Synergistic Coupling of Tribovoltaic and Moisture-Enabled Electricity Generation in Layered-Double Hydroxides

Ubiquitous energy harvesting technologies require new types of renewable, sustainable, and clean energy to solve the problems of fossil fuels. Although various nanogenerators have been developed over the last decade, low current density, requirements for complicated management circuits, generation of direct current (DC) outputs, and significant performance degradation under humid atmospheres have been problems limiting practical applications. This paper reports that the tribovoltaic and moisture-enabled electricity generation effects can be achieved in a layered double hydroxide (LDH) by applying a metal brushing mode. The ZnAl-LDH shows enhanced tribovoltaic nanogenerator (TVNG) performance even in a high-humidity environment coupled with the moisture-enabled electricity generated by the concentration gradient of a water molecule through the interlamellar structures of the LDHs. The spontaneous dissociation of water in the interior of LDHs removes the hole generated by the tribovoltaic effect, allowing high efficiency of an output voltage of 693.38 mV and current density of 65.48 mA m⁻² even under low-applied force (≈3.5 mN) at relative humidity 80%. The proposed TVNG provides a proof of concept for an all-in-one device consisting of a generator and capacitor because the LDH reveals a spontaneous charging performance similar to that of a capacitor.     

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.     

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.     

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.     

Charge Pumping Strategy for Rotation and Sliding Type Triboelectric Nanogenerators

Triboelectric nanogenerator (TENG) is an emerging approach for harvesting energy from the living environment. But its performance is limited by the maximum density of surface charges created by contact electrification. Here, by rationally designing a synchronous rotation structure, a charge pumping strategy is realized for the first time in a rotary sliding TENGs, which is demonstrated to enhance the charge density by a factor of 9, setting up a record for rotary TENGs. The average power is boosted by more than 15 times compared with normal TENGs, achieving an ultrahigh average power density of 1.66 kW m^?3, under a low drive frequency of 2 Hz. Moreover, the charge pumping mechanism enables decoupling of bound charge generation and the severity of interfacial friction in the main TENG, allowing surface lubricants to be applied for suppressing abrasion and lowering heat generation. The adaptability of the strategy to rotation and sliding type TENGs in low‐frequency agitations provides a breakthrough to the bottleneck of power output for mechanical energy harvesting, and should have a great impact on high‐power TENG design and practical applications in various fields.     

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.     

Design of Mechanical Frequency Regulator for Predictable Uniform Power from Triboelectric Nanogenerators

Mechanical energy scavengers convert irregular input mechanical energy into irregular electrical output. There is a need to enable uniform and predictable electric output from energy scavengers regardless of the variability in the mechanical input. So, in this work, a mechanical frequency regulator is proposed that fixes the input forces and input frequency acting on a triboelectric nanogenerator, thus enabling predictable electric output. The irregular low frequency mechanical input energy is first stored in a spiral spring following which the energy is released at the desired frequency by means of an appropriate design of gear train, cam, and flywheel. By regulating the nanogenerator output at 50 Hz, a standard power transformer can be optimally driven to increase the output current to 6.5 mA and reduce its voltage to 17 V. This output is highly compatible for powering wireless node sensors as is demonstrated in this work.     

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.     

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.     

Sustainable Energy Source for Wearable Electronics Based on Multilayer Elastomeric Triboelectric Nanogenerators

Wearable electronics have attracted a wide range of attention with various functions due to the development of semiconductor industry and information technology. This work focuses on a triboelectric nanogenerator‐based self‐charging power system as a continuous energy source for wearable electronics. The triboelectric nanogenerator has a multilayer elastomeric structure with closely stacked arches as basic functional units. Owing to material and structural innovations, this triboelectric nanogenerator performs outstanding electric output with the maximum volume charge density ≈0.055 C m^?3 and practical properties for energy harvesting from body motions. Utilizing the triboelectric nanogenerator as outsole to harvest energy from walking or jogging, a pair of shoes is fabricated with the maximum equivalent charge current of each shoe being around 16.2 µA and specific fitness functions realized on each shoe separately without complex connections.     

