Hydrophobic sponge structure-based triboelectric nanogenerator

Advanced Triboelectric Applications of Biomass-Derived Materials: A Comprehensive Review

The utilization of triboelectric materials has gained considerable attention in recent years, offering a sustainable approach to energy harvesting and sensing technologies. Biomass-derived materials, owing to their abundance, renewability, and biocompatibility, offer promising avenues for enhancing the performance and versatility of triboelectric devices. This paper explores the synthesis and characterization of biomass-derived materials, their integration into triboelectric nanogenerators (TENGs), and their applications in energy harvesting, self-powered sensors, and environmental monitoring. This review presents an overview of the emerging field of advanced triboelectric applications that utilize the unique properties of biomass-derived materials. Additionally, it addresses the challenges and opportunities in employing biomass-derived materials for triboelectric applications, emphasizing the potential for sustainable and eco-friendly energy solutions.

A robust thin-film droplet-induced electricity generator

The pursuit of cost-effective, high-voltage electricity generators activated by droplets represents a new frontier in hydropower technology. This study presents an economical method for crafting droplet generators using common materials such as solid polytetrafluoroethylene (PTFE) films and readily available tapes, eliminating the need for specialized cleanroom facilities. A thorough investigation into voltage-limiting factors, encompassing device capacitance and induced electrode charges, reveals specific areas with potential for optimization. A substantial enhancement in the open-circuit voltage (Voc) was achieved, reaching approximately 282.2 ± 27.9 V-an impressive increase of around 60 V compared to earlier benchmarks. One device showcased its capability to power 100 LEDs concurrently, underscoring its efficacy. Ten such devices created diverse luminous patterns with uniform light intensity for each LED, showcasing the practical potential of the approach. The methodology's cost-effectiveness results in a remarkable cost reduction compared to solution-based materials, paving the way for the widespread adoption of large-scale water droplet energy harvesting.

High-performance self-desalination powered by triboelectric-electromagnetic hybrid nanogenerator

Freshwater is an essential resource in today's world, and how to produce freshwater with low or even zero power consumption is a major challenge. Here, a desalination system powered by a triboelectric-electromagnetic hybrid nanogenerator (TEHG) is presented, which can utilize the water's own energy to remove the salt ions from itself, demonstrating a new concept of "self-desalination". At a relatively low rotation speed of 150 rpm, the system can dilute NaCl brine from 4000 ppm to 145 ppm with a high salt removal rate of 147.1 μg cm-2 min-1 and a freshwater productivity of up to 31.1 L m-2 h-1. The actual seawater can also be treated with a total ion removal efficiency of 99.6 % and a freshwater productivity of 2.7 L m-2 h-1, which is superior to other renewable-energy-powered desalination systems. More importantly, fully self-powered desalination process can be realized by manual cranking and hydrokinetic energy impact, both of which are capable of treating 1000 ppm salt feed to the drinking water level. The TEHG-powered desalination system not only provides excellent desalination performance but also addresses the challenges of power consumption and limited capacity, which offers a completely new paradigm of "self-desalination".

The Potential of Electrospinning to Enable the Realization of Energy-Autonomous Wearable Sensing Systems

The market for wearable electronic devices is experiencing significant growth and increasing potential for the future. Researchers worldwide are actively working to improve these devices, particularly in developing wearable electronics with balanced functionality and wearability for commercialization. Electrospinning, a technology that creates nano/microfiber-based membranes with high surface area, porosity, and favorable mechanical properties for human in vitro and in vivo applications using a broad range of materials, is proving to be a promising approach. Wearable electronic devices can use mechanical, thermal, evaporative and solar energy harvesting technologies to generate power for future energy needs, providing more options than traditional sources. This review offers a comprehensive analysis of how electrospinning technology can be used in energy-autonomous wearable wireless sensing systems. It provides an overview of the electrospinning technology, fundamental mechanisms, and applications in energy scavenging, human physiological signal sensing, energy storage, and antenna for data transmission. The review discusses combining wearable electronic technology and textile engineering to create superior wearable devices and increase future collaboration opportunities. Additionally, the challenges related to conducting appropriate testing for market-ready products using these devices are also discussed.

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

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

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

Polydimethylsiloxane (PDMS)-the simplest and most common silicone compound-exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS-based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS-based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS-based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next-generation soft materials and devices.

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.

Porous Polymer Materials in Triboelectric Nanogenerators: A Review

Since the invention of the triboelectric nanogenerator (TENG), porous polymer materials (PPMs), with different geometries and topologies, have been utilized to enhance the output performance and expand the functionality of TENGs. In this review, the basic characteristics and preparation methods of various PPMs are introduced, along with their applications in TENGs on the basis of their roles as electrodes, triboelectric surfaces, and structural materials. According to the pore size and dimensionality, various types of TENGs that are built with hydrogels, aerogels, foams, and fibrous media are classified and their advantages and disadvantages are analyzed. To deepen the understanding of the future development trend, their intelligent and multifunctional applications in human-machine interfaces, smart wearable devices, and self-powering sensors are introduced. Finally, the future directions and challenges of PPMs in TENGs are explored to provide possible guidance on PPMs in various TENG-based intelligent devices and systems.

