| Author: | Guan, Xiaoyang |
| Title: | Study of flexible and wearable nanogenerators for biomechanical energy harvesting and self-powered sensing |
| Advisors: | Xu, Bin-gang (ITC) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Energy harvesting Nanoscience Hong Kong Polytechnic University -- Dissertations |
| Department: | Institute of Textiles and Clothing |
| Pages: | 186 pages : color illustrations |
| Language: | English |
| Abstract: | With the rapid advancement of smart textile and wearable electronics, the demand for corresponding flexible and sustainable power supply units is continuously growing. However, traditional chemical batteries, which are still the most widely used portable energy source so far, cannot meet the requirements of wearable electronics due to their inherent limitations of rigid complex structure, heavy weight, bulky volume, persistent recharging/replacement, and limited lifetime. To address these challenges, one of the most promising solutions is to develop self-powered energy harvesters to scavenge waste biomechanical energy from human movements, which is ubiquitously available and can be generated continuously and inexhaustibly without ambient environment restriction. To date, a variety of flexible nanogenerators (NGs) with the advantages of light weight, simple configuration, low cost, environment friendliness and widespread availability have been actively explored. In particular, the fiber/fabric-based NGs with the advantages of high air-permeability, good three-dimensional (3D) deformation and robust damage tolerance have become a burgeoning focus as the most promising and feasible candidates for the practical applications in harvesting biomechanical energy and sensing human motions. However, to fabricate NGs with both high output performance and good wearability is still a great challenge. The significant relationship among material, structure and properties inspired us to design and fabricate novel fiber/fabric based NGs by utilizing more common fiber/fabric structures and processing technologies in combination with the high-performance active materials. This work is carried out by designing and developing flexible and wearable piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs) with different fiber/fabric structures, including coaxial sheath-core fiber structured TENG, nanofiber nonwoven structured PENG, woven structured TENG and sandwich-like textile TENG. Firstly, a novel type of auxetic fiber shaped TENG (AXF-TENG) with a distinct coreshell coaxial architecture for self-powered sensing was designed and fabricated, in which a brand-new negative Poisson-ratio auxetic core fiber was axially inserted into a commercial hollow circular tube. The developed auxetic core fiber was rationally designed by selecting a helical-structure stainless steel yarn as the stretchable electrode and employing polydimethylsiloxane (PDMS) to cover the spiral stainless-steel yarns (SSYs) as the active triboelectric layer. Owing to the advanced structure design, contact and separation between the triboelectric materials become more effective, which contribute to harvesting more sufficient mechanical energy from stretching. Subsequently, a new, facile and efficient approach to prepare polydopamine (Pdop)modified barium titanate (BT) nanoparticles (NPs) anchored poly (vinylidene fluorideco-trifluoroethylene) (PVDF-TrFE) [Pdop-BT@P(VDF-TrFE)] composite membranes with a hierarchical structure for high performance flexible PENGs was designed and developed. The hierarchically architected Pdop-BT@P(VDF-TrFE) nanocomposite was fabricated via electrospinning P(VDF-TrFE) mat and anchoring Pdop-BT on the surface of electrospun P(VDF-TrFE) nanofibers using an ultrasonication process. The nonwoven membrane-based PENG made from Pdop-BT@P(VDF-TrFE) nanocomposite exhibited excellent flexibility, significantly enhanced piezoelectricity and durability. Specifically, output voltage and current of Pdop-BT@P(VDF-TrFE) based PENG can reach up to ~6 V and ~1.5 μA, which are 4.8 times and 2.5 times over P(VDF-TrFE) PENG. As a demonstration, the fabricated flexible PENG was employed to efficiently scavenge biomechanical energy and detect human body movements as self-powered sensors. In order to meet the compatibility for large-scale manufacturing, commercial textile was used as the substrate for fabricating wearable TENGs with enhanced output performance, excellent conformal deformability and breathability. By constructing 3D conformal porous microstructure layer of PS-block-polybutadiene-block-PS (SBS) on the woven cotton textiles (cotton-SBS 3CPMTs) through a facile breath figure (BF) technique, the sandwich-like textile TENG was obtained by encapsulating a piece of copper-nickel coated polyester fabric (CNF) electrode between two pieces of cotton-SBS 3CPMTs, which exhibited both enhanced triboelectric outputs and effective waterproof performance, with open circuit voltage (Voc) of ~ 30 V, short circuit current (Isc) of ~ 3 μA and maximum instantaneous power density of 25 mW/m2, respectively. As a demonstration, the application potential of sandwich-like textile triboelectric nanogenerator as a useful power source was investigated. Lastly, to further develop wearable TENG with desirable flexibility, breathability and washability, a route to develop a new kind of woven-structured triboelectric nanogenerator (WS-TENG) with a facile, low-cost, and scalable electrospinning technique was explored. The WS-TENG was fabricated with commercial stainless-steel yarns wrapped by electrospun polyamide 66 (PA66) nanofiber and P(VDF-TrFE) nanofiber, respectively. The open-circuit voltage, short-circuit current and maximum instantaneous power density from the WS-TENG could reach up to 166 V, 8.5 μA and 93 mW/m2, respectively. By virtue of high flexibility, desirable breathability, good washability and excellent durability, the fabricated WS-TENG was demonstrated to be a reliable power textile to light up 58 light-emitting diodes (LED) connected serially, charge commercial capacitors and drive portable electronics. A smart glove with stitched WS-TENGs was made to detect finger motion in different circumstances. In summary, this thesis has carried out a systematic study on designing, exploring and developing flexible and wearable fiber/fabric based NGs in different device structures. By combining the highly electroactive materials with flexible fiber/fabric structures, NGs with both high electric output performance and flexibility were successfully obtained. Moreover, methods for synthesizing/processing the electroactive materials were carefully designed and adopted to sustain the inherent advantages of textiles. The series of flexible and wearable NGs designed and developed in this research, including coaxial fiber-shaped TENGs, nonwoven membrane based PENGs, woven structured TENGs, and sandwich-like textile TENGs, provide promising solutions to pave the way for the development and innovation of fiber/fabric based flexible NGs for biomechanical energy harvesting and self-powered sensing. |
| Rights: | All rights reserved |
| Access: | open access |
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