Long‐Lifetime Triboelectric Nanogenerator Operated in Conjunction Modes and Low Crest Factor

The high‐output triboelectric nanogenerator (TENG) is indispensable for its practical applications toward industrial products. However, the electricity loss in simple parallel connection among all units and the typically high crest factor output seriously hamper the practical applications of TENG. Here, a rectified TENG is reported in parallel structure to solve the problem of electricity loss in simple parallel connection. The rotational contact–separation structure with phase difference between rectified TENGs addresses high crest factor output and extends service life of rotational TENG simultaneously. The current crest factor is dramatically decreased to 1.31 in multiple rectifier multiple TENG in parallel (MRM‐TENG), while that of TENG in simple parallel is higher than 6. Meanwhile, the current output can retain up to ≈93% of its initial performance after 7 200 000 rotations under 2.00 r s^?1 of 1000 h. Furthermore, the equivalent current can be in linear growth with low crest factor by making MRM‐TENG in parallel for distributed energy supply without electricity loss. This work may provide a new strategy for TENG in parallel to achieve a low crest factor output and long‐term cycling stability power generation in distributed energy harvesting for large‐scale power application.     

自驱动健康监测及生理功能调节器件的研究进展

纳米发电机(摩擦纳米发电机和压电纳米发电机)技术自被提出以来得到了迅速发展,该技术可将人体动能、风能、声波能、海洋能等各种机械能转化为电能,并应用于自驱动健康监测及生理功能调节,如脉搏传感、神经电刺激、心脏起搏等。文中综述了纳米发电机的结构、工作原理、输出性能及其在循环系统、神经系统、生物组织、睡眠及水下救援等方面的最新研究进展,并在此基础上进一步分析了纳米发电机技术应用到临床治疗所面临的挑战。未来纳米发电机有望成为辅助电源,甚至取代传统电池类电源用于驱动医疗电子器件,实现人体自驱动健康监测及生理功能调节。     

Boosting the Charge Density of Triboelectric Nanogenerator by Suppressing Air Breakdown and Dielectric Charge Leakage

Charge generation and charge decay are two essential factors that determine the surface charge density of a triboelectric nanogenerator (TENG). However, research mainly focuses on boosting charge generation, and little attention is paid to suppressing charge decay. Here, a strategy of suppressing charge decay, including the air breakdown and dielectric charge leakage, of TENG with high surface charge density (HCD-TENG) is proposed by utilizing a dual dielectric layer. A series of parameters of different dielectric materials are tested with the assistance of a charge excitation TENG (CE-TENG) to reveal the relationships between charge generation, air breakdown, and dielectric charge leakage in the atmospheric environment. Further, the phenomenon of dielectric charge leakage limiting the maximum output of TENG prior to air breakdown is observed for the first time. With the simultaneous suppression of the air breakdown and dielectric charge leakage, the output of TENG is enhanced to 2.2 mC m⁻². This work not only provides new insight into the performance optimization and material selection of TENG, but also provides significant guidance for obtaining high-output TENG in the future.     

Advanced Design of Light-Assisted Nanogenerators with Multifunctional Perovskites

Enormous efforts are invested in developing multi-energy harvesting technology with simple configuration and high conversion efficiency, and light-assisted nanogenerators are considered a promising solution. Multifunctional perovskites are explored for this light-assisted nanogenerator, owing to its powerful platform characteristics for integrating multiple energy conversion mechanisms and multi-effects coupling phenomenon. Therefore, with the rapid progress of this emerging field, a timely and comprehensive review of this light-assisted nanogenerator is urgently needed for updating the fundamental understanding of coupling mechanism and material-device-performance relationship. In this review, recent advancements of the perovskite light-assisted nanogenerator with their advanced designs are presented. First, the fundamental properties co-existing in perovskites are briefly introduced, as well as some emerging effects (e.g., flexoelectric). Subsequently, the further coupling mechanism between photovoltaic effect and other energy conversion effects in different light-assisted nanogenerator are discussed in categories. And the output characteristics and potential application of various coupled devices are systematically described from the perspective of perovskites selection and device engineering. Finally, some perspectives on existing challenges and further development for light-assisted nanogenerator are put forward, with the aim to provide useful guidance for the design of advanced devices.     

