Abstract
The progress of humankind has been marked by five main waves of innovation that have significantly transformed our industries and societies, which is also coupled with the consumption of resources, pollution, and energy/water shortage. Searching for ways to reduce our reliance on fossil fuels, researchers, engineers, and entrepreneurs are looking for disruptive technologies that can harvest the largely untapped energy from the ambient environment. Covering 70 % of the earth’s surface, the abundant water in fog, vapor, tide, rain, waterfall etc. is the largest battery in the world and could be the next big thing in renewable energy. In recent years, the introduction of wettability has triggered revolutions in water energy harvesting/conversion systems, which not only created great scientific reverberation but also reminiscent of the significance of gas bubble for energy harvesting. However, as the opposite form of water droplet, the ubiquitous gas bubbles that contain limitless energy have received less attention for energy harvesting due to the lack of disruptive, efficient, and scalable technologies.In this thesis, based on the understanding of natural designing principles and bubble wetting science, we put an emphasis on physical fundamentals of bubble behaviors on nature-inspired surfaces for developing high-performance bubble-based electricity generators. Through synergistically combing a transistor-inspired architecture and ingenious surface wettability control, we developed highly efficient bubble-based electricity generators that fundamentally breaks the physical limitations inherent in traditional designs, allowing for effectively and continuously harnessing the inexhaustible and huge energy stored in ubiquitous gas bubbles.
First, this thesis systematically introduced the sights learned from nature and its application in guiding the design of nature-inspired surfaces for power generation. Special interest is then put on understanding the contact dynamics of gas bubbles on nature-inspired wettable surfaces, which lays a theoretical foundation for the design of bubble electricity generator.
Second, to overcome the bottlenecks of low output performance inherent in traditional bubble energy generators, we develop a highly efficient bubble-gated, transistor-inspired electricity generator (B-TEG) that allows for the efficient and continuous electricity generation from the dielectric material with pre-stored high-density surface charges rather than from the limited interfacial triboelectric charges occurring during the bubble impinging process. The B-TEG consists of an electret material (Polytetrafluoroethylene, PTFE), one ITO electrode located below the dielectric layer and another electrode in the water. The electret PTFE is treated with high surface charge density to serve as the charge reservoir, while imparting ingenious surface wettability to promote bubble motion. In analog to the field effect transistor, the electret layer in conjunction with the underlying ITO electrode can be treated as the source terminal, the other electrode placed in water behaves like a drain terminal and the moving bubble serves as the gate. In combination with the ingenious surface wettability control, such a transistor-inspired architecture can circumvent the unwanted interfacial effect, enabling the B-TEG produces ~ 40 V and 2.4 μA with an individual gas bubble, which is 20 times and 4.2 times higher than the best performance of traditional devices. Moreover, the output voltage of B-TEG can be further boosted to 80 V through a synergistic effect using bubble arrays. In addition, the as-designed B-TEG also exhibits advantages of simple architecture, facile fabrication, excellent transparency, and desirable flexibility.
Third, to address the drawback of solid substrate such as vulnerable to mechanical abrasion, biofouling, and strong acid or alkali, we also developed another transistor-like impinging bubble-based electricity generator that inspired by the slippery lubricant-infused porous surface (SLIPS) of the pitcher plant. The combination of SLIPS and bubble creates a gas/liquid interface in underwater environment, which endows SLIPS-BEG with high robustness to mechanical abrasion, biofouling, and strong acid or alkali. Moreover, as compare to a conventional design, the integration of SLIPS and a transistor-like architecture can eliminate the undesirable wetting transition and promote preferential bubble motion as well as transform the unwanted interfacial effect into a favorable bulk effect, all of which are beneficial for efficient charge generation and transportation. Owing to the proper design of electric circuit architecture, porous substrate, lubricant viscosity and dielectric constant, the output voltage of the bubble-based electricity generator (BEG) decorating with SLIPS reaches up to 40 V, which is 40 times higher than that of a conventional design. In addition, the SLIPS-BEG also exhibits promising advantages over conventional designs including optical transparency, configurability, and flexibility. We envision that our innovative design provides an intelligent scheme for the exploration of underwater energy harvesting.
In summary, this thesis designed two high-performance bubble-based electricity generators. The cooperative interplay of nature-inspired wettable surfaces and a transistor-inspired architecture can fundamentally break the physical limitations of inefficient charge transfer and charge generation inherent in traditional bubble electricity generators through mitigating the contrast wettability requirements for bubble affinity and mobility as well as transforming the unwanted interfacial effect into a preferential bulk effect, allowing for the highest output voltage among current bubble electricity generators. Furthermore, we designed another bulk-effect bubble electricity generator featuring a SLIPS, which imparts a smooth surface for continuous and efficient mass/charge transportation as well as high tolerance to harsh working conditions involving mechanical abrasion and strong acid solution. We believe that our work on the high-performance bubble-based electricity generator will provide a deep insight into the fundamental understanding of bubble energy harvesting and pave the way for developing a wide range of self-powered devices in submerged environment.
| Date of Award | 3 Sept 2021 |
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| Original language | English |
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| Supervisor | Zuankai WANG (Supervisor) |