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.     

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.     

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.     

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.     

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.     

Blue Energy Collection toward All‐Hours Self‐Powered Chemical Energy Conversion

The conversion and transmission of blue energy in the ocean are critical issues. By employing triboelectric nanogenerators (TENGs), blue energy can be harvested but the corresponding electricity transmission and storage are still great challenges. In this work, an automatic high‐efficiency self‐powered energy collection and conversion system is proposed that converts blue energy to chemical energy. A gear‐driven unidirectional acceleration TENG is designed to convert disordered and low‐frequency water wave energy to low voltage and high current DC output. The output bias from the TENG can be used to drive a Ti–Fe₂O₃/FeNiOOH based photoelectrochemical cell under sunlight to produce hydrogen. Moreover, under the situation without sunlight, the self‐powered system can be automatically switched to another working state to charge a Co₃O₄ based lithium‐ion battery. The hydrogen production rate reaches to 4.65 µL min^‐1 under sunlight at the rotation speed of 120 rpm. The conversion efficiency of the whole system is calculated to be 2.29%. The system triggered by photoswitches can automatically switch between two working states with or without sunlight and convert the blue energy to either hydrogen energy or battery energy for easy storage and transmission, which widens the future applications for blue energy.     

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.     

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.     

Multilayered‐Electrode‐Based Triboelectric Nanogenerators with Managed Output Voltage and Multifold Enhanced Charge Transport

The open‐circuit voltage of a triboelectric nanogenerator (TENG) increases with the tribo‐charge density and the separated distance between two tribo‐surfaces, which can reach several thousand volts and is much higher than the working voltage required by most electrical devices and energy storage units. Therefore, improving the effective efficiency of TENGs requires reducing the output voltage and enhancing the transferred charges. Here, a multilayered‐electrode‐based TENG (ME‐TENG) is developed in which the output voltage can be managed by controlling the charge flow in a process of multiple (N) steps, which results in N times lower voltage but N times higher total charge transport. The ME‐TENG is demonstrated to work in various modes, including multichannel, single‐channel, and double‐tribo‐surface structures. The effects of insulator layer thickness and total layer number on the output voltage are simulated by the finite element method. The output voltage can be modulated from 14 to 102 V by changing the insulator layer number between two adjacent working electrodes, based on which the 8‐bit logic representations of the characters in the ACSII code table are demonstrated. The ME‐TENG provides a novel method to manage the output power and has potential applications in self‐powered sensors array and human–machine interfacing with logic communications.     

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.     

A Water‐Proof Triboelectric–Electromagnetic Hybrid Generator for Energy Harvesting in Harsh Environments

Packaging is a critical aspect of triboelectric nanogenerators (TENG) toward practical applications, since the performance of TENG is greatly affected by environmental conditions such as humidity. A waterproof triboelectric–electromagnetic hybrid generator (WPHG) for harvesting mechanical energy in harsh environments is reported. Since the mechanical transmission from the external mechanical source to the TENG is through a noncontact force between the paired magnets, a fully isolated packaging of TENG part can be easily achieved. At the same time, combining with metal coils, these magnets can be fabricated to be electromagnetic generators (EMG). The characteristics and advantages of outputs from both TENG and EMG are systematically studied and compared to each other. By using transformers and full‐wave rectifiers, 2.3 mA for total short‐circuit current and 5 V for open‐circuit voltage are obtained for WPHG under a rotation speed of 1600 rpm, and it can charge a supercapacitor (20 mF) to 1 V in 22s. Finally, the WPHG is demonstrated to harvest wind energy in the rainy condition and water‐flow energy under water. The reported WPHG renders an effective and sustainable technology for ambient mechanical energy harvesting in harsh environments. Solid progress in both the packaging of TENG and the practical applications of the hybrid generator toward practical power source and self‐powered systems is presented.     

Direct‐Current Triboelectric Nanogenerator Realized by Air Breakdown Induced Ionized Air Channel

The air breakdown phenomenon is generally considered as a negative effect in previous research on triboelectric nanogenerators (TENGs), which is always accompanied by air ionization. Here, by utilizing the air breakdown induced ionized air channel, a direct‐current triboelectric nanogenerator (DC‐TENG) is designed for harvesting contact‐separation mechanical energy. During working process, the charges first transfer from bottom to top electrodes through an external circuit in contact state, then flow back via the ionized air channel created by air breakdown in the separation process. So a unidirectional flow of electrical charges can be observed in the external circuit. With repeating contact‐separation cycles, continuous pulsed DC output through the external circuit can be realized. This working mechanism was verified by real‐time electrode potential monitoring, photocurrent signal detection, and controllable discharging observation. The DC‐TENG can be used for directly and continuously charging an energy storage unit and/or driving electronic devices without using a bridge rectifier. Owing to its simplicity in structure, the mechanism is further applied to fabricate the first flexible DC‐TENG. This research provides a significant fundamental study for DC‐TENG technology and may expand its application in flexible electronics and flexible self‐charging power systems.     

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.     

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.     

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.     

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.     

Capacitor‐Integrated Triboelectric Nanogenerator Based on Metal–Metal Contact for Current Amplification

The electrical power of triboelectric nanogenerators (TENGs) is increased by surface modifications, and they can successfully power portable devices alone. However, modifying the material and its surface may limit the device lifetime, and most of the portable applications demonstrated in previous studies have excessive input conditions. In this study, a capacitor‐integrated TENG (CI‐TENG) that uses the fundamental mechanisms of the Leyden jar is developed. In this device, a long sheet metal (capacitor electrode)–polymer–metal composite (TENG electrode) is rolled inside the casing cylinder, and a capacitor unit is fabricated at the end of the sheet composite. This new operating mechanism of the CI‐TENG is analyzed in terms of the dielectric constant of the capacitor unit and the metal‐to‐metal contact between electrodes. By instantaneous charging and discharging of the capacitor unit inside the CI‐TENG, it can generate a peak open‐circuit voltage of 156 V and a peak closed‐circuit current of 4.3 mA under manual input. It charges a capacitor more than three times faster than a conventional TENG does. Furthermore, the internal impedance of the CI‐TENG is decreased to 200 kΩ without any external circuit.     

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.     

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.