Dual‐Tube Helmholtz Resonator‐Based Triboelectric Nanogenerator for Highly Efficient Harvesting of Acoustic Energy

An acoustic wave is a type of energy that is clean and abundant but almost totally unused because of its very low density. This study investigates a novel dual‐tube Helmholtz resonator‐based triboelectric nanogenerator (HR‐TENG) for highly efficient harvesting of acoustic energy. This HR‐TENG is composed of a Helmholtz resonant cavity, a metal film with evenly distributed acoustic holes, and a dielectric soft film with one side ink‐printed for electrode. Effects of resonant cavity structure, acoustic conditions, and film tension on the HR‐TENG performance are investigated systematically. By coupling the mechanisms of triboelectric nanogenerator and acoustic propagation, a theoretical guideline is provided for improving energy output and broadening the frequency band. Specifically, the present HR‐TENG generates the maximum acoustic sensitivity per unit area of 1.23 VPa^?1 cm^?2 and the maximum power density per unit sound pressure of 1.82 WPa^?1 m^?2, which are higher than the best results from the literature by 60 and 20%, respectively. In addition, the HR‐TENG may also serve as a self‐powered acoustic sensor.     

A Stretchable Nanogenerator with Electric/Light Dual‐Mode Energy Conversion

As an alternative technology, stretchable electronics attract long‐lasting attention. A newly‐designed stretchable nanogenerator with unique dual‐mode energy conversion is reported. The ability of converting the input mechanical stimuli to either electric or light output is achieved by monolithically integrating a transparent single‐electrode triboelectric nanogenerator (S‐TENG) with a ZnS based mechanoluminescence (ML) composite. This stretchable device with versatile functions promotes the development of the smart systems to efficiently and diversely utilize ubiquitous mechanical energy and demonstrates great potential for artificial e‐skins.     

Unity Convoluted Design of Solid Li‐Ion Battery and Triboelectric Nanogenerator for Self‐Powered Wearable Electronics

Wearable electronics suffer from severe power shortage due to limited working time of Li‐ion batteries, and there is a desperate need to build a hybrid device including energy scavenging and storing units. However, previous attempts to integrate the two units are mainly based on simple external connections and assembly, so that maintaining small volume and low manufacturing cost becomes increasingly challenging. Here a convoluted power device is presented by hybridizing internally a solid Li‐ion battery (SLB) and a triboelectric nanogenerator (TENG), so that the two units are one inseparable entity. The fabricated device acts as a TENG that can deliver a peak output power of 7.4 mW under a loading resistance of 7 MΩ, while the device also acts as an SLB to store the obtained electric energy. The device can be mounted on a human shoe to sustainably operate a green light‐emitting diode, thus demonstrating potential for self‐powered wearable electronics.     

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.     

Thermal–Electric Nanogenerator Based on the Electrokinetic Effect in Porous Carbon Film

Converting low‐grade thermal energy with small temperature gradient into electricity is challenging due to the low efficiency and high cost. Here, a new type of thermal–electric nanogenerator is reported that utilizes electrokinetic effect for effective harvesting thermal energy. The nanogenerator is based on an evaporation‐driven water flow in porous medium with small temperature gradient. With a piece of porous carbon film and deionized water, a maximum open‐circuit voltage of 0.89 V under a temperature difference of 4.2 °C is obtained, having a corresponding pseudo‐Seebeck coefficient of 210 mV K^?1. The large pseudo‐Seebeck coefficient endows the nanogenerator sufficient power output for powering existing electronics directly. Furthermore, a wearable bracelet nanogenerator utilizing body heat is also demonstrated. The unique properties of such conversion process offer great potential for ultra‐low temperature‐gradient thermal energy recovery, wearable electronics, and self‐powered sensor systems.     

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.     

Energy Harvesting‐Storage Bracelet Incorporating Electrochemical Microsupercapacitors Self‐Charged from a Single Hand Gesture

The development of wearable electronics and sensing networks has increased the demand for wearable power modules that have steady output, high energy density, and long cycle life. Current power modules, such as batteries, suffer from low energy density due to their limited storage capacity. One solution to avoid the issue is to build a hybrid device consisting of both energy harvesting elements that continuously harvest ambient mechanical energy, and electrochemical energy storage units to store the harvested energy. Here, a hybrid energy harvesting bracelet, which combines a dual electromagnetic and triboelectric nanogenerator to harvest wrist motions, is reported. The bracelet is able to charge the RuO₂‐based microsupercapacitor to 2 V with a single shake of human wrist, which allows the supercapacitor to power most electronic devices for minutes, such as a calculator, relative humidity, and temperature sensors.     

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.     

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.     

Scavenging Wind Energy by Triboelectric Nanogenerators

To meet future needs for clean and sustainable energy, tremendous progress has been achieved in development for scavenging wind energy. The most classical approach is to use the electromagnetic effect based wind turbine with a diameter of larger than 50 m and a weight of larger than 50 ton, and each of them could cost more than $0.5 M, which can only be installed in remote areas. Alternatively, triboelectric nanogenerators based on coupling of contact‐electrification and electrostatic induction effects have been utilized to scavenge wind energy, which takes the advantages of high voltage, low cost, and small size. Here, the development of a wind‐driven triboelectric nanogenerator by focusing on triboelectric materials optimization, structure improvement, and hybridization with other types of energy harvesting techniques is reviewed. Moreover, the major applications are summarized and the challenges that are needed to be addressed and development direction for scavenging wind energy in future are highlighted.     

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.     

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.     

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.     

