A Thermoelectric Wristband Based on Single-Walled Carbon Nanotubes for Energy Harvesting

A Thermoelectric Wristband Based on Single-Walled Carbon Nanotubes for Energy Harvesting | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article A Thermoelectric Wristband Based on Single-Walled Carbon Nanotubes for Energy Harvesting Xudong Shen, Yizhou Qi, Mingzhu Yuan, Dayi Chen, Yiran Wang, Yanwei Sun, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6259525/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Single-walled carbon nanotubes (SWCNTs) have attracted increasing attention in wearable thermoelectric devices due to their extremely high strength and toughness. Here we introduce a flexible thermoelectric wearable wristband based on SWCNTs. High-performance SWCNTs films were successfully fabricated through ultrasonic dispersion and heat-pressing processes, exhibiting a Seebeck coefficient of 42.5µV/K and a maximum electrical conductivity of 3503 S/cm. The flexible films showed excellent bending durability with less than 9.5% Seebeck coefficient loss after 400 cycles‌. The width and length of the thermoelectric legs were optimized, and a wearable thermoelectric wristband was simulated by connecting the legs in series, thereby analyzing its total output power. Furthermore, a thermoelectric wristband was fabricated by spin-coating onto a flexible printed circuit (FPC) substrate, and it achieved a maximum output power of 10.7µW under a temperature difference of 36.5 K. This research provides an efficient and feasible energy harvesting pathway for utilizing carbon-based materials as thermoelectric materials. Physical sciences/Nanoscience and technology/Nanoscale materials/Carbon nanotubes and fullerenes Physical sciences/Energy science and technology/Energy harvesting/Devices for energy harvesting Figures Figure 1 Figure 2 Figure 3 1. Introduction The booming development of flexible electronics technology has significantly promoted the application of wearable electronic devices in daily life. In recent years, the continuous advancement of self-powered technology, with its unique advantage of not requiring external batteries, has become an indispensable and vital component in the wearable technology field 1 , 2 . Thermoelectric generators(TEGs) efficiently convert thermal energy into electrical energy and are considered as a high-potential pathway for the development of wearable self-powered electronic devices 3 . The skin of the human body possesses a heat dissipation capacity ranging from 100 W to 525 W, rendering it an ideal heat source 4 . However, the development of TEGs that concurrently exhibit high performance, high flexibility, and long-term adaptability to the human micro-environment remains challenging, significantly restricting the widespread adoption of wearable self-powered electronic devices 5 . Thermoelectric efficiency is commonly evaluated by the ZT value, where \(\:ZT={S}^{2}\sigma\:T/k\) . Here ,S, σ, T, and k represent the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity respectively 6 . Currently, inorganic thermoelectric materials are recognized for their excellent thermoelectric properties, which are attributed to their controllable high electrical conductivity (σ) and notable Seebeck coefficient (S) 7 . However, inorganic materials are plagued by defects such as high cost, significant rigidity, and toxicity, which severely restrict their practical applications, particularly in the field of wearable flexible thermoelectric generators (FTEGs) 8 , 9 .In contrast, most organic materials, such as conductive polymers, inherently possess low thermal conductivity (k). However, due to their relatively low Seebeck coefficient and the numerous challenges in effectively enhancing it, their power factor (S²σ) is also relatively low, resulting in significantly different thermoelectric properties compared to those of inorganic materials 10 . Carbon-based thermoelectric materials have garnered considerable attention in the scientific community due to their excellent flexibility, non-toxicity, low cost, and ease of processing. SWCNTs achieve a relatively high Seebeck coefficient, thanks to their high electrical conductivity (σ reaching 10³–10⁴ S/cm) and unique electronic structure 11 .The high electrical conductivity of SWCNTs stems from the high carrier mobility of their long-range conjugated π-electron system, while the quantum confinement effect and chirality-dependent electronic states further enhance their remarkable Seebeck coefficient. This successfully overcomes the traditional trade-off between electrical conductivity and the Seebeck coefficient observed in conventional materials 12 , 13 . By optimizing their structure and interface design, SWCNTs pave a new path for self-powered wearable electronic devices in terms of efficiency, flexibility, and environmental performance. This paper delves into the research on flexible thermoelectric wearable wristbands based on SWCNTs. The main research findings are as follows: (1) Preparation and optimization of SWCNTs dispersions: We successfully prepared a uniform SWCNTs dispersion containing 0.4 wt% conductive agent and 0.6 wt% dispersant. After 30 minutes of ultrasonic treatment, a good dispersion was achieved. Test results of the prepared samples demonstrated a maximum thermoelectric coefficient of 42.5 µV/K and a maximum conductivity of 3503 S/cm. Bending tests confirmed the performance stability of the flexible thermoelectric SWCNTs material after multiple bending cycles. (2) Thermoelectric model simulation and optimization: A three-dimensional model of the FTEGs was established using COMSOL multiphysics software. The performance of a single thermoelectric unit and of 120 thermoelectric units connected in series was simulated and analyzed. By adjusting the external load resistance, the output voltage, current, and power of the thermoelectric wristband were optimized. (3) Design and fabrication of the FTEGs wearable wristband: A PI FPC board was designed, and the copper electrodes were gold-plated to enhance their conductivity. The SWCNTs dispersion was spin-coated onto the FPC board using a shadow mask, followed by drying and heat-pressing processes that improved the density of the SWCNTs film and its bonding strength to the FPC board. (4) A temperature-difference-controllable test platform, designed to simulate the human wrist, was constructed to comprehensively evaluate the actual performance of the FTEGs wearable wristband. The results demonstrated excellent thermoelectric conversion efficiency and outstanding mechanical flexibility, achieving a maximum output power