Structural Optimization of Triboelectric Nanogenerator for Harvesting Water Wave Energy

Self-Powering Gas Sensing System Enabled by Double-Layer Triboelectric Nanogenerators Based on Poly(2-vinylpyridine)@BaTiO3 Core-Shell Hybrids with Superior Dispersibility and Uniformity

Current core-shell hybrids used in diverse energy-related applications possess limited dispersibility and film uniformity that govern their overall performances. Herein, we showcase superdispersible core-shell hybrids (P2VP@BaTiO3) composed of a poly(2-vinylpyridine) (P2VP) (5-20 wt %) and a barium titanate oxide (BaTiO3), maximizing dielectric constants by forming the high-quality uniform films. The P2VP@BaTiO3-based triboelectric nanogenerators (TENGs), especially the 10 wt % P2VP (P2VP10@BaTiO3)-based one, deliver significantly enhanced output performances compared to physically mixed P2VP/BaTiO3 counterparts. The P2VP10@BaTiO3-based double-layer TENG exhibits not only an excellent transferred charge density of 281.7 μC m-2 with a power density of 27.2 W m-2 but also extraordinary device stability (∼100% sustainability of the maximum output voltage for 54,000 cycles and ∼68.7% voltage retention even at 99% humidity). Notably, introducing the MoS2/SiO2/Ni-mesh layer into this double-layer TENG enables ultrahigh charge density of up to 1228 μC m-2, which is the top value reported for the TENGs so far. Furthermore, we also demonstrate a near-field communication-based sensing system for monitoring CO2 gas using our developed self-powered generator with enhanced output performance and robustness.

Durable Roller-Based Swing-Structured Triboelectric Nanogenerator for Water Wave Energy Harvesting

Ocean energy is a kind of clean and renewable energy source, but it cannot be efficiently harvested by traditional electromagnetic generators, due to its low-frequency characteristic. The emergence of triboelectric nanogenerators provides a more promising technology for collecting ocean energy. In this work, a durable roller-based swing-structured triboelectric nanogenerator (RS-TENG) is designed and fabricated for low-frequency water wave energy harvesting. The rolling structure reduces the wear between triboelectric materials and improves the device's durability. After a continuous operation of 1 260 000 cycles, the attenuation of the electrical outputs of the RS-TENG is below 1.6%, exhibiting excellent durability. At the same time, the output current can arrive at 53.2 µA. Under the triggering of water waves, the RS-TENG can generate an output power of 4.27 mW, corresponding to a power density of 1.16 W m-3. After the arraying, the output performance can be doubled, so that the TENG can successfully power an environmental monitoring sensor and ensure long-term stable operation of the sensor. This work provides an effective strategy for improving the device durability, which benefits the practical applications of the TENGs in large-scale blue energy harvesting.

Advanced Dielectric Materials for Triboelectric Nanogenerators: Principles, Methods, and Applications

Triboelectric nanogenerator (TENG) manifests distinct advantages such as multiple structural selectivity, diverse selection of materials, environmental adaptability, low cost, and remarkable conversion efficiency, which becomes a promising technology for micro-nano energy harvesting and self-powered sensing. Tribo-dielectric materials are the fundamental and core components for high-performance TENGs. In particular, the charge generation, dissipation, storage, migration of the dielectrics, and dynamic equilibrium behaviors determine the overall performance. Herein, a comprehensive summary is presented to elucidate the dielectric charge transport mechanism and tribo-dielectric material modification principle toward high-performance TENGs. The contact electrification and charge transport mechanism of dielectric materials is started first, followed by introducing the basic principle and dielectric materials of TENGs. Subsequently, modification mechanisms and strategies for high-performance tribo-dielectric materials are highlighted regarding physical/chemical, surface/bulk, dielectric coupling, and structure optimization. Furthermore, representative applications of dielectric materials based TENGs as power sources, self-powered sensors are demonstrated. The existing challenges and promising potential opportunities for advanced tribo-dielectric materials are outlined, guiding the design, fabrication, and applications of tribo-dielectric materials.

Boosting the output performance of triboelectric nanogenerators via surface engineering and structure designing

Triboelectric nanogenerators (TENGs) have been utilized in a wide range of applications, including smart wearable devices, self-powered sensors, energy harvesting, and high-voltage power sources. The surface morphology and structure of TENGs play a critical role in their output performance. In this review, we analyze the working mechanism of TENGs with the aim to improve their output performance and systematically summarize the morphological engineering and structural design strategies for TENGs. Additionally, we present the emerging applications of TENGs with specific structures and surfaces. Finally, we discuss the potential future development and industrial application of TENGs. By deeply exploring the surface and structural design strategy of high-performance TENGs, it is conducive to further promote the application of TENGs in actual production. We hope that this review provides insights and guidance for the morphological and structural design of TENGs in the future.

Mechanism and optimum pressure for sliding-mode nanogenerator

Triboelectric nanogenerator has extensive applicability because of its capability of harvesting mechanical energy and flexible working modes. To research the optimum pressure and improve the recovered energy of the sliding-mode triboelectric nanogenerator, a contact model of the Al/PTFE tribo-pair is studied by ab initio calculation and finite element simulation. The F-atom of PTFE is proved to be the electron accepter and the charges transferred can be predicted by Bader charge analysis. The mathematical relation between interfacial distance, charges transferred and contact pressure can be fitted. By Gauss’s law, the electric field is simulated and the regeneration energy of the sliding-mode triboelectric nanogenerator can be evaluated by the total electric energy and friction loss. Finally, an optimum pressure can be set to the upper or lower limit of working pressure corresponding to larger recovered energy. And less friction coefficient and larger contact area are also effective methods for recovering energy.

