Highly wearable, machine-washable, and self-cleaning fabric-based triboelectric nanogenerator for wireless drowning sensors
Graphical Abstract
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A fully fabric-based energy harvester is developed through low-cost NHCOO-PFOTS modification, which shows excellent self-healing, self-cleaning performances and extreme durability.
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A self-powered wireless sensor with the ability of drowning warning is demonstrated, which is able to send real-time message to the specified client when connected fabric-based power device falls into the water.
Introduction
Wearable electronics constitute a key element of the Internet of Things technology and are widely applied in human–computer interactions, biomedical/wellness monitors, personalized health care, and shape-adaptive military applications [1], [2]. The gigantic quantities and widespread distributions of electronic devices set higher demands for intelligent terminals powered by conventional electric energy systems [3], [4]. Batteries, the typical power source, are plagued by their bulky appearance, short life span, and potential health risks. Thus, it’s vital to develop a pervasive energy solution and novel energy-harvesting techniques in a sustainable and effective manner [5], [6], [7], [8], [9]. Daily human activities (e.g., breathing, arm lifting, and leg movement) produce kinetic power, as such, the human body is a huge energy container and a potential renewable power source for low-power wearable devices [10], [11]. Therefore, numerous self-powered techniques have been developed to harvest low-frequency biomechanical energy under various working mechanisms, such as piezoelectric nanogenerators, thermoelectric generators, and hybrid generators [12], [13], [14], [15]. Triboelectric nanogenerators (TENGs) based on the coupling of triboelectric and electrostatic effect are firstly emerged in 2012, and have been widely employed in self-powered wearable devices [16], [17], [18], [19]. The introduction of common natural or synthetic yarn materials has endowed TENGs with superior performances compared to common materials, such as increased wearing comfort, high mechanical strength, low weight, high flexibility, and more breathability [20], [21], [22], [23]. The improvement of materials for incorporating TENG devices is a preferable solution toward developing truly wearable electronics in a green, clean, and sustainable manner.
However, several challenges exist in the implementation and further advances of fabric-based TENGs (F-TENGs). On the one hand, it’s a major challenge to improve the energy conversion efficiency of F-TENGs for meeting the increasing power demand. In general, the ability or tendency to attract or donate electrons is closely related to the electron affinity (EA) of the surface atoms. Halogen atoms are the most electronegative, with a high EA to accommodate extra electrons [24], [25]. For example, high-EA compounds of fluorine (F), such as polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), and polytetrafluoroethylene (PTFE), constitute a large proportion of electron-withdrawing polymers. Moreover, fluorine-containing materials repel the adhesion of bacterial pathogens such as Candida albicans, Pseudomonas aeruginosa, and Escherichia coli [26], [27]. Thus, the introduction of additional F atoms onto the surface is a promising approach to increase the charge density of friction materials. There are many previous reports on through PVDF, PTFE and composite nanofibers based on melt-spinning or electro-spinning process for high performance energy harvesting [28], [29]. On the other hand, the original fabrics or nanofibers used as body cover or as parts of assembled TENG devices are mostly soft and super hydrophilic, which cannot resist contaminants and mechanical deformation, thus resulting in performance reduction upon frequent cleaning and friction [30], [31], [32], [33]. Considerable efforts have been put into the research on washable and durable F-TENGs, however, most of them pose problems such as bulkiness, discomfort, poor air permeability, high manufacturing costs [34]. Most importantly, some extreme conditions (high temperature, high salinity, ultraviolet radiation, plasma, etc) make the power fabrics disposable, greatly constraining the long-term use of devices [35], [36]. Therefore, for wearable F-TENGs, self-healing fabrics that can withstand incessant friction and washing is eagerly to be developed, but to our knowledge, few studies give consideration to all of the above problems.
