Boosting the Power and Lowering the Impedance of Triboelectric Nanogenerators through Manipulating the Permittivity for Wearable Energy Harvesting

A micro-dome array triboelectric nanogenerator with a nanocomposite dielectric enhancement layer for wearable pressure sensing and gait analysis

The practical application of a triboelectric nanogenerator (TENG) as a self-powered sensor and an energy harvester is constrained by the need for a wide sensitivity range, significant output power, and structural flexibility. However, most research has focused on physical and chemical surface modifications of the charge-generating layer to enhance the TENG performance. Improving the charge storage ability could otherwise further enhance the overall performance. Here, we propose a flexible TENG design that incorporates a micro-dome array Ecoflex as the tribo-negative layer, coupled with a dielectric enhancement layer composed of a carbon black/Ecoflex composite. The addition of the CB/Eco composite layer to the micro-dome array triboelectric layer enhanced the output voltage performance by forming numerous micro capacitors within the dielectric layer. Furthermore, oxygen-containing fluorocarbon plasma treatment of the micro-dome array increased the surface energy, enhancing the interaction between the triboelectric layers. This leads to an enhancement in the output voltage and energy efficiency, exhibiting a power density of 197.4 mW m-2. The pressure sensitivity of the TENG was systematically investigated, demonstrating 2.57 V kPa-1 in the low-pressure range (0.612 to 8.58 kPa) and 1.70 V kPa-1 in the high-pressure range (8.58 to 20.83 kPa). Additionally, the encapsulated TENG sensor with spacers was integrated into insoles for self-powered gait analysis, providing real-time insights into walking patterns and frequencies. Exploring the TENG's energy harvesting capability revealed a peak-peak voltage of 89.4 V when two TENGs are connected in series. The comprehensive performance characterization of the TENG demonstrates its promising applications in wearable, self-powered sensing, and energy harvesting systems.

Earthworm-Inspired Ultra-Durable Sliding Triboelectric Nanogenerator with Bionic Self-Replenishing Lubricating Property for Wind Energy Harvesting and Self-Powered Intelligent Sports Monitoring

Triboelectric nanogenerators (TENGs), a promising strategy for harvesting distributed low-quality power sources, face inevitable bottlenecks regarding long-term abrasion and poor durability. Herein, both issues are addressed by selecting an earthworm-inspired self-replenishing bionic film (ERB) as the tribo-material of sliding-freestanding TENGs (SF-TENGs), it consists of an interconnected 3D porous network structure capable of storing and releasing lubricant under cyclic mechanical stimuli. Thanks to the superiority of self-replenishing property, there is no need for periodic replenishment and accurate content control of lubricant over the interfacial-lubricating SF-TENGs based on dense tribo-layers. Additionally, an SF-TENG based on ERB film (ERB-TENG) demonstrates remarkable output stability with only a slight attenuation of 1% after continuous operation for 100 000 cycles. Moreover, the ERB-TENG displays a distinguished anti-wear property, exhibiting no distinct abrasion with an ultra-low coefficient of friction (0.077) and maintaining output stability over a prolonged period of 35 days. Furthermore, integration with an energy management circuit enables the ERB-TENG to achieve a 39-fold boost in charging speed. This work proposes a creative approach to enhance the durability and extend the lifespan of TENG devices, which is also successfully applied to wind energy harvesting and intelligent sports monitoring.

Free-Standing Electrode and Fixed Surface Tiny Electrode Implemented Triboelectric Nanogenerator with High Instantaneous Current

Conventional triboelectric nanogenerators (TENGs) face challenges pertaining to low output current density at low working frequencies and high internal impedance. While strategies, such as surface modification to enhance surface charge density, permittivity regulation of materials, and circuit management, have partially mitigated these issues. However, they have also resulted in increased complexity in the fabrication process. Therefore, there is an urgent demand for a universal and simplified approach to address these challenges. To fulfill this need, this work presents a free-standing electrode and fixed surface tiny electrode implemented triboelectric nanogenerator (FFI-TENG). It is fabricated by a straightforward yet effective method: introducing a tiny electrode onto the surface of the tribo-negative material. This approach yields substantial enhancements in performance, notably a more than tenfold increase in output current density, a reduction in effective working frequencies, and a decrease in matching resistance as compared to vertical contact-separation TENGs (CS-TENGs) or single-electrode TENGs (SE-TENGs). Simultaneously, a comprehensive examination and proposition regarding the operational mechanism of FFI-TENG, highlighting its extensive applicability are also offered. Significantly, FFI-TENG excels in mechanical energy harvesting even under ultra-low working frequencies (0.1 Hz), outperforming similar contact-separation models. This innovation positions it as a practical and efficient solution for the development of low-entropy energy harvesters.