A Cantilever Beam-Based Triboelectric Nanogenerator as a Drill Pipe Transverse Vibration Energy Harvester Powering Intelligent Exploitation System

Measurement While Drilling (MWD) is the most commonly used real-time information acquisition technique in offshore intelligent drilling, its power supply has always been a concern. Triboelectric nanogenerators have been shown to harvest low-frequency vibrational energy in the environment and convert it into electricity to power small sensors and electrical devices. This work proposed a cantilever-beam-based triboelectric nanogenerator (CB-TENG) for transverse vibration energy harvesting of a drill pipe. The CB-TENG consists of two vibrators composed of spring steel with PTFE attached and Al electrodes. The structurally optimized CB-TENG can output a peak power of 2.56 mW under the vibration condition of f = 3.0 Hz and A = 50 mm, and the electrical output can be further enhanced with the increased vibration parameters. An array-type vibration energy harvester integrated with eight CB-TENGs is designed to fully adapt to the interior of the drill pipe and improve output performance. The device can realize omnidirectional vibration energy harvesting in the two-dimensional plane with good robustness. Under the typical vibration condition, the short-circuit current and the peak power can reach 49.85 μA and 30.95 mW, respectively. Finally, a series of demonstration experiments have been carried out, indicating the application prospects of the device.

What can AI-TENG do for Low Abundance Biosensing?

Biosensing technology helps prevent, diagnose, and treat diseases and has attracted more and more researchers in recent years. Artificial intelligence-based triboelectric nanogenerators (AI-TENG) are promising for applications in biosensors due to their myriad of merits, including high efficiency and precision, low cost, light weight, and self-powered. This article aims to show how artificial intelligence and triboelectric nanogenerators have been combined to develop biosensors. We first focus on the working principle of triboelectric nanogenerators and the method of combining them with artificial intelligence. Secondly, we highlight the representative research work of AI-TENG in biomolecules sensing, organic compounds, and complex mixture of cells. Finally, this paper concludes with a summary and prospect on the existing challenges and possible solutions in the application of AI-TENG to the field of biosensors.

Performance-Improved Highly Integrated Uniaxial Tristate Hybrid Nanogenerator for Sustainable Mechanical Energy Harvesting

Despite advances in the development of individual nanogenerators, the level of output energy generation must be increased to meet the demands of commercial electronic systems and to broaden their scope of application. To harvest low-frequency ambient mechanical energy more efficiently, we proposed a highly integrated hybridized piezoelectric-triboelectric-electromagnetic (tristate) nanogenerator in a uniaxial structure. In its highly integrated approach, a piezoelectric nanogenerator (PENG) based on CsPbBr₃ (cesium lead bromide) nanoparticles (NPs) and poly(dimethylsiloxane) (PDMS) nanocomposite was fabricated on a triboelectrically negative nanostructured polyimide (PI) substrate. A cylindrical aluminum electrode grooved with permanent magnets was directed to move along a spring-less metallic guide bounded by these nanocomposites, thus essentially forming two single-electrode mode triboelectric nanogenerators (TENGs). By its optimized material design and novel integration approach of the PENGs, TENGs, and electromagnetic generators (EMGs), this uniaxial tristate hybrid nanogenerator (UTHNG) can synergistically produce an instantaneous electrical power of 49 mW at low-frequency ambient vibration (5 Hz). The UTHNG has excellent charging characteristics, ramping up the output voltage of a 22 μF capacitor to 2.7 V in only 12 s, which is much faster than individual nanogenerators. This work will be a superior solution for harvesting low-frequency ambient energies by improving the performance of hybrid nanogenerators, potentially curtailing the technology gap for self-powered micro/nanosystems for the Internet of Things.

Gridding Triboelectric Nanogenerator for Raindrop Energy Harvesting

Triboelectric nanogenerator (TENG) has the great potential to harvest the electrostatic energy and mechanical energy of raindrops. However, raindrops are small and scattered, and it is difficult to harvest their mechanical energy effectively. In this paper, a gridding triboelectric nanogenerator (G-TENG) with an area of 81 cm² is designed and developed to effectively harvest the mechanical energy of raindrops on a large scale. Its peak output power density is 8.56 mW/m², which is 245 times the value of 35 μW/m² of a general TENG without gridding. Each unit of the G-TENG can work independently, which can effectively decrease the mutual counteraction of elastic deformation among the adjacent positions of the raindrop impacting layer and avoid the accumulation of raindrops. Under the impact of simulated raindrops from a shower at a flow rate of 0.137 mL/(cm²·s), the open-circuit voltage (V_oc) and the short-circuit current density (J_sc) of the G-TENG reach 400 V and 2.5 mA/m², respectively. The peak output power density reaches 110 mW/m², which is 42 times the reported maximum value of 2.6 mW/m² of raindrop energy harvesting TENGs with the size larger than 10 cm². Moreover, the G-TENG can harvest the mechanical energy of raindrops at a wide range of raindrop flow rates from 0.055 to 0.219 mL/(cm²·s). This work contributes to the raindrop mechanical energy harvesting on a large scale.

High-Performance Polyimide-Based Water-Solid Triboelectric Nanogenerator for Hydropower Harvesting

Water-solid triboelectric nanogenerators (TENGs) are insensitive to ambient humidity, providing a wide range of possibilities for designing stable water-energy-based harvesters and self-powered sensors. However, the wide application of most water-solid TENGs has been limited by low triboelectrification performance. To boost the output performance of water-solid TENGs, a newly structured TENG has been developed by adding a polyimide (PI) as a charge storage intermediate layer between the friction layer and the conducting layer, significantly improving the output performance (1.260 mW), with a 5-fold increase compared to the water-solid TENG without the PI intermediate layer (0.234 mW). This analysis shows that adding an intermediate layer with a high density of electron capture sites to the TENG results in more triboelectric charge being retained, thereby improving the electrical performance of TENG. The electrical performance of TENG is related to the thickness of the PI layer, but this is not a positive correlation. Contact angles and falling heights between the droplet and the device also affect the output performance. Finally, the water-solid PI-TENG we have developed has promise in hydropower harvesting capabilities and can be used to power warning signals on a dark and rainy night to ensure the safety of people.

