Stimulating Acrylic Elastomers by a Triboelectric Nanogenerator – Toward Self‐Powered Electronic Skin and Artificial Muscle

Dielectric elastomers are a type of actuator materials that exhibit excellent performance as artificial muscles, but a high driving voltage is required for their operation. By using the amazingly high output voltage generated from a triboelectric nanogenerator (TENG), a thin film dielectric elastomer actuator (DEA) can be directly driven by the contact‐separation motion of TENG, demonstrating a self‐powered actuation system. A TENG with a tribo surface area of 100 cm² can induce an expansion strain of 14.5% for the DEA samples (electrode diameter of 0.6 cm) when the system works stably within the contact‐separation velocity ranging from 0.1 to 10 cm s^?1. Finally, two simple prototypes of an intelligent switch and a self‐powered clamper based on the TENG and DEA are demonstrated. These results prove that the dielectric elastomer is an ideal material to work together with TENG and thereby the fabricated actuation system can potentially be applied to the field of electronic skin and soft robotics.     

Self‐Powered Trace Memorization by Conjunction of Contact‐Electrification and Ferroelectricity

Triboelectric nanogenerator (TENG) is a newly invented technology that can effectively harvest ambient mechanical energy from various motions with promising applications in portable electronics, self‐powered sensor networks, etc. Here, by coupling TENG and a thin film of ferroelectric polymer, a new application is designed for TENG as a self‐powered memory system for recording a mechanical displacement/trace. The output voltage produced by the TENG during motion can polarize the dipole moments in the ferroelectric thin film. Later, by applying a displacement current measurement to detect the polarization density in the ferroelectric film, the motion information of the TENG can be directly read. The sliding TENG and the single‐electrode TENG matrix are both utilized for realizing the memorization of the motion trace in one‐dimensional and two‐dimensional space, respectively. Currently, the ferroelectric thin film with a size of 3.1 mm² can record a minimum area changing of 30 mm² and such resolution can still be possibly improved. These results prove that the ferroelectric polymer is an effective memory material to work together with TENG and thereby the fabricated memory system can potentially be used as a self‐powered displacement monitor.     

Triboelectric Nanogenerator for Harvesting Vibration Energy in Full Space and as Self‐Powered Acceleration Sensor

A spherical three‐dimensional triboelectric nanogenerator (3D‐TENG) with a single electrode is designed, consisting of an outer transparent shell and an inner polyfluoroalkoxy (PFA) ball. Based on the coupling of triboelectric effect and electrostatic effect, the rationally developed 3D‐TENG can effectively scavenge ambient vibration energy in full space by working at a hybridization of both the contact‐separation mode and the sliding mode, resulting in the electron transfer between the Al electrode and the ground. By systematically investigating the output performance of the device vibrating under different frequencies and along different directions, the TENG can deliver a maximal output voltage of 57 V, a maximal output current of 2.3 μA, and a corresponding output power of 128 μW on a load of 100 MΩ, which can be used to directly drive tens of green light‐emitting diodes. Moreover, the TENG is utilized to design the self‐powered acceleration sensor with detection sensitivity of 15.56 V g^‐1. This work opens up many potential applications of single‐electrode based TENGs for ambient vibration energy harvesting techniques in full space and the self‐powered vibration sensor systems.     

A Battery‐Less Arbitrary Motion Sensing System Using Magnetic Repulsion‐Based Self‐Powered Motion Sensors and Hybrid Nanogenerator