of 14.96 µW. 2. Discussion and Results 2.1 Preparation and performance analysis of carbon nanotube dispersion The process for fabricating SWCNTs films is depicted in Fig. 1 a, the experimental methods section already provides more detailed experimental steps and conditions. The preparation of SWCNTs films mainly involves three steps: ultrasonic dispersion of SWCNTs in ethanol, spin-coating the dispersion onto the substrate, and heat pressing. Compared with commonly-used methods such as vacuum filtration 14 , 15 and mold casting 16 . Film formation is accomplished using spin-coating method, which is convenient for batch production. Figure 1 b and c show the mixed solution of SWCNTs and the films prepared using the solvent hot pressing method, respectively. Figure 1 c shows five strip samples of the film after spin-coating the PI substrate and cutting it for testing. The flexibility of the sample strip is shown on the upper right corner. Figure 1 d presents SEM characterization of the SWCNTs film strip sample after cutting. The SWCNTs intertwine with each other, forming an extensive conductive network. The hot-pressing treatment compacts the SWCNTs film under vertical pressure, reducing its thickness and leading to stacking and overlapping between layers. To elucidate the impact of heating and press temperature of SWCNTs, five temperature points within the range of 60°C to 140°C were chosen for hot-pressing to prepare the samples (S-60 to S-140). Figure 1 e shows the testing platform for SWCNTs films was self-made using Peltier cooling elements. As illustrated in Fig. 1 f,g, with an increasing temperature, the S of the SWCNT film changes gently, the maximum difference is only between 2–3µV/K, with a maximum thermoelectric coefficient reaching 42.5µV/K, the results indicate the thermal properties of the material exhibit high stability at different temperatures. However, the electrical conductivity exhibits significant differences at different temperatures, with a maximum conductivity of 3503 S/cm obtained after heat pressing at 100℃, this trend is consistent with the findings of Li et al 15 . The reason may be that high temperatures can cause partial brittleness and fracture of the carbon nanotube structure, while low temperatures may affect the effective connections between the carbon nanotubes. To evaluate the performance stability of flexible thermoelectric carbon nanotube materials after multiple bending cycles, a simple bending test platform was constructed, as shown in Fig. 1 h. After bending 400 times, the resistance and Seebeck coefficient decreased no more than 7.6% and 9.5%, and there were no obvious defects and cracks on the film surface, which fully demonstrates the excellent performance stability of the material under bending conditions. 2.2 Theoretical Analysis and Simulation of Flexible Thermoelectric Wristbands The calculation of open-circuit voltage ( \(\:{V}_{oc}\) ) and output power( P ) for SWCNTs FTEGs with multiple legs can be systematically derived from key parameters, such as the Seebeck coefficient ( S ) and electrical conductivity ( σ )。 (1) Calculation of open-circuit voltage( \(\:{V}_{oc}\) ) Open-circuit voltage refers to the potential difference generated by a temperature gradient in a thermoelectric material under open-circuit conditions. For a FTEGs composed of n thermoelectric legs connected in series, its open-circuit voltage \(\:{\text{V}}_{\text{o}\text{c}}\) can be expressed as Eq. ( 1 ): $$\:{V}_{oc}=n\bullet\:s\bullet\:\varDelta\:T\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:$$ 1 Where S is the Seebeck coefficient, a crucial parameter describing the material's thermoelectric conversion capability, representing the potential difference generated per unit temperature gradient. ∆ T is the temperature difference between the two ends of the thermoelectric leg. (2) Calculation of internal resistance ( R ) Internal resistance R includes the internal resistance of the thermoelectric legs and contact resistances among others. To simplify the calculation, we assume that all thermoelectric legs have the same internal resistance and that contact resistances are negligible. In this case, the internal resistance \(\:{R}_{leg}\) of each thermoelectric leg can be expressed as Eq. ( 2 ): $$\:{R}_{leg}=\frac{L}{\sigma\:\bullet\:A}$$ 2 Where σ is the electrical conductivity, and A is the cross-sectional area. Since the n thermoelectric legs are connected in series, the total internal resistance R of the thermoelectric generator can be expressed as Eq. ( 3 ): $$\:R=n*{R}_{leg}=\frac{n\bullet\:L}{\sigma\:\bullet\:A}\:$$ 3 (3) Calculation of output power ( P ) Output power refers to the ability of a thermoelectric generator to convert thermal energy into electrical energy under actual working conditions. For an FTEGs composed of n thermoelectric legs connected in series, its maximum output power P can be expressed as Eq. ( 4 ): $$\:P={\left(\frac{{V}_{oc}}{2}\right)}^{2}\bullet\:\frac{1}{R}$$ 4 Where R is the internal resistance of the thermoelectric generator, including the internal resistances of the thermoelectric legs and contact resistances, among others. To simplify the calculation, we assume that all thermoelectric legs have the same internal resistance and that contact resistances are negligible. By substituting the expressions for \(\:{V}_{oc}\:\) and R into the above equation, we obtain Eq. ( 5 ): $$\:P=({\frac{n\bullet\:s\bullet\:\varDelta\:T}{2})}^{2}\bullet\:\frac{\sigma\:\bullet\:A}{n\bullet\:L}$$ 5 After simplification, we get Eq. ( 6 ): $$\:P=\frac{n\bullet\:{s}^{2}\bullet\:\sigma\:\bullet\:A\bullet\:{(\varDelta\:T)}^{2}}{4L}$$ 6 We conducted an in-depth investigation into the influence of thermoelectric leg width on the V OC , by varying the width from 500 micrometers to 3.5 millimeters. With the leg length maintained constant at 20 millimeters, a hot-side temperature of 309.85K was applied, while the cold side was subjected to natural convection at an ambient temperature of 293.15K. The thermal conductivity coefficient, h, was set at 25 W/m²·K. We observed the maximum V OC for the thermoelectric legs. The V OC output magnitudes across different leg widths are illustrated in Fig. 2a. The variation in width had a minimal impact on thermal conductivity and subsequently on the V OC output, primarily due to the preferential axial propagation of phonons along the carbon nanotubes within the film, where changes in width exert limited influence on phonon propagation paths and interface numbers. Nevertheless, given a constant electrical conductivity, the width is inversely proportional to the resistance of