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A liquid metal (LM) soft sensors for strain monitoring and self‐powered tactile detection in soft robotics are developed. The sensor is fabricated by printing a bilayer of oxidized LM paste and bare LM on a soft substrate. This bilayer design overcomes the challenges in scalable printing of liquid metal and demonstrates soft sensors with exceptional electromechanical performance. Specifically, the sensor exhibits a strain sensing range of over 400% with a gauge factor of over 2, while displaying low hysteresis and high mechanical stability. Furthermore, the sensor utilizes a single electrode triboelectric effect to achieve self‐powered tactile sensing. To demonstrate the potential of these sensors in soft robotics, it is integrated into a soft pneumatic actuator and successfully demonstrate their ability to perceive gestures, motion, and grasping. This work highlights the potential of LM‐based soft sensors in advancing the field of soft sensing and soft robotics. [ABSTRACT FROM AUTHOR]

Graphdiyne (GDY), a new 2D material, has recently proven excellent performance in photodetector applications due to its direct bandgap and high mobility. Different from the zero‐gap of graphene, these preeminent properties made GDY emerge as a rising star for solving the bottleneck of graphene‐based inefficient heterojunction. Herein, a highly effective graphdiyne/molybdenum (GDY/MoS2) type‐II heterojunction in a charge separation is reported toward a high‐performance photodetector. Characterized by robust electron repulsion of alkyne‐rich skeleton, the GDY based junction facilitates the effective electron–hole pairs separation and transfer. This results in significant suppression of Auger recombination up to six times at the GDY/MoS2 interface compared with the pristine materials owing to an ultrafast hot hole transfer from MoS2 to GDY. GDY/MoS2 device demonstrates notable photovoltaic behavior with a short‐circuit current of −1.3 × 10−5 A and a large open‐circuit voltage of 0.23 V under visible irradiation. As a positive‐charge‐attracting magnet, under illumination, alkyne‐rich framework induces positive photogating effect on the neighboring MoS2, further enhancing photocurrent. Consequently, the device exhibits broadband detection (453–1064 nm) with a maximum responsivity of 78.5 A W−1 and a high speed of 50 µs. Results open up a new promising strategy using GDY toward effective junction for future optoelectronic applications. [ABSTRACT FROM AUTHOR]

Prediction of the mechanical to electrical energy harvesting capabilities in [011]C cut PIN-PMN-PT is presented as a function of thermodynamic analysis of hysteresis in the stress induced ferroelectric phase transformation, and phase dependency of the electromechanical coupling factors. Energy conversion rates vary from 0.528 for low transformation hysteresis to 0.432 for high transformation hysteresis. While these predicted values are lower than the experimentally determined value from literature ("approximately 60%"), differences are explained through limitations of the mechanical loading mechanism. This brings the predicted values into agreement with literature. Ferroelectric rhombohedral phase behavior is found to dominate energy harvesting capabilities. [ABSTRACT FROM AUTHOR]

Recently, intelligent wearable flexible sensors for sports monitoring have received extensive attention. Here, we designed a AGO hydrogel-based triboelectric nanogenerator (A-TENG) for bio-mechanical harvesting and basketball posture monitoring. The AGO hydrogel can be rapidly prepared only by a simple mechanical mixing method, and there is no need to heat and add cross-linking agent during the preparation process. Besides, the A-TENG has good environmental adaptability, and the change of environmental humidity will not have irreversible impact on it. Furthermore, according to results, when the external resistance is 9 M Ω , the output power density of A-TENG device reaches a maximum of 3.1 W/m2. The self-powered sensor based on A-TENG device can be used to monitor the basketball posture. In the future, the A-TENG device can have high application value in basketball training, in order to serve intelligent sports monitoring. An AGO hydrogel-based triboelectric nanogenerator (A-TENG) was designed for bio-mechanical harvesting and basketball posture monitoring. The self-powered sensor based on A-TENG device can be used to monitor the basketball posture. In the future, the A-TENG device can have high application value in basketball training, to serve intelligent sports monitoring. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) is an energy harvesting technology from widespread mechanical energy based on the combined effects of triboelectrification and electrostatic induction. TENG devices are promising to be integrated into human daily life and their stability in the ambient environment is quite crucial to guarantee robust output. This requirement is increasing exponentially for powering various wearable/portable electronics and still remains as a challenge. Herein, contact and separation mode‐based, humidity‐ and temperature‐resistant TENG (HT‐TENG) is fabricated utilizing ethylene vinyl acetate and polytetrafluoroethylene tape as frictional layers. By harvesting biomechanical energy, the device could generate peak‐to‐peak open circuit voltage of ≈210 V and short‐circuit current of ≈12.85 μA, respectively. The as‐fabricated device is tolerant to fluctuating relative humidity ranging from 10% to 60% and temperature ranging from 10 to 60 °C. Further, the device is shown to charge 22 and 47 μF commercial capacitors to 3 V using rectifier bridges, glowing light‐emitting diodes, powering digital wrist watches, and a calculator. Thus HT‐TENG as an efficient power source reliably operates not only in typical conditions, but also in desert and frigid environments, thereby extending the applicability and commercialization of the device in the global environments. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) based on sliding metal–semiconductor junctions are an emerging technology that can efficiently convert mechanical into electrical energy. These miniature autonomous power sources can output large direct current (DC) densities, but often suffer from limited durability; hence, their practical scope remains uncertain. Herein, through a combination of conductive atomic force microscopy (C-AFM) and photocurrent decay (PCM) experiments, we explored the underlying cause of surface wear during the operation of DC-TENGs. Using monolayer-functionalized Si(211) surfaces as the model system, we demonstrate the extent to which surface damage develops during TENG operation. We reveal that the introduction of surface defects (oxide growth) during TENG operation is not caused by the passage of the rather large current densities (average output of ~2 × 106 A/m2); it is instead mainly caused by the large pressure (~GPa) required for the sliding Schottky diode to output a measurable zero-bias current. We also discovered that the drop in output during operation occurs with a delay in the friction/pressure event, which partially explains why such deterioration of DC-TENG performance is often underestimated or not reported. [ABSTRACT FROM AUTHOR]

