Design,Principle And Applications Of High Voltage DC Triboelectric Nanogenerator Based On Solid-liquid Contact Electrification

Since the beginning of the 21 st century,emerging technologies such as the Internet of things,big data and artificial intelligence have begun to lead the development of the era.In the future,the world will transform from the old information age to the intelligent age of connecting everything.As a consequence,the number of distributed electronic devices will increase dramatically,and it will develop towards the trend of more and more miniaturization,mobility and multi-function.Traditional energy storage components are far from being able to meet the new supply requirements of distributed energy sources such as mass,wireless,eco-friendly,and sustainability.The development of the smart era will encounter a new "energy crisis"-the problem of distributed energy supply.Moreover,with the proposal of carbon neutrality strategy from China,the urgency and importance of clean energy access have been further increased.Covering71 % of the earth’s surface,water is the largest energy carrier on the earth,and utilizing only a small fraction of it is sufficient to meet the needs of global energy supply.Modern hydropower technology mainly utilizes intensive low-entropy hydropower.However,most of the water energy in nature is distributed energy in the form of high-entropy widely scattered in the environment,such as raindrop energy,stream energy,wave energy,evaporation energy and other small-scale water energy forms.They are easy to obtain but difficult to collect.Therefore,it is urgent to develop technologies of distributed water energy harvesting.Researchers have begun to explore high-entropy water energy harvesting technologies based on electrodynamic effects,triboelectric effects,and hydrovoltaic effects.One of the most promising technologies is the triboelectric nanogenerator(AC-TENG)based on the coupling principle of triboelectricity and electrostatic induction.AC-TENGs have been developed rapidly and proved to be an efficient,economical,low-carbon and sustainable microscale energy harvesting technology.Although they have many advantages such as excellent performance,simple process and diversified structure,the AC output and high impedance are not suitable for driving electronic devices directly.It is still necessary to use the power management circuit(PMC)for rectification,energy storage and conversion before it can be utilized efficiently.In addition,when used in blue energy harvesting applications,the unit of AC-TENG must undergo AC phase synchronization or rectification before it can be integrated into the large-scale power grid,which will greatly increase the cost,complexity and instability of the system.Subsequently,attention has been paid to new strategies and techniques for direct conversion of mechanical energy into direct current,and direct current triboelectric nanogenerators(DC-TENGs)have been developed.In contrast,DC-TENG not only has the potential to realize the direct drive of electronic devices to realize the miniaturization of energy systems,but also can be arrayed without rectification or phase synchronization,which greatly simplifies the complexity of the system.Therefore,the power grid based on DC-TENG is theoreticallly simple,efficient,stable and inexpensive,which is an ideal choice for realizing distributed water energy harvesting.Generally speaking,there are two types of DC-TENGs.The first type is the conversion of pulse AC to DC output by means of ingenious mechanical rectification structure design(such as commutator,etc.).The second type is to directly realize the DC output by means of physical principles or effects(such as tribovoltaic effect,etc.).Among them,a new generation of DC-TENG based on the air breakdown effect achieves high-performance DC output by coupling triboelectrification and electrostatic breakdown effects,which greatly promotes the development of DC-TENGs.However,the only drawback is that most high-performance DC-TENGs are based on the solid-solid contact structure,which is not good enough for water energy harvesting,and also suffers from a lifespan problem caused by material wear.Compared with solid-solid TENG,solid-liquid TENG(S-L TENG)can utilize water itself as a triboelectric material to directly convert the hydrokinetic energy into electricity through contact electrification between water and polymers.Therefore,it not only has high efficiency of water energy harvesting,but also has low cost and long service life.In addition,the research based on S-L TENG is also of great value in the field of solid-liquid electrification mechanism and sensing.Therefore,if a new TENG with the dual advantages of DC output and solid-liquid friction can be developed,it will kill two birds with one stone,potentially solving most difficulties in distributed water energy harvesting.Based on the above research background,we carried out the research topic of this paper.First,the research status of TENG-based distributed water energy harvesting technology is discussed in the introduction section,the research basis of DC-TENG and SL TENG is systematically analyzed,and it is clarified that the development of solid-liquid DC-TENGs may be a good solution to solve this technical problems.Subsequently,we carried out systematic research from multiple perspectives such as contact electrification theory,device architecture design,performance enhancement mechanism and optimized power management,trying to think out of the box in existing TENG design philosophy and develop a simple,efficient and stable self-powered system with energy generation-convertion-storage integeration based on DC solid-liquid TENG technology and finally realize the practical application of distributed high-entropy water energy harvesting.The main research contents of this paper are summarized as follows:1.A novel solid-liquid DC triboelectric nanogenerator(STCS-TENG)based on the principle of spatiotemporal charge separation is constructed.Inspired by the formation process of natural thunderbolt,we utilize the multiple couplings of contact electrification,electrostatic induction,spatiotemporal charge separation,and charge pumping to realize the high-voltage DC design of STCS-TENG with the help of the water charge shuttle structure.The study of the transient physical process