the thermoelectric leg,whereas narrower legs exhibit higher resistance. Therefore, for the ease of fabrication, we opted for a thermoelectric leg width of 3 mm. Furthermore, we examined the effect of altering the thermoelectric leg length on V OC within a range of 5 to 70 millimeters. As depicted in Fig. 2b, an increase in thermoelectric leg length led to an elevation in V OC . Notably, when the thermoelectric leg length exceeded a certain threshold (approximately 20 mm), the V OC began to approach a saturation point of 0.23 mV. Although the V OC output continued to increase with leg length, the rate of increase became progressively flatter, which is consistent with the findings of Milad et al 17 . Given a constant electrical conductivity, the length is directly proportional to the resistance of the thermoelectric leg. Selecting a leg length close to this optimal value achieves the desired V OC without the need for further elongation to maximize the performance of the thermoelectric leg. This approach not only ensures efficient energy harvesting, but also aids in maintaining the overall flexibility and wearability of the device at the optimal thermoelectric leg length. In this study, we selected a thermoelectric leg length of 20 mm. To delve deeper into the power generation performance of the FTEGs wristband, we constructed an FTEGs simulation model in COMSOL multiphysics software. Traditionally, thermoelectric generators have employed inorganic materials such as Bi 2 Te 3 and PbTe, with their hot and cold ends typically designed at the two terminals of the device to generate voltage by controlling the temperature difference 4 , 18 . However, due to the small size of the thermoelectric device, the significant thermal conduction effect causes the temperatures at the two ends of the device to quickly converge, thereby affecting the output voltage. To address this, we adopted organic flexible thermoelectric materials, designed the thermoelectric legs in an elongated shape, and integrated the thermoelectric wristband on both sides of a PI substrate by sharing a common cold end. The simulation results revealed that, at a temperature difference of 36.5 K, the temperature distribution of the FTEGs is shown in Fig. 2c, where the purple area represents the low-temperature zone and the orange-yellow area represents the high-temperature zone. Furthermore, we simulated the variation of the FTEGs's output voltage and power with output current under different temperature differences, as illustrated in Fig. 2d, based on changes in the external load. Under conditions of a temperature difference of 36.5 K and 120 thermoelectric legs, the maximum output power of the FTEGs reached 14.96µW (as shown in Fig. 2e) which is sufficient to meet the power requirements of general low-power consumption products. 2.3 The Fabrication and Performance Testing of the FTEGs Wristband. Figure 3 a shows the as-fabricated FTEGs consists of three parts, the middle section is FTEGs part, and the exterior is covered with a transparent Polydimethylsiloxane (PDMS) protective layer. FTEGs part includes 120 SWCNTs legs, and it is the most critical component that converts thermal energy into electrical energy. The design of PDMS not only enhances the durability of the wristband, but also ensures the stability of the thermoelectric conversion process. The upper right corner photo shows the convenient wearing method of the FTEGs thermoelectric wristband, proving its potential in practical applications. During the preparation of the wristband, we used a flexible FPC board made of PI material to ensure the reliability of the process. To ensure a reliable connection between SWCNTs and the electrodes, we applied a gold immersion process to the electrodes. Compared to the manual application of silver paste method adopted by Hong et al. 19 , our gold immersion process on the FPC board substrate significantly improves the manufacturing efficiency and reliability of the wristband. The traditional manual method of connecting wires is prone to fractures at the junctions of the two materials, especially when there are numerous thermoelectric legs, which can easily lead to instability of the thermoelectric wristband. As illustrated in Fig. 3 b, before spin coating, a meticulously designed mask plate was affixed onto the FPC board. Subsequently, the carbon nanotube dispersion solution prepared earlier was uniformly applied onto the substrate via spin coating, and after drying and heat-pressing processes, the initial preparation of the thermoelectric wristband was completed, compared to the method of fabricating thermoelectric films from carbon nanotubes, cutting them into strips, and connecting them in series 11 . This approach enables the rapid fabrication of thermoelectric wristbands. Figure 3 c shows the photo of the SWCNTs-based FTEGs, and excellent flexibility of FTEGs can be seen. To assess the performance of the FTEGs in a practical application, we constructed a flexible thermoelectric test platform, the schematic diagram of the platform is shown in Fig. 3 d. The actual test platform under different temperature differences is shown in Fig. 3 e, the platform device employs thermally conductive aluminum boxes on both sides of the thermoelectric wristband, and specific temperature water is added for testing, the middle part of the wristband serves as the cold end, where a hydrogel patch is used for cooling control to ensure a temperature difference between the hot and cold ends. As illustrated in Fig. 3 f, the thermoelectric coefficient of the FTEGs wristband at 313.15K is 137.07mV. Although this result is slightly lower than the simulation expectations, it is attributed to the inherent thermal conductivity of the carbon nanotubes during the actual testing process. Additionally, we analyzed the relationship between the output voltage and output current (as shown in Fig. 3 g, and tested the variation of output power with output current at different temperatures (as shown in Fig. 3 h), the results indicated that the maximum output power reached 10.7uW, the FTEGs wristband demonstrated stable thermoelectric conversion performance. 