The dusty plasma environments of airless bodies present challenges for both exploration and science missions to their surfaces. Objects moving on the surface, such as rover wheels, transfer charges onto regolith dust due to the triboelectric effect. The charged dust particles can readily stick to spacesuits as well as the optical, electronic, and mechanical components of equipment and instruments, causing their degradation. This effect is more pronounced in permanently shadowed regions (PSRs) of the Moon, where the charge dissipation rate is low due to a lack of ambient plasma. Here we report the first results of an experimental investigation of the tribocharging effect between dust and rover wheels. Various wheel surface materials along the triboelectric series are selected. The effects of varying wheel speeds and dust types are explored. Results indicate that charge distributions conform to the triboelectric properties of the dust and material it comes into contact with. High charges of up to ∼ 2 pC are measured on dust grains ∼ 100 μ m in diameter, which is equivalent to a surface potential of few hundred volts. Results also suggest that higher wheel speeds may result in more dust-dust interactions, changing the charging behavior of the dust grains. These findings indicate a need for future studies to better understand tribocharging in various exploration scenarios in order to design effective dust mitigation strategies and methods. [ABSTRACT FROM AUTHOR]

Electro-mechanical configurations can be piezo-electric transducers, triboelectric generators, electromagnetic induction, or hybrid systems. Our present study aims at developing energy generation through the piezoelectric principle. Gel-type soft SR with Shore A hardness below 30 was used as a versatile material for an elastomeric substrate. Also, multi-wall carbon nanotube (MWCNT), and diatomaceous earth (DE) were used as reinforcing fillers. This "gel-type" soft SR has crosslinking polymer networks with silicone encapsulated within its structure. Mechanical properties such as modulus or stretchability are of utmost importance for such devices based on "gel-type" soft. From the experiments, some of the mechanical aspect's values are summarized. For example, the stretchability was 99% (control) and changes to 127% (3 phr, MWCNT), 76% (20 phr DE), and 103% (20 phr hybrid). From electro-mechanical tests, the output voltage was 0.21 mV (control) and changed to 0.26 mV (3 phr, MWCNT), 0.19 mV (20 phr DE), and 0.29 mV (20 phr hybrid). Moreover, from real-time biomechanical human motion tests in "gel-type" soft-based composites, a relationship among output voltage from machine to human motions was established. Overall, these configurations make them promising against traditional portable devices such as batteries for small power applications such as mobile phones. [ABSTRACT FROM AUTHOR]

Energy harvesting systems are key elements for the widespread deployment of wireless sensor nodes. Although many energy harvesting systems exist, electric field energy harvesting is a promising choice because it can provide uninterrupted power regardless of external conditions and depends only on the presence of AC voltage in the grid, regardless of the magnitude of the line current, even under no-load conditions. However, it also has some disadvantages, such as low power availability, the need for storage, or reliance on capacitive coupling, which is a complex phenomenon that depends on parasitic capacitances. This paper aims to provide useful and practical information on the possibilities of electric field energy harvesting for both high- and low-voltage applications. Since the objective of this paper is to quantify the physical limit of the harvested energy, it considers only the physical harvester itself and not the electronic circuitry required to transfer the harvested energy to the load. Theoretical, simulation, and experimental results show the feasibility of this energy source for low-power applications such as wireless sensor nodes. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) has attracted attention for flexible electronics in the past decade. MXene is gradually applied in TENGs for performance enhancement, but the surface triboelectrification mechanism still needs to be further investigated experimentally. Herein, an experimental approach of regulating MXene fluorine groups by alkalization as a contrast to validate the mechanism is proposed. The MXene film and alkalized MXene film are studied to exploit the surface state. Compared with alkalized MXene‐based TENGs, MXene‐based TENG obtains enhancement in open‐circuit voltage, short‐circuit current, and output power by 4.1 times, 4.6 times, and even 136.6 times, respectively. The excellent performance enables flexible sensing and energy harvesting. Notably, this work reveals MXene surface triboelectrification mechanism and might motivate a new approach for TENG performance enhancement. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) are key technologies for the Internet of Things with energy harvesting. To improve energy conversion efficiency and convert mechanical energy into electrical energy, high charge density in TENGs plays a crucial role in the design of triboelectric materials and device structures. This paper proposes mechanisms and strategies to increase TENGs' charge density through multi-charge storage layers. We also discuss the realization of higher charge densities through material and structure design. The implementation of novel charge storage strategies holds the potential for significant improvements in charge density. [ABSTRACT FROM AUTHOR]

As a new technology for harvesting distributed energy, the triboelectric nanogenerator (TENG) has been widely used in harvesting wind energy. However, the wind-driven TENG (WD-TENG) faces the problems of high frictional resistance and low mechanical energy conversion efficiency. Here, based on optimizing the structure of the wind turbine, a rotational double-electrode-layer WD-TENG (DEL-WD-TENG) is developed. When the rotational speed is less than 400 round per minute (rpm), the dielectric triboelectric layer rubs with the inner electrode layer under its gravity; when the rotational speed is higher than 400 rpm, the dielectric triboelectric layer rubs with the outer electrode layer under the centrifugal force. The double-electrode-layer structure avoids the energy loss caused by other forces except gravity, centrifugal, and electrostatic adsorption, which improves the mechanical energy conversion efficiency and prolongs the working life of the DEL-WD-TENG. The conversion efficiency from mechanical energy to electricity of the DEL-WD-TENG can reach 10.3%. After 7 million cycles, the transferred charge of the DEL-WD-TENG is reduced by about 5.0%, and the mass loss of dielectric triboelectric layer is only 5.6%. The DEL-WD-TENG with low frictional resistance and high energy conversion efficiency has important application prospects in wind energy harvesting and self-powered sensing systems. [ABSTRACT FROM AUTHOR]

