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Water waves are increasingly regarded as a promising source for large-scale energy applications. Triboelectric nanogenerators (TENGs) have been recognized as one of the most promising approaches for harvesting wave energy. This work examines a freestanding, fully enclosed TENG that encloses a rolling ball inside a rocking spherical shell. Through the optimization of materials and structural parameters, a spherical TENG of 6 cm in diameter actuated by water waves can provide a peak current of 1 μA over a wide load range from a short-circuit condition to 10 GΩ, with an instantaneous output power of up to 10 mW. A multielectrode arrangement is also studied to improve the output of the TENG under random wave motions from all directions. Moreover, at a frequency of 1.43 Hz, the wave-driven TENG can directly drive tens of LEDs and charge a series of supercapacitors to rated voltage within several hours. The stored energy can power an electronic thermometer for 20 min. This rolling-structured TENG is extremely lightweight, has a simple structure, and is capable of rocking on or in water to harvest wave energy; it provides an innovative and effective approach toward large-scale blue energy harvesting of oceans and lakes. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) technology has emerged as a new mechanical energy harvesting technology with numerous advantages. This paper analyzes its charging behavior together with a load capacitor. Through numerical and analytical modeling, the charging performance of a TENG with a bridge rectifier under periodic external mechanical motion is completely analogous to that of a dc voltage source in series with an internal resistance. An optimum load capacitance that matches the TENGs impedance is observed for the maximum stored energy. This optimum load capacitance is theoretically detected to be linearly proportional to the charging cycle numbers and the inherent TENG capacitance. Experiments were also performed to further validate our theoretical anticipation and show the potential application of this paper in guiding real experimental designs. [ABSTRACT FROM AUTHOR]

'Smart' bandages based on multimodal wearable devices could enable real-time physiological monitoring and active intervention to promote healing of chronic wounds. However, there has been limited development in incorporation of both sensors and stimulators for the current smart bandage technologies. Additionally, while adhesive electrodes are essential for robust signal transduction, detachment of existing adhesive dressings can lead to secondary damage to delicate wound tissues without switchable adhesion. Here we overcome these issues by developing a flexible bioelectronic system consisting of wirelessly powered, closed-loop sensing and stimulation circuits with skin-interfacing hydrogel electrodes capable of on-demand adhesion and detachment. In mice, we demonstrate that our wound care system can continuously monitor skin impedance and temperature and deliver electrical stimulation in response to the wound environment. Across preclinical wound models, the treatment group healed ~25% more rapidly and with ~50% enhancement in dermal remodeling compared with control. Further, we observed activation of proregenerative genes in monocyte and macrophage cell populations, which may enhance tissue regeneration, neovascularization and dermal recovery. A wireless 'smart' bandage stimulates wound healing. [ABSTRACT FROM AUTHOR]

Single-electrode triboelectric nanogenerators (SETENGs) significantly expand the application of triboelectric nanogenerators in various circumstances, such as touch-pad technologies. In this work, a theoretical model of SETENGs is presented with in-depth interpretation and analysis of their working principle. Electrostatic shield effect from the primary electrode is the main consideration in the design of such SETENGs. On the basis of this analysis, the impacts of two important structural parameters, that is, the electrode gap distance and the area size, on the output performance are theoretically investigated. An optimized electrode gap distance and an optimized area size are observed to provide a maximum transit output power. Parallel connection of multiple SETENGs with micro-scale size and relatively larger spacing should be utilized as the scaling-up strategy. The discussion of the basic working principle and the influence of structural parameters on the whole performance of the device can serve as an important guidance for rational design of the device structure towards the optimum output in specific applications. [ABSTRACT FROM AUTHOR]

