Triboelectrification-Based Organic Film Nanogenerator for Acoustic Energy Harvesting and Self-Powered Active Acoustic Sensing

As a vastly available energy source in our daily life, acoustic vibrations are usually taken as noise pollution with little use as a power source. In this work, we have developed a triboelectrification-based thin-film nanogenerator for harvesting acoustic energy from ambient environment. Structured using a polytetrafluoroethylene thin film and a holey aluminum film electrode under carefully designed straining conditions, the nanogenerator is capable of converting acoustic energy into electric energy <i>via</i> triboelectric transduction. With an acoustic sensitivity of 9.54 V Pa^–1 in a pressure range from 70 to 110 dB and a directivity angle of 52°, the nanogenerator produced a maximum electric power density of 60.2 mW m^–2, which directly lit 17 commercial light-emitting diodes (LEDs). Furthermore, the nanogenerator can also act as a self-powered active sensor for automatically detecting the location of an acoustic source with an error less than 7 cm. In addition, an array of devices with varying resonance frequencies was employed to widen the overall bandwidth from 10 to 1700 Hz, so that the nanogenerator was used as a superior self-powered microphone for sound recording. Our approach presents an adaptable, mobile, and cost-effective technology for harvesting acoustic energy from ambient environment, with applications in infrastructure monitoring, sensor networks, military surveillance, and environmental noise reduction

Triboelectrification-Based Organic Film Nanogenerator for Acoustic Energy Harvesting and Self-Powered Active Acoustic Sensing

As a vastly available energy source in our daily life, acoustic vibrations are usually taken as noise pollution with little use as a power source. In this work, we have developed a triboelectrification-based thin-film nanogenerator for harvesting acoustic energy from ambient environment. Structured using a polytetrafluoroethylene thin film and a holey aluminum film electrode under carefully designed straining conditions, the nanogenerator is capable of converting acoustic energy into electric energy <i>via</i> triboelectric transduction. With an acoustic sensitivity of 9.54 V Pa^–1 in a pressure range from 70 to 110 dB and a directivity angle of 52°, the nanogenerator produced a maximum electric power density of 60.2 mW m^–2, which directly lit 17 commercial light-emitting diodes (LEDs). Furthermore, the nanogenerator can also act as a self-powered active sensor for automatically detecting the location of an acoustic source with an error less than 7 cm. In addition, an array of devices with varying resonance frequencies was employed to widen the overall bandwidth from 10 to 1700 Hz, so that the nanogenerator was used as a superior self-powered microphone for sound recording. Our approach presents an adaptable, mobile, and cost-effective technology for harvesting acoustic energy from ambient environment, with applications in infrastructure monitoring, sensor networks, military surveillance, and environmental noise reduction

Harvesting Water Wave Energy by Asymmetric Screening of Electrostatic Charges on a Nanostructured Hydrophobic Thin-Film Surface

Energy harvesting from ambient water motions is a desirable but underexplored solution to on-site energy demand for self-powered electronics. Here we report a liquid–solid electrification-enabled generator based on a fluorinated ethylene propylene thin film, below which an array of electrodes are fabricated. The surface of the thin film is charged first due to the water–solid contact electrification. Aligned nanowires created on the thin film make it hydrophobic and also increase the surface area. Then the asymmetric screening to the surface charges by the waving water during emerging and submerging processes causes the free electrons on the electrodes to flow through an external load, resulting in power generation. The generator produces sufficient output power for driving an array of small electronics during direct interaction with water bodies, including surface waves and falling drops. Polymer-nanowire-based surface modification increases the contact area at the liquid–solid interface, leading to enhanced surface charging density and thus electric output at an efficiency of 7.7%. Our planar-structured generator features an all-in-one design without separate and movable components for capturing and transmitting mechanical energy. It has extremely lightweight and small volume, making it a portable, flexible, and convenient power solution that can be applied on the ocean/river surface, at coastal/offshore areas, and even in rainy places. Considering the demonstrated scalability, it can also be possibly used in large-scale energy generation if layers of planar sheets are connected into a network

Harvesting Water Wave Energy by Asymmetric Screening of Electrostatic Charges on a Nanostructured Hydrophobic Thin-Film Surface

Energy harvesting from ambient water motions is a desirable but underexplored solution to on-site energy demand for self-powered electronics. Here we report a liquid–solid electrification-enabled generator based on a fluorinated ethylene propylene thin film, below which an array of electrodes are fabricated. The surface of the thin film is charged first due to the water–solid contact electrification. Aligned nanowires created on the thin film make it hydrophobic and also increase the surface area. Then the asymmetric screening to the surface charges by the waving water during emerging and submerging processes causes the free electrons on the electrodes to flow through an external load, resulting in power generation. The generator produces sufficient output power for driving an array of small electronics during direct interaction with water bodies, including surface waves and falling drops. Polymer-nanowire-based surface modification increases the contact area at the liquid–solid interface, leading to enhanced surface charging density and thus electric output at an efficiency of 7.7%. Our planar-structured generator features an all-in-one design without separate and movable components for capturing and transmitting mechanical energy. It has extremely lightweight and small volume, making it a portable, flexible, and convenient power solution that can be applied on the ocean/river surface, at coastal/offshore areas, and even in rainy places. Considering the demonstrated scalability, it can also be possibly used in large-scale energy generation if layers of planar sheets are connected into a network

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

Single-Electrode-Based Rotating Triboelectric Nanogenerator for Harvesting Energy from Tires