of STCS-TENG shows that during the working of the device,water droplets not only act as a source of charge generation,but also act as a charge shuttle to deliver negative charges in water to the top electrode and positive charges to the bottom electrode in turn,thereby outputting direct current.Through a delicate yet very simple design of water charge shuttle structure,the device completes the integration of power generation,rectification and energy storage functions without the need of external PMC,and realizes the pulsed DC output of high instantaneous power.Furthermore,STCS-TENG has a high open-circuit voltage of over 1600 V,so a single droplet is enough to light up400 commercial LEDs.This work is the first time to propose the design idea of introducing the conduction current into the internal structure of the nanogenerator,explain the synergistic enhancement mechanism of displacement current and conduction current inside the nanogenerator,and propose the design concept of the total-current nanogenerator.2.Using the STCS-TENG device as a probe,the charge transfer mechanism at the solid-liquid interface is studied.First,the STCS-TENG has a dual working mode of DC and AC.In the AC mode,the device is a classic single-electrode S-L TENG,which generates a consecutive AC pulse peak from a droplet;in the DC mode,the device is working on the principle of spatiotemporal charge separation,two separate codirectional pulse peaks are generated from a droplet.Subsequently,we analyze the dual-mode output characteristics and working mechanism of STCS-TENG,and propose a contact resistance model for the water/electrode interface.We further analyze the contributions of conduction current and displacement current in STCS-TENG,and propose that the electron conduction process may be the dominant process of interfacial charge transfer in STCS-TENG.Secondly,we further verify that the main components of the charge carriers in water are electrons and holes by using the simulation experiments of the water droplet power generation process and the analysis of the influence of the electrolyte composition on the charge transfer process.This work proposes a resistance model at the water/electrode interface by using the STCS-TENG as a probe.The revealed electron conduction can be the main process of interfacial charge transfer,which is of great significance for in-depth understanding of the synergistic effect of displacement current and conduction current,providing a new perspective for the design of TENGs.3.The array,power management circuit and applications of STCS-TENG are systematically studied.From the four aspects of constructing water charge shuttle,solid-liquid interface,electrode array and simplified PMC,the four obstacles of low device output efficiency,short service life,difficult array construction and complex management circuit faced by TENGs towards practical applications are solved respectively.First,based on the above research basis,high output efficiency is achieved by constructing a water charge shuttle structure in STCS-TENG,and a long service life is achieved based on the natural advantage of solid-liquid electrification.Second,we utilize the DC output characteristics of STCS-TENG to realize the device array design by ingeniously constructing the surface electrode array.We analyze the working mechanism of the arrayed STCS-TENG,establish an equivalent circuit model,and verify that the arrayed STCS-TENG has very good high-voltage DC output performance,and the performance of each unit is superimposed.Third,in order to further tap the output potential of STCS-TENG,a simplified PMC matching the device is developed.The PMC composed of only two components can increase the output current by 100 times and effectively improve the output voltage at the same time.Finally,we built a self-powered lighting system composed of arrayed STCS-TENG,PMC units and LED light panels.The LED array lit by the self-powered system is very bright.This work not only addresses the main obstacles to the practical application of STCS-TENG,but also demonstrates a self-powered system design paradigm with promising practical application.4.In addition to the above work,a novel self-powered p H sensor application based on solid-liquid triboelectric nanogenerator technology is developed in this paper,and the application prospect of solid-liquid contact electrification in the sensing field is explored.First,a solid-liquid triboelectric nanogenerator test platform is built and a transistor-like-inspired droplet-based generator with two-electrode structure is constructed.Then,the influencing factors of the solid interface,liquid composition and electrode structure on the output performance of the droplet-based generator are discussed respectively,and the charge transfer mechanism during the electrification process of the solid-liquid contact is deeply analyzed.Secondly,based on the above research results,we develope a self-powered p H sensor,which shows that HCl solution may have different charge transfer mechanisms between different PTFE films,and confirm that the p H sensor has good sensitivity and dynamic responsiveness.Finally,the demonstration of p H test of sample solution further confirms the potential application value of S-L TENG technology in the field of p H sensing.This work provides a research idea for the design of real-time sensing of liquid composition based on S-L TENG technology,and contributes to a deep understanding of the charge transfer mechanism during solid-liquid contact electrification.Based on the above research,this work uses the inspiration of thunderbolt to construct a new solid-liquid DC triboelectric nanogenerator based on the principle of spatiotemporal charge separation,systematically discusses its design philosophy,working mechanism,output characteristics and application development,and overcomes the main obstacles of distributed water energy harvesting.Therefore,this work finally completes the expected research goal above.This work not only has important research significance in the field of micro-scale water energy harvesting for self-powered technology,but also shows great application value in the field of large-scale water energy harvesting,which is expected to solve the practical problem of high-entropy water energy harvesting and help the realization of the blue energy dream.