공학박사 학위논문 저주파수 기계 에너지 하베스팅을 위한 액체-고체 마찰전기 나노발전기 개발 Development of Liquid-Solid Triboelectric Nanogenerators Towards Low-Frequency Mechanical Energy Harvesting 울산대학교 대학원 기계공학부 Development of Liquid-Solid Triboelectric Nanogenerators Towards Low-Frequency Mechanical Energy Harvesting Supervisor: Professor KYOUNG KWAN AHN A Dissertation Submitted to the Graduate School of the University of Ulsan In partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Mechanical Engineering by LE CHAU DUY Department of Mechanical Engineering University of Ulsan, Korea February 2023 ACKNOWLEDGEMENTS This Ph. dissertation is completed under the guidance, the support and the assistance from a lot of esteemed people. I would like to extend my sincerest gratitude to all of them. First of all, I would like to express my highest respect to my advisor, Professor Kyoung Kwan Ahn, for having me the chance to join his lab as well as his precious guidance and encouragement throughout my Ph.
I am certain that without his supports, I would never be able to complete my dissertation. Besides, I also would like to give my special thanks to the professors serving on my dissertation committee who take up their valuable times to improve my dissertation. It is an honor that these prestigious professors attend as my committee members. I would like to derive my appreciation to my research group members and my friends in University of Ulsan, who warmly assisted and promoted me, during my Ph.
I have received tremendous help from them, and without their kindness, I could not have gone this far. Last but not least, I would like to deliver my heartfelt gratitude and appreciation to my family for their endless supports and encouragement. i ABSTRACT Over the past several decades, the global demand for energy has become larger and more persistent due to the population growth in associated with human activities (i., residential, commercial, transportation and industrial) where the fossil fuels play a dominant role. However, the fast depletion and environmental impact of fossil fuels are big challenges for our sustainable development; therefore, harvesting energy from surroundings has significantly increased for years and can be recognized as an excellent approach to replace traditional energy generation.
Mechanical energy is one of the most universally-existing, diversely-presenting, but usually-wasted energies in the natural environment. Triboelectric nanogenerator (TENG) has been introduced recently as a novel and potent technology for this purpose, and the use of TENG for mechanical energy harvesting has been investigated to some extent. The liquid-solid TENG, with its remarkable strengths, has opened an additional direction for harvesting environmental energy such as water wave, river flow or rainfall. However, there is less awareness of generating power from low-frequency behaviors by using liquid-solid TENG even though they are omnipresent in human life.
In this dissertation, the research efforts have led to develop and analyze TENG- based energy harvesters to scavenge energy of low-frequency mechanical motion utilizing liquid-solid contact electrification principle. Through rational structural design, different types of solid-liquid contact electrification TENG for low-frequency mechanical energy harvesting was proposed. Initially, a rotational switched-mode water-based triboelectric nanogenerator for harvesting the rotational kinetic energy as well as road slope and wheel speed detection was carried out. Then, a discontinuous-conduction based rotational triboelectric nanogenerator with radially symmetrical design to effectively improve the instantaneous power was developed.
Lastly, an impulsive kinetic energy regulator for harvesting mechanical energy through low frequency impulse-excited motion was fabricated and experimentally evaluated to demonstrate the functionality of harvesting mechanical energy from human and machine activities. The above results ascertain the development of liquid-solid TENGs for low-frequency mechanical energy harvesting and brought a big potential of impacting people’s everyday life. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS. ii LIST OF FIGURES.
