Natural Leaf Made Triboelectric Nanogenerator for Harvesting Environmental Mechanical Energy

Distributed environmental mechanical energy is rarely collected due to its fluctuating amplitudes and low frequency, which is usually attributed as “random” energy. Considering the rapid development of the Internet of things (IoT), there is a great need for a large number of distributed and sustainable power sources. Here, a natural leaf assembled triboelectric nanogenerator (Leaf‐TENG) is designed by utilizing the green leaf as an electrification layer and electrode to effectively harvest environmental mechanical energy. The Leaf‐TENG with good adaptability has the maximum output power of ≈45 mW m^?2, which is capable of driving advertising LEDs and commercial electronic temperature sensors. Besides, a tree‐shaped energy harvester is integrated with natural Leaf‐TENG to harvest large‐area environmental mechanical energy. This work provides a new prospect for distributed and environmental‐friendly power sources and has potential applications in the IoT and self‐powered systems.     

Triboelectric Nanogenerator Based on Fully Enclosed Rolling Spherical Structure for Harvesting Low‐Frequency Water Wave Energy

Water waves are increasingly regarded as a promising source for large‐scale energy applications. Triboelectric nanogenerators (TENGs) have been recognized as one of the most promising approaches for harvesting wave energy. This work examines a freestanding, fully enclosed TENG that encloses a rolling ball inside a rocking spherical shell. Through the optimization of materials and structural parameters, a spherical TENG of 6 cm in diameter actuated by water waves can provide a peak current of 1 μA over a wide load range from a short‐circuit condition to 10 GΩ, with an instantaneous output power of up to 10 mW. A multielectrode arrangement is also studied to improve the output of the TENG under random wave motions from all directions. Moreover, at a frequency of 1.43 Hz, the wave‐driven TENG can directly drive tens of LEDs and charge a series of supercapacitors to rated voltage within several hours. The stored energy can power an electronic thermometer for 20 min. This rolling‐structured TENG is extremely lightweight, has a simple structure, and is capable of rocking on or in water to harvest wave energy; it provides an innovative and effective approach toward large‐scale blue energy harvesting of oceans and lakes.     

Robust Swing‐Structured Triboelectric Nanogenerator for Efficient Blue Energy Harvesting

Ocean wave energy is a promising renewable energy source, but harvesting such irregular, “random,” and mostly ultra‐low frequency energies is rather challenging due to technological limitations. Triboelectric nanogenerators (TENGs) provide a potential efficient technology for scavenging ocean wave energy. Here, a robust swing‐structured triboelectric nanogenerator (SS‐TENG) with high energy conversion efficiency for ultra‐low frequency water wave energy harvesting is reported. The swing structure inside the cylindrical TENG greatly elongates its operation time, accompanied with multiplied output frequency. The design of the air gap and flexible dielectric brushes enable mininized frictional resistance and sustainable triboelectric charges, leading to enhanced robustness and durability. The TENG performance is controlled by external triggering conditions, with a long swing time of 88 s and a high energy conversion efficiency, as well as undiminished performance after continuous triggering for 4 00 000 cycles. Furthermore, the SS‐TENG is demonstrated to effectively harvest water wave energy. Portable electronic devices are successfully powered for self‐powered sensing and environment monitoring. Due to the excellent performance of the distinctive mechanism and structure, the SS‐TENG in this work provides a good candidate for harvesting blue energy on a large scale.     

Broadband Vibrational Energy Harvesting Based on a Triboelectric Nanogenerator

Vibrations in living environments are generally distributed over a wide frequency spectrum and exhibit multiple motion directions over time, which renders most of the current vibration energy harvesters unpractical for their harvesting purposes. Here, a 3D triboelectric nanogenerator (3D‐TENG) is designed based on the coupling of the triboelectrification effect and the electrostatic induction effect. The 3D‐TENG operates in a hybridization mode of conjuntioning the vertical contact‐separation mode and the in‐plane sliding mode. The innovative design facilitates harvesting random vibrational energy in multiple directions over a wide bandwidth. An analytical model is established to investigate the mechano‐triboelectric transduction of 3D‐TENG and the results agree well with experimental data. The 3D‐TENG is able to harvest ambient vibrations with an extremely wide working bandwidth. Maximum power densities of 1.35 W m^‐2 and 1.45 W m^‐2 are achieved under out‐of‐plane and in‐plane excitation, respectively. The 3D TENG is designed for harvesting ambient vibration energy, especially at low frequencies, under a range of conditions in daily life and has potential applications in environmental/infrastructure monitoring and charging portable electronics.     

