| Author: | Yang, Yujue |
| Title: | Design, modeling and characterization of wearable triboelectric nanogenerators as a functional and structural integrity |
| Advisors: | Xu, Bingang (SFT) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Magneto-electric machines Nanoelectromechanical systems Wearable technology Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Fashion and Textiles |
| Pages: | xxi, 148 pages : color illustrations |
| Language: | English |
| Abstract: | Recently, advancements in modern technology such as the Internet of Things (IoT) and sensor networks have led to a growing interest in portable electronics in daily human life. However, the heavy use of conventional batteries as the main power source hinders the sustainable development of the environment and energy. As a harvesting technology and a self-powered system, triboelectric nanogenerators (TENGs) could effectively utilize sustainable sources and facilitate the conversion of ubiquitous ambient energy (i.e. wind, wave, and mechanical energies) into electricity. TENGs are composed of electronegative and electropositive as well as electrode-conductive materials. They offer several advantages, including lightweight, low cost, small size, easy fabrication, high output and high energy conversion efficiency. To meet the self-powered requirements of portable electronics, wearable TENGs with various structures and properties have been designed to harvest energies from human motions. These bring potential feasibility for the further development of e-textiles and wearable portable devices. However, wearable TENGs still face several limitations and challenges such as low structural integrity, stability, and output performance. Herein, this research study has explored and designed different wearable TENGs, including a design of a fiber-based TENG (F-TENG) with structural integrity and customizable functionalities, a study of the quantitative relationship between functional materials and properties of fiber-based TENGs, a fabrication of a flexible triboelectric-photovoltaic coupled hybrid nanogenerator and a breathable nanofiber composite hybrid TENG. The detailed descriptions are provided in the following sections. Firstly, a new conductive composite fiber (CCF) with functional and structural integrity was designed for application in a fiber-based TENG (CCF-TENG). By adopting a core-spun yarn coating strategy, organic triboelectric materials (i.e. polydimethylsiloxane (PDMS) or thermoplastic polyurethanes (TPU)) could be better coated onto the surface of conductive metal materials (i.e. Ag-coated nylon yarn) with the assistance of staple fibers (i.e. cotton) as a sheath layer in a core-spun yarn to prepare a new composite structure with improved interfacial compatibility, effectively improving the interfacial failure problems between materials in fiber-based TENG. As a demonstration, the output performance of CCF-TENG could reach 117 V for open-circuit voltage and 213 mW/m2 for power density. Furthermore, based on the flexible characteristic, CCF could be made into a two-dimensional (2D) energy fabric to serve as a wearable sensor for motion detection. A new strategy was proposed in this work for creating one-dimensional composite fiber with customizable functionalities and structural integrity for applications in energy harvesting and smart wearables. Then, a design enabled by statistical modeling was explored for high-performance CCF to analyze the underlying relationship between parameters and properties of CCF-TENG. Two statistical methods, namely fractional factorial design (FFD) and response surface methodology (RSM), were used to effectively reduce the number of experiments and optimize the preparation parameters, thereby facilitating the design of high-performance CCF-TENG. The optimized CCF-TENG could act as a wearable sensor for wireless motion monitoring by connecting with a Bluetooth system. This proposed statistical modeling enabled strategy provided new insights in exploring quantitative relationships for applications of advanced materials with desired and optimized performance. Furthermore, to address the limitations of the low current density of TENG, hybrid nanogenerators that can simultaneously harvest mechanical and solar energies have been designed and fabricated. More specifically, a flexible fluorine-doped hybrid nanogenerator coupling triboelectric and photovoltaic effects was designed and developed to enhance the current density of TENGs by incorporating perovskite materials composed of CsPbBr3 doped with CaF2. The fluoride with high electronegativity can effectively passivate the defect density of the perovskite film and further enhance its dielectric constant to minimize the ability of defects to capture charges. As a result, the output current performance was about 9.7 μA under illumination, which could show a 25-fold enhancement as compared to that under dark conditions. Additionally, the flexible substrate, in replacement of traditional rigid substrate, could realize wearability to collect energies from human motion. This work proposed a flexible hybrid nanogenerator with high-output performance, providing feasibility for the potential application in wearable triboelectric-photovoltaic hybrid nanogenerators. Lastly, considering the enhanced breathability and stability of perovskite-based TENG, a wearable nanofiber composite hybrid nanogenerator was fabricated using an electrospinning strategy. The perovskite materials could produce electrons and holes under illumination, promoting more efficient charge transport and thus enhancing the current density of TENG. Through the electrospinning method, polymers could effectively form a protective layer to improve the stability of perovskite on the one hand, and on the other hand, the polarization effect induced during the manufacturing process was more conducive to promoting the separation of carriers and increasing the current density of TENG. More importantly, the nanofiber composite hybrid nanogenerator could realize breathability and flexibility for wearable devices. In conclusion, this thesis has designed and explored wearable triboelectric nanogenerators with a functional and structural integrity. A new composite structure with enhanced interfacial compatibility was achieved to prepare a high-performance and structurally stable F-TENG. Subsequently, the quantitative relationship between parameters and properties of the previously prepared TENG was built up to analyze the significant effect of fabricated parameters and obtain optimized parameters for desired triboelectric performance. Moreover, the study on a flexible triboelectric-photovoltaic coupled hybrid nanogenerator could address the limitation of the low output current density of TENGs and realize a hybrid nanogenerator with flexibility and wearability. Furthermore, by utilizing electrospinning technology, a triboelectric-photovoltaic coupled nanofiber-based hybrid nanogenerator was prepared to achieve high performance and enhanced breathability and stability. All these strategies provide potential ideas and possibilities for the further development of wearable triboelectric nanogenerators for application in portable electronic devices. |
| Rights: | All rights reserved |
| Access: | open access |
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