High-Performance All-Textile Triboelectric Nanogenerator toward Intelligent Sports Sensing and Biomechanical Energy Harvesting

Merging textiles with advanced energy harvesting technology via triboelectric effects brings novel insights into self-powered wearable textile electronics. However, fabrication of a comfortable textile-based triboelectric nanogenerator (TENG) with high outputs remains challenging. Herein, we propose a highly flexible, tailorable, single-electrode all-textile TENG (t-TENG) with both wear comfort and high outputs. A dielectric modulated porous composite coating containing poly(vinylidene fluoride)-hexafluoropropylene copolymer and barium titanate nanoparticles is constructed on conductive fabric to counterpart with highly positive glass fiber fabric through knotted yarn bonding, maintaining the superiority of textiles and strong triboelectricity. Through the synergistic optimization of charge storage via dielectric modulation and charge dissipation offset by electrical poling, remarkable outputs (261 V, 1.5 μA, and 12.7 nC) are obtained from a miniaturized, lightweight t-TENG (2 × 2 cm2, 130 mg) with an instantaneous power density of 654.48 mW·m-2, as well as excellent electrical robustness and device durability over 20,000 cycles. The t-TENG also exhibits a high sensitivity of 3.438 V·kPa-1 in the force region (1-10 N), demonstrating great potential in TENG-based intelligent sports sensing applications for monitoring and correcting the basketball shooting hand and foot arch posture. Furthermore, over 110 light-emitting diode arrays can be lightened up by gently tapping this miniaturized t-TENG. It also offers a wearable power source scheme through integrating the single-electrode device into clothing and utilizing the skin as the grounded electrode, revealing its ease of integration and biomechanical energy harvesting capability. This work provides an attractive paradigm for next-generation textile electronics with well-balanced device performance and wear comfort.

A high-current hydrogel generator with engineered mechanoionic asymmetry

Mechanoelectrical energy conversion is a potential solution for the power supply of miniaturized wearable and implantable systems; yet it remains challenging due to limited current output when exploiting low-frequency motions with soft devices. We report a design of a hydrogel generator with mechanoionic current generation amplified by orders of magnitudes with engineered structural and chemical asymmetry. Under compressive loading, relief structures in the hydrogel intensify net ion fluxes induced by deformation gradient, which synergize with asymmetric ion adsorption characteristics of the electrodes and distinct diffusivity of cations and anions in the hydrogel matrix. This engineered mechanoionic process can yield 4 mA (5.5 A m-2) of peak current under cyclic compression of 80 kPa applied at 0.1 Hz, with the transferred charge reaching up to 916 mC m-2 per cycle. The high current output of this miniaturized hydrogel generator is beneficial for the powering of wearable devices, as exemplified by a controlled drug-releasing system for wound healing. The demonstrated mechanisms for amplifying mechanoionic effect will enable further designs for a variety of self-powered biomedical systems.

Outstanding Synergy of Sensitivity and Linear Range Enabled by Multigradient Architectures

Flexible pressure sensors are devices that mimic the sensory capabilities of natural human skin and enable robots to perceive external stimuli. One of the main challenges is maintaining high sensitivity over a broad linear pressure range due to poor structural compressibility. Here, we report a flexible pressure sensor with an ultrahigh sensitivity of 153.3 kPa-1 and linear response over an unprecedentedly broad pressure range from 0.0005 to 1300 kPa based on interdigital-shaped, multigradient architectures, featuring modulus, conductivity, and microstructure gradients. Such multigradient architectures and interdigital-shaped configurations enable effective stress transfer and conductivity regulation, evading the pressure sensitivity-linear range trade-off dilemma. Together with high pressure resolution, high frequency response, and good reproducibility over the ultrabroad linear range, proof-of-concept applications such as acoustic wave detection, high-resolution pressure measurement, and healthcare monitoring in diverse scenarios are demonstrated.