From Biological Source to Energy Harvesting Device: Surface Protective Ionic Liquid Coatings for Electrical Performance Enhancement of Wood-Based Electronics

This study explores task-specific ionic liquids (TSILs) in smart floor systems, highlighting their strong electrical rectification abilities and previously established wood preservative properties. Two types of TSILs, featuring a "sweet" anion and a terpene-based cation, were used to treat selected wood samples, allowing for a comparison of their physical and electrical performance with untreated and commercially treated counterparts. Drop shape analysis and scanning electron microscopy were employed to evaluate the surface treatment before and after coating. Near-IR was used to confirm the presence of a surface modifier, and thermogravimetric analysis (TGA) was utilized to assess the thermal features of the treated samples. The different surface treatments resulted in varied triboelectric nanogenerator (TENG) parameters, with the molecular structure and size of the side chains being the key determining factors. The best results were achieved with TSILs, with the instantaneous voltage increasing by approximately five times and the highest voltage reaching 300 V under enhanced loading. This work provides fresh insights into the potential application spectrum of TSILs and opens up new avenues for directly utilizing tested ionic compounds in construction systems.

Fundamental Understanding of Multicellular Triboelectric Nanogenerator with Different Electrical Configurations

The single-cell triboelectric nanogenerator (TENG) often produces insufficient energy, leading to the use of a multicellular TENG structure. This work experimented with and simulated a dual-cell TENG with various configurations in parallel and series arrangements. The working principle of charge generation during each phase of a contact-separation cycle was explained through the analysis and comparison of five electrical configurations of a dual-cell TENG. Our observations indicate that measuring the output charge of a TENG provides a more reliable performance comparison. Finally, multicellular TENG with four cells arranged in an X-shape (X-TENG), self-supporting structure is fabricated and further experimented with, validating our conjectures derived from a dual-cell TENG.

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.

Recent Advances in Mechanical Vibration Energy Harvesters Based on Triboelectric Nanogenerators

With the development of autonomous/smart technologies and the Internet of Things (IoT), tremendous wireless sensor nodes (WSNs) are of great importance to realize intelligent mechanical engineering, which is significant in the industrial and social fields. However, current power supply methods, cable and battery for instance, face challenges such as layout difficulties, high cost, short life, and environmental pollution. Meanwhile, vibration is ubiquitous in machinery, vehicles, structures, etc., but has been regarded as an unwanted by-product and wasted in most cases. Therefore, it is crucial to harvest mechanical vibration energy to achieve in situ power supply for these WSNs. As a recent energy conversion technology, triboelectric nanogenerator (TENG) is particularly good at harvesting such broadband, weak, and irregular mechanical energy, which provides a feasible scheme for the power supply of WSNs. In this review, recent achievements of mechanical vibration energy harvesting (VEH) related to mechanical engineering based on TENG are systematically reviewed from the perspective of contact-separation (C-S) and freestanding modes. Finally, existing challenges and forthcoming development orientation of the VEH based on TENG are discussed in depth, which will be conducive to the future development of intelligent mechanical engineering in the era of IoT.

Rational Design of Cellulosic Triboelectric Materials for Self-Powered Wearable Electronics

With the rapid development of the Internet of Things and flexible electronic technologies, there is a growing demand for wireless, sustainable, multifunctional, and independently operating self-powered wearable devices. Nevertheless, structural flexibility, long operating time, and wearing comfort have become key requirements for the widespread adoption of wearable electronics. Triboelectric nanogenerators as a distributed energy harvesting technology have great potential for application development in wearable sensing. Compared with rigid electronics, cellulosic self-powered wearable electronics have significant advantages in terms of flexibility, breathability, and functionality. In this paper, the research progress of advanced cellulosic triboelectric materials for self-powered wearable electronics is reviewed. The interfacial characteristics of cellulose are introduced from the top-down, bottom-up, and interfacial characteristics of the composite material preparation process. Meanwhile, the modulation strategies of triboelectric properties of cellulosic triboelectric materials are presented. Furthermore, the design strategies of triboelectric materials such as surface functionalization, interfacial structure design, and vacuum-assisted self-assembly are systematically discussed. In particular, cellulosic self-powered wearable electronics in the fields of human energy harvesting, tactile sensing, health monitoring, human-machine interaction, and intelligent fire warning are outlined in detail. Finally, the current challenges and future development directions of cellulosic triboelectric materials for self-powered wearable electronics are discussed.

Self-Assembled Porous-Reinforcement Microstructure-Based Flexible Triboelectric Patch for Remote Healthcare

Realizing real-time monitoring of physiological signals is vital for preventing and treating chronic diseases in elderly individuals. However, wearable sensors with low power consumption and high sensitivity to both weak physiological signals and large mechanical stimuli remain challenges. Here, a flexible triboelectric patch (FTEP) based on porous-reinforcement microstructures for remote health monitoring has been reported. The porous-reinforcement microstructure is constructed by the self-assembly of silicone rubber adhering to the porous framework of the PU sponge. The mechanical properties of the FTEP can be regulated by the concentrations of silicone rubber dilution. For pressure sensing, its sensitivity can be effectively improved fivefold compared to the device with a solid dielectric layer, reaching 5.93 kPa-1 under a pressure range of 0-5 kPa. In addition, the FTEP has a wide detection range up to 50 kPa with a sensitivity of 0.21 kPa-1. The porous microstructure makes the FTEP ultra-sensitive to external pressure, and the reinforcements endow the device with a greater deformation limit in a wide detection range. Finally, a novel concept of the wearable Internet of Healthcare (IoH) system for real-time physiological signal monitoring has been proposed, which could provide real-time physiological information for ambulatory personalized healthcare monitoring.