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

In this paper we report the study of mechanical energy harvesting of ambient energy based on triboelectric effect. We choose the bulk form of poly-tetrafluoroethylene (PTFE) as electronegative (E-) material and human hand and plywood as the electropositive (E+) materials, respectively making a single electrode based triboelectric generator (TEG). The E+ and E-material were rubbed together to produce a voltage output, which was measured by using a sensitive electrometer. This investigation was carried out for different surface morphology, surface areas of contact, thickness and types of electrode contacts and rubbing frequency. It was observed that sufficient voltage and charge generation was achieved to power low energy devices like LED bulbs, with the highest voltage generation of ~6.2 V for rectangular PTFE sheet, having one surface coated with a thin film of copper for making electrode and other one is made rough using sandpaper, as the E-material and plywood as the E+ material. We observed that the voltage output is influenced by the surface morphology, type of E+ material for the same E-material, frequency of rubbing strokes and frictional area of contact. [ABSTRACT FROM AUTHOR]

Non-contact electrostatic measurements were used to the characterization of flexoelectric potentials in dielectrics under tensile, compressive, and flexural loads. Kelvin probes are capable to detect localized potential gradients on stretched natural latex that would hardly be detected at the macroscopic scale using standard methods for flexoelectric characterization. The high deformability of rubbers under tensile (or compressive) loads or dielectrics in fully folded states during flexural tests is a really challenging task for measurements using attached or compliant electrodes to detect flexoelectricity but is easily assessed with Kelvin probes. Moreover, non-contact electrostatic measurements are effective to avoid triboelectric effects, which are important sources of electricity on contacting surfaces. [ABSTRACT FROM AUTHOR]

Polymer piezoelectric nanogenerators (PENGs) have attracted extensive interest in mechanical energy conversion and wearable electronics for the advantages they have to offer owing some of their characteristics, e.g., the fact that they are light weight, possess a desirable flexibility, and benefit from a high adaptability and simple large-scale manufacturing processes. In this paper, a high-performance organic flexible PENG based on a poly(vinylidene fluoride-trifluorethylene) [P(VDF-TrFE)] film doped with a SnS nanosheet (NS) micropillar array has been prepared and characterized. The piezoelectric coefficient of the P(VDF-TrFE)/SnS NSs (0.3 wt. %) nanocomposite has been greatly enhanced compared with that of the pristine P(VDF-TrFE) film, from 13 to 21 pC N−1. It also demonstrates outstanding open-circuit voltage (Voc) and short-circuit current (Isc) outputs of 17.28 V cm−2 and 0.94 μA cm−2 under the pressure of 0.5 MPa, which represents a 6-fold and 4-fold improvement, respectively, compared with what a neat P(VDF-TrFE) film was able to deliver. The device was capable of producing a high output power density of 10.69 μW cm−2 under an applied pressure of 0.5 MPa. The dramatic enhancement obtained using nanocomposite micropillar array films results from a more developed β-phase content in the organic film, the higher piezoelectric properties of SnS NSs, and the better alignment of dipoles induced by the micropillar array structure. These remarkably enhanced PENG performances seem to hold much promise for the development of wearable electronics exploiting ambient mechanical energy, thanks to its ability to produce different signals depending on the nature of the source of stimuli. [ABSTRACT FROM AUTHOR]

Nanopatterned tribocharge can be generated on the surface of elastomers through their replica molding with nanotextured molds. Despite its vast application potential, the physical conditions enabling the phenomenon have not been clarified in the framework of analytical mechanics. Here, we explain the final tribocharge pattern by separately applying two models, namely cohesive zone failure and cumulative fracture energy, as a function of the mold nanotexture’s aspect ratio. These models deepen our understanding of the triboelectrification phenomenon.

Triboelectric nanogenerators (TENGs), using Maxwell's displacement current as the driving force, can effectively convert mechanical energy into electricity. In this work, an extensive review of theoretical models of TENGs is presented. Based on Maxwell's equations, a formal physical model is established referred to as the quasi-electrostatic model of a TENG. Since a TENG is electrically neutral at any time owing to the low operation frequency, it is conveniently regarded as a lumped circuit element. Then, using the lumped parameter equivalent circuit theory, the conventional capacitive model and Norton's equivalent circuit model are derived. Optimal conditions for power, voltage, and total energy conversion efficiency can be calculated. The presented TENG models provide an effective theoretical foundation for understanding and predicting the performance of TENGs for practical applications. [ABSTRACT FROM AUTHOR]

This document discusses the advancements in energy harvesters/nanogenerators and self-powered sensors in the context of the Internet of Things (IoT). It highlights the potential benefits of self-sustained systems powered by various energy harvesting technologies, such as piezoelectric, triboelectric, electromagnetic, thermoelectric, pyroelectric, and photovoltaic methods. The document includes research papers and review articles that explore the design, manufacture, integration, characterization, and use of energy harvesters, self-powered sensors, nanogenerators, and systems. It also features specific examples of innovative technologies, such as displacement sensors, solar-blind ultraviolet photodetectors, and ocean energy harvesters. The document concludes by expressing gratitude to the authors, reviewers, editors, and MDPI team for their contributions to the special issue. [Extracted from the article]

A black aluminum (B-Al) film was deposited onto the surface of a stack structure of platinum/Pb(ZrxTi1 − x)O3/platinum (Pt/PZT/Pt) to convert light into a heat variation and the heat variation into a polarization change. A comparison was performed between B-Al/Pt/PZT/Pt and conventional Pt/PZT/Pt structures. An absorbance higher than 95% was measured for the B-Al layer over a large range of wavelengths varying from 350 nm to 1000 nm. The theoretical model shows that heat diffusion was extremely fast through the layers, and the sample holder played a key role in the variation and stabilization of the system temperature. A doubled variation of the polarization was observed when the light was applied onto the surface of the stack structure with stable B-Al on the top. This behavior was interpreted by the larger temperature variations induced under the highly absorptive B-Al layers, in good correlation with the theoretical model prediction based on the heat fluxes in the structures. This result is very promising for possible pyroelectric energy harvesting applications. [ABSTRACT FROM AUTHOR]