Recent Study Advances in Flexible Sensors Based on Polyimides

With the demand for healthy life and the great advancement of flexible electronics, flexible sensors are playing an irreplaceably important role in healthcare monitoring, wearable devices, clinic treatment, and so on. In particular, the design and application of polyimide (PI)-based sensors are emerging swiftly. However, the tremendous potential of PI in sensors is not deeply understood. This review focuses on recent studies in advanced applications of PI in flexible sensors, including PI nanofibers prepared by electrospinning as flexible substrates, PI aerogels as friction layers in triboelectric nanogenerator (TENG), PI films as sensitive layers based on fiber Bragg grating (FBG) in relative humidity (RH) sensors, photosensitive PI (PSPI) as sacrificial layers, and more. The simple laser-induced graphene (LIG) technique is also introduced in the application of PI graphitization to graphene. Finally, the prospect of PIs in the field of electronics is proposed in the review.

Self-powered TENG probe for scanning surface charge distribution

Triboelectric nanogenerators are remarkable devices that show great potential in harvesting energy from mechanical work and are generally used for sensing purposes. Here we report a novel method for the fabrication of ZnO microspheres and the formation of TENG based on ZnO/PDMS composite. The zinc oxide microspheres with needle decorated structure via thermal oxidation of metallic zinc was grown at 500 °C. The TENG was then fabricated using ZnO/PDMS composite with Au sputtered electrode. While PDMS is a good triboelectric material, its output power density is low. Embedding ZnO micro/nanostructures in PDMS increases the output power of PDMS-based TENG manifolds. ZnO with a high dielectric constant exhibits semiconductor properties as well as piezoelectric properties. This combines with the triboelectric properties of PDMS and gives a significant boost to the TENG performance. This composite structure is used for the fabrication of high output power density TENG using contact separation mode, where the power density of 27Wm-2was achieved. Consequently, a novel device application to detect surface charge density through the fabricated TENG is reported and the subsequent reconstruction of surface charge topology based on the detected surface charge density on large surfaces is presented. This technique may be used for the study of surface charge morphology, electrostatics, triboelectric constants, and various other material properties for characterization and application purposes.

Highly porous and rough polydimethylsiloxane film-based triboelectric nanogenerators and its application for electrochemical cathodic protection

The development and utilization of triboelectric nanogenerator (TENG) are very important for realizing energy cleaning in electrochemical processes. However, limited electrical output performance plays a major stumbling block to this process. Herein, a porous and high-roughness PDMS (PR/PDMS) negative friction layer was obtained by doping PDMS with powdered chitosan and casting using a sacrificial anodic alumina template. A TENG was fabricated by the PR/PDMS with Al film (PR-TENG). The PR-TENG exhibited much better performance than the pure PDMS-based TENG, which was attributed to the porous properties of the PR/PDMS. Under the driving of external mechanical force at 5 Hz, the PR-TENG showed a maximum output open-circuit voltage (Voc) and short-circuit current density (Jsc) of 77.1 V and 33.9 mA/m2, respectively. To prove the concept, the electrochemical cathodic protection system with PR-TENG was constructed. Ultimately, the application prospects of the PR-TENG as a clean energy source for electrochemical processes were explored and evaluated.

Touchless Artificial Perception beyond Fingertip Probing

Touchless perception technology allows us to acquire information beyond the contact interfaces, making it ideal for scenarios where physical engagements are not possible. Unlike tactile devices, which have so far achieved impressive results, touchless strategies are fascinating yet underdeveloped. We envisage that touchless technologies could be powerful supplements to current haptics. In this Perspective, we include emerging touchless electronics, aiming to provide a broader and comprehensive picture toward artificial perceptual realm. We overview popular touchless protocols, sketch what could be detected by touchless probing, and summarize their latest spectacular achievements. In addition, we present the promises and challenges posed by touchless technologies and discuss possible directions for their future deployments.