Cellulose-based superhydrophobic wrinkled paper and electrospinning film as green tribolayer for water wave energy harvesting

Water waves are viable low-carbon and renewable sources of power that can be optionally combined with triboelectric nanogeneration (TENG). Herein, we report on the synthesis of a TENG device based on green wrinkled paper tribolayers (W-TENG) assembled in grids (G-TENG) with channels that enable contact-separation modes involving metal balls that roll in phase with the waves. The paper's wrinkle wavelength and amplitude were adjusted by using a crepe blade at a given angle with respect to a drying cylinder, as well as the speed and torque. Polar hierarchical superhydrophobic cellulose micro/nanostructures, proposed as positive tribolayers with enhanced contact area and triboelectric density. The negative (biodegradable) tribolayers were prepared by electrospinning aqueous suspensions of polyvinyl alcohol and poly (ethylene oxide) reinforced with cellulose nanofibers. The charge transfer by the W-TENG reached up to 40 nC in air and retained 27 nC under 85 % relative humidity, ~5 and 7 times higher than those measured in planar TENG counterparts. A G-TENG array charging time (100-μF capacitor) of ~188 s was measured when the voltage of the capacitor raised to ~1.5 V. Overall, we introduce a new, scalable TENG system that is demonstrated for its remarkable ability to harvest blue energy.

Ag-Cellulose Hybrid Filler for Boosting the Power Output of a Triboelectric Nanogenerator

The triboelectric nanogenerator (TENG) is a newly developed energy harvesting technology that can convert mechanical energy into electricity. The TENG has received extensive attention due to its potential applications in diverse fields. In this work, a natural based triboelectric material has been developed from a natural rubber (NR) filled with cellulose fiber (CF) and Ag nanoparticles. Ag nanoparticles are incorporated into cellulose fiber (CF@Ag) and are used as a hybrid filler material for the NR composite to enhance the energy conversion efficiency of TENG. The presence of Ag nanoparticles in the NR-CF@Ag composite is found to improve the electrical power output of the TENG by promoting the electron donating ability of the cellulose filler, resulting in the higher positive tribo-polarity of NR. The NR-CF@Ag TENG shows significant improvement in the output power up to five folds compared to the pristine NR TENG. The findings of this work show a great potential for the development of a biodegradable and sustainable power source by converting mechanical energy into electricity.

Rational Design of Advanced Triboelectric Materials for Energy Harvesting and Emerging Applications

The properties of materials play a significant role in triboelectric nanogenerators (TENGs). Advanced triboelectric materials for TENGs have attracted tremendous attention because of their superior advantages (e.g., high specific surface area, high porosity, and customizable macrostructure). These advanced materials can be extensively applied in numerous fields, including energy harvester, wearable electronics, filtration, and self-powered sensors. Hence, designing triboelectric materials as advanced functional materials is important for the development of TENGs. Herein, the structural modification methods based on electrospinning to improve the triboelectric properties and the latest research progress in this kind of TENGs are systematically summarized. Preparation methods and design trends of nanofibers, microspheres, hierarchical structures, and doping nanomaterials are highlighted. The factors influencing the formation and properties of triboelectric materials are considered. Furthermore, the latest progress on the applications of TENGs is systematically elaborated. Finally, the challenges in the development of triboelectric materials are discussed, thereby guiding researchers in the large-scale application of TENGs.

Electrospun Cyclodextrin/Poly(L-lactic acid) Nanofibers for Efficient Air Filter: Their PM and VOC Removal Efficiency and Triboelectric Outputs

In this work, PLLA and CD/PLLA nanofibers were fabricated using electrospinning and utilized as a particulate matter (PM) and volatile organic compounds (VOCs) filter. The electrospun PLLA and CD/PLLA were characterized with various techniques, including SEM, BET, FTIR, XRD, XPS, WCA, DSC, tensile strength testing, PM and VOCs removal efficiency, and triboelectric performance. The results demonstrated that the best air filter was 2.5 wt%CD/PLLA, which performed the highest filtration efficiencies of 96.84 ± 1.51% and 99.38 ± 0.43% for capturing PM_2.5 and PM₁₀, respectively. Its PM_2.5 removal efficiency was 16% higher than that of pure PLLA, which were contributed by their higher surface area and porosity. These 2.5 wt%CD/PLLA nanofibers also exhibited the highest and the fastest VOC entrapment. For triboelectric outputs, the 2.5 wt%CD/PLLA-based triboelectric nanogenerator provided the highest electrical outputs as 245 V and 84.70 μA. These give rise to a three-fold enhancement of electrical outputs. These results indicated that the 2.5 wt%CD/PLLA can improve surface charge density that could capture more PM via electrostatic interaction under surrounding vibration. Therefore, this study suggested that 2.5 wt%CD/PLLA is a good candidate for a multifunction nanofibrous air filter that offers efficient PM and VOC removal.

Anisotropic Wooden Electromechanical Transduction Devices Enhanced by TEMPO Oxidization and PDMS

In order to increase the number and contact probability of electric dipole on cellulose, acid and alkali treatment was employed to extract hemicellulose and lignin from original wood to gain a highly oriented cellulose frame. The combined means with 2,2,6,6-tetramethylpiperidine-1-oxyl-NaBr-NaClO oxidation and impregnation of PDMS with compression was subsequently used to enhance its mechanical performance and electromechanical conversion. The assembled wooden electromechanical device (10 mm × 10 mm × 1 mm) exhibits the maximum open-circuit voltage (V _OC) of 11.75 V and short-circuit current (I _SC) of 211.01 nA as stepped by foot. It can be sliced to fabricate a flexible sensor with high sensitivity displaying V _OC of 2.88 V and I _SC of 210.09 nA under the tapped state. Its highly oriented wood fiber makes it display significant anisotropy in terms of mechanical and electromechanical performance for multidirectional sense. This strategy will exactly provide reference for developing other high-performance piezoelectric devices.