A Contact-Mode Triboelectric Nanogenerator for Energy Harvesting from Marine Pipe Vibrations

Structural health monitoring is of great significance to ensure the safety of marine pipes, while powering the required monitoring sensors remains a problem because the ocean environment is not amenable to the traditional ways of providing an external power supply. However, mechanical energy due to the vortex-induced vibration of pipelines may be harvested to power those sensors, which is a convenient, economic and environmentally friendly way. We here exploit a contact-separation mode triboelectric nanogenerator (TENG) to create an efficient energy harvester to transform the mechanical energy of vibrating pipes into electrical energy. The TENG device is composed of a tribo-pair of dielectric material films that is connected to a mass-spring base to guarantee the contact-separation motions of the tribo-pair. Experimental tests are conducted to demonstrate the output performance and long-term durability of the TENG device by attaching it to a sample pipe. A theoretical model for the energy harvesting system is developed for predicting the electrical output performance of the device. It is established that the normalized output power depends only on two compound variables with all typical factors taken into consideration simultaneously. The simple scale law is useful to reveal the underlying mechanism of the device and can guideline the optimization of the device based on multi-parameters analyses. The results here may provide references for designing contact-mode TENG energy harvesting devices based on the vibration of marine pipes and similar structures.

Triboelectric Nanogenerator: Structure, Mechanism, and Applications

With the rapid development of the Internet of Things (IoT), the number of sensors utilized for the IoT is expected to exceed 200 billion by 2025. Thus, sustainable energy supplies without the recharging and replacement of the charge storage device have become increasingly important. Among various energy harvesters, the triboelectric nanogenerator (TENG) has attracted considerable attention due to its high instantaneous output power, broad selection of available materials, eco-friendly and inexpensive fabrication process, and various working modes customized for target applications. The TENG harvests electrical energy from wasted mechanical energy in the ambient environment. Three types of operational modes based on contact-separation, sliding, and freestanding are reviewed for two different configurations with a double-electrode and a single-electrode structure in the TENGs. Various charge transfer mechanisms to explain the operational principles of TENGs during triboelectrification are also reviewed for electron, ion, and material transfers. Thereafter, diverse methodologies to enhance the output power considering the energy harvesting efficiency and energy transferring efficiency are surveyed. Moreover, approaches involving not only energy harvesting by a TENG but also energy storage by a charge storage device are also reviewed. Finally, a variety of applications with TENGs are introduced. This review can help to advance TENGs for use in self-powered sensors, energy harvesters, and other systems. It can also contribute to assisting with more comprehensive and rational designs of TENGs for various applications.

Novel Flexible Triboelectric Nanogenerator based on Metallized Porous PDMS and Parylene C

Triboelectric nanogenerators (TENGs) have recently become a powerful technology for energy harvesting and self-powered sensor networks. One of their main advantages is the possibility to employ a wide range of materials, especially for fabricating inexpensive and easy-to-use devices. This paper reports the fabrication and preliminary characterization of a novel flexible triboelectric nanogenerator which could be employed for driving future low power consumption wearable devices. The proposed TENG is a single-electrode device operating in contact-separation mode for applications in low-frequency energy harvesting from intermittent tapping loads involving the human body, such as finger or hand tapping. The novelty of the device lies in the choice of materials: it is based on a combination of a polysiloxane elastomer and a poly (para-xylylene). In particular, the TENG is composed, sequentially, of a poly (dimethylsiloxane) (PDMS) substrate which was made porous and rough with a steam-curing step; then, a metallization layer with titanium and gold, deposited on the PDMS surface with an optimal substrate–electrode adhesion. Finally, the metallized structure was coated with a thin film of parylene C serving as friction layer. This material provides excellent conformability and high charge-retaining capability, playing a crucial role in the triboelectric process; it also makes the device suitable for employment in harsh, wet environments owing to its inertness and barrier properties. Preliminary performance tests were conducted by measuring the open-circuit voltage and power density under finger tapping (~2 N) at ~5 Hz. The device exhibited a peak-to-peak voltage of 1.6 V and power density peak of 2.24 mW/m2 at ~0.4 MΩ. The proposed TENG demonstrated ease of process, simplicity, cost-effectiveness, and flexibility.

Advances in portable electrospinning devices for in situ delivery of personalized wound care

Electrospinning and electrospun fibrous assemblies have attracted interest in a variety of biomedical fields including woundcare, tissue engineering and drug delivery, due to the large surface-area-to-volume ratio and high porosity of nanofibrous webs. Normally, wound dressings are manufactured well before the point of care, and then packaged and distributed for use at a later stage. More recently, in situ electrospinning of fibers directly onto wound sites has been proposed as a route to personalized wound dressing manufacture, tailored to the needs of individual patients. Practically, in situ deposition of nanofibers on to a wound could be envisaged using a portable or hand-held electrospinning device that is safe and easy to operate. This review focuses on recent advances in portable electrospinning technology and potential applications in woundcare and regenerative medicine. The main research challenges and future trends are also considered.

Triboelectric filtering for air purification

Air pollution becomes more and more serious with the rapid development of the society, and the haze caused by particulate matters (PMs) has become a global problem. Thus seeking an effective technology for removing the airborne PMs or other pollutants is much desirable for alleviating the air pollution. The newly invented triboelectric nanotechnology can realize efficient air filtering with obvious advantages over traditional fibrous filtering and electrostatic precipitation. Here, a review is provided for recent progress in air filter by utilizing the triboelectric nanotechnology, starting from the choices of triboelectric materials and main features of triboelectric nanotechnology. The mechanism of triboelectric air filtering technology was presented as the coupling of triboelectric filtering and mechanical filtering. Then the approaches of air filtering were summarized as the triboelectric nanogenerator (TENG)-driven air filtering, TENG-enhanced nanofiber air filtering, and self-powered triboelectric air filtering. The device structure, working principle and filtering performance were systematically discussed. Furthermore, the industry products which have been developed based on the triboelectric filtering technology were introduced.

