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The unique characteristics of graphene have generated a lot of interest in the research community. A concept of utilizing graphene and its derivatives in the development of energy harvesters has just appeared in recent decades. This paper focuses on the application of reduced graphene oxide (rGO), a graphene derivative, in the development of wearable mechanical energy-harvesters to enable self-powered wearable sensing systems. Harvesting of energy has been a state-of-the-art phenomenon due to the ever-increasing requirement of power to run the sensing systems. Flexible systems that used rGO to gather energy with intensities ranging from a few microwatts to a few hundreds of microwatts have been used. Some examples are presented, focusing on the class of piezoelectric and triboelectric-based energy harvesters, with descriptions of their material composition, manufacturing methods, operating principle, and performance. Finally, the challenges and drawbacks of rGO-based energy harvesters are discussed, along with some of the potential solutions.

Highlights •Mechanical stimuli-triggered optical responses of cholesteric liquid crystal devices are realized.•Self-powered bistable smart window and E-paper are demonstrated.•Self-powered optical switch is developed for remote control.Intelligent responsive devices are crucial for a variety of applications ranging from smart electronics to robotics. Electro-responsive cholesteric liquid crystals (CLC) have been widely applied in display panels, smart windows, and so on. In this work, we realize the mechanical stimuli-triggered optical responses of the CLC by integrating it with a triboelectric nanogenerator (TENG), which converts the mechanical motion into alternating current electricity and then tunes the different optical responses of the CLC. When the voltage applied on the CLC is relatively low (15–40 V), the TENG drives the switching between the bistable planar state and focal conic state of the CLC, which shows potential applications in self-powered smart windows or E-paper displays. When the voltage supplied by the TENG is larger than 60 V, a self-powered optical switch is demonstrated by utilizing the transformation between focal conic state and instantons homeotropic state of the CLC. This triboelectric-optical responsive device consumes no extra electric power and suggests a great potential for future smart electronics.

Sensors have recently gathered significant attention owing to the rapid growth of the Internet of Things (IoT) technology for the real-time monitoring of surroundings and human activities. Particularly, recently discovered nanogenerator-based self-powered sensors are potential candidates to overcome the existing problems of the conventional sensors, including regular monitoring, lifetime of a power unit, and portability. Halide perovskites (HPs), with an excellent photoactive nature, dielectric, piezoelectric, ferroelectric, and pyroelectric properties, have been potential candidates for obtaining flexible and self-powered sensors including light, pressure, and temperature. Additionally, the photo-stimulated dielectric, piezoelectric, and triboelectric properties of HPs make them efficient entrants for developing bimodal and multimode sensors to sense multi-physical signals individually or simultaneously. Therefore, we provide an update on the recent progress in self-powered sensors based on pyroelectric, piezoelectric, and triboelectric effects of HP materials. First, the detailed working mechanism of HP-based piezoelectric, triboelectric, and pyroelectric nanogenerators—operated as self-powered sensors—is presented. Additionally, the effect of light on piezoelectric and triboelectric effects of HPs, which is indispensable in multimode sensor application, is also systematically discussed. Furthermore, the recent advances in nanogenerator-based self-powered bimodal sensors comprising HPs as light-active materials are summarized. Finally, the perspectives and continuing challenges of HP-based self-powered sensors are presented with some opportunities for future development in self-powered multimode sensors.

We report the development of low-cost triboelectric nanogenerators (TENGs) based on polypropylene (PP) fabrics formulated via an inexpensive melt-blowing process with an output voltage as high as 50 V. By disinfection methods such as exposure to steam, ethanol, and dry heat at 75 °C, the commercial medical masks and N95 filtering facepiece respirators (FFRs) can be reused to fabricate PP fiber based TENGs, which provide a novel regime for energy-harvesting devices based on reusable materials. As a power source, the output of one TENG can drive 15 serially connected light-emitting diodes (LEDs) or a commercial electric calculator. PP fabric TENGs can also work as self-powered sensors for the high-sensitivity detection of mechanical impact. We provide examples where the TENG is used to detect biomechanical motion such as that associated with the extension of an elbow, the touch of a finger, the impact of footsteps, and the bending of a knee without an external power supply. Most importantly, these PP fabrics for TENGs can be obtained from decontaminated medical masks that are generated as tremendous wastes every day, which provide a great potential as sustainable energy. These properties suggest that PP fabric based TENGs are promising for harvesting energy from biological systems and that they may facilitate the large-scale production of a new range of inexpensive self-powered multifunctional wearable sensors for applications in healthcare, security, and information networks.

Schottky-contacted sensors have been demonstrated to show high sensitivity and fast response time in various sensing systems. In order to improve their sensing performance, the Schottky barriers height (SBH) at the interface of semiconductor and metal electrode should be adjusted to appropriate range to avoid low output or low sensitivity, which was induced by excessively high or low SBH, respectively. In this work, a simple and effective SBH tuning method by triboelectric generator (TENG) is proposed, the SBH can be effectively lowered by voltage pulses generated by TENG and gradually recover over time after withdrawing the TENG. Through combining the TENG treatment with piezotronic effect, a synergistic effect on lowering SBH was achieved. The change of SBH is increased by 3.8 to 12.8 times, compared with dependent TENG treatment and piezotronic effect, respectively. Furthermore, the recovery time of the TENG-lowered SBH can be greatly shortened from 1.5 h to 40 s by piezotronic effect. This work demonstrated a flexible and feasible SBH tuning method, which can be used to effectively improve the sensitivity of Schottky-contact sensor and sensing system. Our study also shows great potential in broadening the application scenarios of Schottky-contacted electronic devices.