Multiple‐Frequency High‐Output Triboelectric Nanogenerator Based on a Water Balloon for All‐Weather Water Wave Energy Harvesting

Energy and the environment are two of the main issues facing the world today. As a consequence abundant renewable green energy sources such as wave energy, have become hot topics. Here, a multiple‐frequency triboelectric nanogenerator based on the water balloon (WB‐TENG) is proposed for harvesting water wave energy in any direction. Owing to the high elasticity of the water balloon, the WB‐TENG can realize a multiple‐frequency response to low‐frequency external mechanical simulations to generate high‐frequency electrical output. In addition, the water balloon can achieve self‐support without any additional supporting structure because of its tension, to make WB‐TENG still produce electrical output under slight vibration, which can also bring high energy conversion efficiency. Moreover, the fabricated WB‐TENG generates a maximum instantaneous short‐circuit current and an open‐circuit voltage of 147 µA and 1221 V, respectively. Most noteworthy, under the same conditions, the total transferred charge of WB‐TENG is 28 times than that of traditional TENG based on double plate structure during one working cycle. Therefore, this design can provide an effective way to promote the development of TENGs in blue energy.     

Oblate Spheroidal Triboelectric Nanogenerator for All‐Weather Blue Energy Harvesting

Triboelectric nanogenerators (TENGs) provide one of the most promising techniques for large‐scale blue energy harvesting. However, lack of reasonable designs has largely hindered TENG from harvesting energy from both rough and tranquil seas. In this paper, an oblate spheroidal TENG assembled by two novel TENG parts is elaborately designed for both situations. The TENG in the upper part is based on spring steel plates without other substrate materials, which makes it possible to output considerable power in rough seas and occupy small space. The TENG in the lower part consists of two copper‐coated polymer films and a rolling ball which can capture small wave energy from tranquil seas. The working mechanism and output performance are systematically studied. A maximum open‐circuit voltage of 281 V and a short‐circuit current of 76 µA can be achieved by one upper part, enough to charge a commercial capacitor for potential applications. More important, the proposed oblate spheroidal shell not only guarantees high sensitivity of the TENG in the lower part, but also qualifies the TENG with unique self‐stabilization and low consumables for the next generation of TENGs with new structural design toward all‐weather blue energy harvesting.     

A Soft and Robust Spring Based Triboelectric Nanogenerator for Harvesting Arbitrary Directional Vibration Energy and Self‐Powered Vibration Sensing

Vibration is a common mechanical phenomenon and possesses mechanical energy in ambient environment, which can serve as a sustainable source of power for equipment and devices if it can be effectively collected. In the present work, a novel soft and robust triboelectric nanogenerator (TENG) made of a silicone rubber‐spring helical structure with nanocomposite‐based elastomeric electrodes is proposed. Such a spring based TENG (S‐TENG) structure operates in the contact‐separation mode upon vibrating and can effectively convert mechanical energy from ambient excitation into electrical energy. The two fundamental vibration modes resulting from the vertical and horizontal excitation are analyzed theoretically, numerically, and experimentally. Under the resonant states of the S‐TENG, its peak power density is found to be 240 and 45 mW m^?2 with an external load of 10 MΩ and an acceleration amplitude of 23 m s^?2. Additionally, the dependence of the S‐TENG's output signal on the ambient excitation can be used as a prime self‐powered active vibration sensor that can be applied to monitor the acceleration and frequency of the ambient excitation. Therefore, the newly designed S‐TENG has a great potential in harvesting arbitrary directional vibration energy and serving as a self‐powered vibration sensor.     