Self‐powered arbitrary motion sensors are in high demand in the field of autonomous controlled systems. In this work, a magnetic repulsion‐assisted self‐powered motion sensor is integrated with a hybrid nanogenerator (MRSMS–HNG) as a battery‐less arbitrary motion sensing system. The proposed device can efficiently detect the motion parameters of a moving object along any arbitrary direction and simultaneously convert low frequency (<5 Hz) vibrations into useful electricity. The MRSMS–HNG consists of a central magnet for the electromagnetic (EMG)–triboelectric (TENG) nanogenerator and four side magnets for motion sensors. Because all the magnets are aligned in the same magnetization direction, the repulsive force owing to the movement of the central magnet actuates the side magnets to achieve self‐powered arbitrary motion sensing. These self‐powered motion sensors exhibit a high sensitivity of 981.33 mV g^?1 under linear motion excitation and have a tilting angle sensitivity of 9.83 mV deg^?1. The proposed device can deliver peak powers of 27 mW and 56 µW from the EMG and TENG, respectively. By integrating the self‐powered motion sensors and hybrid nanogenerator on a single device, real‐time wireless transmission of motion sensor data to a smartphone is successfully demonstrated, thus realizing a battery‐less arbitrary motion‐sensing system for future autonomous control applications.     

Electrically Responsive Materials and Devices Directly Driven by the High Voltage of Triboelectric Nanogenerators

Smart materials with electrically responsive characteristics and devices relying on different electrostatic effects can be directly driven by triboelectric nanogenerators (TENGs). The open circuit voltage from a TENG can easily reach thousands of volts with a separation distance of a few millimeters and this high output voltage can be used to effectively drive or control some devices with high internal resistance. This kind of combination is the most straightforward way for achieving a self‐powered smart system. Hence, a detailed survey of electrically responsive materials and devices that can be successfully combined with TENG is summarized, including dielectric elastomers, piezoelectric materials, ferroelectric materials, electrostatic manipulators, electrostatic air cleaners, and field emission and mass spectrometers. Moreover, key factors in determining suitable materials or devices to work with TENG are clarified and an in‐depth discussion of the current challenges related to these combined systems is provided. With the cost‐effectiveness and simple manufacturing process, these TENG‐based composite systems have great application prospects in the field of smart mechanics, human–machine interaction systems, intelligent storage systems, self‐powered microfluidic chips, portable mass spectrometers, and so on.     

Rolling Friction Enhanced Free‐Standing Triboelectric Nanogenerators and their Applications in Self‐Powered Electrochemical Recovery Systems

Heavy metals contained in wastewater are one of the most serious pollutions in natural resources. A self‐powered electrochemical recovery system for collecting Cu ions in wastewater by incorporating a rolling friction enhanced freestanding triboelectric nanogenerator (RF‐TENG) is developed here. The RF‐TENG utilizes integrated cylindrical surfaces using the conjunction of rolling electrification and freestanding electrostatic induction, which shows outstanding output performance and ultrarobust stability. By using the kinetic energy of flowing water, a collection efficiency of up to 80% for Cu²⁺ ions in wastewater has been achieved. Self‐powered electrochemical systems are one of the most promising applications of TENGs for independent and sustainable driving of electrochemical reactions without the need for any additional power supply. This research is a substantial advancement towards the practical applications of triboelectric nanogenerators and self‐powered electrochemical systems.     

Fully Elastic and Metal‐Free Tactile Sensors for Detecting both Normal and Tangential Forces Based on Triboelectric Nanogenerators

A tactile sensor should be able to detect both normal and tangential forces, which is mandatory for simulating human hands, but this fundamental function has been overlooked by most of the previous studies. Here, based on a triboelectric nanogenerator (TENG) with single‐electrode mode, the fully elastic and metal‐free tactile sensor that can detect both normal and tangential forces is proposed. With tiny burr arrays on the contact interface to facilitate the elastic deformation, the detected normal pressure by the device can reach to 1.5 MPa with a sensitivity of about 51.43 kPa V⁻¹, and a large range of tangential forces can be detected ranging from 0.5 to 40 N with rough sensitivity of 0.83 N V⁻¹ (0.5–3 N) and 2.50 N V⁻¹ (3–40 N). Meanwhile, the applied tangential forces from different directions can also be clearly distinguished by the four‐partitioned electrode structure. Moreover, a shield film is coated on the top surface of the device, which can screen the electrostatic interference and enhance the repeatability of the device. The demonstrated concept of this self‐powered tactile sensor has excellent applicability for industrial robotics, human–machine interactions, artificial intelligence, etc.     

