Hybridizing Triboelectrification and Electromagnetic Induction Effects for High-Efficient Mechanical Energy Harvesting

The recently introduced triboelectric nanogenerator (TENG) and the traditional electromagnetic induction generator (EMIG) are coherently integrated in one structure for energy harvesting and vibration sensing/isolation. The suspended structure is based on two oppositely oriented magnets that are enclosed by hollow cubes surrounded with coils, which oscillates in response to external disturbance and harvests mechanical energy simultaneously from triboelectrification and electromagnetic induction. It extends the previous definition of hybrid cell to harvest the same type of energy with multiple approaches. Both the sliding-mode TENG and contact-mode TENG can be achieved in the same structure. In order to make the TENG and EMIG work together, transformers are used to match the output impedance between these two power sources with very different characteristics. The maximum output power of 7.7 and 1.9 mW on the same load of 5 kΩ was obtained for the TENG and EMIG, respectively, after impedance matching. Benefiting from the rational design, the output signal from the TENG and the EMIG are in phase. They can be added up directly to get an output voltage of 4.6 V and an output current of 2.2 mA in parallel connection. A power management circuit was connected to the hybrid cell, and a regulated voltage of 3.3 V with constant current was achieved. For the first time, a logic operation was carried out on a half-adder circuit by using the hybrid cell working as both the power source and the input digit signals. We also demonstrated that the hybrid cell can serve as a vibration isolator. Further applications as vibration dampers, triggers, and sensors are all promising

Quantitative Measurements of Vibration Amplitude Using a Contact-Mode Freestanding Triboelectric Nanogenerator

A vibration sensor is usually designed to measure the vibration frequency but disregard the vibration amplitude, which is rather challenging to be quantified due to the requirement of linear response. Here, we show the application of triboelectric nanogenerator (TENG) as a self-powered tool for quantitative measurement of vibration amplitude based on an operation mode, the contact-mode freestanding triboelectric nanogenerator (CF-TENG). In this mode, the triboelectrically charged resonator can be agitated to vibrate between two stacked stationary electrodes. Under the working principle with a constant capacitance between two electrodes, the amplitudes of the electric signals are proportional to the vibration amplitude of the resonator (provided that the resonator plate is charged to saturation), which has been illuminated both theoretically and experimentally. Together with its capability in monitoring the vibration frequency, the CF-TENG appears as the triboelectrification-based active sensor that can give full quantitative information about a vibration. In addition, the CF-TENG is also demonstrated as a power source for electronic devices

Noncontact Free-Rotating Disk Triboelectric Nanogenerator as a Sustainable Energy Harvester and Self-Powered Mechanical Sensor

In this work, we introduced an innovative noncontact, free-rotating disk triboelectric nanogenerator (FRD-TENG) for sustainably scavenging the mechanical energy from rotary motions. Its working principle was clarified through numerical calculations of the relative-rotation-induced potential difference, which serves as the driving force for the electricity generation. The unique characteristic of the FRD-TENG enables its high output performance compared to its working at the contact mode, with an effective output power density of 1.22 W/m² for continuously driving 100 light-emitting diodes. Ultrahigh stability of the output and exceptional durability of the device structure were achieved, and the reliable output was utilized for fast/effective charging of a lithium ion battery. Based on the relationship between its output performance and the parameters of the mechanical stimuli, the FRD-TENG could be employed as a self-powered mechanical sensor, for simultaneously detecting the vertical displacement and rotation speed. The FRD-TENG has superior advantages over the existing disk triboelectric nanogenerator, and exhibits significant progress toward practical applications of nanogenerators for both energy harvesting and self-powered sensor networks

Sliding-Triboelectric Nanogenerators Based on In-Plane Charge-Separation Mechanism

