Design And Study Of Triboelectric Nanogenerator For Low-Frequency Energy Harvesting

With the rapid development of society,the demand for clean energy is steadily increasing.Triboelectric nanogenerator(TENG)is a new technology to generate electric energy without pollution developed in recent years,which shows an absolute advantage in collecting low frequency mechanical energy.It can harvest various mechanical energy in nature or human society and convert it into electrical energy.The ocean occupies 71%of the earth’s area,with abundant mechanical energy.Due to the low efficiency in harvesting low-frequency,and irregular motion,bulky electromagnetic generators are not suitable to harvest this kind energy.Triboelectric nanogenerator is a new kind device with many merits such as its small weight and low cost,which is appropriate to harvest low frequency and irregularly energy.At present,triboelectric nanogenerators with different materials and structures have been proposed to harvest the ocean energy.However,the output performances of these devices are still relatively low.Therefore,developing a new approach to improve the output performance and ocean energy collection efficiency of triboelectric nanogenerators has always been a critical issue.To this end,this thesis first proposes a new structural system that can convert the low-frequency random mechanical motion in the ocean into relatively high-frequency,unidirectional mechanical motion.Also,it is applicable to many triboelectric nanogenerators with different structures,greatly improving the energy harvesting efficiency.Secondly,the thesis proposes a strategy of using flexible contacts to improve the output performance.In addition,the triboelectric nanogenerator can also be used as an active sensor.The combination of power supply and sensor provides a new idea for the collection of clean energy and the realization of interconnected sensing systems in this new era.Besides the ocean energy,the human body also contains a large amount of undeveloped lowfrequency mechanical energy.Triboelectric nanogenerators can also be used to harvest the low frequency mechanical energy from human body movement to power various wearable electronic devices.At present,research on wearable triboelectric nanogenerators mainly focuses on the study of stretchable electrodes and stretchable triboelectric materials,ignoring the systematic research of energy harvesting.In this thesis,we fabricate a fully stretchable energy harvesting and management system of stretchable transistor-based rectifier and stretchable supercapacitor in contact separation mode,which provides a new choice for power supply of wearable/implantable functional electronic devices.The main contents of this thesis are as follows:(1)We designed a system that can utilize the atmospheric pressure difference for energy conversion.The design of this device is mainly used to collect the energy of intermittent,lowfrequency water waves,and then convert this kind of the energy into stored energy,and then release it in the form of high-speed airflow to trigger continuous high-frequency.It greatly improves the working efficiency of the traditional triboelectric nanogenerator.In addition,through the ingenious design of the soft membrane,this method can achieve a good waterproof effect through the external frame.Also,this system can well match the waves of different frequencies with different TENG designs.In order to prove the feasibility of this system,we prepared two different kinds triboelectric nanogenerators as examples:a flutter-driven TENG driven by a low-speed airflow and a disc-shaped TENG triggered by a high-speed airflow.In addition,we also demonstrated the concept of realizing ocean energy harvesting,further expanding the practical application of triboelectric nanogenerators in large-scale energy harvesting in the ocean.(2)Through the optimization of the material and the design of structure,we have achieved a great improvement in the output performance of the soft spherical triboelectric nanogenerator(SSTENG).With acrylic hollow sphere as the shell and rolling flexible liquid/silicone rubber as the soft core,the soft-contact SS-TENG is compared with ordinary polytetrafluoroethylene(PTFE)hard-contact spherical triboelectric nanogenerator(S-TENG),and the maximum transferred charges are increased to 10 times,this is due to the significant increase in contact area.In addition,the output of the SS-TENG can be tuned by controlling the softness of the liquid/silicone core.After testing and comparing the SS-TENG and S-TENG in a simulated water environment,the SS-TENG shows significant advantages.It provides a brand-new optimization method,and shows a broader prospect in water waves,weak but ubiquitous wind energy,and other forms of largescale energy harvesting.(3)Based on the flexible contact triboelectric nanogenerator,a fully enclosed self-powered active spherical flow speed sensor is designed to detect the fluid speed.Based on the phenomenon of contact electrification and electrostatic induction,the charges transfer back and forth between the two electrodes.The sensor can effectively convert the mechanical energy of the fluid flow into electric energy.After processing the output electrical signals by Fourier transform,the frequency and rotating speed of the sensor can be obtained.Then,the flow speed of the fluid can be calculated based on the relationship between the flow speed and the rotational speed.In addition,after optimizing the structural parameters of the sensor,we can obtain a high-precision,small average standard deviation,a wide range(2 m/s to 18 m/s),tunable range,and a waterproof sensor.The fully enclosed self-powered active spherical triboelectric flow speed sensor can be used for more than half a year with high stability.In addition,this technology can be used for the measurement of various fluid flow rate,such as wind speed monitoring.(4)By using fully stretchable materials,a fully intrinsic stretchable triboelectric generator energy collection and management system is proposed to harvest the human body energy to supply various wearable electronics.A high-density contact-separation mode TENG is adopted to largely improve the output performance.As a triboelectric material,Styrene-Ethylene/Butylene-Styrene block copolymer(SEBS)provides the device structure with excellent separation characteristics and output performances.The peak power density under 100%strain reaches about 1.1 mW/m2.We successfully realized the collection of mechanical energy in human joints and pig heart.Integrated with a stretchable triboelectric nanogenerator,rectifier and supercapacitor,the 100%strain stretchability has been incorporated into every component of this system.The intrinsic stretchable power generation and management system guarantee the electric energy for the practical application of stretchable/wearable electronic devices in the future.