Nanowire solar cells are promising candidates for poweringnanosystemsand flexible electronics. The strain in the nanowires, introducedduring growth, device fabrication and/or application, is an importantissue for piezoelectric semiconductor (like CdS, ZnO, and CdTe) basedphotovoltaic. In this work, we demonstrate the first largely enhancedperformance of n-CdS/p-Cu2S coaxial nanowire photovoltaic(PV) devices using the piezo-phototronics effect when the PV deviceis subjected to an external strain. Piezo-phototronics effect couldcontrol the electron–hole pair generation, transport, separation,and/or recombination, thus enhanced the performance of the PV devicesby as high as 70%. This effect offers a new concept for improvingsolar energy conversation efficiency by designing the orientationof the nanowires and the strain to be purposely introduced in thepackaging of the solar cells. This study shed light on the enhancedflexible solar cells for applications in self-powered technology,environmental monitoring, and even defensive technology. [ABSTRACT FROM AUTHOR]

A stretchable-rubber-based (SR-based) triboelectric nanogenerator (TENG) is developed that can not only harvest energy but also serve as self-powered multifunctional sensors. It consists of a layer of elastic rubber and a layer of aluminum film that acts as the electrode. By stretching and releasing the rubber, the changes of triboelectric charge distribution/density on the rubber surface relative to the aluminum surface induce alterations to the electrical potential of the aluminum electrode, leading to an alternating charge flow between the aluminum electrode and the ground. The unique working principle of the SR-based TENG is verified by the coupling of numerical calculations and experimental measurements. A comprehensive study is carried out to investigate the factors that may influence the output performance of the SR-based TENG. By integrating the devices into a sensor system, it is capable of detecting movements in different directions. Moreover, the SR-based TENG can be attached to a human body to detect diaphragm breathing and joint motion. This work largely expands the applications of TENG not only as effective power sources but also as active sensors; and opens up a new prospect in future electronics. [ABSTRACT FROM AUTHOR]

Motion tracking is of great importance in a wide range of fields such as automation, robotics, security, sports and entertainment. Here, a self-powered, single-electrode-based triboelectric sensor (TES) is reported to accurately detect the movement of a moving object/body in two dimensions. Based on the coupling of triboelectric effect and electrostatic induction, the movement of an object on the top surface of a polytetrafluoroethylene (PTFE) layer induces changes in the electrical potential of the patterned aluminum electrodes underneath. From the measurements of the output performance (open-circuit voltage and short-circuit current), the motion information about the object, such as trajectory, velocity, and acceleration is derived in conformity with the preset values. Moreover, the TES can detect motions of more than one objects moving at the same time. In addition, applications of the TES are demonstrated by using LED illuminations as real-time indicators to visualize the movement of a sliding object and the walking steps of a person. [ABSTRACT FROM AUTHOR]

Herein,we report a facile and robust route to nanoscale tunabletriboelectric energy harvesters realized by the formation of highlyfunctional and controllable nanostructures via block copolymer (BCP)self-assembly. Our strategy is based on the incorporation of varioussilica nanostructures derived from the self-assembly of BCPs to enhancethe characteristics of triboelectric nanogenerators (TENGs) by modulatingthe contact-surface area and the frictional force. Our simulationdata also confirm that the nanoarchitectured morphologies are effectivefor triboelectric generation. [ABSTRACT FROM AUTHOR]

The piezoelectric characteristics of nanowires, thin films and bulk crystals have been closely studied for potential applications in sensors, transducers, energy conversion and electronics. With their high crystallinity and ability to withstand enormous strain, two-dimensional materials are of great interest as high-performance piezoelectric materials. Monolayer MoS2 is predicted to be strongly piezoelectric, an effect that disappears in the bulk owing to the opposite orientations of adjacent atomic layers. Here we report the first experimental study of the piezoelectric properties of two-dimensional MoS2 and show that cyclic stretching and releasing of thin MoS2 flakes with an odd number of atomic layers produces oscillating piezoelectric voltage and current outputs, whereas no output is observed for flakes with an even number of layers. A single monolayer flake strained by 0.53% generates a peak output of 15 mV and 20 pA, corresponding to a power density of 2 mW m−2 and a 5.08% mechanical-to-electrical energy conversion efficiency. In agreement with theoretical predictions, the output increases with decreasing thickness and reverses sign when the strain direction is rotated by 90°. Transport measurements show a strong piezotronic effect in single-layer MoS2, but not in bilayer and bulk MoS2. The coupling between piezoelectricity and semiconducting properties in two-dimensional nanomaterials may enable the development of applications in powering nanodevices, adaptive bioprobes and tunable/stretchable electronics/optoelectronics. [ABSTRACT FROM AUTHOR]