Liquid‐Metal Electrode for High‐Performance Triboelectric Nanogenerator at an Instantaneous Energy Conversion Efficiency of 70.6%

Harvesting ambient mechanical energy is a key technology for realizing self‐powered electronics, which has tremendous applications in wireless sensing networks, implantable devices, portable electronics, etc. The currently reported triboelectric nanogenerator (TENG) mainly uses solid materials, so that the contact between the two layers cannot be 100% with considering the roughness of the surfaces, which greatly reduces the total charge density that can be transferred and thus the total energy conversion efficiency. In this work, a liquid‐metal‐based triboelectric nanogenerator (LM‐TENG) is developed for high power generation through conversion of mechanical energy, which allows a total contact between the metal and the dielectric. Due to that the liquid–solid contact induces large contacting surface and its shape adaptive with the polymer thin films, the LM‐TENG exhibits a high output charge density of 430 μC m^?2, which is four to five times of that using a solid thin film electrode. And its power density reaches 6.7 W m^?2 and 133 kW m^?3. More importantly, the instantaneous energy conversion efficiency is demonstrated to be as high as 70.6%. This provides a new approach for improving the performance of the TENG for special applications. Furthermore, the liquid easily fluctuates, which makes the LM‐TENG inherently suitable for vibration energy harvesting.     

Self‐Powered Electrochemical Synthesis of Polypyrrole from the Pulsed Output of a Triboelectric Nanogenerator as a Sustainable Energy System

Triboelectric nanogenerators (TENG) are able to convert mechanical energy into electricity. In this work, a self‐powered electrochemical synthesis circle is designed, in which the electrode material of the TENG, polypyrrole (PPy), is prepared by the pulse output of the PPy‐based TENG itself. The TENG based on PPy from self‐powered synthesis (SPSPPy) presents a competitive performance compared to those made from commercial pulse sources. A supercapacitor that is fabricated from SPSPPy has a far superior performance than that synthesized by the conventional galvanostatic method. Furthermore, a self‐charging power system that integrates a TENG and a supercapacitor is demonstrated to drive an electronic device sustainably. Moreover, the polymerization efficiency is optimized in TENG‐based electrochemical synthesis because its high voltage can sustain multiple reactors simultaneously. Its upper limit is theoretically analyzed for optimal energy utility, and a maximum number of 39 reactors can be powered experimentally. Hence, TENG is validated as an effective pulse generator for the synthesis of PPy as well as other electrochemical technology, and this work greatly improves the understandings of TENG‐based self‐powered electrochemical systems.     

Triboelectric Nanogenerator as an Active UV Photodetector

Self‐powered nanosensors and nanosystems have attracted significant attention in the past decades and have gradually become the most desirable and promising prototype for environmental protection/detection because no battery is needed to power the device. Therefore, in this paper a design is proposed for a self‐powered photodetector based on triboelectric nanogenerator (TENG) configuration. 3D dendritic TiO₂ nanostructures are synthesized as the built‐in UV photodetector as well as the contact material of the TENG. The cost‐effective, robust, and easily fabricated TENG‐based photodetector presents superior photoresponse characteristics, which include an excellent responsivity over 280 A W^?1, rapid rise time (18 ms) and decay time (31 ms), and a wide detection range of light intensity from 20 μW cm^?2 to 7 mW cm^?2. In the last part of the paper, a stand‐alone and self‐powered environmental sensing device is developed by applying poly(methyl methacrylate) (PMMA) substrates and springs to assemble the TENG‐based photodetector. These results indicate that the new prototype sensing device based on the TENG configuration shows great potential as a self‐powered photodetector.     

