Single-electrode Triboelectric Nanogenerator Research Articles

Design of a flexible tactile sensor for material and texture identification utilizing both contact-separation and surface sliding modes for real-life touch simulation

Haptic feedback plays a crucial role, continuously offering individuals vital information about their external surroundings through physical contact. Therefore, rapid advances in human-friendly biomimetic electronics and flexible devices, have allowed the development of advance electronic skins for artificial haptic sensation. In particular, triboelectric nanogenerator-based tactile sensors have garnered significant interest, pursuing enhanced performance in material and texture recognition, coupled with simplicity in fabrication, cost-effectiveness, high resolution and sensitivity. Thus, in this work, we propose a flexible triboelectric tactile sensor, utilizing the freestanding single-electrode triboelectric nanogenerator principle, realizing concurrent material and texture detection in a single device. We leverage a novel hybrid operational regime for tactile sensing, combining the advantages of both contact-separation and surface sliding modes in a single contact-sliding-separation motion. This enables a realistic representation of the surface employing an artificial finger, by gathering material information from the contact-separation events and texture details from the sliding motion. Common materials such as wood, paper, copper and glass were used for the identification study along with textured surfaces made of the same materials with microscopic surface features. Simultaneous classification and recognition of materials and textures was performed by a single, 1D convolutional artificial neural network, achieving an average recognition accuracy of 98.4% across all different surfaces.

Acid- and alkali-resistant, UV-shielding, and photocatalytic self-cleaning nanofiber membrane-based wearable triboelectric nanogenerator for ultra-low-frequency energy-harvesting and self-powered sensors

Wearable single-electrode triboelectric nanogenerators (TENGs), known for their simple design and construction, have attracted significant attentions for their applications in self-powered sensing and human energy harvesting. Herein, fluoride-co-hexafluoropropylene (PVDF-HFP) as the matrix, TiO2 and ZnO nanoparticles modified with 3-methacryloxypropyltrimethoxysilane (MPS) as functional materials, PVDF-HFP/TiO2/ZnO (PTZ) nanofiber membranes, serving as the friction and encapsulation layers for TENG, were prepared by electrospinning. Phytic acid-doped polyaniline (PANI), serving as the electrode layer for TENG, was prepared by in-situ polymerization. The results showed that the frequency of 0.51 Hz, and the thickness of 125 μm, the open-circuit voltage (Voc) and short-circuit current (Isc) of the PTZ-based TENG reached the highest value of 255 V and − 640–615nA, respectively, when using polyoxymethylene (POM) nanofiber membrane as positive material. Moreover, PTZ-based TENG had demonstrated excellent properties, such as the acid- and alkali-resistant, photocatalytic self-cleaning, and UV-shielding, shown the potential for use in extreme environment. Meanwhile, PTZ-based TENG had vividly demonstrated the hydrophobicity, flame retardancy, flexibility, conductive durability, breathability and moisture permeability. The PTZ-based TENG, as a self-powered electricity source, can not only instantly light up 35 LEDs but also charge electronic watch and calculator. Moreover, it can also serve as a sensor switch, integrated into the surface of a lab coat, where it can be lightly touched to activate an alarm system in case of danger. Interestingly, the PTZ-based TENG is also expected to serve as a kind of electrostatic-induction switch, turning light bulbs on or off without direct contact.

A novel triboelectric-optical hybrid tactile sensor for human-machine tactile interaction