Rational Structure Optimized Hybrid Nanogenerator for Highly Efficient Water Wave Energy Harvesting

Water wave energy is a promising renewable energy source that may alleviate the rising concerns over current resource depletion, but it is rarely exploited due to the lack of efficient energy harvesting technologies. In this work, a hybrid system with a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) based on an optimized inner topological structure is reported to effectively harvest water wave energy. The TENG with etched polytetrafluoroethylene films and Cu electrodes utilizing the contact‐freestanding mode is designed into a cubic structure, in which the EMG is well hybridized. An integration of TENG and EMG achieves mutual compensation of their own merits, enabling the hybrid system to deliver satisfactory output over a broad range of operation frequency. The output performance of TENG with varied inner topological structures is experimentally and theoretically compared, and a concept is proposed to further clarify the energy conversion efficiency, which should be considered in designing energy harvesting devices. The influences of oscillation frequency, amplitude, and dielectric materials on the output performance of the hybrid system are comprehensively studied on different platforms. Furthermore, the optimum operation frequency ranges for TENG and EMG are concluded. The proposed hybrid nanogenerator renders an effective approach toward large‐scale blue energy harvesting over a broad frequency range.     

Cylindrical Direct‐Current Triboelectric Nanogenerator with Constant Output Current

In this article, a cylindrical direct‐current triboelectric nanogenerator (DC‐TENG) that can generate an almost constant current output with a low crest factor by phase coupling is reported for the first time. Here, the influence of phases (P) and groups (G) on the DC‐TENG is investigated. Experiments show that the crest factor of current, significantly decreases as the phases increase, and the output performance significantly increases as the groups increase. One phase triboelectric power‐generating unit of the DC‐TENG with three‐phase and five‐group (3P5G) produces an open‐circuit voltage of 149.5 V, short‐circuit current 7.3 μA, and transferred charge of 56.7 nC at 600 rpm. The DC‐TENG can produce a coupling current of 21.6 μA and the average output power of 2.04 mW after each phase output is rectified and superimposed. Additionally, the crest factor of output current is reduced to 1.08, and the high‐performance characteristics of an almost constant direct‐current is achieved. The research is of considerable significance to the practical applications of TENGs in powering sensors of low consumption.     

Ion‐Enhanced Field Emission Triboelectric Nanogenerator

As interest in triboelectric nanogenerators (TENGs) continues to increase, some studies have reported that certain limitations exist in TENG due to high potential difference, resulting in air breakdown and field emission. In addition, with known limitations such as extremely low voltage at low external resistance, a breakthrough is required to overcome the limitations of TENG. Here, a new TENG mechanism is reported, utilizing ion‐enhanced field emission (IEFE). Using a simple IEFE‐inducing layer, which consists of a charge accumulation layer and a metal‐to‐metal contact point, electrons can flow directly to a counter electrode while generating high‐output power. Under vertical contact–separation input, the generated root mean square (RMS) power of IEFE‐TENG is 635% higher compared to conventional TENG. As the fundamental mechanism of the IEFE‐TENG is based on installing this simple IEFE‐inducing layer, the power output of existing TENGs including sliding mode types can be boosted. This new TENG mechanism can be a new standard for metal–metal contact TENGs to effectively amplify the output power and to overcome potential limitations.     

Sea State Adaptation Enhances Power Output of Triboelectric Nanogenerators for Tailored Ocean Wave Energy Harvesting

To face the climate crisis, sustainable energy harvesting systems are critical. Triboelectric nanogenerators (TENGs) are in the spotlight for their inexpensive and non-toxic manufacturing, allied with their excellence in harvesting low frequency vibrations. Ocean waves are a prime example of energy source in this regime, and their successful harvesting with TENGs has been widely demonstrated. However, the influence of wave characteristics on the power output of these devices has so far been overlooked. Here, the existence of a moving element that acts upon the nanogenerators is explored both with multiphysics simulations and an extensive experimental characterization under different operating conditions. It is shown how different sea states modulate the moving body velocity, and how the generator can be optimized to harvest waves with specific characteristics. In parallel, it is demonstrated that the power output is proportional to the contacting triboelectric layers velocity. Optimizing the dynamics of the moving body provides an efficient path to intentionally tune the contacting triboelectric layers velocity, and therefore improve the output of TENGs and their suitability to harvest specific sea states.     

Highly Flexible and Transparent Polyionic‐Skin Triboelectric Nanogenerator for Biomechanical Motion Harvesting

The advances of flexible electronics have raised demand for power sources with adaptability, flexibility, and multifunctionalities. Triboelectric nanogenerators are promising replacements for traditional batteries. Here, a highly soft skin‐like, transparent, and easily adaptable biomechanical energy harvester, based on a hybrid elastomer and with a polyionic hydrogel as the electrification layer and current collector, is developed. By harvesting the energy in human motion, the device generates an open‐circuit voltage of 70 V, a short‐circuit current density of 30.2 mA m^?2, and a maximum power density of 2.79 W m^?2 in a single‐electrode working mode. Further, it is demonstrated that the device can deliver power under bending, curling or by simple tapping when attached to human skin. In addition, the optimal counterpart of the polyionic layer with highest electronegativity difference is selected from a series of contact electrification materials based on a two‐electrode working mode, where a flexible device with the matching counterparts is investigated. Serving as ionic conductor and electrification layer, this polyionic material shows promising application in future development of self‐powered flexible electronics.     