Skin-Contact Triboelectric Nanogenerator for Energy Harvesting and Motion Sensing: Principles, Challenges, and Perspectives

Energy harvesting has become an increasingly important field of research as the demand for portable and wearable devices continues to grow. Skin-contact triboelectric nanogenerator (TENG) technology has emerged as a promising solution for energy harvesting and motion sensing. This review paper provides a detailed overview of skin-contact TENG technology, covering its principles, challenges, and perspectives. The introduction begins by defining skin-contact TENG and explaining the importance of energy harvesting and motion sensing. The principles of skin-contact TENG are explored, including the triboelectric effect and the materials used for energy harvesting. The working mechanism of skin-contact TENG is also discussed. This study then moves onto the applications of skin-contact TENG, focusing on energy harvesting for wearable devices and motion sensing for healthcare monitoring. Furthermore, the integration of skin-contact TENG technology with other technologies is discussed to highlight its versatility. The challenges in skin-contact TENG technology are then highlighted, which include sensitivity to environmental factors, such as humidity and temperature, biocompatibility and safety concerns, and durability and reliability issues. This section of the paper provides a comprehensive evaluation of the technological limitations that must be considered when designing skin-contact TENGs. In the Perspectives and Future Directions section, this review paper highlights various advancements in materials and design, as well as the potential for commercialization. Additionally, the potential impact of skin-contact TENG technology on the energy and healthcare industries is discussed.

Recent Advances in Triboelectric Nanogenerators: From Technological Progress to Commercial Applications

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

Biomedical Applications of Electrets: Recent Advance and Future Perspectives

Recently, electrical stimulation, as a non-pharmacological physical stimulus, has been widely exploited in biomedical and clinical applications due to its ability to significantly enhance cell proliferation and differentiation. As a kind of dielectric material with permanent polarization characteristics, electrets have demonstrated tremendous potential in this field owing to their merits of low cost, stable performance, and excellent biocompatibility. This review provides a comprehensive summary of the recent advances in electrets and their biomedical applications. We first provide a brief introduction to the development of electrets, as well as typical materials and fabrication methods. Subsequently, we systematically describe the recent advances of electrets in biomedical applications, including bone regeneration, wound healing, nerve regeneration, drug delivery, and wearable electronics. Finally, the present challenges and opportunities have also been discussed in this emerging field. This review is anticipated to provide state-of-the-art insights on the electrical stimulation-related applications of electrets.

Phase-Separated Dielectric Gels Based on Christiansen Effect

Phase separation is a trivial phenomenon but a mature strategy in materials science. The flexible materials are provided toughness and strength by phase separation, yet there are few applications in optics and electronics industry. A novel phase-separated dielectric gel (PSDG) with a strong Christiansen effect is prepared via radical polymerization using hydroxyethyl methacrylate as a monomer, 4-cyano-4'-pentylbiphenyl and tributyl citrate as mixed solvents, and polyethylene glycol as a softener. The solvent ratios and ambient conditions can efficiently change the color of PSDG which makes it strongly selective for the wavelength of transmitted light. Besides, it has a high dielectric constant (10 at 1 kHz), sensitively responding to the electric field. The phase separation degree of PSDG varies with applied electric field, which will induce its transmittance alteration accordingly. The current field sensitive PSDG provides a novel idea for "smart windows". Additionally, varying the size and shape of the electrodes can precisely control the phase separation in PSDG and also enables the function of free writing on flexible materials. Therefore, the designed PSDG has great application potential for flexible touch and interesting interactions.

A Wearable Multidimensional Motion Sensor for AI-Enhanced VR Sports

Regular exercise paves the way to a healthy life. However, conventional sports events are susceptible to weather conditions. Current motion sensors for home-based sports are mainly limited by operation power consumption, single-direction sensitivity, or inferior data analysis. Herein, by leveraging the 3-dimensional printing technique and triboelectric effect, a wearable self-powered multidimensional motion sensor has been developed to detect both the vertical and planar movement trajectory. By integrating with a belt, this sensor could be used to identify some low degree of freedom motions, e.g., waist or gait motion, with a high accuracy of 93.8%. Furthermore, when wearing the sensor at the ankle position, signals generated from shank motions that contain more abundant information could also be effectively collected. By means of a deep learning algorithm, the kicking direction and force could be precisely differentiated with an accuracy of 97.5%. Toward practical application, a virtual reality-enabled fitness game and a shooting game were successfully demonstrated. This work is believed to open up new insights for the development of future household sports or rehabilitation.