The distributed network of receptors, neurons, and synapses in the somatosensory system efficiently processes complex tactile information. We used flexible organic electronics to mimic the functions of a sensory nerve. Our artificial afferent nerve collects pressure information (1 to 80 kilopascals) from clusters of pressure sensors, converts the pressure information into action potentials (0 to 100 hertz) by using ring oscillators, and integrates the action potentials from multiple ring oscillators with a synaptic transistor. Biomimetic hierarchical structures can detect movement of an object, combine simultaneous pressure inputs, and distinguish braille characters. Furthermore, we connected our artificial afferent nerve to motor nerves to construct a hybrid bioelectronic reflex arc to actuate muscles. Our system has potential applications in neurorobotics and neuroprosthetics. [ABSTRACT FROM AUTHOR]

The development of wearable and large-area fabric energy harvester and sensor has received great attention due to their promising applications in next-generation autonomous and wearable healthcare technologies. Here, a new type of 'single' thread-based triboelectric nanogenerator (TENG) and its uses in elastically textile-based energy harvesting and sensing have been demonstrated. The energy-harvesting thread composed by one silicone-rubber-coated stainless-steel thread can extract energy during contact with skin. With sewing the energy-harvesting thread into a serpentine shape on an elastic textile, a highly stretchable and scalable TENG textile is realized to scavenge various kinds of human-motion energy. The collected energy is capable to sustainably power a commercial smart watch. Moreover, the simplified single triboelectric thread can be applied in a wide range of thread-based self-powered and active sensing uses, including gesture sensing, human-interactive interfaces, and human physiological signal monitoring. After integration with microcontrollers, more complicated systems, such as wireless wearable keyboards and smart beds, are demonstrated. These results show that the newly designed single-thread-based TENG, with the advantage of interactive, responsive, sewable, and conformal features, can meet application needs of a vast variety of fields, ranging from wearable and stretchable energy harvesters to smart cloth-based articles. [ABSTRACT FROM AUTHOR]

Contact electrification is aboutthe charge transfer between thesurfaces of two materials in a contact-separation process. This effecthas been widely utilized in particle separation and energy harvesting,where the charge transfer is preferred to be maximized. However, thiseffect is always undesirable in some areas such as electronic circuitsystems due to the damage from the accumulated electrostatic charges.Herein, we introduced an approach to purposely manipulate the contactelectrification process both in polarity and magnitude of the chargetransfer through an applied electric field between two materials.Theoretical modeling and the corresponding experiments for controllingthe charge transfer between a Pt coated atomic force microscopy tipand Parylene film have been demonstrated. The modulation effect ofthe electric field on contact electrification is enhanced for a thinnerdielectric layer. This work can potentially be utilized to enhancethe output performance of energy harvesting devices or nullify contactelectric charge transfer in applications where this effect is undesirable. [ABSTRACT FROM AUTHOR]