This work details the triboelectric characteristics of diamond‐like carbon (DLC) film where a proportioned sp3:sp2 bond ratio is engineered through a patented pulsed DC magnetron sputtering process to achieve a durable commercial energy harvesting material. A triboelectric nanogenerator (TENG) is fabricated by creating the triboelectric interface between DLC and PTFE. The presence and synchronization of σ – σ and σ – π bonds between DLC‐PFTE contact surface amplify the electronic cloud overlap between their atoms leading to an enhancement of the triboelectric surface charge density. The inherent hardness and reduced friction achieved through DLC and PTFE respectively prevent the mass transfer, and consequent power loss upon consecutive mechanical contact and achieves a stable electric power output of 141 mW m−2. The DLC durability achieved with PTFE in TENG demonstrates its significant potential as low frequency (1 – 10 Hz) energy harvesting devices and self‐/low‐power electronic devices and sensors. The paper uniquely contributes to a better understanding of the triboelectrification mechanism by insightfully detailing the band‐to‐band transition of electrons between the PTFE and DLC tribo‐interface, as well as discussing gap and frequency limitation of the tribo‐pair on the triboelectric charge yield, storage, transfer, and on the friction layer electric field. [ABSTRACT FROM AUTHOR]

As a result of the widespread use of small‐scale and low‐power electronic devices, the demand for micro‐energy sources has increased, in particular the potential to harvest the wide variety of energy sources present in their surrounding environment. In this paper, a novel coupled nanogenerator that can realize energy harvesting for multiple energy sources is reported. Based on the unique electrical properties of ferroelectric Bi0.5Na0.5TiO3 (BNT) materials, it is possible to combine a photovoltaic cell, pyroelectric nanogenerator, and triboelectric‐piezoelectric nanogenerator in a single element to harvest light, heat, and mechanical energy simultaneously. To evaluate the effectiveness of coupling for different materials, a Yang coupling factor (kC,Q) is defined in terms of transferred charge, where BNT has the largest kC,Q of 1.29 during heating, indicating that BNT has the best coupling enhancement compared to common ferroelectric materials. This new criterion and novel device structure therefore provide a new basis for the future development of coupled nanogenerators which are capable of harvesting multiple sources of energy. [ABSTRACT FROM AUTHOR]

To achieve high charge density for the triboelectric polymer is a crucial task for fabricating triboelectric nanogenerators (TENGs). This work has developed a quenching polarization (QP) method to create ultrahigh and long‐persistent triboelectric charge on the triboelectric polymer with weak dipole polarity. The Ethylene chlorotrifluoroethylene copolymer (ECTFE) film can reach a charge density of 391 µC m−2 in the vertical contact mode by using this QP treatment, which is 200% higher than the result achieved by the most widely used method of corona polarization. The mechanism of the improvement through QP on the triboelectric properties is studied on the basis of the polarization induced grain refinement and interfacial trapping. The QP‐treated ECTFE can maintain ultra‐high charge density for both solid‐solid and solid‐liquid TENG. More interestingly, the charge induced by QP treatment is so persistent that it produces a recoverable discharging phenomenon for solid‐liquid TENG, which has never been observed before. This QP method provides a different approach for fabricating high‐performance triboelectric materials, while the QP‐induced changes in crystallization and tribo‐charge density can help to complete the physical understanding of the electrification mechanism of triboelectric polymer. [ABSTRACT FROM AUTHOR]

Tribovoltaic nanogenerators (TVNG) are an emerging energy technology featuring high direct current density and continuous power output. Recently, a new kind of perovskite/metal Schottky‐based TVNG has attracted increasing attention, which can co‐harvest mechanical and solar energy to dramatically improve the DC output performance. However, the instability of the perovskite‐metal interface and unnecessary carrier recombination loss limit its practicability. Here, a novel light‐assisted TVNG based on a dynamic N‐type perovskite/P‐type perovskite homojunction is developed. The homojunction design can ensure stable interface contact, and contributes to forming a strong built‐in electric field to promote efficient carrier separation/extraction and decrease interfacial charge recombination loss. In addition, the innovative design of the dual perovskite functional electrode maximizes its photovoltaic characteristics and further facilitates the excitation of more charges based on tribo‐photovoltaic coupling effects. Eventually, the output voltage and current of dynamic perovskite homojunction can boost up to ≈8.72 V and ≈30.84 µA under illumination, showing outstanding performance among the state‐of‐the‐art perovskite‐based TVNGs. These findings demonstrate the great potential of perovskite materials in generating DC power and present a feasible strategy to construct efficient, multifunctional TVNGs. [ABSTRACT FROM AUTHOR]

The tribovoltaic effect can convert semiconductor interfacial frictional mechanical energy into direct current (DC) electricity, but the flexibility and durability of semiconductor materials limit its application in wearable electronic. Herein, a robust flexible textile tribovoltaic nanogenerator is presented based on a 2D dynamic heterojunction of 2H‐MoS2/Ta4C3 (MTNG). During the friction process, a built‐in electric field (Eb) and an additional interfacial electric field (ECE) are generated in a continuous dynamic contact of 2H‐MoS2/Ta4C3, and through the 2H‐MoS2/Ta4C3 dynamic heterojunction, a significant number of electron‐hole pairs are excited and move directionally to generate a DC. The influences of mechanical pressure and sliding speed on output performance of MTNGs are systematically investigated. The MTNGs deliver excellent output power density (39.15 mW m2) and outstanding robustness (43 000 cycles). Ten MTNGs can be connected in series to obtain a DC voltage of 3.3 V and in parallel to obtain a DC current of 75 µA. Furthermore, the MTNGs can effectively power a variety of commercial electronic watches and calculators by harvesting human kinetic energy. A 2D dynamic heterojunction 2H‐MoS2/Ta4C3 DC nanogenerator is described and offers a workable option for the creation of flexible DC power sources and self‐powered wearable electronics. [ABSTRACT FROM AUTHOR]