Recent Advances in Carbon Nanotube-Based Energy Harvesting Technologies

There has been enormous interest in technologies that generate electricity from ambient energy such as solar, thermal, and mechanical energy, due to their potential for providing sustainable solutions to the energy crisis. One driving force behind the search for new energy-harvesting technologies is the desire to power sensor networks and portable devices without batteries, such as self-powered wearable electronics, human health monitoring systems, and implantable wireless sensors. Various energy harvesting technologies have been demonstrated in recent years. Among them, electrochemical, hydroelectric, triboelectric, piezoelectric, and thermoelectric nanogenerators have been extensively studied because of their special physical properties, ease of application, and sometimes high obtainable efficiency. Multifunctional carbon nanotubes (CNTs) have attracted much interest in energy harvesting because of their exceptionally high gravimetric power outputs and recently obtained high energy conversion efficiencies. Further development of this field, however, still requires an in-depth understanding of harvesting mechanisms and boosting of the electrical outputs for wider applications. Here, various CNT-based energy harvesting technologies are comprehensively reviewed, focusing on working principles, typical examples, and future improvements. The last section discusses the existing challenges and future directions of CNT-based energy harvesters.

Fabrication of Advanced Cellulosic Triboelectric Materials via Dielectric Modulation

The rapid rise of triboelectric nanogenerators (TENGs), which are emerging energy conversion devices in advanced electronics and wearable sensing systems, has elevated the interest in high-performance and multifunctional triboelectric materials. Among them, cellulosic materials, affording high efficiency, biodegradability, and customizability, are becoming a new front-runner. The inherently low dielectric constant limits the increase in the surface charge density. However, owing to its unique structure and excellent processability, cellulose shows great potential for dielectric modulation, providing a strong impetus for its advanced applications in the era of Internet of Things and artificial intelligence. This review aims to provide comprehensive insights into the fabrication of dielectric-enhanced cellulosic triboelectric materials via dielectric modulation. The exceptional advantages and research progress in cellulosic materials are highlighted. The effects of the dielectric constant, polarization, and percolation threshold on the charge density are systematically investigated, providing a theoretical basis for cellulose dielectric modulation. Typical dielectric characterization methods are introduced, and their technical characteristics are analyzed. Furthermore, the performance enhancements of cellulosic triboelectric materials endowed by dielectric modulation, including more efficient energy harvesting, high-performance wearable electronics, and impedance matching via material strategies, are introduced. Finally, the challenges and future opportunities for cellulose dielectric modulation are summarized.

An Advanced Strategy to Enhance TENG Output: Reducing Triboelectric Charge Decay

The Internet of Things (IoT) is poised to accelerate the construction of smart cities. However, it requires more than 30 billion sensors to realize the IoT vision, posing great challenges and opportunities for industries of self-powered sensors. Triboelectric nanogenerator (TENG), an emerging new technology, is capable of easily converting energy from surrounding environment into electricity, thus TENG has tremendous application potential in self-powered IoT sensors. At present, TENG encounters a bottleneck to boost output for large-scale commercial use if just by promoting triboelectric charge generation, because the output is decided by the triboelectric charge dynamic equilibrium between generation and decay. To break this bottleneck, the strategy of reducing triboelectric charge decay to enhance TENG output is focused. First, multiple mechanisms of triboelectric charge decay are summarized in detail with basic theoretical principles for future research. Furthermore, recent advances in reducing triboelectric charge decay are thoroughly reviewed and outlined in three aspects: inhibition and application of air breakdown, simultaneous inhibition of air breakdown and triboelectric charge drift/diffusion, and inhibition of triboelectric charge drift/diffusion. Finally, challenges and future research focus are proposed. This review provides reference and guidance for enhancing TENG output.

A Controlled Biodegradable Triboelectric Nanogenerator Based on PEGDA/Laponite Hydrogels

Implantable and wearable transient electronics based on nanogenerators have been applied in self-powered sensing, electrical-stimulation therapy, and other fields. However, the existing devices have a poor ability to match with the shapes of human tissues, and the degradation processes cannot meet individual needs. In this work, a PEGDA/Lap nanocomposite hydrogel was prepared that was based on biocompatible polyglycol diacrylate (PEGDA) and laponite, and a biodegradable single-electrode triboelectric nanogenerator (BS-TENG) was built. The PEGDA/Lap hydrogel has enhanced flexibility and mechanical and electrical performance. Its strain was 1001.8%, and the resistance was 10.8. The composite hydrogel had a good biocompatibility and could effectively promote the adhesion of cells. The BS-TENG could be used as a self-powered device to light an LED and serve as an active sensor for real-time monitoring of breath and various human movements. More importantly, the device could be degraded controllably without any harm. Therefore, BS-TENGs will be mainstream in diagnosis and treatment and play an important role in biomedical science.

