Triboelectric Devices Research Articles

Triboelectric nanogenerator-based wearable electronic devices and systems: Toward informatization and intelligence

Nowadays, wearable electronic devices with rich functions have significantly facilitated individual combat in the military and daily lives of people. To achieve implanting and sustainable wearable electronic systems, it is necessary to develop self-powered sensors utilizing environmental energy harvesting with superior mechanical stretchability and flexibility. Triboelectric nanogenerators (TENGs) can capture the low-frequency mechanical energy in human motion and convert it into electricity, which is expected to be a potential solution for this urgent need. In this review, based on advanced applications, the rich functions of TENG-based wearable devices are thoroughly discussed, including human body perception and human-machine interaction, personnel identification, as well as generation and recognition of coded information. Then, we elaborate on three crucial strategies for achieving an optimal design of TENG-based wearable devices, including selection and optimization of flexible materials, structural design and optimization, and synergistic information acquisition using multiple sensors. The representative signal processing methods are investigated to exploit the potential information behind the output signals, including basic qualitative waveform features and quantization thresholds, anti-interference processing and joint processing of multiple signals, and implementation of complex functions based on artificial intelligence. The review concludes with an overview of the remaining key challenges and potential technologies that can achieve the ultimate goal of a “fully self-powered wearable microsystem”.

Design and engineering of high‐performance triboelectric nanogenerator for ubiquitous unattended devices

AbstractThe ability of future electronics to derive operational power from the working environment is attractive for realizing self‐powered unattended electronics. Triboelectric nanogenerator (TENG) effectively harvests the otherwise wasted ubiquitous mechanical energy. Despite the recent advances in the design and development of various triboelectric devices, these devices' output still falls short in meeting the practical needs of directly powering electronics and sensors. Here, we review the recent progress in the design and optimization strategies for improving the TENG output performance, including but not limited to theoretical simulation, materials engineering, device engineering, and power management. The ubiquitous applications of the TENGs in micro/high‐voltage power source, multifunctional intelligence, blue energy harvesting, and self‐powered electrochemical system are also discussed. Finally, we provide our perspectives regarding the challenges and opportunities for the future development of triboelectric devices with engineered high‐performance and designer functionalities.image

Wearable Nanogenerators: Working Principle and Self-Powered Biosensors Applications

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

Materials‐Related Strategies for Highly Efficient Triboelectric Energy Generators

AbstractSince 2012, triboelectric energy harvesting technologies have received a substantial amount of attention as they constitute one of the most efficient ways of transforming vibrational and frictional energy into electrical energy, regardless of location and environmental conditions. One of the most significant advantages of this technology is in the suitability of a very wide range of materials that can be readily incorporated into devices. In order to achieve efficient energy harvesting performance, advances in materials science and nanotechnology have been applied to develop high‐performance triboelectric energy harvesters, which have witnessed a tremendous growth in popularity. However, even though a large number of materials, including polymers, metals, inorganic and composite materials, have been separately studied for triboelectric energy harvesting applications, the key features of these different classes of materials have never been presented together or summarized, to provide valuable insight for future materials development in this field. Here, a comprehensive review of the up‐to‐date materials‐driven progress of triboelectric energy harvesting devices is provided, with emphasis on the study of materials‐related operating mechanisms and emergent materials design strategies for highly efficient triboelectric devices. The discussion includes several issues and challenges that need to be addressed for further improvement of triboelectric devices.

Triboelectrification of nanocomposites using identical polymer matrixes with different concentrations of nanoparticle fillers

This research investigates the principle of insulating polymeric triboelectrification based on the mass transfer mechanism by using nanocomposites experimentally and computationally for the efficient development of triboelectric energy devices.

Interfacial polarization-induced high-k polymer dielectric film for high-performance triboelectric devices

Output performance of triboelectric devices critically depends on their surface charge density that is greatly influenced by the dielectric constant of material. However, contrary to polymer composites, the dielectric constant cannot be substantially increased in pure polymers. This study shows that interfacial polarization in bilayer polymer films significantly enhances their dielectric constants, increasing the surface charge density and triboelectric performance. This is the first report of the introduction of interfacial polarization of dielectric materials for the enhancement of triboelectric output performance. The elastic bilayer films consisting of polydimethylsiloxane (PDMS) coated with poly (2,2,2-trifluoroethyl methacrylate) (PTF) and poly (L-lysine) (PLL) as negative and positive triboelectric materials, respectively, are utilized in triboelectric devices, which show a dramatic increase in the dielectric constants (24.4 for PTF-PDMS and 15.2 for PLL-PDMS bilayers at 10 kHz) through interfacial polarization, resulting in significant enhancement of triboelectric performance when compared with hard single-layer films. For proofs of concept, we fabricated a temperature-sensitive triboelectric sensor and vibration-based triboelectric nanogenerator. The sensor showed the highest temperature sensitivities among triboelectric sensors whereas the nanogenerator provided vibration-induced sustainable power for LED operation without rectification, which was attributed to the charge accumulation in the bi-layered dielectric films.