Tactile interaction is one of the primary modes of human-machine interaction, which requires artificial devices to possess tactile sensing abilities. In recent years, to enrich the tactile information perceived by artificial devices, tactile sensors based on hybrid sensing mechanisms have attracted extensive attention. However, for wearable or flexible artificial devices, the development of tactile sensors with a simple structure and preparation process, low cost and power consumption, and good maintainability and integration remains a tough challenge. Herein, we presented a triboelectric-optical hybrid tactile sensor (TOHTS) with a separable modular structure, comprising two units: a triboelectric unit designed based on the single-electrode triboelectric nanogenerator to receive external tactile stimuli, and a photoelectric unit with a liquid-membrane liquid lens structure and a function of translating the tactile stimuli into a photoelectric signal. Both units exhibit a simple structure, and their parts can be easily cannibalized and replaced. The triboelectric unit can control the on-off behavior of the light source embedded in the photoelectric unit to minimize power consumption and improve tactile response speed, according to its output signal. The photoelectric unit possesses superior electromagnetic interference immunity, making the TOHTS accurately and quantitatively perceive contact force. The sensing performance test results validate the TOHTS’s advantages of a short response time (about 9 ms), strong linearity (R2≈0.9952) in sensing contact force, and excellent durability and stability. Due to the above features, the TOHTS exhibits outstanding practicability in tactile interactive tasks, which is proved by some interactive input experiments, and it will have extensive application prospects for human-machine interactive devices.

Triboelectrically active hydrogel drives self-charging zinc-ion battery and human motion sensing

The fast advancement of flexible electronic technology hastens an ever-growing demand for power sources that are adaptable and flexible, and the arrival of innovative energy harvesting technologies such as triboelectric nanogenerator (TENG) further endow the potable electronics with versatility and sustainability. Herein, polyvinyl alcohol/ polyacrylamide/ zinc sulfate (PPZ) hydrogel was synthesized via an one-step UV-initiated polymerization. The hydrogel demonstrates exceptional tensile properties (with a large strain of 915 % and a corresponding tensile strength of 231 KPa), excellent electrical conductivity and light transmittance. A highly flexible and easily adaptable single-electrode TENG was thus fabricated on the base of the as-synthetized PPZ (PPZ-TENG), where the PPZ hydrogel functions as both the charging layer and current collector. While promoting a high electrical output performance of the PPZ-TENG (an open circuit voltage of 176 V and a power density of 328 mW/m2), the PPZ hydrogel also serves as an efficient ion-conductive electrolyte to construct highly flexible self-charging zinc ion batteries (ZIBs). Besides, highly sensitive strain response toward environmental stimuli was also demonstrated, which makes the integration strategy a promising solution for future development self-powered flexible wearable electronics toward the sustainable monitoring of human vital signs such as pulse and limb movement.

Charge-defect tuned PVDF based ternary biocompatible composite as skin touch actuated single electrode triboelectric nanogenerator for wireless healthcare monitoring

Here, PVDF/ZnO/Ag (PVDF – poly(vinylidene fluoride)) based ternary biocompatible composites with the unique feature of improved conductivity have been developed which have enabled enhanced energy harvesting performance. A single-electrode triboelectric mechanism has been used here to use the films directly on the human body (as they are biocompatible). The optimized piezoelectric nanogenerator (PENG) device has shown a very high output with ∼28 V of open-circuit voltage (VOC), 1.2 μA of short-circuit current (ISC), and 17 μW/cm2 of power density. On the other hand, the optimized single electrode triboelectric nanogenerator (SETENG) device has been found to show ∼175 V of VOC, 21 μA of ISC, and 170 μW/cm2 of power density. The enhanced output performance has been correlated with improved polarity, enhanced charge-defects, and improved tribo-negativity of the composites caused by Ag addition. Due to this high output, both the PENGs and SETENGs have been used here for different real-life applications including pressure sensing, vibration sensing, touch sensing, and powering small electronics. The biocompatibility of the films and the unique design of SETENGs with wireless activity have enabled them to harvest electricity from body movement and sense body movement, which was very advantageous for healthcare monitoring and phonation monitoring purposes.