Deep Trap Boosted Ultrahigh Triboelectric Charge Density in Nanofibrous Cellulose-Based Triboelectric Nanogenerators

For their use in self-powered implantable or wearable electronics, cellulose nanofiber (CNF)-based triboelectric nanogenerators (TENGs) have drawn a lot of attention. However, the low triboelectric charge density (TECD) hinders its further application as a tribolayer for TENGs. In this work, a sulfonated cellulose nanofiber was prepared as an electropositive tribolayer for TENGs to obtain ultrahigh electrical output performance. Since the introduction of sulfonic acid effectively increased the dielectric properties and hole deep trap density of the CNF film, the triboelectric charge storage capacity of the CNF-SO₃Na film was improved. The results showed that the TECD of the CNF-SO₃Na film increased by 460% compared with the pristine CNF film. Furthermore, the dielectric constant and deep trap density of the CNF-SO₃Na film increased by 2.4 times and 8.1 times. This work encourages the use of TENGs in real-world wireless transmission applications by outlining an easy and effective method for building high-performance TENGs.

Improving Relative Permittivity and Suppressing Dielectric Loss of Triboelectric Layers for High-Performance Wearable Electricity Generation

High relative permittivity and low dielectric loss are two desired parameters of a triboelectric layer to enhance its mechanical-to-electrical energy conversion efficiency in a triboelectric nanogenerator (TENG). However, the elevated permittivity of the triboelectric layer is always accompanied by increasing dielectric loss, limiting further improvement or even reducing the electrical output. Herein, we report a method for improving the relative permittivity and suppressing the dielectric loss of the triboelectric layer via nanoscale design at the particle-polymer interface. When incorporated with 2 wt % Ag@C, the triboelectric-layer-enhanced TENG (TLE-TENG) presents a 2.6-fold increment in relative permittivity and a 302% current enhancement. An instantaneous peak power density of 1.22 W m^-2, an excellent pressure sensitivity of 90.95 V kPa^-1, and an optimized sheet resistance (∼0.14 Ω/sq) are attributes of this greatly enhanced device. Such improvements bode well for the implementation of these enhancing strategies to help position TLE-TENGs as pervasive and sustainable power sources and active self-powered sensors in the era of the Internet of Things.

Light-Controlled Triple-Shape-Memory, High-Permittivity Dynamic Elastomer for Wearable Multifunctional Information Encoding Devices

Self-powered information encoding devices (IEDs) have drawn considerable interest owing to their capability to process information without batteries. Next-generation IEDs should be reprogrammable, self-healing, and wearable to satisfy the emerging requirements for multifunctional IEDs; however, such devices have not been demonstrated. Herein, an integrated triboelectric nanogenerator-based IED with the aforementioned features was developed based on the designed light-responsive high-permittivity poly(sebacoyl diglyceride-co-4,4'-azodibenzoyl diglyceride) elastomer (PSeDAE) with a triple-shape-memory effect. The electrical memory feature was achieved through a microscale shape-memory property, enabling spatiotemporal information reprogramming for the IED. Macroscale shape-memory behavior afforded the IED shape-reprogramming ability, yielding wearable and detachable features. The dynamic transesterifications and light-heating groups in the PSeDAE afforded a remotely controlled rearrangement of its cross-linking network, producing the self-healing IED.