Abstract Harvesting abundant mechanical energy has been considered one of the promising technologies for developing autonomous self-powered active sensors, power units, and Internet-of-Things devices. Among various energy harvesting technologies, the triboelectric harvesters based on contact electrification have recently attracted much attention because of their advantages such as high performance, light weight, and simple design. Since the first triboelectric energy-harvesting device was reported, the continuous investigations for improving the output power have been carried out. This review article covers various methods proposed for the performance enhancement of triboelectric nanogenerators (TENGs), such as a triboelectric material selection, surface modification through the introduction of micro-/nano-patterns, and surface chemical functionalization, injecting charges, and their trapping. The main purpose of this work is to highlight and summarize recent advancements towards enhancing the TENG technology performance through implementing different approaches along with their potential applications. Graphic Abstract This paper presents a comprehensive review of the TENG technology and its factors affecting the output power as material selection, surface physical and chemical modification, charge injection, and trapping techniques.

Self-powered implantable devices have the potential to extend device operation time inside the body and reduce the necessity for high-risk repeated surgery. Without the technological innovation of in vivo energy harvesters driven by biomechanical energy, energy harvesters are insufficient and inconvenient to power titanium-packaged implantable medical devices. Here, we report on a commercial coin battery-sized high-performance inertia-driven triboelectric nanogenerator (I-TENG) based on body motion and gravity. We demonstrate that the enclosed five-stacked I-TENG converts mechanical energy into electricity at 4.9 μW/cm3 (root-mean-square output). In a preclinical test, we show that the device successfully harvests energy using real-time output voltage data monitored via Bluetooth and demonstrate the ability to charge a lithium-ion battery. Furthermore, we successfully integrate a cardiac pacemaker with the I-TENG, and confirm the ventricle pacing and sensing operation mode of the self-rechargeable cardiac pacemaker system. This proof-of-concept device may lead to the development of new self-rechargeable implantable medical devices., Self-powered implantable devices have the potential to extend device operation, though current energy harvesters are both insufficient and inconvenient. Here the authors report on a commercial coin battery-sized high-performance inertia-driven triboelectric nanogenerator based on body motion and gravity that can be used to charge a lithium-ion battery and integrated into a cardiac pacemaker.

Establishing a sustainable energy supply is necessary for intelligent greenhouse environmental management. Compared with traditional energy, green and eco-friendly energy is more conducive to protecting the agricultural production environment. In this study, a fluorinated superhydrophobic greenhouse film is proposed as a negative triboelectric layer material for the construction of a triboelectric nanogenerator that harvests raindrop energy (RDE-TENG). Moreover, an upgraded configuration is adopted, where the bulk effect between the lower/upper electrode and film replaces the interfacial effect of the liquid-solid interface, thereby promoting charge transfer. The results show that the RDE-TENG can serve as a sustainable energy source for greenhouse temperature and humidity sensors that assists in realizing intelligent control of the environment and guides agricultural production processes. This device exhibits high-voltage and a stable output; thus, it has the potential to replace traditional energy sources, which helps toward realizing a self-powered intelligent greenhouse planting mode.

An intelligent monitoring lubricant is essential for the development of smart machines because unexpected and fatal failures of critical dynamic components in the machines happen every day, threatening the life and health of humans. Inspired by the triboelectric nanogenerators (TENGs) work on water, we present a feasible way to prepare a self-powered triboelectric sensor for real-time monitoring of lubricating oils via the contact electrification process of oil–solid contact (O–S TENG). Typical intruding contaminants in pure base oils can be successfully monitored. The O–S TENG has very good sensitivity, which even can respectively detect at least 1 mg mL–1 debris and 0.01 wt % water contaminants. Furthermore, the real-time monitoring of formulated engine lubricating oil in a real engine oil tank is achieved. Our results show that electron transfer is possible from an oil to solid surface during contact electrification. The electrical output characteristic depends on the screen effect from such as wear debris, deposited carbons, and age-induced organic molecules in oils. Previous work only qualitatively identified that the output ability of liquid can be improved by leaving less liquid adsorbed on the TENG surface, but the adsorption mass and adsorption speed of liquid and its consequences for the output performance were not studied. We quantitatively study the internal relationship between output ability and adsorbing behavior of lubricating oils by quartz crystal microbalance with dissipation (QCM-D) for liquid–solid contact interfaces. This study provides a real-time, online, self-powered strategy for intelligent diagnosis of lubricating oils.

Interfaces between a liquid and a solid (L-S) are the most important surface science in chemistry, catalysis, energy, and even biology. Formation of an electric double layer (EDL) at the L-S interface has been attributed due to the adsorption of a layer of ions at the solid surface, which causes the ions in the liquid to redistribute. Although the existence of a layer of charges on a solid surface is always assumed, the origin of the charges is not extensively explored. Recent studies of contact electrification (CE) between a liquid and a solid suggest that electron transfer plays a dominant role at the initial stage for forming the charge layer at the L-S interface. Here, we review the recent works about electron transfer in liquid-solid CE, including scenerios such as liquid-insulator, liquid-semiconductor, and liquid-metal. Formation of the EDL is revisited considering the existence of electron transfer at the L-S interface. Furthermore, the triboelectric nanogenerator (TENG) technique based on the liquid-solid CE is introduced, which can be used not only for harvesting mechanical energy from a liquid but also as a probe for probing the charge transfer at liquid-solid interfaces.

With advancements in the Internet of things (IoT) technology, the construction of the self-powered distributed sensor network is important. Here, we proposed a low-cost triboelectric nanogenerator based on soil (S-TENG) to convert mechanical energy into electrical energy, and meanwhile, it can serve as the self-powered pressure sensor. The natural soil and polytetrafluoroethylene (PTFE) film play the role of triboelectric layers. The electrical performance of the S-TENG (size: 5 cm × 5 cm) is 344.7 V, 34.8 µA, 68.95 nC, and 0.99 mW. Besides, we also design a self-powered pressure sensor based on the S-TENG, and the brightness of light-emitting diodes (LEDs) can reflect the pressure. This research can release a new applications for pressure monitoring.