Tooth backlash inspired comb-shaped single-electrode triboelectric nanogenerator for self-powered condition monitoring of gear transmission

Gear transmissions are an integral part of most rotation machinery. Their abnormalities can affect the reliable operation of the equipment. Most sensors that monitor gear transmissions lack self-powered capability and have weak features due to the restricted mounting locations. In this study, the tooth backlash inspired triboelectric nanogenerator (TB-TENG) is proposed for self-powered condition monitoring of the gear transmissions. A series of comb-shaped copper foil electrodes is arranged on the non-load tooth sides to create a single-electrode TENG. Through the rational use of the tooth backlash space, the TB-TENG does not affect the tooth meshing or participate in the load transmission, ensuring both durability and structural compactness. The TB-TENG outputs are evaluated under various working conditions, structural optimizations, and different working environments based on the established TB-TENG test system. Consequently, the maximum output power density corresponding to the optimal resistance is obtained. Based on the output signal model, the effectiveness of the TB-TENG in self-powered condition monitoring is verified. Moreover, the denoising convolutional auto-encoder (DCAE) is trained based on the TB-TENG voltage signals, achieving a diagnostic accuracy of 98.4%, equivalent to accuracy based on vibration signals. The practical applicability of the proposed TB-TENG is demonstrated through deployment testing in an industrial parallel-gear transmission system. Specifically, TB-TENG can accurately monitor gear speed under variable speed conditions to assess operation stability and health status. Finally, the theoretical and experimental basis for the TB-TENG is provided with applications for self-powered condition monitoring.

Electrostatic-driven self-assembled chitin nanocrystals (ChNCs)/MXene films for triboelectric nanogenerator

With the rapid development of smart wearable electronics, self-powered devices are urgently needed to overcome the limitations of conventional power sources. The single electrode triboelectric nanogenerator (TENG) attracts much attention owing to its simple fabrication, carrying convenience, and easy use as a power source for wearable electronic devices. Herein, a flexible, responsive, and multifunctional single electrode TENG based on renewable chitin nanocrystals (ChNCs) and MXene composite film (CM-TENG) is developed. ChNCs act as interfacial adhesives to facilitate the assembly of the MXene nanosheets, which significantly improves the composite film's mechanical properties and electrical conductivity. Positively charged ChNCs neutralize the negative charges of MXene nanosheet surfaces, enabling the composite film to rapidly transfer charges during the electrostatic induction process. The output performance of the CM-TENG can achieve 99.5 mW m−2 power density so it can be utilized for self-powered strain and tactile sensors. This work presents a new strategy for constructing stable and flexible power sources and self-powered sensors via electrostatic-driven self-assembled of ChNCs and MXene, which shows promising application in low frequency mechanical energy harvesting and self-powered wearable electronics.

Bionic tribo-sensors with sweat and smudge-resistant as electronic skin for personal authentication

The increasing prevalence of the internet in our daily lives has made cybersecurity and banking security crucial concerns. Traditional methods such as passwords, fingerprints, and face recognition are becoming replicable and susceptible to hacking. To address this issue, we developed innovative biometric keystroke dynamics for personal authentication utilizing friction electric sensors. A single-electrode triboelectric nanogenerator utilizes the skin as a positive friction layer, allowing direct contact with the sensor. This arrangement enables the detection of subtle mechanical changes during pressing. To mitigate the impact of sweat and organic pollutants, a bionic rose petal friction layer is incorporated, ensuring consistent output and long-term effectiveness. The sensor efficiently converts mechanical keystroke actions into electrical signals for individuals and transmits them to an artificial neural network-based AI system. By utilizing a self-powered sweat- and dirt-proof biometric authentication system, along with the LSTM neural network algorithm, we have achieved an impressive accuracy rate of 97%. This system provides a promising security layer against password cracking and user privacy vulnerabilities.

An Environment-Tolerant Ion-Conducting Double-Network Composite Hydrogel for High-Performance Flexible Electronic Devices

HighlightsNovel double-network (DN) ion-conducting hydrogel (ICH) based on a poly(ionic liquid)/MXene/poly(vinyl alcohol) system (named PMP DN ICH) was synthesized using freeze–thawing and ionizing radiation technology.The PMP DN ICH possesses a multiple cross-linking mechanism and exhibits outstanding ionic conductivity (63.89 mS cm−1), excellent temperature resistance (−60–80 °C) and decent mechanical performance.The well-designed PMP DN ICH shows considerable potential in wearable sensing, energy storage, and energy harvesting.