Limited carriers migration and separation efficiency are key factors affecting the photo-electric catalysis performance of semiconductors. In this paper, the mechanical stress field and temperature field are combined to realize the piezo-pyro-photo-electric catalysis by using the coupling effect of the two external fields, which greatly improves the catalysis performance of Ba 0·7 Sr 0·3 TiO 3 semiconductor. At 20–50 °C alternating heating and cooling, ultrasonic excitation, light and bias conditions, the current density of Ba 0·7 Sr 0·3 TiO 3 increased to 1.01 mA cm−2. It is 1.22 and 1.31 times higher than that of piezo-photo-electric catalysis (0.83 mA cm−2) under single mechanical stress field and pyro-photo-electric catalysis (0.77 mA cm−2) under temperature field, respectively. The coupled external stimulation is beneficial to the improvement of photo-electric catalysis performance. Due to the presence of polarization charge imbalance and piezoelectric/pyroelectric polarization induced built-in electric field piezoelectric/pyroelectric potential, thereby increasing the total concentration of carriers, accelerating the separation and transfer efficiency of carriers. This study realizes the synergistic utilization of various clean energy sources such as solar energy, thermal energy, mechanical energy and electrical energy, and provides a key idea for designing electrodes with excellent catalytic performance. [Display omitted] • Piezo-pyro-photo-electric catalysis of Ba 0·7 Sr 0·3 TiO 3 using a combination of mechanical stress field and temperature field. • The current density of Ba 0·7 Sr 0·3 TiO 3 under two fields is significantly higher than other single conditions. • The induced piezoelectric/pyroelectric potential accelerating charge separation and transfer. • SynErgistic utilization of various clean energy sources can be realized. [ABSTRACT FROM AUTHOR]

Highlights: The MXene-boosted rapid gelling expedites the assembly of flexible thermocell arrays, overcoming the typical constraint of complicated device fabrication processes. The hydrogel electrolyte can sustain stable thermoelectrochemical performance under various challenging conditions, including large, repeated, and sustained deformations, and multiple cut-healing cycles. The as-assembled thermocell array exhibits device-level self-healing capability and high adaptability to human body, efficiently harvesting low-grade heat for wearable applications. The evolution of wearable technology has prompted the need for adaptive, self-healable, and energy-autonomous energy devices. This study innovatively addresses this challenge by introducing an MXene-boosted hydrogel electrolyte, which expedites the assembly process of flexible thermocell (TEC) arrays and thus circumvents the complicated fabrication of typical wearable electronics. Our findings underscore the hydrogel electrolyte's superior thermoelectrochemical performance under substantial deformations and repeated self-healing cycles. The resulting hydrogel-based TEC yields a maximum power output of 1032.1 nW under the ΔT of 20 K when being stretched to 500% for 1000 cycles, corresponding to 80% of its initial state; meanwhile, it sustains 1179.1 nW under the ΔT of 20 K even after 60 cut-healing cycles, approximately 92% of its initial state. The as-assembled TEC array exhibits device-level self-healing capability and high adaptability to human body. It is readily applied for touch-based encrypted communication where distinct voltage signals can be converted into alphabet letters; it is also employed as a self-powered sensor to in-situ monitor a variety of body motions for complex human actions. The swift assembly approach, combined with the versatile functionality of the TEC device, paves the way for future advancements in wearable electronics targeting at fitness monitoring and human–machine interfaces. [ABSTRACT FROM AUTHOR]

The urgent need for renewable energy source has led to a significant interest in triboelectric nanogenerators (TENGs) as a new energy technology. In contrast to traditional polymer TENGs, semiconductor direct-current TENGs are more suitable for miniaturization and integration with electronic devices. This study proposes a friction material made of depletion mode GaN high electron mobility transistors (HEMTs), which exhibit superior properties such as high two-dimensional electron gas concentration. By sliding a titanium sheet on a depletion mode GaN-based heterostructure, we have designed a metal-semiconductor direct-current triboelectric nanogenerator that achieved voltage up to 45.5 V and a peak power density of 2.32 W/m2. This generator can be used to supply DC power to 14 LEDs in series and drive a digital watch directly. In particular, the generation of direct current is predominantly influenced by the surface states of the undoped GaN cap that produce a large number of electrons and are associated with an additional electric field in the direction of the two-dimensional electron gas created in the u-GaN/AlGaN/AlN/GaN heterostructure of depletion mode GaN-based HEMTs. This research not only introduces a nitride semiconductor material of GaN-based HEMTs for the metal-semiconductor interface friction in the DC TENGs but also elucidates the current generation mechanism of GaN-based HEMT TENGs. [ABSTRACT FROM AUTHOR]

The tribovoltaic effect is the direct‐current (DC) output that results from sliding a p‐type semiconductor on top of an n‐type semiconductor, and it is caused by the electron–hole pairs generated However, the rigid structure of traditional semiconductor limits its potential application in wearable fields. Here, p–type and n–type fabric with semiconductor properties are prepared by doping small organic molecules of cetyltrimethylammonium bromide and sodium dodecylbenzene sulfonate on the carbon atoms of single–wall carbon nanotubes (SWCNTs), and three all‐fabric direct‐current triboelectric nanogenerators based on the tribovoltaic effect (AFDC‐TENG) are developed , which exhibit high flexibility, satisfactory comfort, and stable DC output. In addition, the effects of structural parameters and environmental factors on the electrical output of AFDC‐TENG are systematically discussed. The output voltage, current, and power density of p‐type AFDC‐TENG can reach 0.2 V, 0.29 µA, and 45.5 mV m−2 at a maximum speed of 0.2 m s−1 and a sliding frequency of 1 Hz, respectively. This work proposes a simple and scalable design form for all‐fabric DC power supply devices, which has potential applications in the future micro/nano energy or self‐powered flexible sensors. [ABSTRACT FROM AUTHOR]

