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.     

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.     

Self‐Powered Wireless Sensor Node Enabled by a Duck‐Shaped Triboelectric Nanogenerator for Harvesting Water Wave Energy

This paper presents a fully enclosed duck‐shaped triboelectric nanogenerator (TENG) for effectively scavenging energy from random and low‐frequency water waves. The design of the TENG incorporates the freestanding rolling mode and the pitch motion of a duck‐shaped structure generated by incident waves. By investigating the material and structural features, a unit of the TENG device is successfully designed. Furthermore, a hybrid system is constructed using three units of the TENG device. The hybrid system achieves an instantaneous peak current of 65.5 µA with an instantaneous output power density of up to 1.366 W m^?2. Following the design, a fluid–solid interaction analysis is carried out on one duck‐shaped TENG to understand the dynamic behavior, mechanical efficiency, and stability of the device under various water wave conditions. In addition, the hybrid system is experimentally tested to enable a commercial wireless temperature sensor node. In summary, the unique duck‐shaped TENG shows a simple, cost‐effective, environmentally friendly, light‐weight, and highly stable system. The newly designed TENG is promising for building a network of generators to harvest existing blue energy in oceans, lakes, and rivers.     

High‐Output Triboelectric Nanogenerator Based on Dual Inductive and Resonance Effects‐Controlled Highly Transparent Polyimide for Self‐Powered Sensor Network Systems

High‐output triboelectric nanogenerators (TENGs) are demonstrated based on polyimide (PI)‐based polymers by introducing functionalities (e.g., electron‐withdrawing and electron‐donating groups) into the backbone. The TENG based on 6FDA‐APS PI, possessing the most negative electrostatic potential and the low‐lying lowest unoccupied molecular orbital level, produces the highest effective charge density of about 860 µC m^?2 in practical working conditions with the ion injection process. This may be ascribed to the excellent charge‐retention characteristics as well as the enhanced charge transfer capability, which increases the output power by 7 times compared to the commercially available Kapton film‐based TENG. Finally, a 6FDA‐APS‐driven sensor network system is demonstrated, providing the identity of three gases (H₂, CO, and NO₂) by illuminating the light‐emitting diodes within several seconds.     

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.     

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.     

Multifunctional TENG for Blue Energy Scavenging and Self‐Powered Wind‐Speed Sensor

Triboelectric nanogenerator (TENG) has been considered to be a more effective technology to harvest various types of mechanic vibration energies such as wind energy, water energy in the blue energy, and so on. Considering the vast energy from the blue oceans, harvesting of the water energy has attracted huge attention. There are two major types of “mechanical” water energy, water wave energy in random direction and water flow kinetic energy. However, although the most reported TENG can be used to efficiently harvest one type of water energy, to simultaneously collect two or more types of such energy still remains challenging. In this work, two different freestanding, multifunctional TENGs are successfully developed that can be used to harvest three types of energies including water waves, air flowing, and water flowing. These two new TENGs designed in accordance with the same freestanding model yield the output voltages of 490 and ≈100 V with short circuit currents of 24 and 2.7 µA, respectively, when operated at a rotation frequency of 200 rpm and the movement frequency of 3 Hz. Moreover, the developed multifunctional TENG can also be explored as a self‐powered speed sensor of wind by correlating the short‐circuit current with the wind speed.     

Environmentally Friendly Hydrogel‐Based Triboelectric Nanogenerators for Versatile Energy Harvesting and Self‐Powered Sensors

Triboelectric nanogenerators (TENGs), as a promising energy harvesting technology, have been rapidly developed in recent years. However, the research based on fully flexible and environmentally friendly TENGs is still limited. Herein, for the first time, a hydrogel‐based triboelectric nanogenerator (Hydrogel‐TENG) with high flexibility, recyclability, and environmental friendliness simultaneously has been demonstrated. The standard Hydrogel‐TENG can generate a maximum output power of 2 mW at a load resistance of 10 MΩ. The tube‐shaped Hydrogel‐TENG can harvest mechanical energy from various human motions, including bending, twisting, and stretching. Furthermore, the system can serve as self‐powered sensors to detect the human motions. Additionally, the utilized Polyvinyl Alcohol hydrogel employed in this study is recyclable to benefit for fabricating the renewable TENG. The open‐circuit voltage of renewed hydrogel‐TENG can reach up to 92% of the pristine output voltage. This research will pave a potential approach for the development of flexible energy sources and self‐powered motion sensors in environmentally friendly way.     