Mxene-based wearable self-powered and photothermal triboelectric nanogenerator patches for wound healing acceleration and tactile sensing

Recently, wearable triboelectric nanogenerators (TENGs) had attracted extensive attention for the application in wound healing acceleration. In this work, a single-electrode TENG skin patch (TESP) was prepared based on the conductive and photothermal hydrogel containing MXene and gelatin. MXene exhibited electrical conductivity and excellent photothermal conversion properties, while gelatin displayed phase transition capability and flexibility. TESP could collect biophysical energy, generate an electric field around the damaged tissues and combine with the near-infrared photothermal effect to promote wound healing. TESP could also serve as a real-time monitoring sensor of physiological signals. The peak-to-peak voltage and current outputs of the TESPs reached 163.7 V and 8.1 μA, respectively. TESP, with both photothermal heating and real-time electrical stimulation, accelerated cell migration of mouse fibroblasts in vitro. In the animal studies, TESP effectively promoted collagen deposition and angiogenesis, thus accelerating tissue regeneration and wound healing. To the best of our knowledge, this is the first-time report of the MXene-based TENG for wound healing acceleration. We believe that this work not only provides self-powered wearable electronics a novel path for the treatment of wounds, but also shed light on their applications as advanced sensing systems.

Core–shell yarn-structured triboelectric nanogenerator for harvesting both waterdrop and biomechanics energies

Wearable energy harvesters (WEHs) have garnered significant attention recently due to their promising capabilities in powering wearable devices. In this research, we present a core–shell yarn-structured triboelectric nanogenerator (CY-TENG) that operates in two modes: the single-electrode TENG (SE-TENG) and the droplet-based electricity generator. This design facilitates energy harvesting from both waterdrops and biomechanics. The CY-TENG is fabricated using fluorinated ethylene propylene ultrafine heat-shrink tubes combined with stainless-steel yarns, ensuring its flexibility, durability, and weavability. Such attributes underscore its potential as a dual-function WEH.

A single-electrode mode triboelectric nanogenerator based on natural leaves for harvesting energy

This work reports a single-electrode mode triboelectric nanogenerator (G-TENG) based on natural leaf as the friction layer for application in the field of outdoor self-power supply.

Self-powered biodegradable and antibacterial MoS2-based triboelectric nanogenerators for the acceleration of wound healing in diabetes

Recently, there has been significant interests in the use of wearable triboelectric nanogenerators (TENGs) to accelerate wound healing. In this study, a single-electrode TENG skin patch was developed using MoS2 and a biocompatible gelatin-methacryloyl (GelMA) hydrogel. MoS2 demonstrated electrical conductivity and excellent photothermal conversion properties, while GelMA exhibited good biocompatibility. The TENG device could harvest biophysical energy, create an electric field around the damaged tissues, and leverage the near-infrared photothermal effect to enhance wound healing. Additionally, the TENG served as a real-time sensor to monitor physiological signals. The TENG prototype achieved a peak-to-peak voltage output of 48.80 V and current output of 0.57 μA. In vitro experiments utilizing mouse fibroblasts concluded that the TENG, with the combined effects of photothermal heating and real-time electrical stimulation, accelerated cell migration. The results of animal studies further confirmed that the TENG effectively promoted collagen deposition and angiogenesis, ultimately enhancing tissue regeneration and wound healing. Notably, this study is the first report of a MoS2-based TENG for accelerating wound healing. It is expected that this work will not only present a new avenue for the use of self-powered wearable electronics in wound treatment but also highlight their potential as advanced sensing systems.

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 (0.1Hz), outperforming similar contact-separation models. This innovation positions it as a practical and efficient solution for the development of low-entropy energy harvesters.