3. Methods 3.1 Preparation of carbon nanotube dispersions SWCNTs and PVP (polyvinylpyrrolidone) dispersant were purchased from Suqian NCT Materials Co., Ltd. A solution was prepared by dissolving 0.2 g of SWCNTs and 0.3 g of PVP dispersant in 50 milliliters of deionized water. The mixture was stirred at 300 rpm for 2 hours, yielding a uniform dispersion with a conductive agent content of 0.4 wt% and a dispersant content of 0.6 wt%. Subsequently, the dispersion underwent ultrasonic treatment in an ice bath for 30 minutes to prevent changes due to overheating during the ultrasonication process. Finally, the processed carbon nanotube dispersion was stored in a suitable container. Then, a certain amount of the dispersion was drawn using a syringe and spin-coated onto a PI substrate with dimensions of 20 mm by 5 mm. During the spin-coating process, care was taken to ensure uniform thickness. The coated substrate was subsequently dried on a heating plate at 100°C for 1 hour and then subjected to a vertical pressure of 2 MPa using a press for 10 minutes. 3.2 Simulation of thermoelectric models A three-dimensional model of the FTEGs was created utilizing COMSOL Multiphysics 6.1, which can be accessed at https://www.comsol.com . Initially, the performance of a single thermoelectric element was tested within the COMSOL multiphysics environment. Subsequently, 120 Legs were integrated in series, and steady-state simulations were conducted using the thermoelectric effect and circuit modules. Circuit nodes were utilized to connect the ammeter, external load, FTEGs, and voltmeter, thus constructing the circuit simulation model. By varying the resistance of the external load, data were collected from the ammeter and voltmeter. 3.3 Design of the FTEGs-based wearable wristband Based on the simulation results, we designed a FPC board made of PI material and applied gold plating to the copper electrodes to enhance their conductivity. To ensure better spin-coating results and improve efficiency, we first designed a mask and placed it over the FPC board. The SWCNTs dispersion was then applied to the FPC board using a syringe for spin-coating, ensuring a uniform coating to avoid thickness variations. The coated FPC board was subsequently placed in an oven and dried at 100°C for 1 hour. After drying, the FPC board was subjected to heat-pressing with a vertical pressure of 2 MPa for 10 minutes to enhance the density of the SWCNTs film and to ensure tight bonding with the flexible FPC board. 3.4 Performance evaluation of the FTEGs wearable wristband To evaluate the performance and practical application of the FTEGs wearable wristband, a temperature-difference-controllable test platform was established. A thermally conductive aluminum box filled with water at a specific temperature was utilized. The FTEGs wearable wristband was then tightly attached to the outer sides of the aluminum box, while a hydrogel was applied to the middle section of the wristband to serve as the cold end for thermal insulation and cooling. Temperature data were collected using a UNI-T contact thermometer probe. By controlling the temperature, the actual performance of the device was measured. The FTEGs wearable wristband was tested with external resistors of different values, and the relationships between voltage, current, and output power were recorded by varying the external load resistance. During the performance testing, the measured data were processed to calculate both the mean and variance, as shown in Equations ( 7 ) and ( 8 ). Therefore, each data point in the graphs represents the average of the measured data, and a smaller variance indicates that the data set deviates less from the mean, making the data more reliable. 3 . $$\:\mu\:=\frac{{x}_{1}+{x}_{2}+\cdots\:{x}_{n}}{n}$$ 7 $$\:\delta\:=\sqrt{\frac{1}{n}\sum\:_{i=1}^{n}{({x}_{i}-\mu\:)}^{2}}$$ 8 4. Conclusion In this study, we presented a FTEGs wearable wristband based on SWCNTs. Through a meticulous fabrication process, a uniformly dispersed carbon nanotube film with excellent electrical conductivity was obtained. Utilizing COMSOL Multiphysics for simulation and optimization, the thermoelectric wristband demonstrated promising thermoelectric conversion performance. By fabricating a thermoelectric wristband and conducting tests, it was shown that the maximum output power of the wristband reached 10.7 µW at a temperature difference of 36.5 K. This thermoelectric wristband proposes an effective solution in the field of carbon-based thermoelectric wearable devices. Future research will focus on further optimizing the material composition and device structural design, aiming to enhance the output power and improve long-term durability. Declarations 6. Contributions X.D.S. nvestigation,Methodology,Writing – original draft, Y.Z.Q. , Y.R.W and Y.W.S Writing – review & editing, M.Z.Y., D.Y.C. Methodology, G.S. Funding acquisition,Methodology,Project administration,Resources,Supervision,Writing – review & editing. 7. Acknowledgements This research is supported by the National Natural Science Foundation of China, China under Grant 62334006, Grant 62271275, Grant 62131010 and Grant U22A2013 in part by the Zhejiang Provincial Natural Science Foundation of China, China under Grant LR22F010001, the Project of Scientific and Technological Plan of Zhejiang Province, China under Grant 2024C01, and the Project of Jiaxing Science and Technology , Grant 2023AY11027,Project of the Zhejiang Provincial Department of Education, Grant Y202250242. 8. Declaration of Competing interests The authors declare no competing interests. 9. Data Availability The data supporting the plots in this paper are available from the corresponding author upon reasonable request. 10. Additional information Correspondence and requests for materials should be addressed to Ge Shi or Yizhou Qi. Reprints and permissions information is available at www.nature.com/reprints. 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Integration of tau-shaped fins and perforated polyimide substrate for enhanced power output in flexible thermoelectric generator for human body heat harvesting. (2025). Hong, M. et al. Advances in printing techniques for thermoelectric materials and devices. Soft Sci. 3 , (2023). Contributions. nvestigation, X. D. S. Methodology,Writing – original draft, Y.Z.Q., Y.R.W and Y.W.S Writing – review & editing, M.Z.Y., D.Y.C. Methodology, G.S. Funding acquisition,Methodology,Project administration,Resources,Supervision,Writing – review & editing. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6259525","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":440348756,"identity":"e9a6b028-df54-472f-8d35-fd2b4d7eebeb","order_by":0,"name":"Xudong Shen","email":"","orcid":"","institution":"China Jiliang University","correspondingAuthor":false,"prefix":"","firstName":"Xudong","middleName":"","lastName":"Shen","suffix":""},{"id":440348757,"identity":"cfa26ca5-117e-43f5-bd54-48b40e6fdc84","order_by":1,"name":"Yizhou Qi","email":"","orcid":"","institution":"China Jiliang University","correspondingAuthor":false,"prefix":"","firstName":"Yizhou","middleName":"","lastName":"Qi","suffix":""},{"id":440348758,"identity":"368884a9-e882-4725-ad31-a7b440f94d00","order_by":2,"name":"Mingzhu Yuan","email":"","orcid":"","institution":"China Jiliang University","correspondingAuthor":false,"prefix":"","firstName":"Mingzhu","middleName":"","lastName":"Yuan","suffix":""},{"id":440348759,"identity":"68621e7d-b3b7-4ae1-b9a1-31b3bd83ec87","order_by":3,"name":"Dayi Chen","email":"","orcid":"","institution":"China Jiliang University","correspondingAuthor":false,"prefix":"","firstName":"Dayi","middleName":"","lastName":"Chen","suffix":""},{"id":440348760,"identity":"1afccde0-3699-4240-a149-ddf40f517c7b","order_by":4,"name":"Yiran Wang","email":"","orcid":"","institution":"China Jiliang University","correspondingAuthor":false,"prefix":"","firstName":"Yiran","middleName":"","lastName":"Wang","suffix":""},{"id":440348761,"identity":"3fd54d68-b662-41de-8402-fb44c70dd235","order_by":5,"name":"Yanwei Sun","email":"","orcid":"","institution":"China Jiliang University","correspondingAuthor":false,"prefix":"","firstName":"Yanwei","middleName":"","lastName":"Sun","suffix":""},{"id":440348762,"identity":"d1e71431-0cc9-41ef-89d3-97ef9ab72c09","order_by":6,"name":"Ge Shi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAy0lEQVRIiWNgGAWjYDACCcYGBoYKBmY+EIeHeC1nGJjZSNACxIxtDAzEa5Gf3dz84uM8O3Y2iQTGB2/bGOTNCWkxuHOwzXLmtmRmoBZmw7ltDIY7GwhpkUhsM+bddgCkhU2at40hweAAIYfNAGr5Oweshf03UVoYbiQ2P2ZsgNjCTJQWgxuJbYw9x4B+4XnYLDnnnIThBsIOS3/84UeNXTI/e/LBD2/KbOQJOwwYI6CoSQbGTgMDJJoIA+YPQMKOKKWjYBSMglEwMgEAF5w6R0Kp8L8AAAAASUVORK5CYII=","orcid":"","institution":"China Jiliang University","correspondingAuthor":true,"prefix":"","firstName":"Ge","middleName":"","lastName":"Shi","suffix":""}],"badges":[],"createdAt":"2025-03-19 08:38:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6259525/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6259525/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-12751-8","type":"published","date":"2025-07-23T15:58:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":80563427,"identity":"15dd6304-919b-4972-89ff-219e46b7ad6c","added_by":"auto","created_at":"2025-04-14 17:04:38","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1281072,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) Synthesis process and characterization methods of carbon nanotube film‌.(b) Self-prepared carbon nanotube dispersion solution.(c) Flexible thermoelectric film fabricated via conventional process.(d) SEM image of strip-shaped thermoelectric film sample.‌(e) Custom-built testing platform for thermoelectric films.(f) Temperature-dependent variation of Seebeck coefficient.(g) Temperature-dependent electrical conductivity.(h) Bending test experiment.(i) Variation rate of Seebeck coefficient as a function of bending cycle.(j) Resistance variation of sample under different bending cycles.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6259525/v1/5898225c1b7f624ebb5a91dd.png"},{"id":80563428,"identity":"bf93eb4e-6744-415e-824f-a73198459edc","added_by":"auto","created_at":"2025-04-14 17:04:38","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":625847,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) The influence of thermoelectric leg width on open-circuit voltage. (b) The influence of thermoelectric leg width on open-circuit voltage. (c) Temperature distribution of the thermoelectric wristband at ∆T of 36.5K. (d) Relationship between voltage, power, and current in the FTEGs under different temperature gradients(15K,25K,36.5K). (e) Power, voltage, and current generated by the FTEGs under different temperature differences.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6259525/v1/5166d4937b005730f6479649.png"},{"id":80564105,"identity":"cd83d783-bc97-4767-b535-0863f758808b","added_by":"auto","created_at":"2025-04-14 17:12:38","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1062378,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) Schematic diagram of the structure of the FTEGs wristband. (b) The fabrication progress of the FTEGs wristband. (c) Photo of the FTEGs wristband. (d) Schematic diagram of the testing platform for the FTEGs wristband. (e) Photo of testing platform for the FTEGs wristband. (f) Relationship between open-circuit output voltage and temperature difference. (g) Relationship between output voltage and output current. (h) Relationship between output power and output current.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6259525/v1/4ec8ce94d493733966dca95d.png"},{"id":87756740,"identity":"0e81c8b5-6de7-4c6a-9841-85b2d652b593","added_by":"auto","created_at":"2025-07-28 16:08:34","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3983548,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6259525/v1/6caaaca4-5e7b-4907-95c4-9507d4e05c72.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A Thermoelectric Wristband Based on Single-Walled Carbon Nanotubes for Energy Harvesting","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe booming development of flexible electronics technology has significantly promoted the application of wearable electronic devices in daily life. In recent years, the continuous advancement of self-powered technology, with its unique advantage of not requiring external batteries, has become an indispensable and vital component in the wearable technology field\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Thermoelectric generators(TEGs) efficiently convert thermal energy into electrical energy and are considered as a high-potential pathway for the development of wearable self-powered electronic devices\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. The skin of the human body possesses a heat dissipation capacity ranging from 100 W to 525 W, rendering it an ideal heat source \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. However, the development of TEGs that concurrently exhibit high performance, high flexibility, and long-term adaptability to the human micro-environment remains challenging, significantly restricting the widespread adoption of wearable self-powered electronic devices\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThermoelectric efficiency is commonly evaluated by the ZT value, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:ZT={S}^{2}\\sigma\\:T/k\\)\u003c/span\u003e\u003c/span\u003e. Here ,S, σ, T, and k represent the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity respectively\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Currently, inorganic thermoelectric materials are recognized for their excellent thermoelectric properties, which are attributed to their