Liquid-solid triboelectric nanogenerator (L-S TENG) is one of the major techniques to collect energy from tiny liquids, while the saturated charge density at the L-S interface is the key element to decide its performance. Here, we found that the saturated charge density of L-S contact electrification (CE) can be further increased under the illumination of an ultraviolet (UV) light. The fluorine-containing polymers and SiO2 are chosen as the electrification materials and with and without UV illumination on the L-S TENG. A series of experiments have been done to rule out the possible influences of anion generation, chemical change of solid surface, ionization of water, and so on. Therefore, we proposed that electrons belonging to water molecules can be excited to high energy states under UV illumination, which then transfer to solid surface and captured by the solid surface. Finally, a photoexcited electron transfer model is proposed to explain the enhancement of CE under the UV illumination. This work not only helps to further understand CE at L-S interface, but also offers an approach to further enhance the performance of L-S TENG, which can promote the TENG applications in the field of microfluidic systems, liquid energy harvesting, and droplet sensory.

Summary Water-wave energy, as one of the important renewable energies, is greatly difficult to efficiently harvest due to its characteristics of low frequency and randomly moving direction. Herein, we report an active resonance triboelectric nanogenerator (AR-TENG) system fabricated by using simple pendulum, tumbler, and flexible ring TENG, which can harvest omnidirectional and frequency varying water-wave energy through excellent structural design and resonance effect. Besides, thanks to the high-frequency damped motion of simple pendulum and tumbler, the high-frequency output generated by the AR-TENG system under the driving condition of low-frequency water wave can greatly improve the efficiency of wave energy harvesting. More importantly, based on the low damping coefficient, resonance effect, and elimination of water screening effect, the output performance of AR-TENG system in the water wave is closest to the simulated test. This work not only can realize the omnidirectional water-wave energy harvesting by TENG but also provide a method for large-scale blue energy harvesting.

Textile triboelectric nanogenerator (TENG) is a kind of smart textile technology that integrates traditional flexible and wearable textile materials with emerging and advanced TENG science, which not only embraces the capabilities of autonomous energy harvesting and active self-powered sensing, but also maintains original wearability and desired comfortability. With the help of the burden-free and self-sufficient wearable intelligent system, individuals can achieve convenient acquisition and efficient utilization of electric energy, which will help to promote the future development of human-oriented on-body electronics and artificial intelligence. Here, some fundamental knowledge and core elements, including the operational modes and corresponding service occasions, charge generation and transfer mechanisms, remaining challenges and potential solutions are comprehensively summarized and systematically discussed. Based on these analyses, a roadmap toward the scientific research and large-scale commercial application of textile TENGs in the next decade is highlighted at the end of the article. We believe that textile TENGs will become an indispensable part of daily clothing in the future, thus benefiting all humankind and human civilization.

Ion mobility analysis is a well-known analytical technique for identifying gas-phase compounds in fast-response gas-monitoring systems. However, the conventional plasma discharge system is bulky, operates at a high temperature, and inappropriate for volatile organic compounds (VOCs) concentration detection. Therefore, we report a machine learning (ML)-enhanced ion mobility analyzer with a triboelectric-based ionizer, which offers good ion mobility selectivity and VOC recognition ability with a small-sized device and non-strict operating environment. Based on the charge accumulation mechanism, a multi-switched manipulation triboelectric nanogenerator (SM-TENG) can provide a direct current (DC) bias at the order of a few hundred, which can be further leveraged as the power source to obtain a unique and repeatable discharge characteristic of different VOCs, and their mixtures, with a special tip-plate electrode configuration. Aiming to tackle the grand challenge in the detection of multiple VOCs, the ML-enhanced ion mobility analysis method was successfully demonstrated by extracting specific features automatically from ion mobility spectrometry data with ML algorithms, which significantly enhance the detection ability of the SM-TENG based VOC analyzer, showing a portable real-time VOC monitoring solution with rapid response and low power consumption for future internet of things based environmental monitoring applications.

For human beings of different ages and physical abilities, the inherent balance control system is ubiquitous and active to prevent falling, especially in motion states. A hybridized electromagnetic-triboelectric nanogenerator (HETNG) is prepared to harvest biomechanical energy during human balance control processes and achieve significant monitoring functions. The HETNG is composed of a symmetrical pendulum structure and a cylinder magnet rolling inside. Four coils are divided into two groups which form into two electromagnetic generators (EMGs). Besides, two spatial electrodes attached to the inner wall constitute a freestanding mode triboelectric nanogenerator (TENG). With a rectification circuit, the HETNG presents a high output power with a peak value of 0.55 W at a load of 160 Ω. Along with human balance control processes during walking, the HETNG can harvest biomechanical energy at different positions on the trunk. Moreover, the HETNG applied in artificial limb has been preliminarily simulated with the positions on thigh and foot, for monitoring the actions of squat and stand up, and lifting the leg up and down. For the elder that walks slowly with a walking aid, the HETNG equipped on the walking aid can help to record the motions of forwarding and unexpected falling, which is useful for calling for help. This work shows the potential of biomechanical energy-driven HETNG for powering portable electronics and monitoring human motions, also shows significant concerns to people lacked action capability or disabled.