Nanogenerators as a Sustainable Power Source: State of Art, Applications, and Challenges

A sustainable power source to meet the needs of energy requirement is very much essential in modern society as the conventional sources are depleting. Bioenergy, hydropower, solar, and wind are some of the well-established renewable energy sources that help to attain the need for energy at mega to gigawatts power scale. Nanogenerators based on nano energy are the growing technology that facilitate self-powered systems, sensors, and flexible and portable electronics in the booming era of IoT (Internet of Things). The nanogenerators can harvest small-scale energy from the ambient nature and surroundings for efficient utilization. The nanogenerators were based on piezo, tribo, and pyroelectric effect, and the first of its kind was developed in the year 2006 by Wang et al. The invention of nanogenerators is a breakthrough in the field of ambient energy-harvesting techniques as they are lightweight, easily fabricated, sustainable, and care-free systems. In this paper, a comprehensive review on fundamentals, performance, recent developments, and application of nanogenerators in self-powered sensors, wind energy harvesting, blue energy harvesting, and its integration with solar photovoltaics are discussed. Finally, the outlook and challenges in the growth of this technology are also outlined.

A Hybridized Triboelectric-Electromagnetic Water Wave Energy Harvester Based on a Magnetic Sphere

Blue energy harvested from ocean waves is an important and promising renewable energy source for sustainable development of our society. Triboelectric nanogenerators (TENGs) and electromagnetic energy harvesters (EMGs) both are considered promising approaches for harvesting blue energy. In this work, a hybridized triboelectric-electromagnetic water wave energy harvester (WWEH) based on a magnetic sphere is presented. A freely rolling magnetic sphere senses the water motion to drive the friction object sliding on a solid surface for TENG back and forth. At the same time, two coils transform the motion of the magnetic sphere into electricity according to the electromagnetic induction effect. For harvesting the blue energy from any direction, the electrodes of the TENG are specified as the Tai Chi shape, the effective of which is analyzed and demonstrated. Based on a series of experimental comparisons, the two friction layers and the two coils are specified to be connected in parallel and in series, respectively. A paper-based supercapacitor of ∼1 mF is fabricated to store the generated energy. The WWEH is placed on a buoy to test in Lake Lanier. During 162 s, the supercapacitor can be charged to 1.84 V, the electric energy storage in it is about 1.64 mJ. This work demonstrates that the WWEH can be successfully used for driving distributed, self-powered sensors for environmental monitoring.

Self-Powered Intelligent Water Meter for Electrostatic Scale Preventing, Rust Protection, and Flow Sensor in a Solar Heater System

Triboelectric nanogenerators (TENGs) have been investigated for mechanical energy harvesting because of their high-energy conversion efficiency, low cost, ease of manufacturing, and so on. This paper deals with designing a kind of water-fluid-driven rotating TENG (WR-TENG) inspired by the structure of a water meter. The designed WR-TENG is effectively integrated into a self-powered electrostatic scale-preventing and rust protection system. The WR-TENG can generate a constant DC voltage up to about 7.6 kV by using a voltage-doubling rectifier circuit (VDRC) to establish a high-voltage electrostatic field in the water tank. A WR-TENG, a VDRC, and an electric water heating tank are the components of the whole system. The system is convenient to be installed in any waterway system, effectively preventing the rusting of stainless steel and restraining the formation of scale when the water is heated to 65 ± 5 °C. Moreover, the approximately linear relationship between the short-circuit current and the rotation rate of the WR-TENG makes employing it as a self-powered water flow sensor possible. This work enables a facile, safe, and effective approach for electrostatic scale prevention, rust protection, and flow sensing in solar heaters, which will enrich the high-voltage applications of TENGs.

Theoretical System of Contact-Mode Triboelectric Nanogenerators for High Energy Conversion Efficiency

As the rapid expansion of next-generation electronics, portable and efficient energy sources has become one of the most important factors impeding the market development. Triboelectric nanogenerators (TENGs) are a potential candidate for its unsurpassed features. Herein, we deeply analyzed the power and conversion efficiency of contact-mode TENGs considering the whole energy conversion process. Firstly, reaching beyond the conventional analysis, a compressive force was introduced to derive a more versatile motion profile, which provided a better understanding of the working principle of contact-separation process. Then, we deeply analyzed the influence of various parameters on its performance. Especially, the maximum efficiency TENGs can be obtained under optimum force. It is realistic and useful for more efficient TENGs. Furthermore, this research stands a good chance of establishing standards for quantifying the efficiency of TENGs, which lays the basis for the further industrialization and multi-functionization of TENGs technology.

Self-Powered All-in-One Fluid Sensor Textile with Enhanced Triboelectric Effect on All-Immersed Dendritic Liquid-Solid Interface

Enormous interests have been attracted on exploiting interfacial triboelectric effects for sensor and energy applications but immensely limited by the inefficient liquid-solid electrification in terms of immersed applications in fluid. Here, we have presented a flexible self-powered all-in-one fluid sensor textile, for simultaneously monitoring the velocity, acceleration, and chemical composition based on an enhanced liquid-solid triboelectric effect. The textile was woven from flexible dendritic cable electrodes surrounded by arrays of micrometal dendrites, which could be further coated with a layer of polytetrafluoroethylene nanofibers. Even when completely immersed in the fluid, the textile can efficiently output a combined electric signal for parsing the velocity, acceleration, and chemical composition information. Furthermore, a textile of 6 cm² can charge a commercialized capacitor to 1 V within 80 s by harvesting flow energy on the liquid/solid interface, showing a potential use as the power supply of a signal-processing circuit. It has proposed a promising fluid sensor without extra power cables, for alerting possible leakage or blockage inside chemical and petroleum pipelines.