Bioinspired Triboelectric Nanogenerators as Self‐Powered Electronic Skin for Robotic Tactile Sensing

Electronic skin (e‐skin) has been under the spotlight due to great potential for applications in robotics, human–machine interfaces, and healthcare. Meanwhile, triboelectric nanogenerators (TENGs) have been emerging as an effective approach to realize self‐powered e‐skin sensors. In this work, bioinspired TENGs as self‐powered e‐skin sensors are developed and their applications for robotic tactile sensing are also demonstrated. Through the facile replication of the surface morphology of natural plants, the interlocking microstructures are generated on tribo‐layers to enhance triboelectric effects. Along with the adoption of polytetrafluoroethylene (PTFE) tinny burrs on the microstructured tribo‐surface, the sensitivity for pressure measurement is boosted with a 14‐fold increase. The tactile sensing capability of the TENG e‐skin sensors are demonstrated through the characterizations of handshaking pressure and bending angles of each finger of a bionic hand during handshaking with human. The TENG e‐skin sensors can also be utilized for tactile object recognition to measure surface roughness and discern hardness. The facile fabrication scheme of the self‐powered TENG e‐skin sensors enables their great potential for applications in robotic dexterous manipulation, prosthetics, human–machine interfaces, etc.     

Self‐Powered Electrowetting Valve for Instantaneous and Simultaneous Actuation of Paper‐Based Microfluidic Assays

In this work, a self‐powered electrowetting valve (SPEV) driven by an energy‐harvesting triboelectric nanogenerator (TENG) is reported. The TENG (5 × 5 cm²) can produce an open‐circuit voltage of 380 V by applying a mechanical stimulus, which is much higher than the actuation voltage of the SPEV (130 V). Once actuated, the electrowetting valve can be instantly switched on at a response time of 0.18 s, allowing liquid reagent to flow through the valve. The SPEV can be used for simultaneous addition of multiple reagents in an enzyme‐linked immunosorbent assay on a paper‐based microfluidic analytical device (µPAD). This assay involves a chromogenic reaction that achieves effective detection of alpha‐fetoprotein, a critical tumor marker for early diagnosis of liver cancer. The SPEV reported in this work can be potentially used in other complex multiprocedure µPADs, which will potentially enable portable, accessible, and cost‐effective assays for early diagnosis, food safety, pollution detection, etc.     

Cellulose II Aerogel‐Based Triboelectric Nanogenerator

Cellulose‐based triboelectric nanogenerators (TENGs) have gained increasing attention. In this study, a novel method is demonstrated to synthesize cellulose‐based aerogels and such aerogels are used to fabricate TENGs that can serve as mechanical energy harvesters and self‐powered sensors. The cellulose II aerogel is fabricated via a dissolution–regeneration process in a green inorganic molten salt hydrate solvent (lithium bromide trihydrate), where. The as‐fabricated cellulose II aerogel exhibits an interconnected open‐pore 3D network structure, higher degree of flexibility, high porosity, and a high surface area of 221.3 m² g^?1. Given its architectural merits, the cellulose II aerogel‐based TENG presents an excellent mechanical response sensitivity and high electrical output performance. By blending with other natural polysaccharides, i.e., chitosan and alginic acid, electron‐donating and electron‐withdrawing groups are introduced into the composite cellulose II aerogels, which significantly improves the triboelectric performance of the TENG. The cellulose II aerogel‐based TENG is demonstrated to light up light‐emitting diodes, charge commercial capacitors, power a calculator, and monitor human motions. This study demonstrates the facile fabrication of cellulose II aerogel and its application in TENG, which leads to a high‐performance and eco‐friendly energy harvesting and self‐powered system.     