A comprehensiveinvestigation was carried out on n-type ZnO nanowiresfor studying the temperature dependence of the piezotronic effectfrom 77 to 300 K. In general, lowering the temperature results ina largely enhanced piezotronic effect. The experimental results showthat the behaviors can be divided into three groups depending on thecarrier doping level or conductivity of the ZnO nanowires. For nanowireswith a low carrier density (<1017/cm3at77 K), the pieozotronic effect is dominant at low temperature fordictating the transport properties of the nanowires; an opposite changeof Schottky barrier heights at the two contacts as a function of temperatureat a fixed strain was observed for the first time. At a moderate doping(between 1017/cm3and 1018/cm3at 77 K), the piezotronic effect is only dominant at onecontact, because the screening effect of the carriers to the positivepiezoelectric polarization charges at the other end (for n-type semiconductors).For nanowires with a high density of carriers (>1018/cm3at 77 K), the piezotronic effect almost vanishes.This studynot only proves the proposed fundamental mechanism of piezotroniceffect, but also provides guidance for fabricating piezotronic devices. [ABSTRACT FROM AUTHOR]

Emulation of the sensation of touch through high-resolution electronic means could become important in future generations of robotics and human-machine interfaces. Here, we demonstrate that a nanowire light-emitting diode-based pressure sensor array can map two-dimensional distributions of strain with an unprecedented spatial resolution of 2.7 µm, corresponding to a pixel density of 6,350 dpi. Each pixel is composed of a single n-ZnO nanowire/p-GaN light-emitting diode, the emission intensity of which depends on the local strain owing to the piezo-phototronic effect. A pressure map can be created by reading out, in parallel, the electroluminescent signal from all of the pixels with a time resolution of 90 ms. The device may represent a major step towards the digital imaging of mechanical signals by optical means, with potential applications in artificial skin, touchpad technology, personalized signatures, bio-imaging and optical microelectromechanical systems. [ABSTRACT FROM AUTHOR]

We introduce an innovative designof a disk triboelectric nanogenerator(TENG) with segmental structures for harvesting rotational mechanicalenergy. Based on a cyclic in-plane charge separation between the segmentsthat have distinct triboelectric polarities, the disk TENG generateselectricity with unique characteristics, which have been studied byconjunction of experimental results with finite element calculations.The role played by the segmentation number is studied for maximizingoutput. A distinct relationship between the rotation speed and theelectrical output has been thoroughly investigated, which not onlyshows power enhancement at high speed but also illuminates its potentialapplication as a self-powered angular speed sensor. Owing to the nonintermittentand ultrafast rotation-induced charge transfer, the disk TENG hasbeen demonstrated as an efficient power source for instantaneouslyor even continuously driving electronic devices and/or charging anenergy storage unit. This work presents a novel working mode of TENGsand opens up many potential applications of nanogenerators for harvestingeven large-scale energy. [ABSTRACT FROM AUTHOR]

Aiming at harvesting ambient mechanicalenergy for self-poweredsystems, triboelectric nanogenerators (TENGs) have been recently developedas a highly efficient, cost-effective and robust approach to generateelectricity from mechanical movements and vibrations on the basisof the coupling between triboelectrification and electrostatic induction.However, all of the previously demonstrated TENGs are based on verticalseparation of triboelectric-charged planes, which requires sophisticateddevice structures to ensure enough resilience for the charge separation,otherwise there is no output current. In this paper, we demonstrateda newly designed TENG based on an in-plane charge separation processusing the relative sliding between two contacting surfaces. UsingPolyamide 6,6 (Nylon) and polytetrafluoroethylene (PTFE) films withsurface etched nanowires, the two polymers at the opposite ends ofthe triboelectric series, the newly invented TENG produces an open-circuitvoltage up to ∼1300 V and a short-circuit current density of4.1 mA/m2with a peak power density of 5.3 W/m2, which can be used as a direct power source for instantaneouslydriving hundreds of serially connected light-emitting diodes (LEDs).The working principle and the relationships between electrical outputsand the sliding motion are fully elaborated and systematically studied,providing a new mode of TENGs with diverse applications. Comparedto the existing vertical-touching based TENGs, this planar-slidingTENG has a high efficiency, easy fabrication, and suitability formany types of mechanical triggering. Furthermore, with the relationshipbetween the electrical output and the sliding motion being calibrated,the sliding-based TENG could potentially be used as a self-powereddisplacement/speed/acceleration sensor. [ABSTRACT FROM AUTHOR]