How Far Are We from Achieving Self‐Powered Flexible Health Monitoring Systems: An Energy Perspective

AbstractThe rapid development of flexible electronics and sensing technologies have made it possible for the detection of various human vital signs and biomarkers through an extremely light‐weight and soft device attached to the skin. To support such sensing devices for multi‐parameter tracking and continuous operation, a powerful energy supply unit, which is compact, mobile, and with high energy density and self‐charging capability, is desired. The recently emerged energy harvesting devices have demonstrated the potential of utilizing ambient and human‐based energy sources to power sensor systems. In this context, this review aims to investigate the question of whether the capacity of current flexible energy devices can meet the energy demand of wireless flexible sensor systems in long‐term health monitoring applications. First, the total energy demand of typical sensor systems is estimated by analyzing the energy consumption of each building block of the relevant systems. The design of the energy supply architecture is discussed by considering batteries/supercapacitors as the energy storage unit and photovoltaic, thermoelectric, piezoelectric, and triboelectric devices as the energy‐harvesting unit. Based on the analysis, health monitoring protocols that could be readily realized with self‐powered system designs are suggested and the core challenges for further development of the technologies for practical applications are identified.

Nylon‐11 nanowires for triboelectric energy harvesting

AbstractTriboelectric energy harvesting from ambient mechanical sources relies on motion‐generated surface charge transfer between materials with different electron affinities. In order to achieve highly efficient energy harvesting performance, choosing materials with a high surface charge density is crucial, and odd‐numbered polyamides (Nylons), such as Nylon‐11, are particularly promising due to their strong electron‐donating characteristics and the possibility to achieve dipolar alignment leading to high surface potential. The use of Nylon‐11 as a material for triboelectric energy harvesting has been rather limited due to the extreme processing conditions required for film fabrication, and the high‐voltage poling process required for dipole alignment. However, several methods to achieve “self‐poled” Nylon‐11 nanowires via facile nanoconfinement techniques have been demonstrated recently, leading to highly efficient Nylon‐11 nanowire‐based triboelectric nanogenerators. Here, we review the most recent advances in the fabrication of Nylon‐11 nanowires, with a focus on how nanoconfinement‐based fabrication methods can be used to control phase and crystallinity. These growth methods lead to self‐poled nanowires without the requirement for subsequent electrical poling, facilitating their integration into triboelectric energy harvesting devices. Strategies to fabricate Nylon‐11 nanowires for applications in triboelectric devices can be extended to other polymeric families as well.image

Triboelectric Charging and Electrostatic Separation of Granular Polymers Containing Brominated Flame Retardants

The general purpose of the present article is to study the feasibility of removing brominated flame retardant (BFR) polymers from mixed granular wastes using triboelectric charging and electrostatic separation techniques. The study was carried out on mixtures consisting of equal quantities of plastic particles either BFR-free or containing 4.8% of hexabromobenzene (i.e., 40 000 ppm of bromine). Three triboelectric charging devices were used-a vibrating tribocharger [a container made of stainless steel, polystyrene (PS), or polypropylene (PP), and fixed on a vibrating table], a rotating cylinder tribocharger made of polyvinyl chloride, or a fluidized bed tribocharger, the walls of which were made of either poly methyl methacrylate, PS, PP, or polyethylene (PE). The experiments were carried out on three granular mixtures [BFR high impact PS (HIPS)/BFR-free HIPS, BFR PP/BFR-free PP, BFR PE/BFR-free PE]. The selective sorting of the granular mixtures was performed using a roll-type electrostatic separator. The results confirm that separating BFR plastics from BFR-free plastics is feasible. Best separation results were obtained for the mixtures tribocharged in the fluidized bed tribocharger.

Triboelectric and Piezoelectric Nanogenerators for Future Soft Robots and Machines.