The posture monitoring of basketball is very important for daily training and skill improvement, and the research and development of related sensor technology is extremely urgent. Here, we design a box-shaped triboelectric nanogenerator (BS-TENG) to harvest mechanical energy and serve as the smart sport sensor. The BS-TENG can realize two working modes, leading to harvest both active and passive mechanical energy. This unique box structure enables to be integrated on the floor, which can play the role of smart sport floor. Furthermore, under different basketball posture (such as walk with the ball, dribble and shoot), the BS-TENG can generate different voltage signal, which make BS-TENG can serve as the self-powered sport sensor. We think this design will promote the development of intelligent sports devices. A box-shaped triboelectric nanogenerator (BS-TENG) was reported to harvest mechanical energy and serve as the smart sport sensor. Under different basketball posture (such as walk with the ball, dribble, and shoot), the BS-TENG can generate different voltage signal. This design will promote the development of intelligent sports devices. [ABSTRACT FROM AUTHOR]

Molecular engineering is a unique methodology to take advantage of the electrochemical characteristics of materials that are used in energy-harvesting devices. Particularly in triboelectric nanogenerator (TENG) studies, molecular grafting on dielectric metal oxide surfaces can be regarded as a feasible way to alter the surface charge density that directly affects the charge potential of triboelectric layers. Herein, we develop a feasible methodology to synthesize organic–inorganic hybrid structures with tunable triboelectric features. Different types of self-assembled monolayers (SAMs) with electron-donating and withdrawing groups have been used to modify metal oxide (MO) surfaces and to modify their charge density on the surface. All the synthetic routes for hybrid material production have been clearly shown and the formation of covalent bonds on the MO's surface has been confirmed by XPS. The obtained hybrid structures were applied as dopants to distinct polymer matrices with various ratios and fiberization processes were carried out to the prepare opposite triboelectric layers. The formation of the fibers was analyzed by SEM, while their surface morphology and physicochemical features have been measured by AFM and a drop shape analyzer. The triboelectric charge potential of each layer after doping and their contribution to the TENG device's parameters have been investigated. For each triboelectric layer, the best-performing tribopositive and tribonegative material combination was separately determined and then these opposite layers were used to fabricate TENG with the highest efficiency. A comparison of the device parameters with the reference indicated that the best tribopositive material gave rise to a 40% increase in the output voltage and produced 231 V, whereas the best tribonegative one led to a 33.3% rise in voltage and generated 220 V. In addition, the best device collected ~83% more charge than the reference device and came up with 250 V that corresponds to 51.5% performance enhancement. This approach paved the way by addressing the issue of how molecular engineering can be used to manipulate the triboelectric features of the same materials. [ABSTRACT FROM AUTHOR]

Traditional optical communication mode with single‐band photodetector depicts terrible confidentiality and it depends on sophisticated cryptography schemes to obtain a secure communication process. Dual‐band photodetectors have potential to realize a secure optical communication with a straightforward optical encryption strategy. However, previous reports of dual‐band organic photodetectors (OPD) relied on the multi‐stacked photosensitive layers thus there remain challenges in spectral matching and interfaces contacting. Here, a structurally simple bidirectional and UV–vis dual‐band OPD is proposed, with single photosensitive layer sitting between electrodes. By elaborately regulating the optical field distribution and vertical phase segregation of the bulk heterojunction (BHJ), this OPD presents completely distinct spectral response ranges under bidirectional illuminations. Finally, this OPD outputs outstanding self‐powered UV and vis dual‐band responsivities (up to 30 and 50 mA W−1) as the light illuminates from forward and backward direction, respectively. In addition, a stable and reliable optical communication system is realized based on this OPD where the UV response conveys valid information and further superimposes vis response for encryption. This design concept offers a simple alternative for achieving varied response windows and opens up a novel optical encryption method, which has potential be applied in a close‐range private communication process. [ABSTRACT FROM AUTHOR]

Recently, flexible multifunctional sensors have attracted widespread attention from around the world. Here, we propose a novel PS/MXene-based triboelectric nanogenerator (PM-TENG), which has a drum structure design. Through comparative experiments, the optimal ratio of polystyrene (PS) materials was explored. The PS film and nylon film form the triboelectric materials, and copper foil acts as the conducive electrode. From the results, the open-circuit voltage (Voc) and short-circuit current (Isc) of the PM-TENG based on 35 mg/ml content of PS can reach 141 V and 5.9 µA, respectively. In addition, when the resistance value of the external load is 50 MΩ, the PM-TENG exhibits a maximum output power of 123 µW. Due to its excellent flexibility, the PM-TENG can be installed on the shoulders, neck, wrist, elbow, knee, and ankle to achieve all-round motion monitoring of football players. This research can promote the application of TENG sensors in the football monitoring field. [ABSTRACT FROM AUTHOR]

In this study, a concept and design of a self-powered sensor that utilizes a triboelectric effect to evaluate the condition of tensile bolted joints was proposed. Based on the fact that the triboelectric charge yields electrostatic voltage induced by the separation of the contacting rough surfaces, the proposed sensor is a film-shaped triboelectric sensor made of inexpensive materials being installed between the objects to be fastened. The principle of the sensor is that it detects microscale relative motions between the contacting surfaces against an external vibratory load when the integrity of the fastened joint is compromised due to a decrease in the bolt's fastening force. In this study, we designed and fabricated triboelectric sensor and tested it on a tensile bolted joint specimen subjected to inertial vibratory loading, and it was experimentally shown that the output voltage amplitude of the sensor increased as the bolt's fastening force decreased. In addition, a modeling study was performed to explain the unexpected decrease in voltage amplitude observed at medium preloads, by combining the triboelectric and mechanical models with the experimental results of two different external circuit configurations. Estimation of the triboelectric charge density at the contacting surfaces was performed, which was found to be consistent with the contact mechanics model assumed. Finally, the calculation of the sensor output voltage based on the presented mechanical/triboelectric model was provided, confirming the validity of the modeling study. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) are new energy collection devices that have the characteristics of high efficiency, low cost, miniaturization capability, and convenient manufacture. TENGs mainly utilize the triboelectric effect to obtain mechanical energy from organisms or the environment, and this mechanical energy is then converted into and output as electrical energy. Bioelectricity is a phenomenon that widely exists in various cellular processes, including cell proliferation, senescence, apoptosis, as well as adjacent cells' communication and coordination. Therefore, based on these features, TENGs can be applied in organisms to collect energy and output electrical stimulation to act on cells, changing their activities and thereby playing a role in regulating cellular function and interfering with cellular fate, which can further develop into new methods of health care and disease intervention. In this review, we first introduce the working principle of TENGs and their working modes, and then summarize the current research status of cellular function regulation and fate determination stimulated by TENGs, and also analyze their application prospects for changing various processes of cell activity. Finally, we discuss the opportunities and challenges of TENGs in the fields of life science and biomedical engineering, and propose a variety of possibilities for their potential development direction. [ABSTRACT FROM AUTHOR]