Aiming at harvesting ambient mechanical energy for self-powered systems, triboelectric nanogenerators (TENGs) have been recently developed as a highly efficient, cost-effective and robust approach to generate electricity from mechanical movements and vibrations on the basis of the coupling between triboelectrification and electrostatic induction. However, all of the previously demonstrated TENGs are based on vertical separation of triboelectric-charged planes, which requires sophisticated device structures to ensure enough resilience for the charge separation, otherwise there is no output current. In this paper, we demonstrated a newly designed TENG based on an in-plane charge separation process using the relative sliding between two contacting surfaces. Using Polyamide 6,6 (Nylon) and polytetrafluoroethylene (PTFE) films with surface etched nanowires, the two polymers at the opposite ends of the triboelectric series, the newly invented TENG produces an open-circuit voltage up to ∼1300 V and a short-circuit current density of 4.1 mA/m² with a peak power density of 5.3 W/m², which can be used as a direct power source for instantaneously driving hundreds of serially connected light-emitting diodes (LEDs). The working principle and the relationships between electrical outputs and the sliding motion are fully elaborated and systematically studied, providing a new mode of TENGs with diverse applications. Compared to the existing vertical-touching based TENGs, this planar-sliding TENG has a high efficiency, easy fabrication, and suitability for many types of mechanical triggering. Furthermore, with the relationship between the electrical output and the sliding motion being calibrated, the sliding-based TENG could potentially be used as a self-powered displacement/speed/acceleration sensor

Robust Triboelectric Nanogenerator Based on Rolling Electrification and Electrostatic Induction at an Instantaneous Energy Conversion Efficiency of ∼55%

In comparison to in-pane sliding friction, rolling friction not only is likely to consume less mechanical energy but also presents high robustness with minimized wearing of materials. In this work, we introduce a highly efficient approach for harvesting mechanical energy based on rolling electrification and electrostatic induction, aiming at improving the energy conversion efficiency and device durability. The rolling triboelectric nanogenerator is composed of multiple steel rods sandwiched by two fluorinated ethylene propylene (FEP) thin films. The rolling motion of the steel rods between the FEP thin films introduces triboelectric charges on both surfaces and leads to the change of potential difference between each pair of electrodes on back of the FEP layer, which drives the electrons to flow in the external load. As power generators, each pair of output terminals works independently and delivers an open-circuit voltage of 425 V, and a short-circuit current density of 5 mA/m². The two output terminals can also be integrated to achieve an overall power density of up to 1.6 W/m². The impacts of variable structural factors were investigated for optimization of the output performance, and other prototypes based on rolling balls were developed to accommodate different types of mechanical energy sources. Owing to the low frictional coefficient of the rolling motion, an instantaneous energy conversion efficiency of up to 55% was demonstrated and the high durability of the device was confirmed. This work presents a substantial advancement of the triboelectric nanogenerators toward large-scope energy harvesting and self-powered systems

Triboelectric Nanogenerator Built on Suspended 3D Spiral Structure as Vibration and Positioning Sensor and Wave Energy Harvester

An unstable mechanical structure that can self-balance when perturbed is a superior choice for vibration energy harvesting and vibration detection. In this work, a suspended 3D spiral structure is integrated with a triboelectric nanogenerator (TENG) for energy harvesting and sensor applications. The newly designed vertical contact–separation mode TENG has a wide working bandwidth of 30 Hz in low-frequency range with a maximum output power density of 2.76 W/m² on a load of 6 MΩ. The position of an in-plane vibration source was identified by placing TENGs at multiple positions as multichannel, self-powered active sensors, and the location of the vibration source was determined with an error less than 6%. The magnitude of the vibration is also measured by the output voltage and current signal of the TENG. By integrating the TENG inside a buoy ball, wave energy harvesting at water surface has been demonstrated and used for lighting illumination light, which shows great potential applications in marine science and environmental/infrastructure monitoring

Temperature Dependence of the Piezotronic Effect in ZnO Nanowires

A comprehensive investigation was carried out on n-type ZnO nanowires for studying the temperature dependence of the piezotronic effect from 77 to 300 K. In general, lowering the temperature results in a largely enhanced piezotronic effect. The experimental results show that the behaviors can be divided into three groups depending on the carrier doping level or conductivity of the ZnO nanowires. For nanowires with a low carrier density (<10¹⁷/cm³ at 77 K), the pieozotronic effect is dominant at low temperature for dictating the transport properties of the nanowires; an opposite change of Schottky barrier heights at the two contacts as a function of temperature at a fixed strain was observed for the first time. At a moderate doping (between 10¹⁷/cm³ and 10¹⁸/cm³ at 77 K), the piezotronic effect is only dominant at one contact, because the screening effect of the carriers to the positive piezoelectric polarization charges at the other end (for n-type semiconductors). For nanowires with a high density of carriers (>10¹⁸/cm³ at 77 K), the piezotronic effect almost vanishes. This study not only proves the proposed fundamental mechanism of piezotronic effect, but also provides guidance for fabricating piezotronic devices