Loss of tactile sensation is a common occurrence in patients with traumatic peripheral nerve injury or soft tissue loss, but as yet, solutions for restoring such sensation are limited. Implanted neuro-prosthetics are a promising direction for tactile sensory restoration, but available technologies have substantial shortcomings, including complexity of use and of production and the need for an external power supply. In this work, we propose, fabricate, and demonstrate the use of a triboelectric nanogenerator (TENG) as a relatively simple, self-powered, biocompatible, sensitive, and flexible device for restoring tactile sensation. This integrated tactile TENG (TENG-IT) device is implanted under the skin and translates tactile pressure into electrical potential, which it relays via cuff electrodes to healthy sensory nerves, thereby stimulating them, to mimic tactile sensation. We show that the device elicits electrical activity in sensory neuronsiin vitro/i, and that the extent of this activity is dependent on the level of tactile pressure applied to the device. We subsequently demonstrate the TENG-ITiin vivo/i, showing that it provides tactile sensation capabilities (as measured by a von Frey test) to rats in which sensation in the hindfoot was blocked through transection of the distal tibial nerve. These findings point to the substantial potential of self-powered TENG-based implanted devices as a means of restoring tactile sensation.

Triboelectric generators (TENGs) have been extensively studied as a new energy for low cost and the universally applicable prospect. Meanwhile, perovskites have been applied in TENG and show a good performance in view of high carrier mobility, long life and dielectric properties. The asymmetry structure of the orthogonal phase CsPbBr3 perovskite endows it with ferroelectric property and induces the misalignment of the positive and negative charge centers. Herein, the surface energy of halogen doped inorganic CsPbX3 (X = Cl-, Br-) perovskites are theoretically investigated by density functional theory (DFT) calculation, the crystal polarizability of pristine CsPbBr3 is improved from 0.47 Ry a.u. to 0.52 Ry a.u. (CsPbCl3), indicating the polarizability of CsPbCl3 is higher than CsPbBr3. In addition, the build-in electric field (Ebuild-in) of perovskite materials can be enhanced by the spontaneous polarization and the aligned dipoles in the Ebuild-in could further improve the tribo-electrostatic electric field by retaining more triboelectric surface charges. In the end, CsPbCl3 achieved a power of 3.06 W m-2 compared to the power of 1.34 W m-2 of CsPbBr3. This work focuses on the regulation of crystal planes using spontaneous polarization of perovskite toward achieving a high built-in electric field for enhancing triboelectric surface charge density.

The triboelectric effect (TE), simply described as the generation of electricity from tribology or friction, has been known for over 1500 years. TE arises from charge transfer between surfaces under contact, typically attributed to electron transfer. However, emerging understanding shows how the ion transfer and material transfer (bond cleavage) mechanisms play a key role in TE. An engineering focus on increasing the porosity, surface roughness, and use of hetero-genous materials has resulted in a recent explosion in triboelectric literature, particularly towards soft and flexible polymer devices. Here, we critically evaluate recent progress in TE generators and link engineered performance to the fundamental driving forces of triboelectricity, using the exemplar triboelectric polymer, poly(dimethylsiloxane).

Safety concerns require the frequently check for leaks in gas pipelines. Also, in coal mines the type gases permeating from the ground need to be monitored. Triboelectric nanogenerators (TENGs) can be applied for gas sensing without external power supply. In this paper, a two-dimensional model of a TENG was established, and a gas jet a rectangular cross section was added between two triboelectric materials. The TENG could generate distinguishable electrical signals according to the different types of gas and the different gas injection areas. This work contributes to the area of self-powered gas sensing.

Recently, piezoelectric/triboelectric nanogenerators based on piezoelectric composite materials have been intensively studied to achieve high electrical output performance. In this work, flexible BaTiO3 (BT)/PDMS nanocomposite films with various sizes and concentrations were fabricated and used as the nanogenerators. The influence of dielectric properties on the electrical output of nanogenerators was studied as well as the structure of the composites. The dielectric constant increased from 6.5 to 8 with the concentration of BT nanoparticles and decreased with the frequency from 102 to 106 Hz. Furthermore, the dielectric constant showed 11% decrease with the temperature range from 30 to 180 °C. It was found that the concentration of BT nanoparticles has promoted the electrical output of nanogenerators. The output voltage and current are all enhanced with the BT nanoparticles, which reached 200 V and 0.24 °A in TENG with 40 wt% BT nanoparticles, respectively. The selected device exhibited the power of 0.16 mW and employed to demonstrate its ability to power wearable/portable electronics by lighting the LEDs.

Micromechanical vibration, as one of the most prevalent forms of energy in an ambient environment, has surpassing application potentials as the power source for self-powered electronics. A triboelectric nanogenerator (TENG) can effectively convert vibrational energy to electricity, which has the unique benefit of a wide-band over a traditional vibration energy harvester due to the contact electrification mechanism. Herein, the frequency band characteristics of vibrational TENG (V-TENG) were systematically elaborated. The mechanical model of V-TENG was established to explore its working mechanism for wide-band vibrational energy harvesting. By simulation analysis and experimental validation, the bandwidth dependence of V-TENG on acceleration magnitude, proof mass, stiffness, and gap distance was investigated in detail. With optimized structural parameters, an ultra-wide-band vibration energy harvester (UVEH) was developed by a tandem spring-mass structure. Within the ultra-wide-band range from 3 to 45 Hz, the UVEH can invariably illuminate 36 serial light-emitting diodes (LEDs) and charge a 33 μF capacitor to 1.5 V within 35 s. This work has quantitatively studied frequency band characteristics of V-TENG and provided a promising strategy for wide-band vibrational energy harvesting from a machine, bridge, water wave, and human motion.