Multifunctional wearable devices detect electric signals responsive to various biological stimuli and monitor present body motions or conditions, necessitating flexible materials with high sensitivity and sustainable operation. Although various dielectric polymers have been utilized in self-powered wearable applications in response to multiple external stimuli, their intrinsic limitations hinder further device performance enhancement. Because triboelectric devices comprising dielectric polymers are based on triboelectrification and electrostatic induction, multilayer-stacking structures of dielectric polymers enable significant improvements in device performance owing to enhanced interfacial polarization through dissimilar permittivity and conductivity between each layer, resulting in self-powered high-performance wearable devices. Moreover, novel triboelectric polymers with unique chemical structures or nano-additives can control interfacial polarization, allowing wearable devices to respond to multiple external stimuli. This review summarizes the recent insights into multilayered functional triboelectric polymers, including their fundamental dielectric principles and diverse applications. [ABSTRACT FROM AUTHOR]

Triboelectrification between a liquid and a solid is a common phenomenon in our daily life and industry. Triboelectric charges generated at liquid/solid interfaces have effects on energy harvesting, triboelectrification-based sensing, interfacial corrosion, wear, lubrication, etc. Knowing the amount of triboelectric charge transfer is very useful for studying the mechanism and controlling these phenomena, in which an accurate method is absolutely necessary to measure the triboelectric charge generated at the solid—liquid interface. Herein, we established a method for measuring the charge transfer between different solids and liquids. An equipment based on the Faraday cup measurement was developed, and the leakage ratio (rl) was quantified through simulation based on an electrostatic field model. Typical experiments were conducted to validate the reliability of the method. This work provides an effective method for charge measurement in triboelectrification research. [ABSTRACT FROM AUTHOR]

Body area network has attracted extensive attention for its applications in athletics, medical, diagnosis, and rehabilitation training in the next generation personalized health care solutions. Here, a contact‐separation direct current triboelectric nanogenerators (CSDC‐TENGs) based self‐powered wireless body area network (SWBAN) is reported that enables multi‐joint movements monitoring for human motion. The CSDC‐TENG is designed as a flexible active sensor with an internal contact switch, and the flexible substrate makes the TENG‐sensor stick onto skin easily. Due to the internal switch, the CSDC‐TENG could generate a DC current, a large instantaneous output voltage exceeds 700 V, and an instantaneous power can reach 1.076 W, which is more than 23 000 times higher than that of the traditional contact‐separation mode TENG in same size and materials without the switch. By coupling with flexible coil, the fixed high‐frequency radio signals can be modulated and emitted clearly ranging from 6 to 16 MHz, which can be wirelessly received and demodulated through a reader. Moreover, the SWBAN is demonstrated in a real time monitoring system for joints motion. This work has realized the wearable TENG for self‐powered wireless real‐time monitoring of body movements driven by low‐frequency human daily activities, which may promote a tremendous development of intelligent healthcare, wireless sensing system and body area network. [ABSTRACT FROM AUTHOR]

With the great demand for flexible self‐powered sensors and nanogenerators, polyvinylidene fluoride (PVDF) is widely investigated for outstanding piezoelectric and dielectric constant. In the pursuit for increasing β content, electrospinning is exhibited to be an effective method without external high voltage pooling or mechanical stretching and thus is considered a cost‐effective and simple method, because the molecular dipoles in the PVDF can be aligned during the process of electrospinning with high voltage field and stretching. The methods for improving piezoelectric characteristics are briefly introduced in this review, electrospinning fibers including uniaxial fibers, highly aligned fibers, core–shell fibers and Janus fibers are revealed, and research on theoretical modeling is carried out for efficiency in the design of piezoelectric nanogenerator. Last, studies on prospective applications based on electrospun PVDF and its copolymer PVDF‐TrFE, from sensors to smart skin, from energy harvesters to electronic textiles, are being conducted. [ABSTRACT FROM AUTHOR]

With the speed of industrialization accelerating, the traditional energy is in the predicament of being exhausted. Humans urgently need a clean energy to maintain the peace and development. Triboelectric nanogenerator (TENG) is a tiny device that collects and converts the renewable energy, such as wind, vibration and tidal/blue energy, into electrical energy. As the most significant working principle of TENG, contact electrification (CE) has been broadly studied since it was documented thousands of years ago. A large number of related researches are reported. However, most of them are focused on the polymer materials, device structures and potential applications. There are few literatures about the mechanism of CE, especially in the semiconductor–semiconductor case. Semiconductor–semiconductor CE is a promising method to generate electricity, which has been used in many fields, such as the photodetector and displacement sensor. Therefore, it is necessary to establish a serious and detailed theory in order to deeply explain the underlying mechanisms of semiconductor–semiconductor CE. In this work, a novel Fermi level model based on energy band theory is proposed to illustrate the semiconductor–semiconductor CE mechanism. By assembling a ZnO/Si vertical contact-separation (CS) mode TENG, the charge transfer introduced by CE is systematically measured. According to the energy band theory and TENG governing equation, the experimental data is qualitatively and quantitatively analyzed. Moreover, the effects of different concentrations of growth solutions on the morphology of ZnO nanowires and the Fermi level difference between ZnO and Si are explored as well. Results show that it is the Fermi level difference that dominates the short circuit transfer charge amount and direction of semiconductor–semiconductor CE mechanism. Our work can be applied to understand the CE mechanism in semiconductor–semiconductor case and broaden the application prospects of semiconductor-based TENG. [ABSTRACT FROM AUTHOR]