1 Introduction and General Background .1 Fundamentals of TENGs .1 Origin of triboelectrification.2 Principle theory and mathematical model of TENG .3 Working mechanism and operation modes of TENG .4 Potential applications of TENG .2 An early view of liquid-solid TENG .3 Motivation and Objectives .4 Organization of the Thesis. 13 Revision of Liquid-Solid Triboelectric Nanogenerator: Fundamentals, Structures and Applications .1 Fundamentals of liquid-solid triboelectrification.2 Mechanism of liquid-solid triboelectric nanogenerator .3 Structural design of liquid-solid triboelectric nanogenerator .1 Droplet-based TENGs .2 Bulk liquid-based TENGs .3 Liquid-filled TENGs .4 Applications of liquid-solid TENGs.1 Micro/nano power sources .2 Active self-powered sensors .3 Networks of liquid-solid TENG for blue energy harvesting. 28 iii Development and Analysis of a Rotational Switched-Mode Liquid-Solid Triboelectric Nanogenerator for Vehicle Monitoring System .1 Fabrication of the RSW-TENG .3 Results and Discussion .1 Basic operation and working mechanism of the RSW-TENG .2 Output performance of the RSW-TENG.4 RSW-TENG as vehicle monitoring device. 44 Development and Analysis of a Liquid-Solid Triboelectric Nanogenerator based Radially Symmetrical Structure for Mechanical Energy Harvester .1 Fabrication of PVDF nanoporous membrane.2 Fabrication of the DCR-TENG .3 Results and Discussion .1 Characteristics of PVDF nanoporous membrane .2 Working principle of the single-cell DCR-TENG.3 Output performance of single cell DCR-TENG .4 Output performance of multiple cell DCR-TENG.
60 Development and Analysis of a Harmonic Oscillator driven Liquid-Solid Triboelectric Nanogenerator for Intermittent Excitation Input .1 Fabrication of the rotary TENG.2 Fabrication of the mechanical motion rectifier .3 Results and Discussion .1 Working principle of the IKER .2 Performance of the IKER on vertical effort .3 Performance of the IKER on horizontal effort .4 Demonstration of the IKER under realistic intermittent excitation. 83 Conclusion and Future Work .1 Summary and conclusions .2 Recommendations for Future Works. 86 v LIST OF FIGURES Figure 1.1 Global primary energy consumption 1978-2018 (Exajoules).2 Electron-cloud-well-potential model for explaining triboelectrification with respect to electron transfer and release between two materials .3 Schematic showing the principle theory of displacement current for nanogenerators (including TENG) that derived from the expanded Maxwell’s equations .4 The ideal structure and equivalent circuit (capacitive) model of the contact- separation TENG .5 Basic operation modes of TENG. The TENG operation has been categorized into four modes, including vertical contact-separation (CS) mode, relative-sliding (RS) mode, single-electrode (SE) mode, and freestanding (FT) mode with their own merits and demerits .6 Four major applications of TENG including micro/nano direct power sources for self-powered systems (MDPS), active self-powered sensors (ASPS), basic network units for harvesting low-frequency water wave energy (LFWE), and direct power sources for high voltage instruments (HVPS) .1 Illustration of hybrid EDL model with “two-step” process formation.
(a) In the first step, water molecules and ions in the solution contact with the solid surface, causing electron transfer as well as ion adsorption on the solid surface. (b) In the second step, free ions in the solution are attracted by the induced electrostatic field and concentrate at the region close to the electrified surface, forming the EDL .2 Effect of surface hydrophobicity on the electron transfer and the ion transfer. When the water contact angle is higher than 90º, the ratio of electron transfers to ion transfers (E/I) increases rapidly, asserting the dominance of electron transfer. This can be explained by the chemical bond of hydrophilic (1) and hydrophobic (2) surface .3 Mechanism of water-PDMS based TENG.
(a) Initial state when no force is applied. (b) PDMS layer and water contact each other. (c) PDMS layer separates from water. (d) Separation completes and the PDMS layer comes back to original position.
(e) PDMS layer come to contact with water again, starting a new cycle .4 Different structural designs of droplet-based TENG for harvesting raindrop energy. (a) Schematic diagram and single-electrode mechanism of the multi-unit vi transparent TENG (MT-TENG) in integrating with vehicle and building. (d) Schematic diagram of the integrated system consisting of solar cell and water-drop TENG as well as the mechanism of the TENG .5 Different structural designs of bulk liquid-based TENG for harvesting water energy. (a) Schematic diagram and working principle of ww-TENG driven by flowing river.
(b) Schematic diagram and working principle of ww-TENG driven flowing water. (c) Schematic diagram and working principle of LSEG for harvesting energy from a variety of water motions. (d) Schematic diagram and working principle of Ū-shape electrode TENG for extracting power from waves’ flood and ebb processes. (e) Schematic diagram and working principle of liquid-immersed TENG.6 Different structural designs of liquid-filled TENG for harvesting water energy.