Using clean and sustainable stochastic energy from the environment to eliminate pollution caused by gaseous aldehydes would be an effective strategy to achieve the sustainable development of energy and preserve the environment. Here, a piston-based triboelectric nanogenerator (P-TENG) was used to enhance gaseous acetaldehyde absorption and photocatalytic degradation. An external electric field could be generated on a conductive substrate by the P-TENG, converting wind energy into electricity. This made it possible to efficiently degrade gaseous acetaldehyde in the photocatalytic system. Driven by a light breeze (3.0 m/s), the acetaldehyde removal rate of the system reached 63% within 30 min. The presence of an external electric field could generate more hydroxyl radicals (•OH), superoxide radicals (•O2-), and holes (h+), which has a positive effect on the photocatalytic degradation of acetaldehyde. The design and concept of this study not only realized the efficient conversion of renewable and sustainable random energy but also could be applied to the efficient removal of gaseous aldehydes, providing an effective way to create a cleaner environment.

Drill string vibration during the drilling must be measured in real-time as it will cause damage to the construction. This paper proposed a self-powered downhole vibration sensor based on the triboelectric nanogenerator. The downhole vibration sensor relies on the drill string vibration to induce triboelectric charge and electrostatic induction of nanomaterials, thereby realizing self-powered vibration measurement. Sensing performance test results show that the measurement range is between 0 to 5 Hz, the measurement error does not exceed 3.5%, and the output voltage amplitude with a range of 2 V to 5.5 V decreases with the increases of vibration frequency. Self-powered performance test results show that the output current can reach a maximum value of about 35 × E−8 A when a 50 ohm resistance is connected in series, the output power can reach a maximum value of about 924.5 × E−12 W when a 20k ohm resistance is connected in series at a vibration frequency of 0.8 Hz, and the output current and power all decrease with the increase of the vibration frequency.

Nanogenerators have attracted particular attention during the last decade. Here, a novel functional triboelectric nanogenerator based on the foam (F-TENG) was inverted. In this design, the foam and...

MXenes (Ti3C2TX) are two-dimensional transition-metal carbides and carbonitrides with high conductivity and optical transparency. However, transparent MXene electrodes with high environmental stability suitable for various flexible organic electronic devices have rarely been demonstrated. By laminating a thin polymer film onto a solution-processed MXene layer to protect the MXene film from harsh environmental conditions, we present transparent and flexible MXene electronic devices. A thin polymer layer spin-coated onto a transparent MXene electrode provides environmental stability even under air exposure longer than 7 d at high temperatures (up to 70 °C) and humidity levels (up to 50%) without degrading the transparency of the electrode. The resulting polymer-laminated (PL) MXene electrode facilitates the development of a variety of field-driven photoelectronic devices by exploiting the electric field exerted between the MXene layer and the counter electrode through the insulating polymer. Field-induced electroluminescent displays, based on both organic and inorganic phosphors, with PL-MXene electrodes are demonstrated with high transparency and mechanical flexibility. Furthermore, our PL-MXene electrode exhibits high versatility through successful implementation in capacitive-type pressure sensors and triboelectric nanogenerators, resulting in field-driven sensing and energy harvesting electronic devices with excellent operation reliability.

In this work, the surface modification using a two-steps plasma etching has been developed for enhancing energy conversion performance in polytetrafluoroethylene (PTFE) triboelectric nanogenerator (TENG). Enhancing surface area by a powerful O2 and Ar bipolar pulse plasma etching without the use of CF4 gas has been demonstrated for the first time. TENG with modified surface PTFE using a sequential two-step O2/Ar plasma has a superior power density of 9.9 Wm−2, which is almost thirty times higher than that of a pristine PTFE TENG. The synergistic combination of high surface area and charge trapping sites due to chemical bond defects achieved from the use of a sequential O2/Ar plasma gives rise to the intensified triboelectric charge density and the enhancement of power output of PTFE-based TENG. The effects of plasma species and plasma etching sequence on surface morphologies and surface chemical species were investigated by a field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The correlation of surface morphology, chemical structure, and TENG performance was elucidated. In addition, the applications of mechanical energy harvesting for lighting, charging capacitors, keyboard sensing and operating a portable calculator were demonstrated.

Development of ocean energy conversion technique is a strategic requirement to optimize the energy structure and expand the "blue economic" space. Triboelectric nanogenerator (TENG) provides a potential approach for efficiently capturing wave energy with its unique advantages. Herein, a nodding duck structure multi-track freestanding triboelectric-layer nanogenerator (NDM-FTENG) is developed for ocean wave energy harvesting at a low-frequency range. Configuration parameters including track numbers, connection approach, oscillation frequency, and swing amplitude on electrical output performances of NDM-FTENG are systematically investigated and optimized; the maximum instantaneous power density of 4 W/m3 is obtained by one NDM-FTENG block with 320 LEDs lighted up simultaneously. Overall, NDM-FTENG is proved to be an efficient device for driving small electronics with excellent stability and durability in a real water wave environment, and the power potential can be further magnified by combining more NDM-FTENG devices in parallel to form a network toward large-scale blue energy harvesting.

Low output performance and poor anti-wear characteristics are still obstacles for further development of triboelectric nanogenerators (TENG). Here, a novel approach to reinforce the output performa...

The output power of the triboelectric nanogenerator (TENG) strongly depends on the performance of triboelectric materials, especially microstructures and functional groups of them. In this work, aiming at the excellent triboelectric ability, alternate-layered MXene composite films-based TENG with abundant fluorine groups(-F) through layer-by-layer stacking are designed and fabricated. Benefitting from the uniform intrinsic microstructure and increased dielectric constant, when the amount of the Nb2CTx nanosheets increases to 15 wt%, the TENG based on Nb2CTx/Ti3C2Tx composite nanosheets films achieves the maximum output. The short-circuit current density of 8.06 μA/cm2 and voltage of 34.63 V are 8.4 times and 3.5 times over that of pure Ti3C2Tx films, and 3.3 times and 4.3 times over that of commercial poly(tetrafluoroethylene) (PTFE) films, respectively. Furthermore, the fabricated TENG could be attached to human body to harvest energy from human motions, such as typing, texting, and hand clapping. The results demonstrate that the alternate-layered MXene composite nanosheet films through layer-by-layer stacking possess remarkably triboelectric performance, which broaden the choice of negative triboelectric materials and supply a new choice for high output TENG.