Robust integration of "top-down" strategy and triple-structure design for nature-skin derived e-skin with superior elasticity and ascendency strain and vibration sensitivity

The rapid advancement of bio-integrated electronics in recent years has been paralleled by increased interest in the research of stretchable, elastic, conductive, and multi-dimensional sensing electronic skin (e-skin) due to its potential integration with electronic devices and soft tissues. In this work, we presented the fabrication of a nature-skin derived e-skin, denoted as S-P/G@PU e-skin, achieved through an on-demand "top-down" strategy and a triple structure design, employing integrated in-situ polymerization, impregnation, and encapsulation techniques. The collagen fibers weaved hierarchical 3D structure of natural skin, was strategically employed to host conductive polypyrrole and combined with a binary solvent system of glycerin and water. Subsequently, this composite natural skin was coated with polyurethane films, resulting in the engineering of the S-P/G@PU e-skin. This innovative e-skin exhibited remarkable properties, including high tensile strength (8.76 MPa), excellent elasticity (0–180 %), anti-freezing capacity, moisture retention, substantial conductivity (6.3 S/m), and outstanding multi-dimensional sensing capabilities. Importantly, the S-P/G@PU e-skin functioned as both a slow adaptive resistance strain sensor and a fast adaptive single-electrode triboelectric nanogenerator, making it a versatile sensing system that enabled real-time monitoring of various physiological signals from the human body and wide-frequency vibration signals from devices such as cellphones and motors. This study serves as a proof of concept for transforming nature-skin into e-skin, showcasing the potential for integrated wearable electronics, artificial intelligence, and human-machine interfaces.

Ring-shaped single-electrode triboelectric nanogenerator (RSE-TENG) for energy harvesting and liquid flow rate monitoring of gas-liquid two-phase flow

Online measurement of liquid flow rate in high-speed gas-liquid two-phase flow remains a considerable challenge for practical engineering applications. Owing to the non-linear and non-smooth characteristics, it is not easy to achieve effective measurement of liquid-phase flow without separation of gas-liquid two-phase using conventional methods. An alternative, the solid/liquid-based triboelectric nanogenerator, has a great potential for self-powered sensing of liquid states. Herein, a ring-shaped single-electrode triboelectric nanogenerator (RSE-TENG) by combining contact electrification (CE) and electrostatic induction is designed for energy harvesting and parameter monitoring of gas-liquid two-phase flow. The RSE-TENG can achieve stable short-circuit current and open-circuit voltage peaks of 24 µA and 344 V, respectively. And a self-powered real-time liquid-phase flow monitoring system with a measurement range of 4–20 mL/min for gas-liquid two-phase flow is developed based on the RSE-TENG. It has the advantages of simple structure, low cost, fast response time, and can achieve effective non-contact measurement of liquid-phase flow without separation of gas-liquid two-phase. This measurement method based on the electric signal of triboelectricity at the solid-liquid interface can provide guidance and reference for the related research on fluid mechanics.

Smart battery-free and wireless bioelectronic platform based on a nature-skin-derived organohydrogel for chronic wound diagnosis, assessment, and accelerated healing

Using smart electroactive hydrogels with emerging bioelectronics to monitor wound status wirelessly in real-time is a promising approach as an unremitting therapy for refractory chronic wounds. Based on a natural skin-derived organohydrogel (SGC@MA-Gel) triboelectric nanogenerator, a bioresorbable, battery-free, and wireless smart wound treatment bioelectronic system for pharmacological treatment, nanogenerator-driven electrostimulation, and visual wound condition assessment was engineered in this study. The inherent hierarchical architecture and origins of natural skin, in tandem with the substantial loading capabilities of collagen-based biomaterials, endowed SGC@MA-Gel with favorable characteristics. These included mechanical and adhesive robustness, electrical conductivity, antibacterial properties, controlled on-demand drug release capabilities, and human physiological signal monitoring performance. The customizable bioelectronic system, developed in-house, employs a single-electrode triboelectric nanogenerator, which facilitates skin wound healing via electrostimulation. Consequently, the system's biosensors can simultaneously measure glucose, uric acid, and pH at wound sites, thereby enabling accurate wound diagnosis and real-time assessment. This system accelerates cell proliferation and wound healing in vitro and in vivo, which validates its effectiveness in chronic wound treatment. The results demonstrated that the smart wound treatment bioelectronic system could provide a facile therapeutic strategy to assist with integrated wound monitoring, diagnosis, and therapy for hospitalized patients and those recovering at home.