controllable high electrical conductivity (σ) and notable Seebeck coefficient (S)\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. However, inorganic materials are plagued by defects such as high cost, significant rigidity, and toxicity, which severely restrict their practical applications, particularly in the field of wearable flexible thermoelectric generators (FTEGs)\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.In contrast, most organic materials, such as conductive polymers, inherently possess low thermal conductivity (k). However, due to their relatively low Seebeck coefficient and the numerous challenges in effectively enhancing it, their power factor (S\u0026sup2;σ) is also relatively low, resulting in significantly different thermoelectric properties compared to those of inorganic materials\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eCarbon-based thermoelectric materials have garnered considerable attention in the scientific community due to their excellent flexibility, non-toxicity, low cost, and ease of processing. SWCNTs achieve a relatively high Seebeck coefficient, thanks to their high electrical conductivity (σ reaching 10\u0026sup3;\u0026ndash;10⁴ S/cm) and unique electronic structure \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e.The high electrical conductivity of SWCNTs stems from the high carrier mobility of their long-range conjugated π-electron system, while the quantum confinement effect and chirality-dependent electronic states further enhance their remarkable Seebeck coefficient. This successfully overcomes the traditional trade-off between electrical conductivity and the Seebeck coefficient observed in conventional materials\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. By optimizing their structure and interface design, SWCNTs pave a new path for self-powered wearable electronic devices in terms of efficiency, flexibility, and environmental performance.\u003c/p\u003e \u003cp\u003eThis paper delves into the research on flexible thermoelectric wearable wristbands based on SWCNTs. The main research findings are as follows:\u003c/p\u003e \u003cp\u003e(1) Preparation and optimization of SWCNTs dispersions: We successfully prepared a uniform SWCNTs dispersion containing 0.4 wt% conductive agent and 0.6 wt% dispersant. After 30 minutes of ultrasonic treatment, a good dispersion was achieved. Test results of the prepared samples demonstrated a maximum thermoelectric coefficient of 42.5 \u0026micro;V/K and a maximum conductivity of 3503 S/cm. Bending tests confirmed the performance stability of the flexible thermoelectric SWCNTs material after multiple bending cycles.\u003c/p\u003e \u003cp\u003e(2) Thermoelectric model simulation and optimization: A three-dimensional model of the FTEGs was established using COMSOL multiphysics software. The performance of a single thermoelectric unit and of 120 thermoelectric units connected in series was simulated and analyzed. By adjusting the external load resistance, the output voltage, current, and power of the thermoelectric wristband were optimized.\u003c/p\u003e \u003cp\u003e(3) Design and fabrication of the FTEGs wearable wristband: A PI FPC board was designed, and the copper electrodes were gold-plated to enhance their conductivity. The SWCNTs dispersion was spin-coated onto the FPC board using a shadow mask, followed by drying and heat-pressing processes that improved the density of the SWCNTs film and its bonding strength to the FPC board.\u003c/p\u003e \u003cp\u003e(4) A temperature-difference-controllable test platform, designed to simulate the human wrist, was constructed to comprehensively evaluate the actual performance of the FTEGs wearable wristband. The results demonstrated excellent thermoelectric conversion efficiency and outstanding mechanical flexibility, achieving a maximum output power of 14.96 \u0026micro;W.\u003c/p\u003e"},{"header":"2. Discussion and Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Preparation and performance analysis of carbon nanotube dispersion\u003c/h2\u003e \u003cp\u003eThe process for fabricating SWCNTs films is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, the experimental methods section already provides more detailed experimental steps and conditions. The preparation of SWCNTs films mainly involves three steps: ultrasonic dispersion of SWCNTs in ethanol, spin-coating the dispersion onto the substrate, and heat pressing. Compared with commonly-used methods such as vacuum filtration\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e and mold casting\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFilm formation is accomplished using spin-coating method, which is convenient for batch production. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb and c show the mixed solution of SWCNTs and the films prepared using the solvent hot pressing method, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec shows five strip samples of the film after spin-coating the PI substrate and cutting it for testing. The flexibility of the sample strip is shown on the upper right corner. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed presents SEM characterization of the SWCNTs film strip sample after cutting. The SWCNTs intertwine with each other, forming an extensive conductive network. The hot-pressing treatment compacts the SWCNTs film under vertical pressure, reducing its thickness and leading to stacking and overlapping between layers.\u003c/p\u003e \u003cp\u003eTo elucidate the impact of heating and press temperature of SWCNTs, five temperature points within the range of 60\u0026deg;C to 140\u0026deg;C were chosen for hot-pressing to prepare the samples (S-60 to S-140). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee shows the testing platform for SWCNTs films was self-made using Peltier cooling elements. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef,g, with an increasing temperature, the S of the SWCNT film changes gently, the maximum difference is only between 2\u0026ndash;3\u0026micro;V/K, with a maximum thermoelectric coefficient reaching 42.5\u0026micro;V/K, the results indicate the thermal properties of the material exhibit high stability at different temperatures. However, the electrical conductivity exhibits significant differences at different temperatures, with a maximum conductivity of 3503 S/cm obtained after heat pressing at 100℃, this trend is consistent with the findings of Li et al\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. The reason may be that high temperatures can cause partial brittleness and fracture of the carbon nanotube structure, while low temperatures may affect the effective connections between the carbon nanotubes.