Air-flow sensing is essential in broad applications of weather forecasting, ocean monitoring, gas leakage alarming, and health monitoring. However, in severe environments where electrical power supply and cable connection are not available, the sensing of air flow in a self-powered way is a challenging issue. In this work, we reported a tribo-induced smart reflector to achieve the self-powered wireless sensing of the air flow by combining an aerodynamics-driven triboelectric nanogenerator (TENG) and a silver-coated polymer network liquid crystal. Upon being driven by the air flow, the developed reflector performed specular and diffused reflectance without and with charging by the TENG, respectively, enabling wireless sensing through mechanical-electrical-optical signal conversion. In the developed sensing paradigm, the sensing module can be fully self-powered without the need of signal pre-amplification, which is electrically separated from the light source and detection modules without cable connections. The applications of self-powered wireless wind speed sensing and breath monitoring were performed to demonstrate the effectiveness of the developed paradigm toward self-powered wireless sensing nodes in the internet of things.

With the advantages of superior wear resistance, mechanical durability, and stability, the liquid-solid mode triboelectric nanogenerator (TENG) has been attracting much attention in the field of energy harvesting and self-powered sensors. However, most reports are primarily observational, and there still lacks a universal model of this kind of TENG. Here, an equivalent circuit model and corresponding governing equations of a water-solid mode TENG are developed, which could easily be extended to other types of liquid-solid mode TENGs. Based on the first-order lumped circuit theory, the full equivalent circuit model of water-solid mode TENG is modeled as a series connection of two capacitors and a water resistor. Accordingly, its output characteristics and critical influences are examined, to investigate the relevant physical mechanism behind them. Afterward, a three-dimensional water-solid TENG array constructed from many single-wire TENGs is fabricated, which can not only harvest tiny amounts of energy from any movement of water, but also can verify our theoretical predictions. The fundamentals of the water-solid mode TENG presented in this work could contribute to solving the problem of electrical phenomena on a liquid-solid interface, and may establish a sound basis for a thorough understanding of the liquid-solid mode TENG.

The development of triboelectric nanogenerator (TENG) technology which can directly convert ambient mechanical energy into electric energy may affect areas from green energy harvesting to emerging wearing electronics. And, the material of triboelectric layer is critical to the mechanical robustness and electrical output characteristics of the TENGs. Herein, a MXene enhanced electret polytetrafluoroethylene (PTFE) film with a high mechanical property and surface charge density is developed. The MXene/PTFE composite film was synthesized by spraying and annealing treatment. With the doping of MXene, the crystallinity of composite film could be tuned, leading to an enhancement in the tensile property of 450% and reducing the wear volume about 80% in the friction test. Furthermore, the as-fabricated TENG with this composite film outputs 397 V of open-circuit voltage, 21 µA of short-circuit current, and 232 nC of transfer charge quantity, which are 4, 6, and 6 times higher than that of the TENG made by pure PTFE film, respectively. Therefore, this work provides a creative strategy to simultaneously improve the mechanical property and electrical performance of the TENGs, which have great potential in improving device stability under a complex mechanical environment.

The development of wireless monitoring is currently restricted by the short lifetime of batteries, requiring frequent replacement. Utilization of abundant mechanical energy from the surrounding environment has attracted increasing attention in real-time monitoring. Herein, a coil-levitated hybrid generator was developed for the efficient harvesting of mechanical energy from mechanical motion. The novel coil-levitated structure adapted to the metal and magnetic environment. The output currents were systematically analyzed at different operation modes based on the unique combination of triboelectrification, electromagnetic induction, and piezoelectric effect. Under the excitation of vibration frequency and amplitude of 8 Hz and 5 mm respectively, the as-constructed triboelectric nanogenerator delivered a peak power density of 11.40 W/m3 at 10 MΩ. Meanwhile, the middle electromagnetic part and bottom piezoelectric generator provided peak power densities of 6.97 and 79.93 W/m2 at 10000 Ω, respectively. More importantly, the battery charging experiment was verified, in which a 30 mA h Li-ion battery can be charged from 2.57 to 3.27 V in about 90 min. In sum, a self-powered temperature and vibration monitoring system was successfully developed based on hybrid generator, promising for realizing wireless monitoring of mechanical equipment without any external power supply.

Distributed renewable kinetic energies are ubiquitous but with irregular amplitudes and frequencies, which, as one category of "high-entropy" energies, are crucial for next-generation self-powered electronics. Herein, we present a flexible waterproof dual-mode textile triboelectric nanogenerator (TENG), which can simultaneously scavenge multiple "high-entropy" kinetic energies, including human motions, raindrops, and winds. A freestanding-mode textile TENG (F-TENG) and a contact-separation-mode textile TENG (CS-TENG) are integrated together. The structure parameters of the textile TENG are optimized to improve the output performances. The raindrop can generate a voltage of up to ∼4.3 V and a current of about ∼6 μA, while human motion can generate a voltage of over 120 V and a peak power density of ∼500 mW m-2. The scavenged electrical energies can be stored in capacitors for powering small electronics. Therefore, we demonstrated a facile preparation of a TENG-based energy textile that is highly promising for kinetic energy harvesting and self-powered electronics.