Honeycomb Structure Inspired Triboelectric Nanogenerator for Highly Effective Vibration Energy Harvesting and Self‐Powered Engine Condition Monitoring

Vibration in mechanical equipment can serve as a sustainable energy source to power sensors and devices if it can be effectively collected. In this work, a honeycomb structure inspired triboelectric nanogenerator (HSI‐TENG) consisting of two copper electrode layers with sponge bases and one honeycomb frame filled with polytetrafluoroethylene (PTFE) balls is proposed to harvest vibration energy. The application of a compact honeycomb structure increases the maximum power density of HSI‐TENG by 43.2% compared to the square grid structure and provides superior advantages in large‐scale manufacturing. More importantly, the nonspring‐assisted HSI‐TENG can generate electricity once the PTFE balls obtain sufficient kinetic energy to separate from the bottom electrode layer regardless of the vibration frequency and direction. This is fundamentally different from the spring‐assisted harvesters that can only work around their natural frequencies. The vibration model and working criteria of the HSI‐TENG are established. Furthermore, the HSI‐TENG is successfully used to serve as a self‐powered sensor to monitor engine conditions by analyzing the electrical output of the HSI‐TENG installed on a diesel engine. Therefore, the nonspring‐assisted HSI‐TENG provides a novel strategy for highly effective vibration energy harvesting and self‐powered machinery monitoring.     

Energy Harvesting from Breeze Wind (0.7–6 m s−1) Using Ultra‐Stretchable Triboelectric Nanogenerator

Wind is one of the most important sources of green energy, but the current technology for harvesting wind energy is only effective when the wind speed is beyond 3.5–4.0 m s^?1. This is mainly due to the limitation that the electromagnetic generator works best at high frequency. This means that light breezes cannot reach the wind velocity threshold of current wind turbines. Here, a high‐performance triboelectric nanogenerator (TENG) for efficiently harvesting energy from an ambient gentle wind, especially for speeds below 3 m s^?1 is reported, by taking advantage of the relative high efficiency of TENGs at low‐frequency. Attributed to the multiplied‐frequency vibration of ultra‐stretchable and perforated electrodes, an average output of 20 mW m^?3 can be achieved with inlet wind speed of 0.7 m s^?1, while an average energy conversion efficiency of 7.8% at wind speed of 2.5 m s^?1 is reached. A self‐charging power package is developed and the applicability of the TENG in various light breezes is demonstrated. This work demonstrates the advantages of TENG technology for breeze energy exploitation and proposes an effective supplementary approach for current employed wind turbines and micro energy structure.     

A Nonencapsulative Pendulum‐Like Paper–Based Hybrid Nanogenerator for Energy Harvesting

The newly invented triboelectric nanogenerator (TENG) is deemed to be a more efficient strategy than an electromagnetic generator (EMG) in harvesting low‐frequency (<2 Hz) water wave energy. Various TENGs with different structures and functions for blue energy have been developed, which can be roughly divided into two types: liquid–solid contact electrification TENGs and fully enclosed solid–solid contact electrification TENGs. Robustness and packaging are critical factors in the development of TENGs toward practical applications. Furthermore, for fully enclosed TENGs, the requirements and costs of packaging are very high, and they can difficult to disassemble after enclosed, if there is something wrong with the devices. Herein, a nonencapsulative pendulum‐like paper based hybrid nanogenerator for energy harvesting is designed, which mainly consists of three parts, one solar panel, two paper based zigzag multilayered TENGs, and three EMG units. This unique structure reveals the superior robustness and a maximum peak power of zigzag multilayered TENGs up to 22.5 mW is realized. Moreover, the device can be used to collect the mechanical energy of human motion in hand shaking. This work presents a new platform of hybrid generators toward energy harvesting as a portable practical power source, which has potential applications in navigation and lighting.     

