biowearable devices and energy harvesters.