The biomolecules offer different metal-binding sites to form a coordination polymer with structural diversity. The coordination directed one-dimensional metal-biomolecule nanofibers (Cu-Asp NFs) designed using copper as metal ion and aspartate as a ligand for triboelectric nanogenerator (TENG) is reported here. The different characterization techniques reveal the detailed characteristics of the synthesized Cu-Asp NFs. The robust coating of the Cu-Asp NFs is achieved using a simple tape cast coater. The bending and water dipping studies suggest the stability of the coated material. The relative polarity test and Kelvin probe force microscopy (KPFM) reveal the position of Cu-Asp in the triboelectric series. The Cu-Asp NFs and Teflon are used as the active material for the fabrication of freestanding mode (NF-TENG) and contact-separation mode (cNF-TENG) TENG. The NF-TENG generates an output of 200 V and 6 μA. The simple ion deposition technique enhances the voltage, current, and transferred charge of cNF-TENG by 2.5, 8, and 3 times. The use of the material for the single electrode sliding mode device further confirms the coated material’s stability and robustness. A selective self-powered thioacetamide sensor is developed with the cNF-TENG, which exhibits a sensitivity of 0.76 v mM–¹. Finally, NF-TENG is demonstrated for powering up numerous portable electronics.

The triboelectric nanogenerator (TENG) is a new mechanical energy harvesting technology in which the typical viscoelastic material polydimethylsiloxane (PDMS) is widely used. Micro-/nano-textures are often fabricated on the PDMS surface to enhance the electrical performance of TENG. As the contact region decreases to micro/nano scale, the adhesive forces become dominant. However, there is still a lack of contact mechanics model considering both material viscoelasticity and the adhesive forces to guide the surface texture design. In this paper, the explicit data-fitting formulas based on the fractional derivative Zener model are firstly derived to identify the viscoelastic constitutive parameters, which can not only avoid the influence of the initial contact point, but also ensure the accurate conversion between the creep compliance and the relaxation modulus function. Then a viscoelastic-adhesive contact model based on the fitted constitutive parameters is established, and the numerical algorithms such as bi-conjugate stabilized (Bi-CGSTAB) method and fast Fourier transform (FFT) technique are employed to analyze the effects of material viscoelasticity and texture sizes on the contact and electrical performance. It is shown that, compared with results from the elastic-adhesive contact model, the contact area ratio based on the viscoelastic-adhesive contact model is significantly larger, which is much closer to the experimental results. Among the selected sizes of pyramid texture, the higher electrical performance can be obtained from the textures with a smaller pitch and a larger width under the heavier applied load. This study can provide a theoretical reference for the design of viscoelastic surface texture of TENG.

Triboelectric generators are excellent candidates for smart textiles applications due to their ability to convert mechanical energy into electrical energy. Such devices can be manufactured into yarns by coating a conductive core with a triboelectric material, but current triboelectric yarns lack the durability and washing resistance required for textile-based applications. In this work, we develop a unique triboelectric yarn comprising a conducting carbon nanotube (CNT) yarn electrode coated with poly(vinylidene fluoride) (PVDF) fibers deposited by a customized electrospinning process. We show that the electrospun PVDF fibers adhere extremely well to the CNT core, producing a uniform and stable triboelectric coating. The PVDF–CNT coaxial yarn exhibits remarkable triboelectric energy harvesting during fatigue testing with a 33% power output improvement and a peak power density of 20.7 μW cm–2 after 200 000 fatigue cycles. This is potentially due to an increase in the active surface area of the PVDF fiber coating upon repeated contact. Furthermore, our triboelectric yarn meets standard textile industry benchmarks for both abrasion and washing by retaining functionality over 1200 rubbing cycles and 10 washing cycles. We demonstrate the energy harvesting and motion sensing capabilities of our triboelectric yarn in prototype textile-based applications, thereby highlighting its applicability to smart textiles.

Triboelectric nanogenerators (TENGs) are an advanced mechanical energy harvesting system that has a wide range of advantages and has great prospects for use in various fields of science and technology. Among the factors that have a significant impact on the performance of TENGs, a special role belongs to the nature of triboelectric polymer materials. Over the past few years, there has been an exponential growth in research on polymers with shape memory assisted self-healing (SMASH) properties for TENGs. This mini review presents the state of the art in SMASH polymers for TENGs and attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Particular attention is paid to the relationship between these polymeric materials and the performance of TENGs. Finally, the problems and promising research directions for polymers with SMASH properties for TENGs are outlined.

The operation cost of an intelligent high-speed train system is greatly increased by the enormous energy demand of large-scale signal and sensor networks. However, the wind energy generated by high...

Wind energy plays an increasingly important role in alleviating the shortage of fossil fuel energy because of the emerging promising technologies such as electromagnetic generators (EMGs), triboele...

Miniaturized mobile electronic devices have aroused great attention due to their convenience to daily life. However, they still face a problem that power supply from the conventional cell needs to be regularly charged or replaced. Portable electricity supply collecting energy from environment is highly desired. Herein, a highly flexible and stretchable Miura folding based triboelectric nanogenerator (MF-TENG) is prepared by using flexible polyethylene terephthalate (PET) as a folding substrate with a double working side design, specifically one side as the main TENG (M-TENG) and other side as the excitation TENG (E-TENG). The E-TENG supplements charge to M-TENG by a half-wave rectifier circuit. This design increases the TENG working area and reduces its volume. The output performance of the TENG based on Miura folding with charge excitation called MF-CE-TENG is greatly boosted. The optimal output charge and maximum peak power of MF-CE-TENG achieves 1.54 µC and 5.17 mW at 1 Hz, respectively, which is 4.61 and 10.55 times as much as that of MF-TENG without charge excitation. To demonstrate its applications, the MF-CE-TENG is used to light up 456 LEDs brightly and charge a 100 µF capacitor to 6.07 V in 5 min. A calculator and a temperature-humidity sensor work normally powered by MF-CE-TENG with an energy management module. This work provides a new strategy to enhance the output energy of Miura folding TENG by applying a charge excitation mode for the first time, which might be an effective approach to be used in other TENGs.