SummaryThe triboelectric nanogenerator (TENG) and piezoelectric nanogenerator (PENG) are two recently developed technologies for effective harvesting of ambient mechanical energy for the creation of self-powered systems. The advantages of TENGs and PENGs which include large open-circuit output voltage, low cost, ease of fabrication, and high conversion efficiency enable their application as new flexible sensors, wearable devices, soft robotics, and machines. This perspective provides an overview of the current state of the art in triboelectric and piezoelectric devices that are used as self-powered sensors and energy harvesters for soft robots and machines; hybrid approaches that combine the advantages of both mechanisms are also discussed. To improve system performance and efficiency, the potential of providing self-powered soft systems with a degree of multifunctionality is investigated. This includes optical sensing, transparency, self-healing, water resistance, photo-luminescence, or an ability to operate in hostile environments such as low temperature, high humidity, or high strain/stretch. Finally, areas for future research directions are identified.

Triboelectric charging behaviors and photoinduced enhancement of alkaline earth ions doped inorganic perovskite triboelectric nanogenerators

Abstract The in-depth understanding on the electrification behavior of dielectric materials is a prerequisite to improve their surface triboelectric charge density in triboelectric nanogenerators (TENGs). Herein, triboelectric charging affinities and polarities of all-inorganic cesium lead tri-bromine (CsPbBr3) and alkaline earth ions doped CsPb1-xMxBr3 (M = Mg2+, Ca2+, Sr2+, Ba2+, x = 0–1) perovskites are systematically investigated by assembling into vertical contact-separation TENGs. An enriched triboelectric series supplemented with pristine CsPbBr3 and CsPb1-xMxBr3 perovskites with quantified triboelectric charging polarity is presented through analyzing the electrical output performances, figure-of-merits (FOM), dielectric property, work function, bond energy and electron binding energy. Systematical analyses of three different configurations of dielectric/perovskite TENG, carbon/perovskite TENG and perovskite solar cell are compared in dark and under illumination. It is found that the photoinduced charges play significant role in enhancing the triboelectrification charges and altering charging polarity of perovskite. Our work supplements inorganic perovskites to triboelectric series and provides new insights on inorganic perovskite in the foundation of tribo-photovoltaic theory and triboelectric devices.

Holistically Engineered Polymer-Polymer and Polymer-Ion Interactions in Biocompatible Polyvinyl Alcohol Blends for High-Performance Triboelectric Devices in Self-Powered Wearable Cardiovascular Monitorings.

The capability of sensor systems to efficiently scavenge their operational power from stray, weak environmental energies through sustainable pathways could enable viable schemes for self-powered health diagnostics and therapeutics. Triboelectric nanogenerators (TENG) can effectively transform the otherwise wasted environmental, mechanical energy into electrical power. Recent advances in TENGs have resulted in a significant boost in output performance. However, obstacles hindering the development of efficient triboelectric devices based on biocompatible materials continue to prevail. Being one of the most widely used polymers for biomedical applications, polyvinyl alcohol (PVA) presents exciting opportunities for biocompatible, wearable TENGs. Here, the holistic engineering and systematic characterization of the impact of molecular and ionic fillers on PVA blends' triboelectric performance is presented for the first time. Triboelectric devices built with optimized PVA-gelatin composite films exhibit stable and robust triboelectricity outputs. Such wearable devices can detect the imperceptible skin deformation induced by the human pulse and capture the cardiovascular information encoded in the pulse signals with high fidelity. The gained fundamental understanding and demonstrated capabilities enable the rational design and holistic engineering of novel materials for more capable biocompatible triboelectric devices that can continuously monitor vital physiological signals for self-powered health diagnostics and therapeutics.

Bio‐Derived Natural Materials Based Triboelectric Devices for Self‐Powered Ubiquitous Wearable and Implantable Intelligent Devices

AbstractThe capability of devices in future ubiquitous networked wearable and implantable electronics to efficiently scavenge and store operational power from their working environment through sustainable pathways would enable viable self‐powering schemes in societally‐pervasive applications such as advanced healthcare and robotics. Triboelectric nanogenerators (TENGs) can efficiently harvest the ubiquitous mechanical energy for powering electronics and sensors. However, the majority of demonstrated TENG prototypes have been built with materials that are not biodegradable or biocompatible, which significantly hinders the application of TENGs for wearable and implantable technologies. In this review, the recent progress of the wearable and implantable triboelectric devices built with bio‐derived natural materials is summarized. The properties of these natural biopolymers are discussed in the context of self‐powered triboelectric applications. The common manufacturing methods for processing these materials into triboelectric devices are also discussed. In addition, the applications of the bio‐derived natural materials based TENGs for in vitro and in vivo applications are discussed. Finally, the outstanding challenges and potential opportunities for the development of bio‐derived natural materials based triboelectric devices targeting wearable and implantable human‐integrated applications are analyzed.

Ferroelectric Multilayer Nanocomposites with Polarization and Stress Concentration Structures for Enhanced Triboelectric Performances.