\u003c/p\u003e \u003cp\u003eTo evaluate the performance stability of flexible thermoelectric carbon nanotube materials after multiple bending cycles, a simple bending test platform was constructed, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh. After bending 400 times, the resistance and Seebeck coefficient decreased no more than 7.6% and 9.5%, and there were no obvious defects and cracks on the film surface, which fully demonstrates the excellent performance stability of the material under bending conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Theoretical Analysis and Simulation of Flexible Thermoelectric Wristbands\u003c/h2\u003e \u003cp\u003eThe calculation of open-circuit voltage (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{V}_{oc}\\)\u003c/span\u003e\u003c/span\u003e) and output power(\u003cem\u003eP\u003c/em\u003e) for SWCNTs FTEGs with multiple legs can be systematically derived from key parameters, such as the Seebeck coefficient (\u003cem\u003eS\u003c/em\u003e) and electrical conductivity (\u003cem\u003eσ\u003c/em\u003e)。\u003c/p\u003e \u003cp\u003e(1) Calculation of open-circuit voltage(\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{V}_{oc}\\)\u003c/span\u003e\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eOpen-circuit voltage refers to the potential difference generated by a temperature gradient in a thermoelectric material under open-circuit conditions. For a FTEGs composed of \u003cem\u003en\u003c/em\u003e thermoelectric legs connected in series, its open-circuit voltage \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{V}}_{\\text{o}\\text{c}}\\)\u003c/span\u003e\u003c/span\u003e can be expressed as Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{V}_{oc}=n\\bullet\\:s\\bullet\\:\\varDelta\\:T\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere S is the Seebeck coefficient, a crucial parameter describing the material's thermoelectric conversion capability, representing the potential difference generated per unit temperature gradient. ∆\u003cem\u003eT\u003c/em\u003e is the temperature difference between the two ends of the thermoelectric leg.\u003c/p\u003e \u003cp\u003e(2) Calculation of internal resistance (\u003cem\u003eR\u003c/em\u003e)\u003c/p\u003e \u003cp\u003eInternal resistance R includes the internal resistance of the thermoelectric legs and contact resistances among others. To simplify the calculation, we assume that all thermoelectric legs have the same internal resistance and that contact resistances are negligible. In this case, the internal resistance \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{leg}\\)\u003c/span\u003e\u003c/span\u003eof each thermoelectric leg can be expressed as Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e):\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{R}_{leg}=\\frac{L}{\\sigma\\:\\bullet\\:A}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere σ is the electrical conductivity, and A is the cross-sectional area. Since the n thermoelectric legs are connected in series, the total internal resistance R of the thermoelectric generator can be expressed as Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e):\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:R=n*{R}_{leg}=\\frac{n\\bullet\\:L}{\\sigma\\:\\bullet\\:A}\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e(3) Calculation of output power (\u003cem\u003eP\u003c/em\u003e)\u003c/p\u003e \u003cp\u003eOutput power refers to the ability of a thermoelectric generator to convert thermal energy into electrical energy under actual working conditions. For an FTEGs composed of n thermoelectric legs connected in series, its maximum output power \u003cem\u003eP\u003c/em\u003e can be expressed as Eq.\u0026nbsp;(\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e):\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:P={\\left(\\frac{{V}_{oc}}{2}\\right)}^{2}\\bullet\\:\\frac{1}{R}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere R is the internal resistance of the thermoelectric generator, including the internal resistances of the thermoelectric legs and contact resistances, among others. To simplify the calculation, we assume that all thermoelectric legs have the same internal resistance and that contact resistances are negligible.\u003c/p\u003e \u003cp\u003eBy substituting the expressions for \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{V}_{oc}\\:\\)\u003c/span\u003e\u003c/span\u003eand \u003cem\u003eR\u003c/em\u003e into the above equation, we obtain Eq.\u0026nbsp;(\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e5\u003c/span\u003e):\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$\\:P=({\\frac{n\\bullet\\:s\\bullet\\:\\varDelta\\:T}{2})}^{2}\\bullet\\:\\frac{\\sigma\\:\\bullet\\:A}{n\\bullet\\:L}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAfter simplification, we get Eq.\u0026nbsp;(\u003cspan refid=\"Equ6\" class=\"InternalRef\"\u003e6\u003c/span\u003e):\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$$\\:P=\\frac{n\\bullet\\:{s}^{2}\\bullet\\:\\sigma\\:\\bullet\\:A\\bullet\\:{(\\varDelta\\:T)}^{2}}{4L}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWe conducted an in-depth investigation into the influence of thermoelectric leg width on the V\u003csub\u003eOC\u003c/sub\u003e, by varying the width from 500 micrometers to 3.5 millimeters. With the leg length maintained constant at 20 millimeters, a hot-side temperature of 309.85K was applied, while the cold side was subjected to natural convection at an ambient temperature of 293.15K. The thermal conductivity coefficient, h, was set at 25 W/m\u0026sup2;\u0026middot;K. We observed the maximum \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eOC\u003c/em\u003e\u003c/sub\u003e for the thermoelectric legs. The \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eOC\u003c/em\u003e\u003c/sub\u003e output magnitudes across different leg widths are illustrated in Fig.\u0026nbsp;2a. The variation in width had a minimal impact on thermal conductivity and subsequently on the \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eOC\u003c/em\u003e\u003c/sub\u003e output, primarily due to the preferential axial propagation of phonons along the carbon nanotubes within the film, where changes in width exert limited influence on phonon propagation paths and interface numbers. Nevertheless, given a constant electrical conductivity, the width is inversely proportional to the resistance of the thermoelectric leg,whereas narrower legs exhibit higher resistance. Therefore, for the ease of fabrication, we opted for a thermoelectric leg width of 3 mm.