In this paper, we present a simple method to prepare highly wearable, washable and self-healing F-TENGs for self-powered wireless drowning warning through the universal liquid-phase fluorination technique. Unlike some F-TENGs developed to date, urethane perfluorooctyl silane (NHCOO-PFOTS) is cost-effective and can be resized and modified for common fabrics through one-step dip coating technique. Both surface and interior of the molecular-engineered fabric have numerous F atoms with low surface energy and strong EA, endowing them with strong electronegativity, excellent washability, high durability, and superior self-cleaning ability. After 70 h washing, water contact angle (CA) of F-silk maintains 130º, and output voltage of F-silk/nylon pairs maintains 96.77% of the origin value (465 V). The superior output performances and durability of F-TENGs are ascribed to the strong electron-attracting ability of fluorine and robust chemical bonds between the hydroxy groups of fabrics and ethoxy groups in NHCOO-PFOTS molecules. The power density of F-TENGs paired with F-silk and nylon fabrics can reach 2.08 W/m2, which can harvest energy from arm swing movements and drive digital watches. In addition, the F-TENGs developed in this study can be employed as energy suppliers and integrated with wireless sensors for drowning prevention. Moreover, simple heating treatment is demonstrated to recover the plasma-destroyed covalent bonds between hydroxyl groups on fabric surface and triethoxysilane groups of NHCOO-PFOTS, owing to the reappearance of countless functional groups inside the fiber under heating conditions. These washable, self-cleaning, and self-healing power generation fabrics provide a new way to sense dangerous situations and drive wearable electronics under biomechanical excitation.
Section snippets
Materials and chemicals
Fabrics (i.e., silk, cotton, polyester, and nylon), commercial polyimide (PI) films (thickness: 25 µm), and copper tape were purchased from the local market. Ni-Cu conductive fabric (PF39B) was procured from Zhejiang Saintyear Electronic Technologies Co., Ltd, China. PVDF (average power: ~534,000 MW by GPC; powder) were bought from Sigma-Aldrich. Nylon-11 (PA11, 98%; piglet) was procured from Tianjin Heowns Biochemical Technology Co., Ltd. Formic acid, acetone, N, N-dimethylacetamide (DMAC),
Results and discussion
Fig. 1a shows the preparation process of liquid-phase fluorinated fabrics and the water CAs of silk (3°) and F-silk (143°). We can see that the hydrophobicity of the fabric has been greatly improved through NHCOO-PFOTS modification (supporting information, Fig. S1). As illustrated in Fig. S1b, hydroxyl (–OH) groups on the fabric surface originating from oxygen plasma treatment are covalently linked with triethoxysilane groups of NHCOO-PFOTS through nucleophilic substitution reaction between –OH
Conclusion
In summary, we developed a simple and general method for preparing hydrophobic fabrics functioning as waterproof covers and human motion energy harvesters through homemade NHCOO-PFOTS fluorination. Employing molecularly engineered triboelectric surfaces regulated by F-terminated groups renders ordinary fabrics with the robust electron-accepting ability and excellent washability. XPS, SEM, and air permeability measurements verified the successful loading of F groups on the fabrics without
CRediT authorship contribution statement
Min Feng: Conceptualization, Methodology, Validation, Investigation, Writing – original draft. Yang Wu: Methodology, Validation. Yange Feng: Conceptualization, Investigation, Software, Funding acquisition, Writing – review & editing. Yang Dong: Methodology, Investigation, Discussion, Data curation. Yubo Liu: Methodology, Discussion. Jialiang Peng: Methodology. Nannan Wang: Methodology. Shiwei Xu: Methodology. Daoai Wang: Conceptualization, Resources, Writing – review & editing, Supervision,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors thank the National Natural Science Foundation of China (No. 51905518), the Program for Taishan Scholars of Shandong Province (No. TS20190965), the National Key Research and Development Program of China (2020YFF0304600), the Innovation Leading Talents Program of Qingdao (19–3–2–23-zhc) in China, the Key Research Program of the Chinese Academy of Sciences (Grant No. XDPB24), and LICP Cooperation Foundation for Young Scholars (HZJJ21–03) for providing financial support.
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