Stretchable‐Rubber‐Based Triboelectric Nanogenerator and Its Application as Self‐Powered Body Motion Sensors

A stretchable‐rubber‐based (SR‐based) triboelectric nanogenerator (TENG) is developed that can not only harvest energy but also serve as self‐powered multifunctional sensors. It consists of a layer of elastic rubber and a layer of aluminum film that acts as the electrode. By stretching and releasing the rubber, the changes of triboelectric charge distribution/density on the rubber surface relative to the aluminum surface induce alterations to the electrical potential of the aluminum electrode, leading to an alternating charge flow between the aluminum electrode and the ground. The unique working principle of the SR‐based TENG is verified by the coupling of numerical calculations and experimental measurements. A comprehensive study is carried out to investigate the factors that may influence the output performance of the SR‐based TENG. By integrating the devices into a sensor system, it is capable of detecting movements in different directions. Moreover, the SR‐based TENG can be attached to a human body to detect diaphragm breathing and joint motion. This work largely expands the applications of TENG not only as effective power sources but also as active sensors; and opens up a new prospect in future electronics.     

Self‐Powered Distributed Water Level Sensors Based on Liquid–Solid Triboelectric Nanogenerators for Ship Draft Detecting

Ship draft measurement is of great significance for ensuring navigation safety and facilitating ship control. In this work, a self‐powered water level sensor based on a liquid–solid tubular triboelectric nanogenerator (LST‐TENG) is proposed and analyzed. The LST‐TENG is made of multiple copper electrodes uniformly distributed along a polytetrafluoroethylene (PTFE) tube. When water flows into the PTFE tube, it induces alternating flows of electrons between the main electrode and the distributed bottom electrodes. The obvious peaks in the derivative of open‐circuit voltage with respect to time are found to correspond with the electrode distribution. Then it can be utilized as a robust and sensitive indicator for detecting the water level as the number of obvious peaks in the derivative of open‐circuit voltage is directly related to the water level height. The ship draft is successfully detected using the LST‐TENG with an accuracy of 10 mm. It shows that the water level sensor has stable performance for liquid–solid interface monitoring. Therefore, this LST‐TENG is self‐powered, robust, and accurate for extensive applications in marine industry.     

Self‐Powered Vehicle Emission Testing System Based on Coupling of Triboelectric and Chemoresistive Effects

Traditional triboelectric nanogenerator (TENG)‐based self‐powered chemical‐sensing systems are demonstrated by measuring the triboelectric effect of the sensing materials altered by the external stimulus. However, the limitations of triboelectric sensing materials and instable outputs caused by ambient environment significantly restrict their practical applications. In this work, a stable and reliable self‐powered chemical‐sensing system is proposed by coupling triboelectric effect and chemoresistive effect. The whole system is constructed as the demo of a self‐powered vehicle emission test system by connecting a vertical contact–separate mode TENG as energy harvester with a series‐connection resistance‐type gas sensor as exhaust detector and the parallel‐connection commercial light‐emitting diodes (LEDs) as alarm. The output voltage of TENG varies with the variable working states of the gas sensor and then directly reflects on the on/off status of the LEDs. The working mechanism can be ascribed to the specific output characteristics of the TENG tuned by the load resistance of the gas sensor, which is responded to the gas environment. This self‐powered sensing system is not affected by working frequency and requires no external power supply, which is favorable to improve the stability and reliability for practical application.     

Whirling‐Folded Triboelectric Nanogenerator with High Average Power for Water Wave Energy Harvesting

Ocean wave energy, as one of the most abundant resources on the earth, is a promising energy source for large‐scale applications. Triboelectric nanogenerators (TENGs) provide a new strategy for water wave energy harvesting; however, its average performance in realistic water wave conditions is still not high. In this work, a whirling‐folded TENG (WF‐TENG) with maximized space utilization and minimized electrostatic shielding is constructed by 3D printing and printed circuit board technologies. The flexible vortex structure responds easily to multiform wave excitation with improved oscillation frequency. A standard water wave tank is established to generate controllable water waves to characterize the device performance. It is found to be determined by wave conditions and internal structure, which is also revealed by a theoretical dynamical analysis. The WF‐TENG can produce a maximum peak power of 6.5 mW and average power of 0.28 mW, which can power a digital thermometer to operate constantly and realize self‐powered monitoring on the TENG network to prevent possible damage in severe environments. Moreover, a self‐charge‐supplement WF‐TENG network is proposed to improve the output performance and stability. This study provides an effective strategy for improving the average power and characterizing the performance of spherical TENG towards large‐scale blue energy.     