Noncontact-mode-operating triboelectric nanogenerators (TENGs), which directly avoid physical contact, are fascinating self-powered systems aimed at long-life operation and minimizing rubbing frict...

The improper disposal and accumulation of polymer waste in the environment cause several ecological damages, and it is a challenge for our society. The mechanical recycling of polymer waste is the most appropriate alternative to decrease these problems. However, polymer recycling is not a trivial process and some difficulties, such as the segregation of different kinds of polymers in post-consume polymeric waste, represent their complexity. The segregation of post-consume polymeric waste is the main barrier for mechanical recycling of polymers. Electrostatic separation of polymeric waste based on tribocharging of polymer particles when rubbed with different surfaces has emerged as a promising method for mechanized separation of polymer waste. In present study, an apparatus for electrostatic separation of polymer waste based on tribocharging in polyvinyl chloride pipe with air flow has been development. The system has showed considerable efficiency for polyvinyl chloride segregation in binary mixtures with high-density polyethylene waste and with polyethylene terephthalate as well as in ternary mixture polyvinyl chloride/high-density polyethylene/polyethylene terephthalate.

Herein, a fully sustainable, flexible, and bio-based piezoelectric-cum-triboelectric energy harvester has been developed using a simple commodity cotton fabric. In the present study, a novel attemp...

Vehicle restraint systems play an irreplaceable role to limit passenger injuries when an accident occurs, in which, the 3D acceleration sensor (AS) is an essential component to detect the collision position and force. However, there are some defects for commercial sensors such as passive sensing, low sensitivity and high manufacturing cost. Here, we report a lightweight, high-sensitivity, low-cost and self-powered 3D AS based on a liquid–metal triboelectric nanogenerator (LM-TENG). In view of the coded strategy of the electrodes, the 3D AS retains the smallest size, lowest weight and highest integration compared to the currently reported self-powered AS. The fabricated sensor possesses wide detection range from 0 to 100 m/s2 in the horizontal direction and 0 to 50 m/s2 in the vertical direction at a sensitivity of 800 mV/g. The open-circuit voltage shows a negligible decrease after continuously operating for 100,000 times, showing excellent stability and durability. Furthermore, the 3D AS is demonstrated as a part of the airbag system to spot the collision position and force of the car simultaneously. This work will further promote the commercialization of TENG-based sensor and exhibits a prospective application in the vehicle restraint system.

The micro/nano surface structure of triboelectric layers possesses a critical impact on the performance of triboelectric nanogenerators (TENG). Here, we present a solution for the enhancement of the triboelectric performance by utilizing a Q-switched Pulsed Laser (QSL) that directly writes on an Aluminum surface in the net configuration. The crinkled nanostructure of the surface of Polytetrafluoroethylene (PTFE) is fabricated by the Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) technology. By adjusting the QSL source parameters, many kinds of Al/PTFE concepts of synthetic devices with built-in contact-separation could systematically be characterized. The optimal triboelectric performance was confirmed by the increase of the open-circuit voltage and the short-circuit current from 75 V to 148 V and from 6.8 μA to 9.6 μA, respectively, and by a nearly 2.5 times higher power than that of a pristine Al-based device. The real-time practical applicability of the SA-TENG concept was confirmed by the lighting up of 92 LEDs connected in series and by the charging up of a 10 μF capacitor to 1.68 V in 30 s. This work provides an effective direct writing process with a Q-switched Pulsed Laser for the fabrication of micro/nano-structures on Aluminum and for the enhancement of the output performance of TENG, which would greatly promote the TENG branding in mass manufacturing and micro-energy utilizations.

Wearable self-powered sensors represent a theme of interest in the literature due to the progress in the Internet of Things and implantable devices. The integration of different materials to harvest energy from body movement or the environment to power up sensors or act as an active component of the detection of analytes is a frontier to be explored. This review describes the most relevant studies of the integration of nanogenerators in wearables based on the interaction of piezoelectric and triboelectric devices into more efficient and low-cost harvesting systems to power up batteries or to use the generated power to identify multiple analytes in self-powered sensors and biosensors.

Equipping wearable electronics with special functions will endow them with more additional values and more comprehensive practical performance. Here, we report an ultraviolet (UV)-protective, self-cleaning, antibacterial, and self-powered all-nanofiber-based triboelectric nanogenerator (TENG) for mechanical energy harvesting and self-powered sensing, which is fabricated with Ag nanowires (NWs)/TPU nanofibers and the TiO2@PAN networks through a facile electrospinning method. Due to the added TiO2 nanoparticles (NPs), the TENG presents excellent UV-protective performance, including the ultraviolet protection factor (UPF) of ∼204, the transmittance of UVA (TUVA) of ∼0.0574%, and the transmittance of UVB (TUVB) ∼0.107%. Furthermore, under solar lighting for 25 min, most surface contamination can be degraded, and the decreased power output would be recovered. Owing to the coupled effects of TiO2 NPs and Ag NWs, the TENG shows excellent antibacterial activity against Staphylococcus aureus. Due to the micro-to-nano hierarchical porous structure, the all-nanofiber-based TENG can serve as self-powered pedometers for detecting and tracking human motion behaviors. As a multifunctional self-powered device, the TENG prompts various applications in the fields of micro/nanopower sources, human movement monitoring, and human-machine interfaces, potentially providing an alternative energy solution and a multifunctional interactive platform for the next-generation wearable electronics.

A new approach to increasing the output voltage of a thermoelectric generator that does not involve material modification is demonstrated. The key component of the device is a dielectric layer and ...