| Triboelectric effect, one of the most ubiquitous phenomena, exists almost everywhere in our daily life. However, triboelectrification is often regarded as a negative effect that in most case was avoided by many technologies. Recently, Zhong Lin Wang’s group in Georgia Institute of Technology has invented a new kind of generator, triboelectric nanogenerator(TENG), which is based on the coupling of electrification and electrostatic effect. It can convert ambient mechanical energy into electricity. TENG, as an innovative energy harvester, in the inner circuit, an electrical potential is created by the contact-electrification due to the charge transfer between two contacting materials that hold opposite tribo-polarity. When the two contacting film separate, the potential will drive the charges to flow to balance the potential difference, leading to the formation of current. This newly technology utilizes the most common materials available in our daily life, such as paper, fabrics, polydimethylsiloxane(PDMS), polytetrafluoroethylene(PTFE), aluminum(Al), polyvinylchloride(PVC), fluorinated ethylene propylene(FEP) etc. TENGs are capable of harvesting various types of mechanical energies, such as human motion, vibration, rotation, wind, acoustic energy, water flow, rain drop, ocean wave and so on. In addition, by converting mechanical motion into electric signal, TENGs can be used as self-powered sensors to detect displacement, velocity, metallic ion, humidity, temperature, UV intensity and so on. In this dissertation, TENGs and TENG based self-powered sensors with diverse structures, working mechanism have been designed and fabricated. Through experimental measurement and theoretical simulation, the working principle of TENGs and self-powered sensors, broadening the application were systematically studied. The details of our work are described as below:1. Methyl Orange(MO) can be degraded by a photocatalytic process using TiO2 under UV irradiation. The photo-generated holes and electrons can migrate to the surface of TiO2 particles and serve as redox sources that react with adsorbed reactants, leading to the formation of superoxide radical anion, hydrogen peroxide and hydroxyl radical for the oxidation of dye pollution. Here, a Polytetrafluoroethylene-Al based TENG was fabricated, the electric power output of which can be used for enhancing the photodegradation of MO with the presence of Ti O2 nanoparticles, because the TENG generated electric field can effectively boost the separation and restrain the recombination of photo-generated electrons and holes. Due to the photoelectrical coupling, the degradation percentages of MO for 120 minutes with and without TENG assistance are 76 % and 27 %, respectively. The fabricated TENGs have the potential applications in wastewater treatment, water splitting, and pollution degradation.2. A self-powered single-electrode-based triboelectric sensor(SE-TES) was proposed and fabricated for detecting object motion inside of tubing. This innovative, cost-effective, simple-designed SE-TES consists of thin-film based Cu electrodes, a PTFE tube. Based on the coupling effect between triboelectrification and electrostatic induction, the sensor generates electric output signals in response to mechanical motion of an object 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, real-time monitoring and mapping were demonstrated on the motion characteristics of the steel ball inside the tube by using a seven-unit array of electrode channels arranged along the tubing. Triggered by the output current signal, green light-emitting diodes(LEDs) 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 self-powered tracking system, blockage detection, flow control, logistics monitoring.3. A fully enclosed cylindrical single-electrode-based TENG(S-TENG) was proposed and prepared, 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: the contact-induced electrification between the PFA ball and the balloon, and the 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 are systematically investigated by conjunction of 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 LEDs. The S-TENGs is a potential power source for gas flow harvester, air navigation and environmental monitoring.4. Energy harvesting from ambient water motion is a desirable but underexplored solution in worldwide range. Here, an interfacial electrification enabled TENG(IE-TENG) was fabricated for harvesting electrostatic energy from water and a hybrid TENG was prepared for collecting electrostatic energy and mechanical energy from water. The IE-TENG consists of fluorinated ethylene propylene(FEP) thin film and an array of electrodes below. The asymmetric screening to the surface charges by the waving water during emerging and submerging process causes the free electrons on the electrodes to flow through an external load, resulting in power generation. The hybrid TENG is comprised of two parts: an interfacial electrification enabled TENG(IE-TENG) and an impact-TENG. The IE-TENG, composed of a FEP thin film and an array of electrodes underneath, is used to harvest electrostatic energy arising from the water-solid interface. The impact-TENG, constructed with nanostructured PTFE thin films and elastic wavy electrodes, is used to scavenge the mechanical impact energy from water wave. Under water waves propagating at a speed of 0.5 m/s, the short-circuit current of the IE-TENG and impact-TENG can reach 5.1 μA and 4.3 μA, respectively, which is able to drive nearly 50 LEDs simultaneously. Considering that natural water bodies may contain minerals and salt, the influence of NaCl concentration on the electric output of device has been investigated. Moreover, the hybrid TENG was developed as a self-powered distress signals emitter that may be used for life saving in water landing or swimming in evening. Considering the scalability of this technology, this work demonstrates the great potential of TENG in areas of hydropower harvesting, environmental monitoring and maritime search and rescue.5. The TENG has been proved as a simple, reliable, cost-effective, and efficient means to harvest ambient mechanical energy in a normal environment, although its performance evaluation under the room temperature is still lacking. Here, the reliance of TENGs output on the ambient temperature spanning from 77 K to 320 K was systematically studied, including the temperature dependence of semiconductor/polymer, modified semiconductor/polymer, metal/polymer type TENGs. The electric output of semiconductor/polymer and modified semiconductor/polymer type TENG deceases with decreasing temperature, while the electric output of metal/polymer type TENG follows a reverse trend. Applicability of triboelectric nanogenerator over a wide range of temperature was confirmed from 77 K to 320 K. As for metal/polymer based TENG, an output enhancement of 79.3 % was experimentally obtained at the temperature of 77 K compared to that at a temperature of 300 K, which is capable of powering 16 LEDs. This work can contribute not only to the design and packaging of triboelectric devices to operate at extreme environmental temperatures, but also to the fundamental understanding of the mechanism of triboelectric effect. |
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