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Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

With the advancement of internet of things and wireless sensing technology, the need for personnel track and position monitoring are greatly increasing. Commercial global positioning system (GPS) and Global system for mobile communications (GSM) position methods cannot meet the demand for low power consumption and three‐dimensional indoor position monitoring. Herein, a self‐powered position monitoring system (SPMS) based on an insole‐type wearable triboelectric nanogenerator (IW‐TENG) and Bluetooth beacon for human kinetic energy harvesting and sustainable position monitoring is proposed. The SPMS consists of an insole‐type wearable triboelectric nanogenerator, an energy management module (EMM), and a Bluetooth low energy (BLE) beacon module. Benefitting from the multilayers structure, a maximum energy of 120 µJ per step can be harvested by the IW‐TENG with EMM for a typical adult. By every 3–4 steps, SPMS can transmit Bluetooth signals to obtain the location information. A single BLE signal transmission consumes only 136 µJ, and the transmission distance can reach 100 m. The SPMS is applied to intelligent attendance in office rooms and shows great prospects in intelligent navigation and trajectory tracking in local area network. [ABSTRACT FROM AUTHOR]

The tribovoltaic effect can convert semiconductor interfacial frictional mechanical energy into direct current (DC) electricity, but the flexibility and durability of semiconductor materials limit its application in wearable electronic. Herein, a robust flexible textile tribovoltaic nanogenerator is presented based on a 2D dynamic heterojunction of 2H‐MoS2/Ta4C3 (MTNG). During the friction process, a built‐in electric field (Eb) and an additional interfacial electric field (ECE) are generated in a continuous dynamic contact of 2H‐MoS2/Ta4C3, and through the 2H‐MoS2/Ta4C3 dynamic heterojunction, a significant number of electron‐hole pairs are excited and move directionally to generate a DC. The influences of mechanical pressure and sliding speed on output performance of MTNGs are systematically investigated. The MTNGs deliver excellent output power density (39.15 mW m2) and outstanding robustness (43 000 cycles). Ten MTNGs can be connected in series to obtain a DC voltage of 3.3 V and in parallel to obtain a DC current of 75 µA. Furthermore, the MTNGs can effectively power a variety of commercial electronic watches and calculators by harvesting human kinetic energy. A 2D dynamic heterojunction 2H‐MoS2/Ta4C3 DC nanogenerator is described and offers a workable option for the creation of flexible DC power sources and self‐powered wearable electronics. [ABSTRACT FROM AUTHOR]

A series of direct‐current tribovoltaic nanogenerators (TVNGs) with high current density have been developed for energy harvesting and mechanical sensing recently, but the lead wires that need to be connected to two relatively moving parts have greatly restricted the application of TVNG. Herein, a freestanding‐mode TVNG (FTVNG) is proposed based on metal, p‐type silicon (p‐Si), and n‐type silicon (n‐Si). As the freestanding part of metal simultaneously rubs against p‐Si and n‐Si, opposite direct current (DC) outputs can be generated, thus forming a DC output from p‐Si to n‐Si in the external circuit. Resulting from the distinctive structure, FTVNGs are applicable for harvesting energy from moving objects without attached wires. Additionally, by using steel needles to precisely control the actual contact area, the electrical output characteristics and influence laws of the tribovoltaic effect under different working parameters such as area and speed are studied. Moreover, FTVNG is integrated into the traditional rolling bearing as a triboelectric bearing, realizing energy recovery from the rotational motion of mechanical parts and speed sensing, which demonstrates the great application potential of TVNG in basic components and parts. [ABSTRACT FROM AUTHOR]

With the extensive application of wireless sensing nodes, the demand for sustainable energy in unattended environments is increasing. Here, we report a self-powered and autonomous vibrational wake-up system (SAVWS) based on triboelectric nanogenerators and micro-electromechanical system (MEMS) switches. The energy triboelectric nanogenerator (E-TENG) harvests vibration energy to power the wireless transmitter through a MEMS switch. The signal triboelectric nanogenerator (S-TENG) controls the state of the MEMS switch as a self-powered accelerometer and shows good linearity in the acceleration range of 1–4.5 m/s2 at 30 Hz with a sensitivity of about 14.6 V/(m/s2). When the acceleration increases, the S-TENG turns on the MEMS switch, and the wireless transmitter transmits an alarm signal with the energy from E-TENG, using only 0.64 mJ. Using TENGs simultaneously as an energy source and a sensor, the SAVWS provides a self-powered vibration monitoring solution for unattended environments and shows extensive applications and great promise in smart factories, autonomous driving, and the Internet of Things. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) can directly harvest energy via solid–liquid interface contact electrification, making them very suitable for harvesting raindrop energy and as active rainfall sensors. This technology is promising for realizing a fully self-powered system for autonomous rainfall monitoring combined with energy harvesting/sensing. Here, we report a raindrop energy-powered autonomous rainfall monitoring and wireless transmission system (R-RMS), in which a raindrop-TENG (R-TENG) array simultaneously serves as a raindrop energy harvester and rainfall sensor. At a rainfall intensity of 71 mm/min, the R-TENG array can generate an average short-circuit current, open-circuit voltage, and maximum output power of 15 μA, 1800 V, and 325 μW, respectively. The collected energy can be adjusted to act as a stable 2.5 V direct-current source for the whole system by a power management circuit. Meanwhile, the R-TENG array acts as a rainfall sensor, in which the output signal can be monitored and the measured data are wirelessly transmitted. Under a rainfall intensity of 71 mm/min, the R-RMS can be continuously powered and autonomously transmit rainfall data once every 4 min. This work has paved the way for raindrop energy-powered wireless hyetometers, which have exhibited broad prospects in unattended weather monitoring, field surveys, and the Internet of Things. [ABSTRACT FROM AUTHOR]