Although ferroelectric composites have been reported to enhance the performance of triboelectric (TE) devices, their performances are still limited owing to randomly dispersed particles. Herein, we introduce high-performance TE sensors (TESs) based on ferroelectric multilayer nanocomposites with alternating poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) and BaTiO3 (BTO) nanoparticle (NP) layers. The multilayers comprising alternating soft/hard layers can induce stress concentration and increase the effective stress-induced polarization and interfacial polarization between organic and inorganic materials, leading to a dielectric constant (17.06) that is higher than those of pure PVDF-TrFE films (13.9) and single PVDF-TrFE/BTO nanocomposites (15.9) at 10 kHz. As a result, the multilayered TESs with alternating BTO NP layers exhibit TE currents increased by 2.3 and 1.5 times compared to pure PVDF-TrFE without BTO NPs and PVDF-TrFE/BTO nanocomposites without multilayer structures, respectively. The multilayered TESs exhibit a high pressure sensitivity of 0.94 V/kPa (48.7 nA/kPa) and output power density of 29.4 μWcm-2, enabling their application in the fabrication of highly sensitive healthcare monitoring devices and high-performance acoustic sensors. The suggested architecture of ferroelectric multilayer nanocomposites provides a robust platform for TE devices and self-powered wearable electronics.

Charge-trapping-blocking layer for enhanced triboelectric nanogenerators

Abstract The paramount parameters to determine the electrical output of triboelectric nanogenerator (TENG) are the surface triboelectric charges and the electrostatic induced transferred charges between triboelectric layer and electrode. However, diffusion of surface charge into the triboelectric layer reduces the surface charge density and thus weakens the electrostatic induction effect. In this work, we present a multifunctional layered TENG (ML-TENG) with an addition of reduced graphene oxide and Ag nanoparticles hybrid layer between a PVDF membrane triboelectric layer and bottom Al electrode to trap and block the interfacial charges. The output performance of ML-TENGs significantly yields 50 μC m−2 in charge density, which is improved by 500% compared with that of a traditional TENG. The surface potential of the PVDF membrane before triboelectrification drops with the insertion of the rGO-AgNPs hybrid layer, demonstrating the larger triboelectric potential difference and a better output performance. The trapping effect of rGO caused by sp2-hybrid structured carbon-atom coupled with the enhanced polarization effect by AgNPs to prevent interfacial charges from diffusing and drifting, providing efficient enhancements in TENG output. The output peak power from the TENG with a rGO-AgNPs hybrid layer reaches approximately 5.4 mW, which is 67.5 times that of a pristine TENG. Finally, the mechanism of the rGO-AgNPs layer working as the charge-trapping-blocking sites has been investigated and elaborated. It is anticipated to offer a new insight to the material science and device structure design for improving the performance of triboelectric devices.

3D printed stretchable triboelectric nanogenerator fibers and devices

Abstract Triboelectric generators and sensors have a great potential as self-powered wearable devices for energy harvesting, biomedical monitoring, and recording human activity. Here, we report a process for 3D printing stretchable membranes, meshes, and hollow 3D structures on planar, rotating, and non-planar anatomical substrates using elastomeric metal-core triboelectric nanogenerator (TENG) fibers. The triboelectric performance of single 3D-printed elastomeric metal-core silicone-copper (Cu) (cladding-core) fibers and 3D-printed membranes was quantified by cyclic loading tests, which showed maximum power densities of 31.39 and 23.94 mW m−2, respectively. The utility of the flexible silicone-Cu TENG fibers and 3D printing process was demonstrated through applications to wearable mechanosensors for organ and human activity monitoring, specifically, monitoring of perfused organs and speech recognition in the absence of sound production by the speaker (i.e., ‘silent speech’), respectively. 3D-printed wearable triboelectric mechanosensors, in the form of stretchable form-fitting meshes and membranes, in combination with machine-learning signal processing algorithms, enabled real-time monitoring of perfusion-induced kidney edema and speech recognition in the absence of sound production by human subjects (99% word classification accuracy). Overall, this work expands the conductive and functional materials palette for 3D printing and encourages the use of 3D-printed triboelectric devices for self-powered sensing applications in biomanufacturing, medicine, and defense.