Raising the Working Temperature of a Triboelectric Nanogenerator by Quenching Down Electron Thermionic Emission in Contact-Electrification

As previously demonstrated, contact-electrification (CE) is strongly dependent on temperature, however the highest temperature in which a triboelectric nanogenerator (TENG) can still function is unknown. Here, by designing and preparing a rotating free-standing mode Ti/SiO₂ TENG, the relationship between CE and temperature is revealed. It is found that the dominant deterring factor of CE at high temperatures is the electron thermionic emission. Although it is normally difficult for CE to occur at temperatures higher than 583 K, the working temperature of the rotating TENG can be raised to 673 K when thermionic emission is prevented by direct physical contact of the two materials via preannealing. The surface states model is proposed for explaining the experimental phenomenon. Moreover, the developed electron cloud-potential well model accounts for the CE mechanism with temperature effects for all types of materials. The model indicates that besides thermionic emission of electrons, the atomic thermal vibration also influences CE. This study is fundamentally important for understanding triboelectrification, which will impact the design and improve the TENG for practical applications in a high temperature environment.

α- & β-crystalline phases in polyvinylidene fluoride as tribo-piezo active layer for nanoenergy harvester

The manuscript introduces the use of non-electrically polled spin-coated thin polyvinylidene fluoride (PVDF) films as the active layers in a contact electrification-based nanoenergy harvester. The four-layered device utilizes both piezo and triboelectric effect coupled with electrostatic induction. The elucidation of potential generation during contact between crystalline phases ( α and β) of PVDF layer material is investigated in the manuscript. Fourier transform infrared–attenuated total reflectance spectroscopy is carried out to illustrate the α- and β-phases in PVDF pellet, prepared film as well as the film after contact. Dynamic contact mode electrostatic force microscopy (DC-EFM) along with atomic force microscopy is used for the evaluation of reverse piezoelectric, local ferroelectric, triboelectric voltage and adhesive energy of the PVDF films before–after contact process. Quantum chemical calculation is performed using density functional theory to explain possible electron transitions in the active layers between the cylindrically symmetric α-phase and electrical double layer charges in the β-phase of PVDF. The interface study of the film is also carried out both experimentally using DC-EFM and through quantum chemical calculations. The fabricated device with the hybrid piezo-tribo layer promises to be a simple and low-cost energy source for the next-generation self-powered electronic devices. The device can also be used as knock sensor in engines as well as a capacitor.

A spring-assisted hybrid triboelectric-electromagnetic nanogenerator for harvesting low-frequency vibration energy and creating a self-powered security system

With the rapid development of portable electronics, exploring sustainable power sources is becoming more and more urgent. Utilizing a nanogenerator to harvest ambient mechanical energy could be an effective approach to solve this challenge. In this work, a novel spring-assisted hybrid nanogenerator (HG) consisting of a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) was developed for harvesting low-frequency vibration energy. The results show that the TENG with a PTFE surface nanostructure has better output performance than that without the nanostructure. The effect of operating frequency on the open-circuit voltage and short-circuit current of the TENG and EMG is systematically investigated. Under a 2 Hz operating frequency, the EMG and TENG are able to produce a peak power of about 57.6 mW with a resistive load of 2000 Ω and 1682 μW with a resistive load of 50 MΩ, respectively. The impedance matching between the TENG and EMG can be realized by using a transformer to reduce the impedance of the TENG. The charging performance of the HG is much better than that of the individual EMG or TENG. The HG enabled us to develop a self-powered safety system and to power LEDs, and drive some electronic devices. The present work provides a superior solution to improve the output performance of the HG for harvesting low-frequency vibration energy.

Silicone-Based Triboelectric Nanogenerator for Water Wave Energy Harvesting

Triboelectric nanogenerator (TENG) has been proven to be efficient for harvesting water wave energy, which is one of the most promising renewable energy sources. In this work, a TENG with a silicone rubber/carbon black composite electrode was designed for converting the water wave energy into electricity. The silicone-based electrode with a soft texture provides a better contact with the dielectric film. Furthermore, a spring structure is introduced to transform low-frequency water wave motions into high-frequency vibrations. They together improve the output performance and efficiency of TENG. The output performances of TENGs are further enhanced by optimizing the triboelectric material pair and tribo-surface area. A spring-assisted TENG device with the segmented silicone rubber-based electrode structure was sealed into a waterproof box, which delivers a maximum power density of 2.40 W m^-3, as triggered by the water waves. The present work provides a new strategy for fabricating high-performance TENG devices by coupling flexible electrodes and spring structure for harvesting water wave energy.

An alginate film-based degradable triboelectric nanogenerator

Alginate, as a natural linear polysaccharide derived from brown sea algae, has the advantage of low toxicity, good biocompatibility, and biodegradability, which has aroused wide interests in recent years. In this study, a degradable triboelectric generator based on an alginate film is presented. The calcium alginate film, which is prepared by a simple freeze-drying method and a crosslinking reaction, has a form of porous structures that are beneficial for triboelectric power generation. The fabricated TENG has a stable output performance with a maximum voltage, current, and power of 33 V, 150 nA, and 9.5 μW, respectively. The performances of the TENG were investigated at different thicknesses of the calcium alginate film and various concentrations of the sodium alginate solution, as well as the degradability of the film with different thicknesses and temperatures. In addition, the TENG was designed for harvesting water wave energy in a low-frequency range from 1 to 4 Hz. This study is promising to provide new insights to develop degradable and eco-friendly TENG based on ocean plants and expand the application range in blue energy.

A degradable triboelectric generator based on an alginate film has been proposed, which can be used to harvest water wave energy.

Self-Powered Electrostatic Filter with Enhanced Photocatalytic Degradation of Formaldehyde Based on Built-in Triboelectric Nanogenerators

Recently, atmospheric pollution caused by particulate matter or volatile organic compounds (VOCs) has become a serious issue to threaten human health. Consequently, it is highly desirable to develop an efficient purifying technique with simple structure and low cost. In this study, by combining a triboelectric nanogenerator (TENG) and a photocatalysis technique, we demonstrated a concept of a self-powered filtering method for removing pollutants from indoor atmosphere. The photocatalyst P25 or Pt/P25 was embedded on the surface of polymer-coated stainless steel wires, and such steel wires were woven into a filtering network. A strong electric field can be induced on this filtering network by TENG, while both electrostatic adsorption effect and TENG-enhanced photocatalytic effect can be achieved. Rhodamine B (RhB) steam was selected as the pollutant for demonstration. The absorbed RhB on the filter network with TENG in 1 min was almost the same amount of absorption achieved in 15 min without using TENG. Meanwhile, the degradation of RhB was increased over 50% under the drive of TENG. Furthermore, such a device was applied for the degradation of formaldehyde, where degradation efficiency was doubled under the drive of TENG. This work extended the application for the TENG in self-powered electrochemistry, design and concept of which can be possibly applied in the field of haze governance, indoor air cleaning, and photocatalytic pollution removal for environmental protection.