Rotational energy is abundant and widely available in our living environment. Harvesting ambient rotational energy has attracted great attention. In this work, we report a single-electrode-based rotating triboelectric nanogenerator (SR-TENG) for converting rotational energy into electric energy. The unique advantage of introducing the single-electrode TENG is to overcome the difficulty in making the connection in harvesting rotational energy such as from a moving and rotating tire/wheel. The fabricated device consists of a rotary acrylic disc with polytetrafluoroethylene (PTFE) blades and an Al electrode fixed on the base. The systematical experiments and theoretical simulations indicate that the asymmetric SR-TENGs exhibit much better output performances than those of the symmetric TENGs at the same rotation rates. The asymmetric SR-TENG with seven PTFE units at the rotation rate of 800 r/min can deliver a maximal output voltage of 55 V and a corresponding output power of 30 μW on a load of 100 MΩ, which can directly light up tens of red light-emitting diodes. The SR-TENG has been utilized to harvest mechanical energy from rotational motion of a bicycle wheel. Furthermore, we demonstrated that the SR-TENG can be applied to scavenge wind energy and as a self-powered wind speed sensor with a sensitivity of about 0.83 V/(m/s). This study further expands the operation principle of a single-electrode-based TENG and many potential applications of TENGs for scavenging ambient rotational energy and as a self-powered environment monitoring sensor

Fully Enclosed Cylindrical Single-Electrode-Based Triboelectric Nanogenerator

We report a fully enclosed cylindrical single-electrode-based triboelectric nanogenerator (S-TENG) consisting of a perfluoroalkoxy (PFA) ball with surface-etched nanowires, a floating latex balloon, and an Al electrode at the end of the balloon. The mechanism of the S-TENG includes two independent processes: contact-induced electrification between the PFA ball and the balloon and electrostatic induction between the charged PFA ball and the Al electrode. The relationships between the electrical outputs and the sliding distance of the PFA ball were systematically investigated by combining experimental results with finite-element calculations. The S-TENG delivers an output voltage up to 236 V and a short-circuit current of 4.8 μA, which can be used as a direct power source for driving tens of green light-emitting diodes (LEDs). The S-TENG is a potential power source for gas-flow harvesters, air navigation, and environmental monitoring

Triboelectric Sensor for Self-Powered Tracking of Object Motion inside Tubing

We report a self-powered, single-electrode-based triboelectric sensor (SE-TES) array for detecting object motion inside of a plastic tube. This innovative, cost-effective, simple-designed SE-TES consists of thin-film-based ring-shaped Cu electrodes and a polytetrafluoroethylene (PTFE) tube. On the basis of the coupling effect between triboelectrification and electrostatic induction, the sensor generates electric output signals in response to mechanical motion of an object (such as a ball) passing through the electrodes. An array of Cu electrodes linearly aligned along the tube enables the detection of location and speed of the moving steel ball inside. The signal-to-noise ratio of this fabricated device reached 5.3 × 10³. Furthermore, we demonstrated real-time monitoring and mapping of the motion characteristics of the steel ball inside the tube by using a seven-unit array of electrode channels arranged along the tube. Triggered by the output current signal, LED bulbs were utilized as real-time indicators of the position of a rolling ball. In addition, the SE-TES also shows the capability of detecting blockage in a water pipe. This work demonstrates potentially widespread applications of the triboelectric sensor in a self-powered tracking system, blockage detection, flow control, and logistics monitoring

Personalized Keystroke Dynamics for Self-Powered Human–Machine Interfacing

The computer keyboard is one of the most common, reliable, accessible, and effective tools used for human–machine interfacing and information exchange. Although keyboards have been used for hundreds of years for advancing human civilization, studying human behavior by keystroke dynamics using smart keyboards remains a great challenge. Here we report a self-powered, non-mechanical-punching keyboard enabled by contact electrification between human fingers and keys, which converts mechanical stimuli applied to the keyboard into local electronic signals without applying an external power. The intelligent keyboard (IKB) can not only sensitively trigger a wireless alarm system once gentle finger tapping occurs but also trace and record typed content by detecting both the dynamic time intervals between and during the inputting of letters and the force used for each typing action. Such features hold promise for its use as a smart security system that can realize detection, alert, recording, and identification. Moreover, the IKB is able to identify personal characteristics from different individuals, assisted by the behavioral biometric of keystroke dynamics. Furthermore, the IKB can effectively harness typing motions for electricity to charge commercial electronics at arbitrary typing speeds greater than 100 characters per min. Given the above features, the IKB can be potentially applied not only to self-powered electronics but also to artificial intelligence, cyber security, and computer or network access control

Automatic Mode Transition Enabled Robust Triboelectric Nanogenerators

Although the triboelectric nanogenerator (TENG) has been proven to be a renewable and effective route for ambient energy harvesting, its robustness remains a great challenge due to the requirement of surface friction for a decent output, especially for the in-plane sliding mode TENG. Here, we present a rationally designed TENG for achieving a high output performance without compromising the device robustness by, first, converting the in-plane sliding electrification into a contact separation working mode and, second, creating an automatic transition between a contact working state and a noncontact working state. The magnet-assisted automatic transition triboelectric nanogenerator (AT-TENG) was demonstrated to effectively harness various ambient rotational motions to generate electricity with greatly improved device robustness. At a wind speed of 6.5 m/s or a water flow rate of 5.5 L/min, the harvested energy was capable of lighting up 24 spot lights (0.6 W each) simultaneously and charging a capacitor to greater than 120 V in 60 s. Furthermore, due to the rational structural design and unique output characteristics, the AT-TENG was not only capable of harvesting energy from natural bicycling and car motion but also acting as a self-powered speedometer with ultrahigh accuracy. Given such features as structural simplicity, easy fabrication, low cost, wide applicability even in a harsh environment, and high output performance with superior device robustness, the AT-TENG renders an effective and practical approach for ambient mechanical energy harvesting as well as self-powered active sensing