Power Output Enhancement of Natural Rubber Based Triboelectric Nanogenerator with Cellulose Nanofibers and Activated Carbon

The growing demand for energy and environmental concern are crucial driving forces for the development of green and sustainable energy. The triboelectric nanogenerator (TENG) has emerged as a promising solution for harvesting mechanical energy from the environment. In this research, a natural rubber (NR)-based TENG has been developed with an enhanced power output from the incorporation of cellulose nanofibers (CNF) and activated carbon (AC) nanoparticles. The highest voltage output of 137 V, a current of 12.1 µA, and power density of 2.74 W/m2 were achieved from the fabricated NR-CNF-AC TENG. This is attributed to the synergistic effect of the electron-donating properties of cellulose material and the large specific surface area of AC materials. The enhancement of TENG performance paves the way for the application of natural-based materials to convert mechanical energy into electricity, as a clean and sustainable energy source.

From Triboelectric Nanogenerator to Multifunctional Triboelectric Sensors: A Chemical Perspective toward the Interface Optimization and Device Integration

Triboelectric nanogenerators (TENGs) have intrigued scientists for their potential to alleviate the energy shortage crisis and facilitate self-powered sensors. Triboelectric interfaces containing triboelectric functionalized molecular groups and tunable surface charge densities are important for improving the electrical output capability of TENGs and the versatility of future electronics. In this review, following an introduction to the fundamental progress of TENG systems for mechanic energy harvesting, surface modifications that aim to increase the surface charge density and functionality are highlighted, with an emphasis on interfacial chemical modification and triboelectric energetics/dynamics optimization for efficient electrostatic induction and charge transfer. Recent advances in assemblies of multifunctional triboelectric sensing are briefly introduced, and future challenges and chemical perspectives in the field of TENG-based electronics are concisely reviewed. This review presents and advances the understanding of the state-of-the-art chemical strategies toward rational triboelectric interface engineering and system assembly and is expected to guide the rational design of highly efficient and versatile triboelectric sensing.

Tapping-Actuated Triboelectric Nanogenerator with Surface Charge Density Optimization for Human Motion Energy Harvesting

In this article, triboelectric effect has been used to harvest mechanical energy from human motion and convert it into electrical energy. To do so, different ways of optimizing the energy generated have been studied through the correct selection of materials, the design of new spacers to improve the contact surface area, and charge injection by high-voltage corona charging to increase the charge density of dielectric materials. Finally, a triboelectric nanogenerator (TENG) has been manufactured, which is capable of collecting the mechanical energy of the force applied by hand tapping and using it to power miniaturized electronic sensors in a self-sufficient and sustainable way. This work shows the theoretical concept and simulations of the proposed TENG device, as well as the experimental work carried out.

Achieving Ultrahigh Effective Surface Charge Density of Direct-Current Triboelectric Nanogenerator in High Humidity

As an emerging energy-harvesting technology, the triboelectric nanogenerator (TENG) is considered a powerful driving force toward the new-era of Internet of Things and artificial intelligence, but its output performance is dramatically influenced by environmental humidity. Herein, a direct current TENG (DC-TENG) based on the triboelectrification effect and electrostatic breakdown is reported to address the problem of output attenuation in high humidity environments for the conventional TENGs. It is found that high humidity not only enhances the sliding triboelectrification effect of hydrophobic triboelectric materials, but also promotes the electrostatic breakdown process for DC-TENG, thus contributing to the improvement of DC-TENG output. Furthermore, taking poly(vinyl chloride) film as the friction layer, the effective surface charge density of DC-TENG with microstructure-designed electrode achieves a milestone value of ≈2.97 mC m^-2 under 90% relative humidity, which is almost 1.42-fold larger than that under 30% RH. This work not only establishes an effective methodology to boost the output performance of TENG in a high humidity environment, but also establishes a foundation for its practical applications in large-scale energy harvesting.

Dynamic and Reprocessable Fluorinated Poly(hindered urea) Network Materials Containing Ionic Liquids to Enhance Triboelectric Performance

Triboelectric nanogenerators (TENGs), a newly developed energy harvesting device that converts surrounding environmental mechanical stimuli into electricity, have been significantly explored as an ideal long-term power source for electrical devices. Despite recent advances, the development of advanced TENG devices with sufficient outputs to sustainably power electronic devices and rapid self-healability under mild conditions to improve their lifetime and function is highly demanded. Here, we report a robust self-healable and reprocessable TENG fabricated with a covalent adaptive network based on mechanically strong fluorinated poly(hindered urea) (F-PHU) integrated with ionic liquid as an efficient dielectric material to improve its triboelectric efficiency and self-healing capability simultaneously. The synthesis and integration of a well-defined reactive copolymer having both pendant fluorinated and t-butylamino bulky groups are the key to fabricate robust F-PHU networks containing fluorinated dangling chains that can interact with ionic liquids to induce ionic polarization, which raises the dielectric constant and thus increases triboelectric performance. They also are cross-linked with dynamic bulky urea linkages for rapid self-healability and high reprocessability through their reversible exchange reactions at moderate temperatures. The developed ionic F-PHU materials exhibit a high TENG output performance (power density of 173.0 mW/m²) as well as high TENG output recovery upon repairing their surface damages. This work demonstrates that such a synergistic design of triboelectric ionic F-PHU materials could have great potential for applications requiring high-performance and long-lasting energy harvesting.