Entirely,Intrinsically, and Autonomously Self‐Healable,Highly Transparent,and Superstretchable Triboelectric Nanogenerator for Personal Power Sources and Self‐Powered Electronic Skins

Power and electronic components that are self‐healable, deformable, transparent, and self‐powered are highly desirable for next‐generation energy/electronic/robotic applications. Here, an energy‐harvesting triboelectric nanogenerator (TENG) that combines the above features is demonstrated, which can serve not only as a power source but also as self‐powered electronic skin. This is the first time that both of the triboelectric‐charged layer and electrode of the TENG are intrinsically and autonomously self‐healable at ambient conditions. Additionally, comparing with previous partially healable TENGs, its fast healing time (30 min, 100% efficiency at 900% strain), high transparency (88.6%), and inherent superstretchability (>900%) are much more favorable. It consists of a metal‐coordinated polymer as the triboelectrically charged layer and hydrogen‐bonded ionic gel as the electrode. Even after 500 cutting‐and‐healing cycles or under extreme 900%‐strain, the TENG retains its functionality. The generated electricity can be used directly or stored to power commercial electronics. The TENG is further used as self‐powered tactile‐sensing skin in diverse human–machine interfaces including smart glass, an epidermal controller, and phone panel. This TENG with merits including fast ambient‐condition self‐healing, high transparency, intrinsic stretchability, and energy‐extraction and actively‐sensing abilities, can meet wide application needs ranging from deformable/portable/transparent electronics, smart interfaces, to artificial skins.     

Self‐Powered Optical Switch Based on Triboelectrification‐Triggered Liquid Crystal Alignment for Wireless Sensing

Here, a self‐powered optical switch (OS) composed of a surface‐etched single‐electrode triboelectric nanogenerator (TENG) and a polymer‐dispersed liquid crystal (PDLC) film is reported. The working principle of the developed OS is that the liquid crystal alignment can be driven by triboelectrification‐generated voltage, inducing the PDLC film to rapidly switch its initial translucent state to an instantaneous transparent state. An output voltage of 360 V is generated upon the PDLC film when a nitrile rubber film contacts with the TENG at an area of 25 cm² and a velocity of 0.4 m s^?1. As such, a wide dimming range with the relative transmitted light intensity from 0.05 to 0.85 can be achieved for the OS. Enabled by the unique mechano‐electro‐optical reaction, the effects of a series of structural parameters on the performance of the OS are methodically studied. Particularly, through integrating the OS with a visible‐light‐operated signal‐processing circuit, a complete wireless sensing system with a fully power‐free sensing node is developed. The paradigms of hand touching and foot stepping triggered wireless alarms are demonstrated, explicitly showing great potential for the system in many possible interactive human–machine interface applications, such as surveillance, security systems, remote operation, and automatic control.     

Triboelectric Nanogenerators as a Self‐Powered Motion Tracking System

Motion tracking is a key area of sensor systems for security, transportation, and high‐tech industry. In this work, a self‐powered motion tracking system is developed to monitor moving speed, direction, acceleration, starting and ending positions, and even the moving path of a moving object. Such a system is based on a set of triboelectric nanogenerators (TENGs) that are composed of two friction layers with opposite triboelectric polarities (Kapton and Aluminum) and operates in the sliding mode. Velocities of a moving object are monitored from ?0.1 m s^‐1 to +0.1 m s^‐1 at a step of 0.01 m s^‐1, and accelerations from ?0.1 m s^‐2 to +0.1 m s^‐2 at a step of 0.02 m s^‐2. Furthermore, an 8 × 8 two‐dimensional coordinates system with 16 groups of TENGs is created, and the moving path of an object is obtained. This study opens up a new area of TENGs as active sensors with great potential in self‐powered systems, positioning detecting, motion tracking, environmental and infrastructure monitoring, and security.