Tribovoltaic Effect on Metal–Semiconductor Interface for Direct‐Current Low‐Impedance Triboelectric Nanogenerators

The triboelectric nanogenerator (TENG) is a new energy technology that is enabled by coupled contact electrification and electrostatic induction. The conventional TENGs are usually based on organic polymer insulator materials, which have the limitations and disadvantages of high impedance and alternating output current. Here, a tribovoltaic effect based metal–semiconductor direct‐current triboelectric nanogenerator (MSDC‐TENG) is reported. The tribovoltaic effect is facilitated by direct voltage and current by rubbing a metal/semiconductor on another semiconductor. The frictional energy released by the forming atomic bonds excites nonequilibrium carriers, which are directionally separated to form a current under the built‐in electric field. The continuous average open‐circuit voltage (10–20 mV), short‐circuit direct‐current output (10–20 µA), and low impedance characteristic (0.55–5 kΩ) of the MSDC‐TENG can be observed during relative sliding of the metal and silicon. The working parameters are systematically studied for electric output and impedance characteristics. The results reveal that faster velocity, larger pressure, and smaller area can improve the maximum power density. The internal resistance is mainly determined by the velocity and the electrical resistance of semiconductor. This work not only expands the material candidates of TENGs from organic polymers to semiconductors, but also demonstrates a tribovoltaic effect based electric energy conversion mechanism.     

Coupled Supercapacitor and Triboelectric Nanogenerator Boost Biomimetic Pressure Sensor

With the fast development of supercapacitor and triboelectric nanogenerator (TENG), it is now possible to fabricate biomimetic pressure sensors with high flexibility and sustainability. Herein, an ultrathin supercapacitor is fabricated with the paper sheet and the solid electrolyte for storing energy generated by TENG. With a sandwich design, the triboelectrodes sandwiched within the two solid supercapacitors can not only store electrical energy by a wireless energy transfer mode but also help TENG imitate the receptor's unique characteristics by simultaneously measuring both static and dynamic pressures in a self‐driven mode. In addition, the voltage of the supercapacitor increases linearly with the vibration times, which hints that this integrated device also endows functions such as vibration counting and frequency computing. This work contributes to new strategies for making multifunctional biomimetic electronics that promote the development of artificial intelligence.     

Multidirection and Multiamplitude Triboelectric Nanogenerator Composed of Porous Conductive Polymer with Prolonged Time of Current Generation

In this work, a sponge structure triboelectric nanogenerator (TENG) named as porous conductive polymer (PCP)‐TENG, is demonstrated. The measured volume charge density of PCP‐TENG is reached to 60 mC m^?3 by utilizing wide inner surface of the sponge structure as contact surface. Moreover, the PCP‐TENG generates a continuous sinusoidal‐like alternative current. Notably, the PCP‐TENG can effectively harvest vibrational mechanical energy from various directions and amplitudes. With these characteristics, the PCP‐TENG can be implemented in a wide variety of settings, such as inside of a tire. It is confirmed that the PCP‐TENG generates electrical power for operating a commercial light‐emitting diode and a humidity sensor even under small deformation of the tire.     

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.     

Versatile Core–Sheath Yarn for Sustainable Biomechanical Energy Harvesting and Real‐Time Human‐Interactive Sensing

The emergence of stretchable textile‐based mechanical energy harvester and self‐powered active sensor brings a new life for wearable functional electronics. However, single energy conversion mode and weak sensing capabilities have largely hindered their development. Here, in virtue of silver‐coated nylon yarn and silicone rubber elastomer, a highly stretchable yarn‐based triboelectric nanogenerator (TENG) with coaxial core–sheath and built‐in spring‐like spiral winding structures is designed for biomechanical energy harvesting and real‐time human‐interactive sensing. Based on the two advanced structural designs, the yarn‐based TENG can effectively harvest or respond rapidly to omnifarious external mechanical stimuli, such as compressing, stretching, bending, and twisting. With these excellent performances, the yarn‐based TENG can be used in a self‐counting skipping rope, a self‐powered gesture‐recognizing glove, and a real‐time golf scoring system. Furthermore, the yarn‐based TENG can also be woven into a large‐area energy‐harvesting fabric, which is capable of lighting up light emitting diodes (LEDs), charging a commercial capacitor, powering a smart watch, and integrating the four operational modes of TENGs together. This work provides a new direction for textile‐based multimode mechanical energy harvesters and highly sensitive self‐powered motion sensors with potential applications in sustainable power supplies, self‐powered wearable electronics, personalized motion/health monitoring, and real‐time human‐machine interactions.     

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.     

Mechanical Regulation Triboelectric Nanogenerator with Controllable Output Performance for Random Energy Harvesting

Recycling of random mechanical energy in the environment has become an important research hotspot. The triboelectric nanogenerators (TENGs) were invented to harvest energy, and have been widely applied due to their simple structure, small size, and low cost. This paper reports a mechanical regulation triboelectric nanogenerator (MR‐TENG) for the first time with controllable output performance used to harvest random or irregular energy in the environment. It comprises a transmission unit, switch structure, generator unit, flywheel, and shell. Random linear motion or rocking motion is transferred via the transmission unit to the flywheel. The rotor of the generator unit fixed on the flywheel and the stator of the generator unit fixed on the shell combine. By controlling the storage and release of energy in the flywheel, the switch structure assists the flywheel to convert random or irregular energy into a controllable and stable energy output. The MR‐TENG can generate an open‐circuit voltage of 350 V, a short‐circuit current of 12 μA, a transfer charge of 130 nC, and a peak power of 2.52 mW. Furthermore, a thermometer and more than 300 light emitting diodes (LEDs) are separately powered by this MR‐TENG in simulated water waves, demonstrating its potential application in water wave energy harvesting.