An AI-Assisted and Self-Powered Smart Robotic Gripper Based on Eco-EGaIn Nanocomposite for Pick-and-Place Operation

High compliance and muscle-alike soft robotic grippers have shown promising performance in addressing the challenges in traditional rigid grippers. Nevertheless, a lack of control feedback (gasping speed and contact force) in a grasping operation can result in undetectable slipping and false positioning. In this study, a pneumatically driven and self-powered soft robotic gripper that can recognize the grabbed object is reported. We integrated pressure (P-TENG) and bend (B-TENG) triboelectric sensors into a soft robotic gripper to transduce the features of gripped objects in a pick-and-place operation. Both the P-TENG and B-TENG sensors are fabricated using a porous structure made of soft Ecoflex and Euthethic Gallium-Indium nanocomposite (Eco-EGaIn). The output voltage of this porous setup has been improved by 63%, as compared to the non-porous structure. The developed soft gripper successfully recognizes three different objects, cylinder, cuboid, and pyramid prism, with a good accuracy of 91.67% and has shown its potential to be beneficial in the assembly lines, sorting, VR/AR application, and education training.

Eco-Friendly Triboelectric Material Based on Natural Rubber and Activated Carbon from Human Hair

The triboelectric nanogenerator (TENG) has emerged as a novel energy technology that converts mechanical energy from surrounding environments to electricity. The TENG fabricated from environmentally friendly materials would encourage the development of next-generation energy technologies that are green and sustainable. In the present work, a green triboelectric material has been fabricated from natural rubber (NR) filled with activated carbon (AC) derived from human hair. It is found that the TENG fabricated from an NR-AC composite as a tribopositive material and a poly-tetrafluoroethylene (PTFE) sheet as a tribonegative one generates the highest peak-to-peak output voltage of 89.6 V, highest peak-to-peak output current of 6.9 µA, and can deliver the maximum power density of 242 mW/m². The finding of this work presents a potential solution for the development of a green and sustainable energy source.

Wearable Sensors for Remote Health Monitoring: Potential Applications for Early Diagnosis of Covid-19

Wearable sensors are emerging as a new technology to detect physiological and biochemical markers for remote health monitoring. By measuring vital signs such as respiratory rate, body temperature, and blood oxygen level, wearable sensors offer tremendous potential for the noninvasive and early diagnosis of numerous diseases such as Covid-19. Over the past decade, significant progress has been made to develop wearable sensors with high sensitivity, accuracy, flexibility, and stretchability, bringing to reality a new paradigm of remote health monitoring. In this review paper, the latest advances in wearable sensor systems that can measure vital signs at an accuracy level matching those of point-of-care tests are presented. In particular, the focus of this review is placed on wearable sensors for measuring respiratory behavior, body temperature, and blood oxygen level, which are identified as the critical signals for diagnosing and monitoring Covid-19. Various designs based on different materials and working mechanisms are summarized. This review is concluded by identifying the remaining challenges and future opportunities for this emerging field.

Tuning the Dielectric Constant and Surface Engineering of a BaTiO3/Porous PDMS Composite Film for Enhanced Triboelectric Nanogenerator Output Performance

In this work, synergistic effects derived from surface engineering and dielectric property tuning were exploited to enhance the output performance of a triboelectric nanogenerator (TENG) based on an inorganic/porous PDMS composite in a contact-separation mode. BaTiO3 (BT)/porous PDMS films with different BT weight ratios were fabricated and evaluated for triboelectric nanogenerator (TENG) application. Maximum output signals of ca. 2500 V, 150 μA, and a power density of 1.2 W m-2 are achieved from the TENG containing 7 wt % BT, which is the best compromise in terms of surface roughness, dielectric constant, and surface contact area as evidenced by SEM and AFM studies. These electrical signals are 2 times higher than those observed for the TENG without BT. The 7BT/porous PDMS-based TENG also shows high stability without a significant loss of output voltage for at least 24 000 cycles. With this optimized TENG, more than 350 LEDs are lit up and a wireless transmitter is operated within 9 s. This work not only shows the promoting effects from porous surfaces and an optimized dielectric constant but also offers a rapid and template/waste-free fabrication process for porous PDMS composite films toward large-scale production.

Self-Powered Smart Arm Training Band Sensor Based on Extremely Stretchable Hydrogel Conductors

The development of elastic electronic technology has promoted the application of triboelectric nanogenerators (TENGs) in flexible wearable electronics. However, most of the flexible electronics cannot achieve the requirements of being extremely stretchable, transparent, and highly conductive at the same time. Herein, we report a TENG constructed using a double-network polymer ionic conductor sodium alginate/zinc sulfate/poly acrylic-acrylamide (SA-Zn) hydrogel, which exhibited outstanding stretchability (>10,000%), high transparency (>95%), and good conductivity (0.34 S·m^-1). The SA-Zn hydrogel TENG (SH-TENG) could harvest energy from typical human movements, such as bending, stretching, and twisting, which could light up 234 green commercial LEDs easily. Additionally, the SH-TENG can be used to prepare a self-powered smart training band sensor for monitoring arm stretching motion. This work may provide an innovative platform for accessing the next generation of sustainable wearable and sports monitoring electronics.