Self-Powered Electrospinning System Driven by a Triboelectric Nanogenerator

Broadening the application area of the triboelectric nanogenerators (TENGs) is one of the research emphases in the study of the TENGs, whose output characteristic is high voltage with low current. Here we design a self-powered electrospinning system, which is composed of a rotating-disk TENG (R-TENG), a voltage-doubling rectifying circuit (VDRC), and a simple spinneret. The R-TENG can generate an alternating voltage up to 1400 V. By using a voltage-doubling rectifying circuit, a maximum constant direct voltage of 8.0 kV can be obtained under the optimal configuration and is able to power the electrospinning system for fabricating various polymer nanofibers, such as polyethylene terephthalate (PET), polyamide-6 (PA6), polyacrylonitrile (PAN), polyvinylidene difluoride (PVDF), and thermoplastic polyurethanes (TPU). The system demonstrates the capability of a TENG for high-voltage applications, such as manufacturing nanofibers by electrospinning.

Simple and rapid fabrication of pencil-on-paper triboelectric nanogenerators with enhanced electrical performance

Paper and pencil have many advantages in triboelectric nanogenerators (TENGs) in terms of low-cost, light weight, and environment friendliness. In this work, a pencil-on-paper triboelectric nanogenerator (PP-TENG) with highly enhanced performance was introduced. In order to use paper as a friction layer and improve its triboelectric performance, a simple and rapid paper-coating process was utilized with polyvinylidene fluoride (PVDF), polyvinyledenedifluoride-trifluoroethylene (PVDF-TrFE), and poly(methyl methacrylate) (PMMA) solutions. The fabrication process of the PP-TENG was completed within 10 minutes via pencil drawing of an electrode followed by a solution coating. With an optimized electrode shape, the PP-TENG showed a maximum power density of 64 mW m^-2, which is more than 19 times higher than that of the uncoated paper TENG. The electrical performance of the PP-TENG was sufficient to drive a few hundred LEDs and charge various capacitors. It was maintained after the paper was folded or even crumpled. The proposed PP-TENG is expected to be utilized with other wearable electronic devices.

Ag-CuO-ZnO metal-semiconductor multiconcentric nanotubes for achieving superior and perdurable photodegradation

Solar energy represents a robust and natural form of resource for environment remediation via photocatalytic pollutant degradation with minimum associated costs. However, due to the complexity of the photodegradation process, it has been a long-standing challenge to develop reliable photocatalytic systems with low recombination rates, excellent recyclability, and high utilization rates of solar energy, especially in the visible light range. In this work, a ternary hetero-nanostructured Ag-CuO-ZnO nanotube (NT) composite is fabricated via facile and low-temperature chemical and photochemical deposition methods. Under visible light irradiation, the as-synthesized ZnO NT based ternary composite exhibits a greater enhancement (∼300%) of photocatalytic activity than its counterpart, Ag-CuO-ZnO nanorods (NRs), in pollutant degradation. The enhanced photocatalytic capability is primarily attributed to the intensified visible light harvesting, efficient charge carrier separation and much larger surface area. Furthermore, our as-synthesised hybrid ternary Ag-CuO-ZnO NT composite demonstrates much higher photostability and retains ∼98% of degradation efficiency even after 20 usage cycles, which can be mainly ascribed to the more stable polar planes of ZnO NTs than those of ZnO NRs. These results afford a new route to construct ternary heterostructured composites with perdurable performance in sewage treatment and photocorrosion suppression.

A Facile Method and Novel Mechanism Using Microneedle-Structured PDMS for Triboelectric Generator Applications

The triboelectric generator (TEG) is a cost-effective, multi-fabricated, friendly mechanical-energy-harvesting device. The traditional TEG, generally formed by two triboelectric materials in multilayers or a simple pattern, generated triboelectricity as it worked in the cycling contact-separation operation. This paper demonstrates a novel, high-aspect-ratio, microneedle (MN)-structured polydimethylsiloxane (PDMS)-based triboelectric generator (MN-TEG) by means of a low-cost, simple fabrication using CO₂ laser ablation on the polymethyl methacrylate substrate and a molding process. The MN-TEG, consisting of an aluminum foil and a microneedle-structured PDMS (MN-PDMS) film, generates an output performance with an open-circuit voltage up to 102.8 V, and a short-circuit current of 43.1 µA, corresponding to the current density of 1.5 µA cm^-2 . With introducing MN-PDMS into the MN-TEG, a great increase of randomly closed bending-friction-deformation (BFD) behavior of MNs leads to highly enhanced triboelectric performance of the MN-TEG. The BFD keeps increasingly on in-contact between MN with Al that results in enhancement of electrical capacitance of PDMS. The effect of aspect ratio and density of MN morphology on the output performance of MN-PDMS TEG is studied further. The MN-TEG can rapidly charge electric energy on a 0.1 µF capacitor up to 2.1 V in about 0.56 s. The MN-TEG source under tapping can light up 53 light-emitting diodes with different colors, connected in series.