(a) Schematic diagram and working principle of rotational water TENG. (b) Schematic diagram and working principle of water tube-based TENG. (c) Schematic diagram and working principle of “SWING stick” TENG. (d) Schematic diagram and working principle of MSW-TENG .7 Liquid-solid TENGs as power sources.
(a) Structure of networked integrated TENG (NI-TENG) with arrayed bridge rectifiers and its ability to power a wireless transmitter. (b) Diagram of the grid of WDSE-TENG for harvesting water impact energy with the potential of driving low-power electronic devices. (c) Diagram of integrated TENG for raindrop energy harvesting and its demonstration of powering small electronic devices .8 Liquid-solid TENG as active self-powered sensors. (a) Schematic diagram and structure of LST-TENG for ship draft measurement.
The water level is detected through the peaks and valleys of voltage derivation signal. (b) Photograph of oil–solid interacting TENG (O–S TENG) for monitoring the engine lubricating oil and its output performance with respect to the fraction of waste oil. (c) Structural diagram of superhydrophobic liquid-solid contact TENG with current output generated by six types of droplets and its biomedical sensor prototype .9 Networks of liquid-solid TENG for blue energy harvesting. (a) Concept of liquid–solid-contact buoy TENG with the illustration of TENG network and different types of triggering movement.
The outputs show linear relation with the unit number. (b) vii Concept and fabrication of droplet-based TENG arrays on ship model with the output performance in water tank .1 3D model design of the RSW-TENG driven by a DC motor.2 Fabrication of RSW-TENG. It includes two components: a cylindrical rotating TENG with extended electrodes and a stationary electric contact with brushes. The electrodes contact the brushes twice every cycle.3 Experimental setup for evaluating the characterization of the RSW-TENG.4 Working mechanism of the RSW-TENG and the corresponding position of electrodes and brushes in one cycle of revolution.5 (a) Output current and (b) output voltage of RSW-TENG regarding clockwise and counterclockwise rotation at zero-degree phase angle and rotating speed of 1.6 Peak output current, peak output voltage and peak output power under different load resistances at zero-degree phase angle and rotating speed of 1.7 (a) Demonstration of the RSW-TENG as power source for (a) continuously lighting up LEDs in series and (b) charging different capacitors.8 Durability and stability of the RSW-TENG over time.9 Diagram of phase angle definition.10 Current and voltage with phase angle from 0 degree to 80 degree at running speed of 1.11 Charge accumulation on 10 μF capacitors at different phase angle.12 Current and voltage with rotating frequency from 0.25 Hz at phase angle of 0 degree.13 3D graph of output current and output voltage under effect of both phase angle and rotating frequency.14 Experimental results for validating the dispersion of water regarding the rotating speed of (a) 1.75 Hz and (c) 2 Hz.15 Experimental setup of vehicle wheel attached RSW-TENG where the wheel TENG prototype is attached on a slope-adjustable framework.16 (a) Assembly of wheel-TENG prototype and (b) Installation of wheel-TENG prototype in cooperation with motor-driven pulley system.17 The voltage signal corresponding to 10-degree slope.18 The voltage signal corresponding to 20-degree slope.19 The voltage signal corresponding to 30-degree slope.20 The voltage signal corresponding to running speed of 0.21 The voltage signal corresponding to running speed of 0.
42 Figure 3 22 The voltage signal corresponding to running speed of 0.1 Assembly model of the DCR-TENG with radially symmetrical design.2 (a) Structural design and (b) Fabrication of the DCR-TENG. Inset: mechanical switch composition.3 (a) FE-SEM image of the PVDF nanoporous membrane with the water contact angle. AFM images of (b) pristine PVDF and (c) nanoporous PVDF membrane with the water contact angle of each material.4 Schematic diagram of the working principle for one completed cycle of single- cell DCR-TENG.5 Output current of single cell DCR-TENG with 20-MΩ external resistance.6 Output voltage of single cell DCR-TENG with 20-MΩ external resistance.