Nanostructured versus flat compact electrode for triboelectric nanogenerators at high humidity

The triboelectric nanogenerator (TENG) is a promising technology for mechanical energy harvesting. TENG has proven to be an excellent option for power generation but typically TENGs output power drops significantly in humid environments. In this work, the effect of electrode's material on power output, considering smooth and nanostructured porous structures with various surface hydrophobicity, is investigated under various humidity conditions. A vertical contact-separation mode TENG is experimentally and numerically studied for four surface morphologies of Ti foil, TiO2 thin film, TiO2 nanoparticulated film, and TiO2 nanotubular electrodes. The results show that the TENG electrical output in the flat structures such as Ti foil and TiO2 thin film at 50% RH is reduced to 50% of its initial state, while in the nanoporous structures such as nanoparticle and nanotube arrays, this is observed at RH above 95%. The results show that the use of porous nanostructures in TENG due to their high surface-to-volume, and that the process of water adsorption on the pore leads to better performance than the flat surface in humid environments. Based on our study, employing nanoporous layers is vital for nanogenerators either for power generation or active sensor applications at high humidity conditions.

PDMS Sponges with Embedded Carbon Nanotubes as Piezoresistive Sensors for Human Motion Detection

Porous piezoresistive sensors offer promising flexible sensing functionality, such as human joint motion detection and gesture identification. Herein, a facile fabrication method is developed using a microwave-based rapid porogen removal technique for the manufacturing of porous nanocomposite sponges consisting of polydimethylsiloxane (PDMS) and well-dispersed carbon nanotubes (CNTs). The porogen amounts and CNT loadings are varied to tailor the porosity and electrical properties of the porous sensors. The sponges are characterized by a scanning electron microscope (SEM) to compare their microstructures, validate the high-quality CNT dispersion, and confirm the successful nanofiller embedding within the elastomeric matrix. Sponges with a 3 wt% CNT loading demonstrate the highest piezoresistive sensitivity. Experimental characterization shows that the sponges with low porosity have long durability and minimal strain rate dependence. Additionally, the developed sponges with 3 wt% CNTs are employed for the human motion detection using piezoresistive method. One experiment includes fingertip compression measurements on a prosthetic hand. Moreover, the sensors are attached to the chest, elbow, and knee of a user to detect breathing, running, walking, joint bending, and throwing motions.

Humidity Sustainable Hydrophobic Poly(vinylidene fluoride)-Carbon Nanotubes Foam Based Piezoelectric Nanogenerator

Light weight lead free, polymer, and carbon nanotubes based flexible piezoelectric nanogenerators have prompted widespread concern for harvesting mechanical energy and powering next generation electronics devices. Herein, lightweight polyvinylidene fluoride (PVDF)-carbon nanotube (CNT) foam was prepared to fabricate humid resistant hydrophobic flexible piezoelectric nanogenerator to converts mechanical energy into electricity for the first time. Hydrophobic piezoelectric PVDF-CNT foam with density of 0.15 g/cm³ was prepared by solution route. PVDF-CNT foam exhibited crystalline and a well-defined chain likes structure with 65% fraction of β-phase. Self-poled PVDF-CNT foam shows piezoelectric charge coefficient (d₃₃) of 9.4 pC/N. High d₃₃ of PVDF-CNT foam is caused by dipole alignment induced by local electric field of CNT in the microcellular structure of PVDF. The developed foam exhibits ultrahigh dielectric constant (ε') ∼ 3048 at 150 Hz. Flexible piezoelectric PVDF-CNT foam based nanogenerator was fabricated, which generates high output voltage ∼12 V and current density of 30 nA/cm² at small compressive pressure of 0.02 kgf. Piezoelectric output performance was measured under different humid condition and an output voltage up to 8 V was achieved even under 60% RH condition. PVDF-CNT foam exhibited hydrophobic behavior and high surface water contact angle of 139°. Such high output voltage even under small pressure, without applying electrical poling and under humid condition was originated though CNT induced self-alignment of electric dipoles in PVDF polymer. These excellent performances of developed foam based device confirmed its potential application in organic based ultrasensitive self-powered nanosensors and nanosystems.

Multiscale surface modified magneto-mechano-triboelectric nanogenerator enabled by eco-friendly NaCl imprinting stamp for self-powered IoT applications

In this paper, we demonstrated a multiscale micro- and nano-structured magneto-mechano-triboelectric nanogenerator (MMTENG) enabled by a salt particle imprinting process to power an internet of thing (IoT) sensor. The fine salt particles were utilized to form a multiscale structure on a triboelectric polymer film by mechanical pressure via an eco-friendly, low-cost, and simple process, thereby reinforcing the contact triboelectrification and electrostatic induction. The surface modified MMTENG can generate an open-circuit peak-to-peak voltage of 851 V, a short-circuit current of 155 μA, and a maximum peak power of 10.3 mW under an AC magnetic field of 8 Oe. The energy device also presented output stability over 124 million operating cycles. Finally, the electricity of the surface enhanced MMTENG device was directly utilized to power an IoT temperature sensor with integration of an energy harvester, energy conversion circuit, and storage capacitor.