Reconfigurable Fiber Triboelectric Nanogenerator for Self-Powered Defect Detection

With the extensive applications of portable, wearable, and stretchable electronics, the fiber triboelectric nanogenerator (TENG) has been developed particularly and rapidly. However, variable stiffness or even switchable stiffness for the fiber TENG is also urgently needed in some specific service conditions. Here, the functional, reconfigurable fiber TENG is presented for harvesting mechanical energy and self-powered sensors. It is mainly composed of soft tubes with filled low-melting-point alloy (LMPA), conductive wire, and electrically heated wire. Under an input frequency of 3 Hz, this fiber TENG produces a maximum peak power density of 348.5 μW/m. Due to its excellent reconfigurable characteristics, it can be switched back and forth in many different application situations. It can be intelligently used not only as a self-powered tactile and mechanical sensor but also as a self-powered splint for postdisaster relief work. Besides, the cracking detection of a gear and a lead screw is also realized using this fiber TENG. This work strongly promotes the application of variable stiffness LMPAs in the TENG, especially for the reconfigurable fiber TENG. It also promotes the potential self-powered applications of the TENG in the fields of sensors and detection, such as mechanical flaw detection and self-powered tactile detection.

Controllable Triboelectric Series Using Gradient Positive and Negative Charge-Confinement Layer with Different Particle Sizes of Mesoporous Carbon Materials

As a method to maximize the energy efficiency of triboelectric nanogenerators (TENGs), high-voltage charge injection (HVCI) on the surface is a simple and effective method for increasing surface charge densities. In this study, positive and negative triboelectric series are controlled using a 3-layer gradient charge-confinement wherein the particle sizes of the mesoporous carbon spheres (mCSs) are sequentially arranged depending on the external surface area of the mCSs. In the gradient charge-confinement layers of this study, the mCS with different sizes perform charge transport from the surface to a deep position during HVCI while mitigating the charge loss through charge confinement to induce the high space charge densities. Through this process, the output voltage-which is initially 15.2 V-is measured to be 600 V after HVCI, thus representing an increase of about 40 times. Further, to amplify the low output current, which is a disadvantage of triboelectric energy, two types of electrical energy-triboelectric and electromagnetic energy-are produced in single mechanical motion. As a result, the output current produced by the cylindrical TENG and electromagnetic generator is recorded as being 1300 times higher, increasing from 12.8 µA to 17.5 mA.

Dielectric Manipulated Charge Dynamics in Contact Electrification

Surface charge density has been demonstrated to be significantly impacted by the dielectric properties of tribomaterials. However, the ambiguous physical mechanism of dielectric manipulated charge behavior still restricts the construction of high-performance tribomaterials. Here, using the atomic force microscopy and Kelvin probe force microscopy, an in situ method was conducted to investigate the contact electrification and charge dynamics on a typical tribomaterial (i.e., BaTiO₃/PVDF-TrFE nanocomposite) at nanoscale. Combined with the characterization of triboelectric device at macroscale, it is found that the number of transferred electrons increases with contact force/area and tends to reach saturation under increased friction cycles. The incorporated high permittivity BaTiO₃ nanoparticles enhance the capacitance and electron trapping capability of the nanocomposites, efficiently inhibiting the lateral diffusion of electrons and improving the output performance of the triboelectric devices. Exponential decay of the surface potential is observed over monitoring time for all dielectric samples. At high BaTiO₃ loadings, more electrons can drift into the bulk and combine with the induced charges on the back electrode, forming a large leakage current and accordingly accelerating the electron dissipation. Hence, the charge trapping/storing and dissipating, as well as the charge attracting properties, should be comprehensively considered in the design of high-performance tribomaterials.

Biomechanical Energy Harvesters Based on Ionic Conductive Organohydrogels via the Hofmeister Effect and Electrostatic Interaction

The recent use of cryoprotectant replacement method for solving the easy drying problem of hydrogels has attracted increasing research interest. However, the conductivity decrease of organohydrogels due to the induced insulating solvent limited their electronic applications. Herein, we introduce the Hofmeister effect and electrostatic interaction to generate hydrogen and sodium bonds in the hydrogel. Combined with its double network, an effective charge channel that will not be affected by the solvent replacement, is therefore built. The developed organohydrogel-based single-electrode triboelectric nanogenerator (OHS-TENG) shows low conductivity decrease (one order) and high output (1.02-1.81 W/m²), which is much better than reported OHS-TENGs (2-3 orders, 41.2-710 mW/m²). Moreover, replacing water with glycerol in the hydrogel enables the device to exhibit excellent long-term stability (four months) and temperature tolerance (-50-100 °C). The presented strategy and mechanism can be extended to common organohydrogel systems aiming at high performance in electronic applications.

Structural and Chemical Modifications Towards High-Performance of Triboelectric Nanogenerators

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. 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.