Since lead-based piezoelectric nanogenerators (PENGs) possess serious health risks, environmental problems, proper disposal issues, and biocompatibility concerns, this work presents the fabrication of a flexible piezoelectric nanogenerator utilizing lead-free orthorhombic AlFeO3 nanorods for biomechanical energy scavenging to sustainably power electronics. Hydrothermal technique is used to synthesize the AlFeO3 nanorods and the PENG was fabricated on Indium tin oxide (ITO) coated Polyethylene terephthalate (PET) flexible film with AlFeO3 nanorods interspersed in polydimethylsiloxane (PDMS). transmission electron microscopy proved that the AlFeO3 nanoparticles are of nanorods shape. Through x-ray Diffraction, it is validated that AlFeO3 nanorods have orthorhombic phase and crystalline structure. A high piezoelectric charge coefficient (d 33) of 400 pm V−1 is obtained from the piezoelectric force microscopy of AlFeO3 nanorods. With optimized concentration of AlFeO3 in the polymer matrix, an open circuit voltage (V OC) of 30.5 V, current density (J C) of 0.7888 ± 0.0001 μ A cm−2 and an instantaneous power density of 240.6 mW m−2 are obtained under the application of a force of 1.25 kgf. To investigate the nanogenerator's practical utility, the PENG is used for lighting multiple LEDs, charging of a capacitor and as a pedometer via biomechanical energy harvesting. Hence, it can be employed for developing various self-powered wearable electronics such as flexible skin, artificial cutaneous sensors, etc. [ABSTRACT FROM AUTHOR]

Energy harvesting is a technology that can be applied to IoT systems to eliminate the need for batteries. Many types of energy sources are available for energy harvesting, such as light, thermal, vibration, and electromagnetic energy. Indoors, where most IoT devices are located, artificial light, such as from LED lamps, can be used for energy harvesting in circuits with very ultra-low power consumption. Integrated switch-capacitor DC-DC converters are required for this type of system to convert the harvested energy into a constant output voltage suitable for powering an electronic circuit. The idea of this work is to use a hysteretic feedback control consisting of comparators and a logic system to adjust the switching frequency and the voltage conversion ratio (VCR) of the converter. With this, the equivalent output resistance is tuned to a value that results in a constant output voltage. A new method for modeling the equivalent output resistance based on charge flow analysis is proposed, which also considers the effects of source resistance. An integrated energy-harvesting system consisting of a switched-capacitor DC-DC converter is implemented to obtain an output voltage of 400 mV using a small photovoltaic cell for energy harvesting from indoor light. The proposed system can power an ultra-low-power device between 20 μ W and 40 μ W with a minimum input voltage of 230 mV. Electrical simulation results show that the implemented converter can achieve a peak efficiency of 81.24% at an input voltage of 260 mV for a 20 μ W load. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) possess significant attributes, such as a simple structure, high energy conversion efficiency, and ease of fabrication, rendering them crucial for powering mobile and distributed low-power electronic devices. In this study, a multilayer spring TENG with a cushion layer structure is proposed that enhances the output performance of the basic TENG structure. The fundamental topology of the energy harvesting circuit is chosen based on the electrical performance parameters of the generator and optimizes the selection of each electronic component in the actual circuit. This allows the small-size TENG (2 cm3) to have a high storable power density (5.45 mW m−2). Finally, the fabrication method of the small-size TENG and how to choose suitable electronic components based on the intrinsic electrical parameters of the TENG were summarized. This work provides valuable guidance for designing and fabricating self-powered IoT node devices. [ABSTRACT FROM AUTHOR]

This article presents the design of an array of rectennas operating at 28.3 THz for infrared (IR) energy harvesting applications. The basic element of the array consists of a Vivaldi-dipole rectenna composed of two arms made with different conductors (gold and titanium). A metal-insulator-metal (MIM) tunnel diode is used to rectify the THz ac current. The proposed MIM diode consists of a very thin layer of Al2O3 sandwiched between the two metal electrodes. Arrays of two, three, and four rectennas are investigated. The improvement of the energy captured by coupling several elements in the same structure with a common gap is also investigated. This array architecture, without feeding network, may reduce the number of rectifying diodes and, therefore, decrease losses and increase the overall efficiency. Finally, it has been found that the four-elements rectenna array has a maximum electric field intensity of 62.4 × 104 V/m at 28.3 THz. [ABSTRACT FROM AUTHOR]

A dual-band metasurface (MS) with a wide reception angle operating at Wi-Fi bands (2.4 GHz and 5.4 GHz) is presented for electromagnetic (EM) energy harvesting applications. The MS unit cell comprises a subwavelength circular split ring resonator printed on the low-loss substrate. An air layer is sandwiched between two low-loss substrates to enhance the harvesting efficiency at operating frequencies. One of the main advantages of the proposed MS is that it uses only one harvesting port (via) to channel the captured power to the optimized load (50 Ω), which simplifies the design of a combined power network. According to the results of full-wave EM simulations, the proposed MS has a near-unity efficiency of 97% and 94% at 2.4 GHz and 5.4 GHz, respectively, for capturing the power of incident EM waves with normal incidence. Furthermore, the proposed MS harvester achieves good performance at up to 60 ° oblique incidence. To validate simulations, the MS harvester with 5 × 5-unit cells is fabricated and tested, and its EM properties are measured, showing good agreement with the simulation results. Because of its high efficiency, the proposed MS harvester is suitable for use in various microwave applications, such as energy harvesting and wireless power transfer. [ABSTRACT FROM AUTHOR]

Owing to their biocompatibility, chemical stability, film-forming ability, cost-effectiveness, and excellent electroactive properties, poly(vinylidene fluoride) (PVDF) and PVDF-based polymers are widely used in sensors, actuators, energy harvesters, etc. In this review, the recent research progress on the PVDF phase structures and identification of different phases is outlined. Several approaches for obtaining the electroactive phase of PVDF and preparing PVDF-based nanocomposites are described. Furthermore, the potential applications of these materials in wearable sensors and human energy harvesters are discussed. Finally, some challenges and perspectives for improving the properties and boosting the applications of these materials are presented. [ABSTRACT FROM AUTHOR]