Recent progress in silk fibroin-based flexible electronics

With the rapid development of the Internet of Things (IoT) and the emergence of 5G, traditional silicon-based electronics no longer fully meet market demands such as nonplanar application scenarios due to mechanical mismatch. This provides unprecedented opportunities for flexible electronics that bypass the physical rigidity through the introduction of flexible materials. In recent decades, biological materials with outstanding biocompatibility and biodegradability, which are considered some of the most promising candidates for next-generation flexible electronics, have received increasing attention, e.g., silk fibroin, cellulose, pectin, chitosan, and melanin. Among them, silk fibroin presents greater superiorities in biocompatibility and biodegradability, and moreover, it also possesses a variety of attractive properties, such as adjustable water solubility, remarkable optical transmittance, high mechanical robustness, light weight, and ease of processing, which are partially or even completely lacking in other biological materials. Therefore, silk fibroin has been widely used as fundamental components for the construction of biocompatible flexible electronics, particularly for wearable and implantable devices. Furthermore, in recent years, more attention has been paid to the investigation of the functional characteristics of silk fibroin, such as the dielectric properties, piezoelectric properties, strong ability to lose electrons, and sensitivity to environmental variables. Here, this paper not only reviews the preparation technologies for various forms of silk fibroin and the recent progress in the use of silk fibroin as a fundamental material but also focuses on the recent advanced works in which silk fibroin serves as functional components. Additionally, the challenges and future development of silk fibroin-based flexible electronics are summarized. (1) This review focuses on silk fibroin serving as active functional components to construct flexible electronics. (2) Recent representative reports on flexible electronic devices that applied silk fibroin as fundamental supporting components are summarized. (3) This review summarizes the current typical silk fibroin-based materials and the corresponding advanced preparation technologies. (4) The current challenges and future development of silk fibroin-based flexible electronic devices are analyzed.

Portable and wearable self-powered systems based on emerging energy harvesting technology

A self-powered system based on energy harvesting technology can be a potential candidate for solving the problem of supplying power to electronic devices. In this review, we focus on portable and wearable self-powered systems, starting with typical energy harvesting technology, and introduce portable and wearable self-powered systems with sensing functions. In addition, we demonstrate the potential of self-powered systems in actuation functions and the development of self-powered systems toward intelligent functions under the support of information processing and artificial intelligence technologies.

A Polymeric Bilayer Multi-Legged Soft Millirobot with Dual Actuation and Humidity Sensing

There are numerous works that report wirelessly controlling the locomotion of soft robots through a single actuation method of light or magnetism. However, coupling multiple driving modes to improve the mobility of robots is still in its infancy. Here, we present a soft multi-legged millirobot that can move, climb a slope, swim and detect a signal by near-infrared irradiation (NIR) light or magnetic field dual actuation. Due to the design of the feet structure, our soft millirobot incorporates the advantages of a single actuation mode of light or magnetism. Furthermore, it can execute a compulsory exercise to sense a signal and analyze the ambience fluctuation in a narrow place. This work provides a novel alternative for soft robots to achieve multimode actuation and signal sensing.

Natural textile based triboelectric nanogenerators for efficient energy harvesting applications

This work reports a facile method to create efficient natural textile based triboelectric nanogenerators (N-TENGs). First, plain natural textiles, cotton and silk, were dip-coated in cyanoalkyl silane and fluoroalkyl silane to transform their surface energy into positive and negative triboelectricity. The N-TENGs were fabricated by stacking an cyanoalkylated siloxane grafted fabric with an fluoralkylated siloxane grafted fabric to assemble a Cu fabric electrode. A single N-TENG generated a maximum output voltage and output current of 216.8 V and 50.3 μA (0.87 μA cm-2), without any nanopatterning. The double stacked N-TENG showed an enhanced output current of 84.8 μA (1.46 μA cm-2), and exhibited a maximum power output of 0.345 mW cm-2 at an external resistance of 0.42 MΩ. In addition, the N-TENG can light up 100 light-emitting diodes (LEDs) and charge capacitors, demonstrating its self-powering applications.

Advances in self-powered chemical sensing via a triboelectric nanogenerator

Chemical sensors allow for continuous detection and analysis of underexplored molecules in the human body and the surroundings and have promising applications in human healthcare and environmental protection. With the increasing number of chemical sensors and their wide-range distribution, developing a continuous, sustainable, and pervasive power supply is vitally important but an unmet scientific challenge to perform chemical sensing. Self-powered chemical sensing via triboelectric nanogenerators (TENGs) could be a promising approach to this critical situation. TENGs can convert mechanical triggers from the surroundings into usable electrical signals for chemical sensing in a self-powered and environment-friendly manner. Moreover, their simple structure, low probability of failure, and wide choice of materials distinguish them from other chemical sensing technologies. This review article discusses the working principles of TENGs and their applications in chemical sensing with respect to the role of TENGs as either a self-powered sensor or a power source for existing chemical sensors. Advances in materials innovation and nanotechnology to optimize the chemical sensing performances are discussed and emphasized. Finally, the current challenges and future prospect of TENG enabled self-powered chemical sensing are discussed to promote interdisciplinary field development and revolutions.

Triangulated Cylinder Origami-Based Piezoelectric/Triboelectric Hybrid Generator to Harvest Coupled Axial and Rotational Motion

Piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs) are representative technologies that can harvest mechanical energy. In general, piezoelectric/triboelectric hybrid generators can harvest considerable energy with a limited input; however, PENGs and TENGs entail different requirements for harvesting energy. Specifically, PENGs produce a large output when a large mechanical strain is applied, and TENGs require a large surface area to produce a high power. Therefore, it is necessary to develop an innovative strategy in terms of the structural design to satisfy the requirements of both PENGs and TENGs. In this study, we developed a triangulated cylinder origami-based piezoelectric/triboelectric hybrid generator (TCO-HG) with an origami structure to enable effective energy harvesting. The proposed structure consists of a vertical contact-separation TENG on the surface of the triangulated cylinder, PENG on the inner hinge, and rotational TENG on the top substrate to harvest mechanical energy from each motion. Each generator could produce a separate electrical output with a single input. The TCO-HG could charge a 22 μF commercial capacitor and power 60 LEDs when operated.