Textile-integrated MoS2-PDMS single electrode triboelectric nanogenerator for vibrational energy harvesting and biomechanical motion sensing

With the increasing demand for portable electronics, durable and flexible textile-based single electrode triboelectric nanogenerators (TENGs) have received a significant amount of attention. In this work, we have proposed a flexible textile based single electrode TENG (STENG) composed of MoS2-PDMS composite film. The effect of the concentration (0–10 wt%) of MoS2 in PDMS on the output performance of the as-fabricated devices was systematically studied. The STENG with a 6 wt% concentration of MoS2 exhibits the best output performance with an open-circuit output voltage, short-circuit output current density, and maximum instantaneous output power density of ∼ 320 V, ∼ 15.4 µA/cm2, and ∼ 3.2 mW/cm2, respectively. The enhancement in the output characteristics of the STENG can be explained by the formation of network of nanocapacitors, where the layers of MoS2 behave as electrodes and the insulating PDMS behaves as a nanodielectric. The powering capability of the as-fabricated STENG was tested by charging commercial capacitors and directly flashing 100 commercially available LEDs without any external charge storage component. The textile-based MoS2-PDMS composite is not only used as STENG, but also as a human motion sensor capable of detecting diverse human actions, including wrist bending, arm bending, and leg bending. As a result of its flexible structure, scalable manufacturing process, and ability to sense human motions, the developed MoS2-PDMS composite STENG has promising applications in self-powered wearable electronics and human-machine interaction.

Electron transfer induced contact-electrification at oil and oleophobic dielectric interface

The oil dielectric has been used for enhancing the performance and durability of triboelectric nanogenerators (TENGs), but little is known about the contact-electrification (CE) (or triboelectrification) characteristics of the oil. Here, the CE behavior of different oil droplets with oleophobic surfaces is systematically investigated by dropping oil on a single-electrode TENG. The electrification trace is clearly imaged using a high-voltage scanning probe approach. Thermally stimulated discharge techniques are adopted for studying the detailed trapping characteristics of contact-generated charges with a homemade instrument, and the results are consistent with the thermionic emission model. The research provides systematic understandings on oil CE with oleophobic surfaces, together with general investigation paradigms and characterization methods for electrification phenomena on surfaces. Meanwhile, because typical oils are regarded as free of ions, their CE is attributed to electron transfer, which may contribute to the understanding of fundamental CE mechanisms.

Flexible composite material for self-powered applications via triboelectricity and mechanoluminescence: PDMS/ZnS:Cu composites

Triboelectricity and mechanoluminescence (ML) arise from the same physical processes of charge separation and recombination within the material. By measuring both phenomena simultaneously, researchers can gain insights into the nature and extent of charge separation and recombination, as well as the correlation between mechanical stress and light emission. This work shows that a composite based on polydimethylsiloxane (PDMS)/ ZnS:Cu particles possess the ideal ML and can also generate electric output by contact electrification. Using mechanoluminescent materials in wearable devices offers a non-invasive and reliable way to measure mechanical deformation and stress, generating crucial data for a wide range of applications. The single-electrode mode-based triboelectric nanogenerator (TENG) was developed to realize the simultaneous ML and TENG output. During pressing motion, the PDMS/ ZnS: Cu-based TENG device delivered an electrical output of 210 V and 800 nA. Furthermore, the bending motion was then utilized to demonstrate the simultaneous ML and TENG output during various self-powered applications, such as the monitoring of bent body parts, finger joints, and harnessing wind flow.