| Author: | Wong, Man Chung |
| Title: | Mechanical energy harvesting and conversion based on utilization of luminescence materials and triboelectric nanogenerator |
| Advisors: | Hao, J. H. (AP) |
| Degree: | Ph.D. |
| Year: | 2020 |
| Subject: | Hong Kong Polytechnic University -- Dissertations Energy harvesting Energy conversion Smart materials |
| Department: | Department of Applied Physics |
| Pages: | xvii, 175 pages : color illustrations |
| Language: | English |
| Abstract: | Mechanical energy is the most ubiquitous energy source in an ambient environment, which exists in various forms such as vibration, shocks or stress, with frequency ranging from few Hz to kHz. With the recent surge of technological advancements in low power devices, the escalating costs of power storage device and the ongoing energy crisis. A significant amount of extensive investigations has been conducted in the field of effectively harvest and converse these mechanical energies through smart materials. On one hand, harvesting and utilization of these mechanical energy could be an efficient strategy to reduce the dependence on the traditional energy source. On the other hand, smart material does not only harvest mechanical energy into electricity, the multi-functional property of various smart materials enables its output to be employed in a wide variety of applications. The study concerning harvesting and conversion of mechanical energy via smart material technology has been attracting wide attention and therefore deserves more attempts. In this thesis, three novel strategies based on utilizing piezophotonic material, aggregation induced luminescence (AIE) materials and triboelectric generator (TENG) to convert and harvest mechanical energy is developed and illustrated. Firstly, a novel strategy is developed to realize the reversible tuning of the emission wavelengths of the piezophotonic material through variation of mechanical excitation frequency. Here, a non-conventional physical approach of temporal and remote tuning of light-emitting wavelength and color of piezoluminescence is demonstrated. It is shown that by modulating the frequency of the mechanical excitation, luminescence wavelength from the flexible composites of piezophosphors induced by the piezophotonic effect can be tuned in in-situ. Further investigation suggests that the observed tunable piezophotonic emission can be ascribed to the tilting band structure of the piezophosphor induced by a high frequency of mechanical excitation. Experiments were performed to verify this real-time and reversible piezoluminescence emission color tuning. Moreover, some proof of concept devices, including red-green-blue full-color displays and tunable white-light sources are been demonstrated simply by modulating the mechanical excitation frequency. This work has provided a new understanding of the fundamentals of piezoluminescence. Secondly, in our society, the process of binding nitrogen with hydrogen under high pressure and temperature that produces fertilizer consumed 1-2 % of the world's energy production. Therefore, the development of green energy-based nitrogen fixation technology is realistically significant for the fertilizer industry and agriculture. Herein, an environmentally friendly microplasma discharge-based nitrogen fixation system driven by harvesting ambient or ignored mechanical energy with a novel triboelectric nanogenerator is conceived. This novel TENG has the capability to generate a high voltage of about 1300 V without additional auxiliary and it was integrated with a discharge reactor. The generated voltage can be utilized to induce microplasma discharge under an atmospheric environment in the discharge reactor. Thereby, this voltage is directly applied between electrodes of the discharge reactor to induce an atmospheric microplasma discharge and nitrogen fixation. It is observed that through this discharge nitrogen gas in the air had been successfully converted into nitrogen compound, including nitrogen dioxide and nitric acid solution, via the TENG-driven microplasma discharge process to finally realize the nitrogen fixation. The NO₃- concentration of 250 ppm can be arrived after continuously operating the TENG for 400 min. Further, the effect of the magnitude of the separation between the discharge electrode on discharge process, including discharge voltage, discharge current and average discharge energy per TENG operation cycle, had been systematically investigated. The TENG-driven microplasma discharge-based nitrogen fixation system was demonstrated its ability to serve as a nitrogenous fertilizer supplier, and correspondingly, NaNO₃ fertilizer was produced via driving the system by human walking stimuli for crop cultivation. After driving the system by human walking stimuli, the NaNO3 fertilizer was produced to benefit the growth of the green bean. This work provides feasibility to develop an energy-saving, environmental-friendly, cost-efficient and safe nitrogen fixation route. This study offers a promising atmospheric nitrogen fixation strategy with energy-saving, environmental friendliness, flexible operation, and high safety. Thirdly, a novel strategy to realized mechanical energy modulation of the AIE emission is purposed. Previously, the majority of switching of AIE luminogen between its on and off states reported were achieved by multiple forms of energy input, namely, mechanical energy preceded by heat or vapor fuming. This significantly hinders the development of a real-time, AIE regulating mechanism based solely on mechanical energy input. Hence, by fabricating a composite by incorporating the AIE luminogen into a polymer matrix. Mechanical stress was applied to the composite to control the free volume around these AIE luminogen, such that restricting the molecular motion of AIE luminogen and these nonradiative decay. Thereby, the emission intensity can be enhanced. These researches investigated mechanical energy harvesting and converting utilizing luminescence materials and triboelectric nanogenerator. The novel findings provide valuable insight and demonstrated promising application in harvesting mechanical energy, such findings shall aid further research on various mechanical energy harvesting and conversion materials. |
| Rights: | All rights reserved |
| Access: | open access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 991022378658403411.pdf | For All Users | 5.18 MB | Adobe PDF | View/Open |
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