[Display omitted] • A stretchable electret achieves high surface charge and long charge stability. • A stretchable electret-based TENG achieves high charge density (0.2 mC m−2). • A power management module enhances power storage efficiency of the TENG. • The self-charging system provides a stable power supply for wearable electronics. Stretchable power sources capable of accommodating large deformations are urgently demanded for various stretchable and wearable electronics. In this work, we report a stretchable electret-based triboelectric nanogenerator (SEB-TENG) consisting of elastomeric electret as electrification materials and organo-hydrogels as electrodes. The electret elastomer, prepared by uniformly dispersing SiO 2 nanoparticles in the elastomer matrix and thermally injecting static charges, obtains a high surface potential, high tensile strain (796%), and long stability. Then, the SEB-TENG device also achieves high stretchability (423%) and high charge density (0.2 mC m−2). Furthermore, a power management module (PMM) is designed to maximize the energy utilization of the SEB-TENG. The integrated self-charging system can be sufficiently used to constantly power a watch, or charge a Li-ion coin cell which subsequently provides sustainable power supplies to a digital thermometer. This work provides a viable approach to simultaneously achieve high output performances and high stretchability of integrated power sources. [ABSTRACT FROM AUTHOR]

[Display omitted] • H-SiO 2 and PF as fillers to improve the dielectric properties of PFS films. • The performance of TENGs delivered an enhancement by 13 times. • Multiple nanoscales is more favorable to achieve high performance of TENGs. Triboelectric nanogenerators (TENGs), capable of harvesting distributed energy from the environment, have provided a viable solution for self-powered wearable electronics. However, their low power density and susceptibility to contamination still severely limit their practical application. Herein, we reported a "two-step" strategy to implement a waterproof self-powered wearable electronic device based on TENG. Firstly, Perfluoropolyether (PF) and hollow hierarchical silica (H-SiO 2) as fillers significantly improve the dielectric properties of polydimethylsiloxane (PDMS) composite films (PFS films) through polarization effect. Then the nano bumps of 10–30 nm are created on the surface of the films by surface etching, the bumps can increase the contact area of TENG. The voltage of TENG is improved from ∼ 67 V to ∼ 910 V and the current is improved from ∼ 1 μA to ∼ 25 μA. What's more, the investigation of the surface structure of the PFS composite films by Atomic Force Microscope (AFM) revealed that the synergistic combination of multiple nanoscales (10–30 nm, 60–80 nm, 300–500 nm) is more favorable to achieve high performance of TENG. The surface structure composed of multiple nanoscales endows PFS with excellent superhydrophobicity. The PFS films remained fine performance after 40,000 drops of water and 90 days. This work achieves high performance and water resistance of TENG, demonstrating great potential in the field of self-powered wearable electronic devices. [ABSTRACT FROM AUTHOR]

Based on the coupling effect of contact electrification and electrostatic induction, the triboelectric nanogenerator (TENG) as an emerging energy technology can effectively harvest mechanical energy from the ambient environment. However, due to its inherent property of large impedance, the TENG shows high voltage, low current and limited output power, which cannot satisfy the stable power supply requirements of conventional electronics. As the interface unit between the TENG and load devices, the power management circuit can perform significant functions of voltage and impedance conversion for efficient energy supply and storage. Here, a review of the recent progress of switching power management for TENGs is introduced. Firstly, the fundamentals of the TENG are briefly introduced. Secondly, according to the switch types, the existing power management methods are summarized and divided into four categories: travel switch, voltage trigger switch, transistor switch of discrete components and integrated circuit switch. The switch structure and power management principle of each type are reviewed in detail. Finally, the advantages and drawbacks of various switching power management circuits for TENGs are systematically summarized, and the challenges and development of further research are prospected. [ABSTRACT FROM AUTHOR]

A compact, springless, easy-to-process kirigami-inspired TENG (KI-TENG) is developed. The frequency responses of the KI-TENG under the influence of mass, acceleration, and initial distance are investigated in detail to optimize its structural design. Moreover, the TENG coupled with the kirigami structure could collect ultra-wide-band vibration energy and as a sensor measuring acceleration. [Display omitted] • A compact and springless kirigami-inspired TENG (KI-TENG) is developed. • The frequency response characteristics of the KI-TENG are investigated. • The KI-TENG can harvest ultra-wide-band vibration energy from 2 to 49 Hz. • The output of the KI-TENG at different vibration tilt angles is explored. • The KI-TENG can effectively monitor acceleration changes from 1 to 9 m/s2. Triboelectric Nanogenerators (TENGs) based on spring-assisted structures play a central role in scavenging vibrational energy that is widely available in the natural environment. However, they suffer from difficulties in adjusting the stiffness and bonding the springs to the triboelectric layer. Here, a kirigami-inspired TENG (KI-TENG) with a kirigami structure is demonstrated, which can be used as an ultra-wide-band vibrational energy harvester and self-powered acceleration sensor. The triboelectric layer of the KI-TENG can be easily processed into the kirigami structure with one or two-degree-of-freedom by laser cutting technology. The frequency responses of the KI-TENG under the influence of mass, acceleration, and initial distance are investigated in detail to optimize the structural design. With optimized structural parameters, the KI-TENG can not only harvest broadband vibration energy from 2 to 49 Hz in vertical vibration state but also obtain high output performance over a wide frequency range in horizontal vibration state. Moreover, the KI-TENG can be used as a sensor measuring acceleration from 1 to 9 m/s2. This work demonstrates a compact TENG coupled with the kirigami structure for energy harvesting and active sensing, which has great prospects in intelligent plants, artificial intelligence, and the internet age. [ABSTRACT FROM AUTHOR]