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.     

Triboelectric Nanogenerator (TENG)—Sparking an Energy and Sensor Revolution

The study presents the fundamental scientific understanding of electron transfer in contact electrification in solid–solid and liquid–solid cases and a newly revised model for the formation of electric double layer. The potential revolutionary impacts of triboelectric nanogenerators as energy sources and sensors are presented in the fields of health care, environmental science, wearable electronics, internet of things, human–machine interfacing, robotics, and artificial intelligence.     

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.     

Rotating‐Disk‐Based Direct‐Current Triboelectric Nanogenerator

An innovative design is reported of a direct‐current triboelectric nanogenerator (DC‐TENG) based on a rotating disk design for harvesting rotational mechanical energy. The DC‐TENG consists of two disks and two pairs of flexible electric brushes that are made of carbon fiber and contact two electrodes, respectively. During the rotation, two disks have distinct triboelectric polarities for a cyclic in‐plane charge separation between them and an alternating current is generated between the two electrodes. Because of the sliding contact and automatically switch between the electric brushes and the two electrodes, the current is reversed in the second half of the cycle and a direct current is generated. The role that the rotating speed and the segmentation number have is thoroughly investigated and shows that there is direct current enhancement not only at higher speed but also with more segments. The DC‐TENG has been demonstrated as a constant current source for directly and continuously driving electronic devices and/or charging an energy storage unit without a rectifier bridge. This work presents a novel DC‐TENG technology and opens up more potential applications for harvesting rotational mechanical energy and powering electronics.     

A Self‐Powered Dynamic Displacement Monitoring System Based on Triboelectric Accelerometer

An integrated self‐powered dynamic displacement monitoring system by utilizing a novel triboelectric accelerometer for structural health monitoring is proposed and implemented in this study, which can show the dynamic displacement and transmit the alarming signal by accurately sensing the vibration acceleration. The fabricated triboelectric accelerometer based on the noncontact freestanding triboelectric nanogenerator consists of an outer transparent sleeve tube and an inner cylindrical inertial mass that is suspended by a highly stretchable silicone fiber. One pair of copper film electrodes is deposited by physical vapor deposition on nylon film and adhered on the inner wall of the outer tube, while a fluorinated ethylene propylene film with nanowire structures is adhered on the surface of the inner cylindrical inertial mass. The experimental results show that proposed triboelectric accelerometer can accurately sense the vibration acceleration with a high sensitivity of 0.391 V s² m^?1. In particular, the developed accelerometer has superior performance within the low‐frequency range. One of the most striking features is that the commercial accelerometer using piezoelectric material is strongly dominated by high‐order harmonics, which can cause confusion in computer data analysis. In contrast, the triboelectric accelerometer is only dominated by the base resonance mode.     

Triboelectric Nanogenerator for Sustainable Wastewater Treatment via a Self‐Powered Electrochemical Process

By harvesting the flowing kinetic energy of water using a rotating triboelectric nanogenerator (R‐TENG), this study demonstrates a self‐powered wastewater treatment system that simultaneously removes rhodamine B (RhB) and copper ions through an advanced electrochemical unit. With the electricity generated by R‐TENG, the removal efficiency (RE) of RhB can reach the vicinity of 100% within just 15 min when the initial concentration of RhB is around 100 ppm at optimized conditions. The removal efficiency of copper ions can reach 97.3% after 3 h within an initial concentration of 150 ppm at an optimized condition. Importantly, a better performance and higher treating efficiency are found by using the pulsed output of R‐TENG than those using direct current (DC) supply for pollutant removal when consuming equal amount of energy. The recovered copper layer on the cathode through R‐TENG is much denser, more uniform, and with smaller grain size (d = 20 nm) than those produced by DC process, which also hints at very promising applications of the R‐TENG in electroplating industry. In light of the merits such as easy portability, low cost, and effectiveness, this R‐TENG‐based self‐powered electrochemical system holds great potential in wastewater treatment and electroplating industry.     