Polydimethylsiloxane nanocomposite macroporous films prepared via Pickering high internal phase emulsions as effective dielectrics for enhancing the performance of triboelectric nanogenerators

Polydimethylsiloxane (PDMS) nanocomposite (NC) macroporous films were prepared by a Pickering high internal phase emulsion (HIPE) templating technique and used as effective dielectrics for enhancing the performance of triboelectric-nanogenerators (TENGs). HIPEs were formulated using commercial PDMS and water as the continuous and dispersed phase, respectively. The formation and solidification of PDMS-based HIPEs were possible through stabilization with silver-nanoparticles (Ag-Nps) and surfactant (Span 20) mixtures. The resulting PDMS-NC-polyHIPE films presented an interconnected 3D macroporous structure with Ag-Nps on their porous surface. The addition of different amounts of Ag-Nps (0, 4, 20, 28, 36 wt%) in HIPE formulations allowed modification of the pore size, total pore volume and dielectric properties of the tribo-materials. Results revealed that both the porosity and dielectric properties of these materials play an important role in enhancing the output performance of TENGs. Thus, the best TENG based on the PDMS-NC-polyHIPE film was achieved with 20 wt% of Ag-Nps, with voltage, current and power values of 4.88 V, 0.433 μA and 2.1 μW, respectively, which gives over 3.28-fold power enhancement compared with the reference TENG (based on a PDMS film without porosity or Ag-Nps). Therefore, the preparation of tribo-materials through a Pickering HIPE templating technique provides a novel, effective and easy way for the improvement of the TENG's performance.

Moisture-Enabled Electricity Generation: From Physics and Materials to Self-Powered Applications

The exploration of the utilization of sustainable, green energy represents one way in which it is possible to ameliorate the growing threat of the global environmental issues and the crisis in energy. Moisture, which is ubiquitous on Earth, contains a vast reservoir of low-grade energy in the form of gaseous water molecules and water droplets. It has now been found that a number of functionalized materials can generate electricity directly from their interaction with moisture. This suggests that electrical energy can be harvested from atmospheric moisture and enables the creation of a new range of self-powered devices. Herein, the basic mechanisms of moisture-induced electricity generation are discussed, the recent advances in materials (including carbon nanoparticles, graphene materials, metal oxide nanomaterials, biofibers, and polymers) for harvesting electrical energy from moisture are summarized, and some strategies for improving energy conversion efficiency and output power in these devices are provided. The potential applications of moisture electrical generators in self-powered electronics, healthcare, security, information storage, artificial intelligence, and Internet-of-things are also discussed. Some remaining challenges are also considered, together with a number of suggestions for potential new developments of this emerging technology.

Leverage Surface Chemistry for High-Performance Triboelectric Nanogenerators

Triboelectric Nanogenerators (TENGs) are a highly efficient approach for mechanical-to-electrical energy conversion based on the coupling effects of contact electrification and electrostatic induction. TENGs have been intensively applied as both sustainable power sources and self-powered active sensors with a collection of compelling features, including lightweight, low cost, flexible structures, extensive material selections, and high performances at low operating frequencies. The output performance of TENGs is largely determined by the surface triboelectric charges density. Thus, manipulating the surface chemical properties via appropriate modification methods is one of the most fundamental strategies to improve the output performances of TENGs. This article systematically reviews the recently reported chemical modification methods for building up high-performance TENGs from four aspects: functional groups modification, ion implantation and decoration, dielectric property engineering, and functional sublayers insertion. This review will highlight the contribution of surface chemistry to the field of triboelectric nanogenerators by assessing the problems that are in desperate need of solving and discussing the field's future directions.

Advances in triboelectric nanogenerators for biomedical sensing

Biomedical sensors have been essential in improving healthcare outcomes over the past 30 years, though limited power source access and user wearability restraints have prevented them from taking a constant and active biomedical sensing role in our daily lives. Triboelectric nanogenerators (TENGs) have demonstrated exceptional capabilities and versatility in delivering self-powered and wear-optimized biomedical sensors, and are paving the way for a novel platform technology able to fully integrate into the developing 5G/Internet-of-Things ecosystem. This novel paradigm of TENG-based biomedical sensors aspires to provide ubiquitous and omnipresent real-time biomedical sensing for us all. In this review, we cover the remarkable developments in TENG-based biomedical sensing which have arisen in the last octennium, focusing on both in-body and on-body biomedical sensing solutions. We begin by covering TENG as biomedical sensors in the most relevant, mortality-associated clinical fields of pneumology and cardiology, as well as other organ-related biomedical sensing abilities including ambulation. We also include an overview of ambient biomedical sensing as a field of growing interest in occupational health monitoring. Finally, we explore TENGs as power sources for third party biomedical sensors in a number of fields, and conclude our review by focusing on the future perspectives of TENG biomedical sensors, highlighting key areas of attention to fully translate TENG-based biomedical sensors into clinically and commercially viable digital and wireless consumer and health products.