A multi-dielectric-layered triboelectric nanogenerator as energized by corona discharge

Triboelectric nanogenerators (TENGs) have been invented recently for meeting the power requirements of small electronics and potentially solving the worldwide energy crisis. Here, we developed a vertical contact-separation mode TENG based on a novel multi-dielectric-layered (MDL) structure, which was comprised of parylene C, polyimide and SiO₂ films. By using the corona discharge approach, the surface charge density was enhanced to as high as 283 μC m^-2, and especially the open-circuit voltage could be increased by a factor of 55 compared with the original value. Furthermore, the theoretical models were built to reveal the output characteristics and store the electrostatic energy of the TENG. The influences of the structural parameters and operation conditions including the effective dielectric thickness, dielectric constant, gap distance and air breakdown voltage were investigated systematically. It was found that the output performances such as the peak voltage and power density are approximately proportional to the thickness of the MDL film, but they would be restricted by the air breakdown voltage. These unique structures and models could be used to deepen the understanding of the fundamental mechanism of TENGs, and serve as an important guide for designing high performance TENGs.

Design guidelines of triboelectric nanogenerator for water wave energy harvesters

Ocean waves are one of the cleanest and most abundant energy sources on earth, and wave energy has the potential for future power generation. Triboelectric nanogenerator (TENG) technology has recently been proposed as a promising technology to harvest wave energy. In this paper, a theoretical study is performed on a duck-shaped TENG wave harvester recently introduced in our work. To enhance the design of the duck-shaped TENG wave harvester, the mechanical and electrical characteristics of the harvester's overall structure, as well as its inner configuration, are analyzed, respectively, under different wave conditions, to optimize parameters such as duck radius and mass. Furthermore, a comprehensive hybrid 3D model is introduced to quantify the performance of the TENG wave harvester. Finally, the influence of different TENG parameters is validated by comparing the performance of several existing TENG wave harvesters. This study can be applied as a guideline for enhancing the performance of TENG wave energy harvesters.

Enhanced performance of ZnO microballoon arrays for a triboelectric nanogenerator

In recent years, triboelectric nanogenerators (TENGs), harvesting energy from the environment as a sustainable power source, have attracted great attention. Currently, many reports focus on the effect of surface modification on the electrical output performance of the TENG. In this work, we have fabricated vertically grown ZnO microballoon (ZnOMB) arrays on top of pyramid-featured PDMS patterned film, contacted with PTFE film to construct the TENG. The electrical output performances of the designed TENG are presented under external forces with different frequencies. The corresponding output open-circuit voltage with ZnOMBs could reach about 57 V the current density about 59 mA m^-2 at 100 Hz, which was about 2.3 times higher than without any ZnO. The global maximum of the instantaneous peak power could reach 1.1 W m^-2 when the external load resistance was about 2 MΩ. Furthermore, the electrical output of the fabricated device could light 30 commercial LED bulbs without any rectifier circuits or energy-storage elements. This clearly suggests that this kind of surface modification can dramatically enhance the output performance of the TENG. Moreover, the design of TENG demonstrated here can be applied to various energy harvesting applications.

Self-Powered Electrochemical Oxidation of 4-Aminoazobenzene Driven by a Triboelectric Nanogenerator

A rotary disc-structured triboelectric nanogenerator (rd-TENG) on the basis of free-standing electrification has been designed, where the aluminum composite panel has not been tailored to the stator becauseit is commercially available and cost-effective, has good electronic conductivity, and is easily processed. With the rotating speed increasing from 200 to 1000 rpm, the short-circuit current (I_sc) is sharply enhanced from 50 μA to 200 μA, while the measured open-circuit voltage (V_oc) and transferred charge (Q_tr) almost keep constant, 600 V and 0.4 μC, respectively. The matched load for the rd-TENG at a rotating speed of 600 rpm is 2.7 MΩ, generating a maximum power of 19.75 mW, which corresponds to a maximum power density of 2.28 W m^-2. Using the electric power generated by such a rd-TENG, highly toxic and carcinogenic 4-aminoazobenzene can be selectively treated to produce CO₂ or an oligomer via reasonably controlling electrochemical oxidation potentials. The underlying mechanism is tentatively proposed based on the cyclic voltammogram, gas chromatograph-mass spectrometer, electrochemical impedance spectroscopy, and UV-vis spectra. Here the electrochemical degradation in a single-compartment cell is more valid, preferable, and feasible. The output V_oc and rectified current of rd-TENG guarantee its extensive application to self-power electrochemical degradation of other azo compounds, i.e., 2-(4-dimethylaminophenylazo) benzoic acid, to CO₂. This work suggests that rd-TENG, sustainable energy, can be feasibly designed to self-power a practical electrochemical treatment of dyeing wastewater by harvesting vibration energy.

Fully Packaged Blue Energy Harvester by Hybridizing a Rolling Triboelectric Nanogenerator and an Electromagnetic Generator

Ocean energy, in theory, is an enormous clean and renewable energy resource that can generate electric power much more than that required to power the entire globe without adding any pollution to the atmosphere. However, owing to a lack of effective technology, such blue energy is almost unexplored to meet the energy requirement of human society. In this work, a fully packaged hybrid nanogenerator consisting of a rolling triboelectric nanogenerator (R-TENG) and an electromagnetic generator (EMG) is developed to harvest water motion energy. The outstanding output performance of the R-TENG (45 cm³ in volume and 28.3 g in weight) in the low-frequency range (<1.8 Hz) complements the ineffective output of EMG (337 cm³ in volume and 311.8 g in weight) in the same range and thus enables the hybrid nanogenerator to deliver valuable outputs in a broad range of operation frequencies. Therefore, the hybrid nanogenerator can maximize the energy conversion efficiency and broaden the operating frequency simultaneously. In terms of charging capacitors, this hybrid nanogenerator provides not only high voltage and consistent charging from the TENG component but also fast charging speed from the EMG component. The practical application of the hybrid nanogenerator is also demonstrated to power light-emitting diodes by harvesting energy from stimulated tidal flow. The high robustness of the R-TENG is also validated based on the stable electrical output after continuous rolling motion. Therefore, the hybrid R-TENG and EMG device renders an effective and sustainable approach toward large-scale blue energy harvesting in a broad frequency range.