Hybrid All‐in‐One Power Source Based on High‐Performance Spherical Triboelectric Nanogenerators for Harvesting Environmental Energy

With the development of the Internet of Things (IoTs), widely distributed electronics in the environment require effective in situ energy harvesting technologies, which is made challenging by the unstable supply and severe conditions in some environments. In this work, a hybrid all‐in‐one power source (AoPS) is demonstrated for widely adaptive environmental energy harvesting. With a novel structure, the AoPS hybridizes high‐performance spherical triboelectric nanogenerators (TENGs) with solar cells, enabling the harvesting of most typical environmental energies from wind, rain drops, and sun light, for complementary supply. The spherical TENG units with a packaged structure can work robustly to collect energy from fluid. Nearly continuous direct current and a high average power of 5.63 mW can be obtained by four TENG units, which is further complemented by solar cells. Typical application scenarios are also demonstrated, achieving self‐powered soil moisture control, forest fire prevention and pipeline monitoring. The work realizes the concept of an environmental power source that can be deployed in the environment with high adaptability to make use of all kinds of surrounding energies for powering electronics in all‐weather conditions, providing a reliable foundation for the era of the IoTs.     

Robust Triboelectric Nanogenerator Achieved by Centrifugal Force Induced Automatic Working Mode Transition

Material abrasion in contact‐based freestanding mode‐triboelectric nanogenerators (FS‐TENGs) seriously deteriorates device mechanical durability and electrical stability, which causes TENGs to be only applicable in the harvesting of mechanical energy at low‐frequency. Here, a wide‐frequency and ultra‐robust rotational TENG is reported that is composed of a built‐in traction rope structure and capable of transforming from contact mode to non‐contact mode automatically as driven by the centrifugal force. With optimizing the fixed x and y position on slider and center shaft, respectively, the mode transition threshold speed can be reduced to 225 rpm. Additionally, the automatic working mode transition TENG exhibits excellent electrical stability, which can maintain 90% electric output after over 24 h of continuous operation, while the contact and non‐contact mode TENGs only retain 30% and 2% output, respectively. The high stability and large output density ensure its usage in the fast and effective charging of commercial capacitors or electronics. This work provides a prospective strategy for rotational TENGs to extend the frequency operation region and mechanical durability for practical applications.     

An Ultrathin Flexible Single‐Electrode Triboelectric‐Nanogenerator for Mechanical Energy Harvesting and Instantaneous Force Sensing

The trends in miniaturization of electronic devices give rise to the attention of energy harvesting technologies that gathers tiny wattages of power. Here this study demonstrates an ultrathin flexible single electrode triboelectric nanogenerator (S‐TENG) which not only could harvest mechanical energy from human movements and ambient sources, but also could sense instantaneous force without extra energy. The S‐TENG, which features an extremely simple structure, has an average output current of 78 μA, lightening up at least 70 LEDs (light‐emitting diode). Even tapped by bare finger, it exhibits an output current of 1 μA. The detection sensitivity for instantaneous force sensing is about 0.947 μA MPa^?1. Performances of the device are also systematically investigated under various motion types, press force, and triboelectric materials. The S‐TENG has great application prospects in sustainable wearable devices, sustainable medical devices, and smart wireless sensor networks owning to its thinness, light weight, energy harvesting, and sensing capacities.     

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

As the world is marching into the era of the internet of things (IoTs) and artificial intelligence, the most vital development for hardware is a multifunctional array of sensing systems, which forms the foundation of the fourth industrial revolution toward an intelligent world. Given the need for mobility of these multitudes of sensors, the success of the IoTs calls for distributed energy sources, which can be provided by solar, thermal, wind, and mechanical triggering/vibrations. The triboelectric nanogenerator (TENG) for mechanical energy harvesting developed by Z.L. Wang's group is one of the best choices for this energy for the new era, since triboelectrification is a universal and ubiquitous effect with an abundant choice of materials. The development of self‐powered active sensors enabled by TENGs is revolutionary compared to externally powered passive sensors, similar to the advance from wired to wireless communication. In this paper, the fundamental theory, experiments, and applications of TENGs are reviewed as a foundation of the energy for the new era with four major application fields: micro/nano power sources, self‐powered sensors, large‐scale blue energy, and direct high‐voltage power sources. A roadmap is proposed for the research and commercialization of TENG in the next 10 years.