Triboelectric Active Sensor Array for Self-Powered Static and Dynamic Pressure Detection and Tactile Imaging

We report an innovative, large-area, and self-powered pressure mapping approach based on the triboelectric effect, which converts the mechanical stimuli into electrical output signals. The working mechanism of the triboelectric active sensor (TEAS) was theoretically studied by both analytical method and numerical calculation to gain an intuitive understanding of the relationship between the applied pressure and the responsive signals. Relying on the unique pressure response characteristics of the open-circuit voltage and short-circuit current, we realize both static and dynamic pressure sensing on a single device for the first time. A series of comprehensive investigations were carried out to characterize the performance of the TEAS, and high sensitivity (0.31 kPa^–1), ultrafast response time (<5 ms), long-term stability (30 000 cycles), as well as low detection limit (2.1 Pa) were achieved. The pressure measurement range of the TEAS was adjustable, which means both gentle pressure detection and large-scale pressure sensing were enabled. Through integrating multiple TEAS units into a sensor array, the as-fabricated TEAS matrix was capable of monitoring and mapping the local pressure distribution applied on the device with distinguishable spatial profiles. This work presents a technique for tactile imaging and progress toward practical applications of nanogenerators, providing potential solutions for accomplishment of artificial skin, human-electronic interfacing, and self-powered systems

Sliding-Triboelectric Nanogenerators Based on In-Plane Charge-Separation Mechanism

Aiming at harvesting ambient mechanical energy for self-powered systems, triboelectric nanogenerators (TENGs) have been recently developed as a highly efficient, cost-effective and robust approach to generate electricity from mechanical movements and vibrations on the basis of the coupling between triboelectrification and electrostatic induction. However, all of the previously demonstrated TENGs are based on vertical separation of triboelectric-charged planes, which requires sophisticated device structures to ensure enough resilience for the charge separation, otherwise there is no output current. In this paper, we demonstrated a newly designed TENG based on an in-plane charge separation process using the relative sliding between two contacting surfaces. Using Polyamide 6,6 (Nylon) and polytetrafluoroethylene (PTFE) films with surface etched nanowires, the two polymers at the opposite ends of the triboelectric series, the newly invented TENG produces an open-circuit voltage up to ∼1300 V and a short-circuit current density of 4.1 mA/m² with a peak power density of 5.3 W/m², which can be used as a direct power source for instantaneously driving hundreds of serially connected light-emitting diodes (LEDs). The working principle and the relationships between electrical outputs and the sliding motion are fully elaborated and systematically studied, providing a new mode of TENGs with diverse applications. Compared to the existing vertical-touching based TENGs, this planar-sliding TENG has a high efficiency, easy fabrication, and suitability for many types of mechanical triggering. Furthermore, with the relationship between the electrical output and the sliding motion being calibrated, the sliding-based TENG could potentially be used as a self-powered displacement/speed/acceleration sensor

Piezo-phototronic Effect Enhanced Visible/UV Photodetector of a Carbon-Fiber/ZnO-CdS Double-Shell Microwire

A branched ZnO-CdS double-shell NW array on the surface of a carbon fiber (CF/ZnO-CdS) was successfully synthesized <i>via</i> a facile two-step hydrothermal method. Based on a single CF/ZnO-CdS wire on a polymer substrate, a flexible photodetector was fabricated, which exhibited ultrahigh photon responsivity under illuminations of blue light (1.11 × 10⁵ A/W, 8.99 × 10^–8 W/cm², 480 nm), green light (3.83 × 10⁴ A/W, 4.48 × 10^–8 W/cm², 548 nm), and UV light (1.94 × 10⁵ A/W, 1.59 × 10^–8 W/cm², 372 nm), respectively. The responsivity of this broadband photon sensor was enhanced further by as much as 60% when the device was subjected to a −0.38% compressive strain. This is because the strain induced a piezopotential in ZnO, which tunes the barrier height at the ZnO–CdS heterojunction interface, leading to an optimized optoelectronic performance. This work demonstrates a promising application of piezo-phototronic effect in nanoheterojunction array based photon detectors