Conducting polymer PPy nanowire-based triboelectric nanogenerator and its application for self-powered electrochemical cathodic protection

As a new type of energy harvesting device, the triboelectric nanogenerator (TENG) can convert almost all kinds of mechanical energy into electricity based on the coupling of triboelectrification and electrostatic induction. Here, a novel TENG is constructed with a conducting polymer polypyrrole nanowire (PPy NW) electrode, which is prepared by an electrochemical polymerization method with anodic aluminum oxide (AAO) as the template. The PPy NW-based TENG shows high output performance with a maximum short circuit current density of 23.4 mA m-2 and output voltage of 351 V, which can light 372 commercial red LEDs. Moreover, a self-powered anticorrosion system powered by the PPy NW-based TENG is designed, which can provide extra electrons to inject into the surface of the protected metals, forming effective impressed current cathodic protection by harvesting mechanical energy or wind energy. This smart device has potential applications for protecting metals from corrosion in daily life, industrial production and ocean exploration by harvesting the energies in the ambient environment.

Charging System Optimization of Triboelectric Nanogenerator for Water Wave Energy Harvesting and Storage

Ocean waves are one of the most promising renewable energy sources for large-scope applications due to the abundant water resources on the earth. Triboelectric nanogenerator (TENG) technology could provide a new strategy for water wave energy harvesting. In this work, we investigated the charging characteristics of utilizing a wavy-structured TENG to charge a capacitor under direct water wave impact and under enclosed ball collision, by combination of theoretical calculations and experimental studies. The analytical equations of the charging characteristics were theoretically derived for the two cases, and they were calculated for various load capacitances, cycle numbers, and structural parameters such as compression deformation depth and ball size or mass. Under the direct water wave impact, the stored energy and maximum energy storage efficiency were found to be controlled by deformation depth, while the stored energy and maximum efficiency can be optimized by the ball size under the enclosed ball collision. Finally, the theoretical results were well verified by the experimental tests. The present work could provide strategies for improving the charging performance of TENGs toward effective water wave energy harvesting and storage.

All-Elastomer-Based Triboelectric Nanogenerator as a Keyboard Cover To Harvest Typing Energy

The drastic expansion of consumer electronics (like personal computers, touch pads, smart phones, etc.) creates many human-machine interfaces and multiple types of interactions between human and electronics. Considering the high frequency of such operations in our daily life, an extraordinary amount of biomechanical energy from typing or pressing buttons is available. In this study, we have demonstrated a highly flexible triboelectric nanogenerator (TENG) solely made from elastomeric materials as a cover on a conventional keyboard to harvest biomechanical energy from typing. A dual-mode working mechanism is established with a high transferred charge density of ∼140 μC/m(2) due to both structural and material innovations. We have also carried out fundamental investigations of its performance dependence on various structural factors for optimizing the electric output in practice. The fully packaged keyboard-shaped TENG is further integrated with a horn-like polypyrrole-based supercapacitor as a self-powered system. Typing in normal speed for 1 h, ∼8 × 10(-4) J electricity could be stored, which is capable of driving an electronic thermometer/hydrometer. Our keyboard cover also performs outstanding long-term stability, water resistance, as well as insensitivity to surface conditions, and the last feature makes it useful to research the typing behaviors of different people.

Transparent and Flexible Self-Charging Power Film and Its Application in a Sliding Unlock System in Touchpad Technology

Portable and wearable personal electronics and smart security systems are accelerating the development of transparent, flexible, and thin-film electronic devices. Here, we report a transparent and flexible self-charging power film (SCPF) that functions either as a power generator integrated with an energy storage unit or as a self-powered information input matrix. The SCPF possesses the capability of harvesting mechanical energy from finger motions, based on the coupling between the contact electrification and electrostatic induction effects, and meanwhile storing the generated energy. Under the fast finger sliding, the film can be charged from 0 to 2.5 V within 2094 s and discharge at 1 μA for approximately 1630 s. Furthermore, the film is able to identify personal characteristics during a sliding motion by recording the electric signals related to the person's individual bioelectricity, applied pressing force, sliding speed, and so on, which shows its potential applications in security systems in touchpad technology.

Triboelectric Nanogenerators for Blue Energy Harvesting

Blue energy in the form of ocean waves offers an enormous energy resource. However, it has yet to be fully exploited in order to make it available for the use of mankind. Blue energy harvesting is a challenging task as the kinetic energy from ocean waves is irregular in amplitude and is at low frequencies. Though electromagnetic generators (EMGs) are well-known for harvesting mechanical kinetic energies, they have a crucial limitation for blue energy conversion. Indeed, the output voltage of EMGs can be impractically low at the low frequencies of ocean waves. In contrast, triboelectric nanogenerators (TENGs) are highly suitable for blue energy harvesting as they can effectively harvest mechanical energies from low frequencies (<1 Hz) to relatively high frequencies (∼kHz) and are also low-cost, lightweight, and easy to fabricate. Several important steps have been taken by Wang's group to develop TENG technology for blue energy harvesting. In this Perspective, we describe some of the recent progress and also address concerns related to durable packaging of TENGs in consideration of harsh marine environments and power management for an efficient power transfer and distribution for commercial applications.

Tribotronic Enhanced Photoresponsivity of a MoS2 Phototransistor

Molybdenum disulfide (MoS₂) has attracted a great attention as an excellent 2D material for future optoelectronic devices. Here, a novel MoS₂ tribotronic phototransistor is developed by a conjunction of a MoS₂ phototransistor and a triboelectric nanogenerator (TENG) in sliding mode. When an external friction layer produces a relative sliding on the device, the induced positive charges on the back gate of the MoS₂ phototransistor act as a "gate" to increase the channel conductivity as the traditional back gate voltage does. With the sliding distance increases, the photoresponsivity of the device is drastically enhanced from 221.0 to 727.8 A W^-1 at the 100 mW cm^-2 UV excitation intensity and 1 V bias voltage. This work has extended the emerging tribotronics to the field of photodetection based on 2D material, and demonstrated a new way to realize the adjustable photoelectric devices with high photoresponsivity via human interfacing.