| Author: | Wang, Qian |
| Title: | Study of silk-based triboelectric nanogenerators for energy harvesting and sensing |
| Advisors: | Xu, Bingang (SFT) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Subject: | Nanogenerators Tribology Sericin Wearable technology Energy harvesting Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Fashion and Textiles |
| Pages: | xxx, 187 pages : color illustrations |
| Language: | English |
| Abstract: | Triboelectric nanogenerators (TENGs) have emerged as a revolutionary technology for converting mechanical energy into electrical energy through the triboelectric effect and electrostatic induction. For wearable devices, the prioritization of flexible and abundant natural fibers has led to extensive research on silk, which excels owing to its biocompatibility, mechanical strength, and biodegradability. Silk, derived from silkworm cocoon (SC), is a multi-layer composite material composed of a single continuous fiber, with fibroin (SF) being hydrophobic and sericin (SS) being hydrophilic, resulting in a semi-crystalline polymer structure. Traditionally, SS has been removed due to its potential to trigger biological immune responses, resulting in a significant waste of resources. In this thesis, a method has been explored to retain SS in the design of silk-based TENGs without compromising output performance. By incorporating various dopants, the performance of these TENGs has been significantly enhanced beyond their original capabilities, achieving superior efficiency and functionality. This innovative approach provides an efficient energy solution for wearable devices. Firstly, a kind of silk-based biocompatible TENGs with integrated SS retention was proposed and fabricated for the first time, where three kinds of silkworm cocoon layers (SCLs) endowed with naturally distinct bulge structures were considered as the positive triboelectric materials while Polydimethylsiloxane (PDMS) was used as the negative tribolayer. The novelty of this methodology lies in utilizing the initial layer of the silkworm cocoon as the tribolayer without undergoing the degumming process, thereby achieving a simplified fabrication approach. The triboelectric properties of different SCLs were investigated and analyzed. The working mechanisms and the influence of operational parameters were thoroughly investigated. Its promising potential for wearable energy harvesting and sensing applications has also been demonstrated. This work broadens the material selection by retaining SS to enhance the output performance of TENGs for practical applications. Subsequently, inspired by the hierarchical structure of silkworm cocoons, silk-based TENGs were designed by retaining SS to leverage the unique properties of both SF and SS. Polyvinyl alcohol (PVA) was utilized as a substrate owing to its excellent film-forming ability and favorable electron-donating ability. The optimal ratio of SS to SF within the PVA matrix was then investigated to achieve the best triboelectric performance. The composite SF/SS/PVA (SFP) membrane serves as the positive tribolayer, while fluoro-nylon (F-Nylon) functions as the negative tribolayer, operating in the contact-separation mode. The surface roughness and secondary structure of the resulting composite films were analyzed to investigate the relationship between triboelectric output performance and structural features. Furthermore, the triboelectric mechanism and output performance were examined to explore potential applications in wearable technology. Thirdly, a scalable SFP membrane integrated with silver nanowires (AgNWs) was synthesized to form a composite film. When paired with a separate F-Nylon film to construct the TENG device, this design, inspired by the rough surface of silkworm cocoons, features interwoven AgNWs that create a similarly textured surface. The integration of AgNWs, renowned for their exceptional electrical conductivity, enabled our TENG device to attain an ultrahigh power density of 7.6 W/m², surpassing the performance metrics of most recently reported silk-based TENGs. This advancement underscores the potential of silk-based membranes in wearable energy harvesting and sensing applications, highlighting their promise in the development of high-performance protein-based triboelectric materials. Lastly, a novel two-dimensional material, MXene, was incorporated into the synthesized SFP matrix. MXene exhibits excellent triboelectric properties, and its tendency to aggregate and difficulty in dispersion are effectively mitigated by the significant disaggregation effects of the SS in the substrate, resulting in a uniformly stable composite membrane. Another innovative aspect of this research is the implementation of a single-electrode operation mode, which simplifies and optimizes the structural design. Remarkably, our engineered silk/MXene-based device demonstrates an exceptionally high instantaneous power density of 35.76 W/m². Furthermore, a comprehensive exploration and analysis of the secondary structure of the silk-MXene composite membrane were conducted. This SS retention-based membrane offers valuable insights into the fabrication of high-performance TENG devices. In summary, a comprehensive investigation into the hierarchical structure of the silkworm cocoon was conducted, uncovering significant insights that can be used to guide the design of composite membranes based on this unique structure. Inspired by the hierarchical structure of the silkworm cocoon and the specific ratio of SF to SS in individual silk fibers, an SFP membrane has been synthesized. By leveraging the natural properties of silk, our SFP membrane exhibits enhanced electrical performance, making it a promising candidate for advanced technological applications in sustainable energy solutions and sensing detection systems. Additionally, incorporating highly conductive AgNWs into the SFP matrix resulted in rough surface morphology, which facilitated the improved charge transfer and significantly enhanced the overall electrical performance. Moreover, MXene, a two-dimensional material known for its exceptional triboelectric properties but prone to aggregation, was incorporated into the SFP matrix. The resulting silk-based TENGs exhibit enhanced electrical outputs by the disaggregation effects of SS. This research study provides an insight on the rational design and development of silk-based TENG devices with enhanced electrical outputs for applications in energy harvesting and sensing. |
| Rights: | All rights reserved |
| Access: | open access |
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