Robust Thin Films‐Based Triboelectric Nanogenerator Arrays for Harvesting Bidirectional Wind Energy

Wind‐driven triboelectric nanogenerators (TENGs) play an important role in harvesting energy from ambient environments. Compared to single‐side‐fixed triboelectric nanogenerator (STENG) arrays for harvesting single‐pathway wind energy, double‐side‐fixed triboelectric nanogenerator (DTENG) arrays are developed to harvest bidirectional wind energy. Electrical performances of the STENG and DTENG can be improved due to sticky, abrasive, and electrical properties of the Ti buffer layers among Al, polytetrafluoroethylene (PTFE), and polyimide (Kapton), configuring in triboelectric PTFE/Ti/Al and Al/Ti/Kapton/Ti/Al thin films. Short‐circuit current (I _SC), open‐circuit voltage (V _OC), and frequencies of the STENG and DTENG increase with increasing wind velocity ranging from 9.2 to 18.4 m s²¹, revealing that the moderate I _SC, V _OC, frequencies, and output powers of the STENG and DTENG reach 67 μA, 57 μA, 334 V, 296 V, 173 Hz, 162 Hz, 5.5 mW and 3.4 mW with a matched load of 4 MΩ at airflow rate of 15.9 m s²¹, respectively. Compared with counterparts of the single‐pathway‐harvested STENG arrays, the I _SC, durability, and stability of the bidirectional‐harvested DTENG can be dramatically improved by a 4 3 1 array connected in parallel because of the improved device configuration, stickiness, and abrasion by adhering Ti buffer layers. The durable DTENG arrays present a step toward practical applications in harvesting bidirectional wind energy for self‐powered systems and wireless sensors.     

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.     

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.     

Rationally Designed Dual‐Mode Triboelectric Nanogenerator for Harvesting Mechanical Energy by Both Electrostatic Induction and Dielectric Breakdown Effects

With the advantages of its light weight, low cost, and high efficiency especially at low operation frequency, the triboelectric nanogenerator (TENG) is considered to be a potential solution for self‐powered sensor networks and large‐scale renewable blue energy. However, the conventional TENG converts mechanical energy into electrical energy only via either electrostatic induction or electrostatic breakdown. Here, a novel dual‐mode TENG is presented, which can simultaneously harvest mechanical energy by electrostatic induction and dielectric breakdown in a single device. Based on the complementary working mechanism, it achieves a great improvement in the output performance with the sum of two TENGs via a single mechanism and reveals the effect of dielectric layer thickness on the triboelectrification, electrostatic induction, and air breakdown. This study establishes a new methodology to optimize TENGs and provides a new tool to investigate the triboelectrification, electrostatic induction and dielectric breakdown simultaneously.     

Networks of High Performance Triboelectric Nanogenerators Based on Liquid–Solid Interface Contact Electrification for Harvesting Low‐Frequency Blue Energy

Blue energy harvested from the ocean is an important and promising renewable energy for the sustainable development of society. Triboelectric nanogenerators (TENGs) are considered one of the most promising approaches for harvesting blue energy. In this work, a liquid–solid‐contact triboelectric nanogenerator (LS TENG) is fabricated to enhance the friction and magnify energy output by 48.7 times, when compared with the solid–solid‐contact TENG with the same area. The buoy‐like LS TENG can harvest energy from different types of low‐frequency vibration (including up–down, shaking, and rotation movements). Moreover, the outputs of the LS TENGs network can reach 290 µA, 16 725 nC, and 300 V, and the LS TENGs network can directly power hundreds of LEDs and drive a radio frequency emitter to form a self‐powered wireless save our souls (SOS) system for ocean emergencies. This work renders an innovative and effective approach toward large‐scale blue energy harvesting and applications.