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.     

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.     

Addressing Triboelectric Nanogenerator Impedance for Efficient CO2 Utilization

Reducing the impedance of a triboelectric nanogenerator (TENG) without power loss is crucial for enhancing its energy conversion efficiency and overall performance. In this paper, a novel signal management structure, based on a newly designed sliding-mode TENG, aimed at effectively reducing impedance by converting narrow, instantaneous signals into broader ones is presented. This transformation is accomplished by adding a grounded electrode connected to a high-inductive inductor and fine-tuning the parasitic capacitance of the dielectric material. Utilizing a highly resistive material like P(VDF–TrFE), a significant improvement in the TENG's performance is achieved, resulting in an increase of output power to 0.352 mW and a decrease in impedance from 3.2 to 0.3 MΩ. This results in a threefold increase in charging speed, which can be attributed to the reduced charge loss and improved matching at lower impedance. Based on these promising findings, the enhanced TENG is successfully connected to power a system for electrochemical CO₂ reduction for CO production. This system effectively reduces the required electrochemical reduction potential by ≈15% under real environments.     

An Approach to Design Highly Durable Piezoelectric Nanogenerator Based on Self‐Poled PVDF/AlO‐rGO Flexible Nanocomposite with High Power Density and Energy Conversion Efficiency

Till date, fabrication of piezoelectric nanogenerator (PNG) with highly durable, high power density, and high energy conversion efficiency is of great concern. Here a flexible, sensitive, cost effective hybrid piezoelectric nanogenerator (HPNG) developed by integrating flexible steel woven fabric electrodes into poly(vinylidene fluoride) (PVDF)/aluminum oxides decorated reduced graphene oxide (AlO‐rGO) nanocomposite film is reported where AlO‐rGO acts as nucleating agent for electroactive β‐phase formation. The HPNG exhibits reliable energy harvesting performance with high output, fast charging capability, and high durability compared with previously reported PVDF based PNGs. This HPNG is capable for harvesting energy from a variety and easy accessible biomechanical and mechanical energy sources such as, body movements (e.g., hand folding, jogging, heel pressing, and foot striking, etc.) and machine vibration. The HPNG exhibits high output power density and energy conversion efficiency, facilitating direct light on different color of several commercial light‐emitting diodes instantly and powers up many portable electronic devices like wrist watch, calculator, speaker, and mobile liquid crystal display (LCD) screen through capacitor charging. More importantly, HPNG retains its performance after long compression cycles (≈158 400), demonstrating great promise as a piezoelectric energy harvester toward practical applications in harvesting biomechanical and mechanical energy for self‐powered systems.     

Wireless Electric Energy Transmission through Various Isolated Solid Media Based on Triboelectric Nanogenerator

Wireless electric energy transmission is an important energy supply technology. However, most wireless energy supply based on electromagnetic induction cannot be used for energy transmission through a metal chamber. Herein, a novel idea for wireless electric energy transmission through various isolated solid media based on triboelectric nanogenerator (TENG) is presented. The electric energy is first transformed into mechanical vibration energy in mechanical wave that can propagate well in solid medium, and then the vibration energy is harvested by a TENG. By employing the spring steel sheets and freestanding triboelectric‐layer structure, the vibration TENG as an energy conversion unit has the advantages of high efficiency and facilitation, boosting this wireless energy transmission technology to be an alternative way of delivering electric energy through metal medium. The working principle and output performance have been systematically studied. A commercial capacitor can be charged from 0 to 10 V in 33 and 86 s isolated by an acrylic plate and a copper plate in thickness of 3 mm, respectively. The wireless electric transmission technology is also applied to deliver electric energy into a vacuum glove box and across glass wall successfully. This novel technology has great potential applications in implantable microelectronic devices, encrypted wireless communication, and even nondestructive testing.