Multifunctional Mechanical Metamaterials with Embedded Triboelectric Nanogenerators

AbstractThe flexibility of planar triboelectric nanogenerators (TENGs) enables them to be embedded into structures with complex geometries and to conform with any deformation of these structures. In return, the embedded TENGs function as either strain‐sensitive active sensors or energy harvesters while negligibly affecting the structure's original mechanical properties. This advantage inspires a new class of multifunctional materials where compliant TENGs are distributed into local operational units of mechanical metamaterial, dubbed TENG‐embedded mechanical metamaterials. This new class of metamaterial inherits the advantages of a traditional mechanical metamaterial, in that the deformation of the internal topology of material enables unusual mechanical properties. The concept is illustrated with experimental investigations and finite element simulations of prototypes based on two exemplar metamaterial geometries where functions of self‐powered sensing, energy harvesting, as well as the designated mechanical behavior are investigated. This work provides a new framework in producing multifunctional triboelectric devices.

Triboelectric energy harvesting in harsh conditions: Temperature and pressure effects in methane and crude oil environments

Abstract Environmental and safety sensing is becoming increasingly important in the oil and gas industry. However, present solutions to feed theses sensors are expensive and dangerous and there is so far no technology able to generate electrical energy in the operational conditions of oil and gas extraction wells. Here, we show that triboelectric nanogenerators (TENGs) can withstand and harvest energy in harsh conditions. TENGs are a new technology able to efficiently harvest mechanical energy from the environment. By conducting thorough experiments in methane and crude oil over large ranges of pressures and temperatures, we were able to extend the operation realm of TENGs. By independently varying temperature (25–80 ∘C) and pressure (28–119 bar) in methane, we demonstrate that temperature is the most critical parameter for TENGs operating in harsh environments. Furthermore, energy harvesting experiments performed in crude oil reveal a decrease of the electric outputs with increasing crude temperature and pressure. Nevertheless, the assembled device continued to generate electrical energy up to pressures of 830 bar and temperatures of 120 ∘C. This study clearly demonstrates the suitability of triboelectric devices to harvest energy in harsh environments opening a wide new range of possible applications.

Self-powered triboelectric/pyroelectric multimodal sensors with enhanced performances and decoupled multiple stimuli

Abstract Self-powered multifunctional sensors have been receiving great attention for their potential use in sustainable wearable electronics. In this work, we demonstrate a facile approach for the development of self-powered multimodal pressure-temperature sensors based on an identical ferroelectric copolymer, poly (vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) for the contact pair materials by switching the triboelectric polarity via ferroelectric polarization. This approach enables the identical material-based triboelectric devices with remarkably enhanced triboelectric and pyroelectric output performances. The inversely-polarized P(VDF-TrFE) device exhibits ~106 and ~12 times higher triboelectric and pyroelectric currents, respectively, compared to those of non-polarized devices. Consequently, our triboelectric device provides the highest pressure sensitivity of 40 nA kPa−1 and 1.4 V kPa−1 with a broad pressure detection range (98 Pa–98 kPa) as well as competitive temperature sensitivity of 0.38 nA °C−1 and 0.27 nA °C−1 in cooling and heating states, respectively, compared to previous PVDF-based self-powered sensors. Furthermore, our self-powered sensor can discriminate multiple stimuli including pressure as well as temperature without signal interference. Our sensor can be utilized for the monitoring of weak pulse pressure as well as multimodal finger touch. This work provides a facile fabrication approach to realize triboelectric and pyroelectric multimodal devices with outstanding output performances.

Rapidly fabricated triboelectric nanogenerator employing insoluble and infusible biomass materials by fused deposition modeling

Limited in their insolubility and non-melting properties, biomass materials are hard to be directly applied to the fabrication of triboelectric nanogenerator (TENG), especially lignin, chitosan (CTS) and cellulose. To tackle these challenges, a novel strategy is proposed for the rapid preparation of insoluble and infusible biomass material based triboelectric nanogenerator (IBTENG) using digital fabrication methods. Insoluble and infusible biomass materials and polydimethylsiloxane (PDMS) were carried by polyamide (PA) and polyethylene (PE) tubes, respectively, to fabricate the porous positive and negative electrodes using fused deposition modeling (FDM). The optimal output of the IBTENG reaches 308 V and 61.6 μA at the frequency of 30 Hz and the power of 3.5 W, while the energy conversion efficiency reaches 78% and the power density is 5.93 W/m2. Compared with TENG prepared by traditional materials, IBTENG with outstanding performance is an extremely competitive candidate for eco-friendly energy-conversion devices based on ubiquitous mechanical energy. Further, it can be utilized directly to light two series-connected LED bulbs rated at 85 V and 3 W. This detailed investigation presented herein is a simple and universal approach for the direct use of insoluble and infusible biomass powders in the field of high-performance triboelectric devices, eliminating the need for complicated dissolution and after processing, which enables rapid fabrication of individualized and materially diverse devices.