\u003c/p\u003e \u003cp\u003eFurthermore, we examined the effect of altering the thermoelectric leg length on \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eOC\u003c/em\u003e\u003c/sub\u003e within a range of 5 to 70 millimeters. As depicted in Fig.\u0026nbsp;2b, an increase in thermoelectric leg length led to an elevation in \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eOC\u003c/em\u003e\u003c/sub\u003e. Notably, when the thermoelectric leg length exceeded a certain threshold (approximately 20 mm), the \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eOC\u003c/em\u003e\u003c/sub\u003e began to approach a saturation point of 0.23 mV. Although the \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eOC\u003c/em\u003e\u003c/sub\u003e output continued to increase with leg length, the rate of increase became progressively flatter, which is consistent with the findings of Milad et al\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Given a constant electrical conductivity, the length is directly proportional to the resistance of the thermoelectric leg. Selecting a leg length close to this optimal value achieves the desired V\u003csub\u003eOC\u003c/sub\u003e without the need for further elongation to maximize the performance of the thermoelectric leg. This approach not only ensures efficient energy harvesting, but also aids in maintaining the overall flexibility and wearability of the device at the optimal thermoelectric leg length. In this study, we selected a thermoelectric leg length of 20 mm.\u003c/p\u003e \u003cp\u003eTo delve deeper into the power generation performance of the FTEGs wristband, we constructed an FTEGs simulation model in COMSOL multiphysics software. Traditionally, thermoelectric generators have employed inorganic materials such as Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e and PbTe, with their hot and cold ends typically designed at the two terminals of the device to generate voltage by controlling the temperature difference\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. However, due to the small size of the thermoelectric device, the significant thermal conduction effect causes the temperatures at the two ends of the device to quickly converge, thereby affecting the output voltage. To address this, we adopted organic flexible thermoelectric materials, designed the thermoelectric legs in an elongated shape, and integrated the thermoelectric wristband on both sides of a PI substrate by sharing a common cold end. The simulation results revealed that, at a temperature difference of 36.5 K, the temperature distribution of the FTEGs is shown in Fig.\u0026nbsp;2c, where the purple area represents the low-temperature zone and the orange-yellow area represents the high-temperature zone. Furthermore, we simulated the variation of the FTEGs's output voltage and power with output current under different temperature differences, as illustrated in Fig.\u0026nbsp;2d, based on changes in the external load. Under conditions of a temperature difference of 36.5 K and 120 thermoelectric legs, the maximum output power of the FTEGs reached 14.96\u0026micro;W (as shown in Fig.\u0026nbsp;2e) which is sufficient to meet the power requirements of general low-power consumption products.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 The Fabrication and Performance Testing of the FTEGs Wristband.\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the as-fabricated FTEGs consists of three parts, the middle section is FTEGs part, and the exterior is covered with a transparent Polydimethylsiloxane (PDMS) protective layer. FTEGs part includes 120 SWCNTs legs, and it is the most critical component that converts thermal energy into electrical energy. The design of PDMS not only enhances the durability of the wristband, but also ensures the stability of the thermoelectric conversion process. The upper right corner photo shows the convenient wearing method of the FTEGs thermoelectric wristband, proving its potential in practical applications.\u003c/p\u003e \u003cp\u003eDuring the preparation of the wristband, we used a flexible FPC board made of PI material to ensure the reliability of the process. To ensure a reliable connection between SWCNTs and the electrodes, we applied a gold immersion process to the electrodes. Compared to the manual application of silver paste method adopted by Hong et al.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, our gold immersion process on the FPC board substrate significantly improves the manufacturing efficiency and reliability of the wristband. The traditional manual method of connecting wires is prone to fractures at the junctions of the two materials, especially when there are numerous thermoelectric legs, which can easily lead to instability of the thermoelectric wristband. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, before spin coating, a meticulously designed mask plate was affixed onto the FPC board. Subsequently, the carbon nanotube dispersion solution prepared earlier was uniformly applied onto the substrate via spin coating, and after drying and heat-pressing processes, the initial preparation of the thermoelectric wristband was completed, compared to the method of fabricating thermoelectric films from carbon nanotubes, cutting them into strips, and connecting them in series\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. This approach enables the rapid fabrication of thermoelectric wristbands. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ec shows the photo of the SWCNTs-based FTEGs, and excellent flexibility of FTEGs can be seen.\u003c/p\u003e \u003cp\u003eTo assess the performance of the FTEGs in a practical application, we constructed a flexible thermoelectric test platform, the schematic diagram of the platform is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ed. The actual test platform under different temperature differences is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, the platform device employs thermally conductive aluminum boxes on both sides of the thermoelectric wristband, and specific temperature water is added for testing, the middle part of the wristband serves as the cold end, where a hydrogel patch is used for cooling control to ensure a temperature difference between the hot and cold ends. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ef, the thermoelectric coefficient of the FTEGs wristband at 313.15K is 137.07mV. Although this result is slightly lower than the simulation expectations, it is attributed to the inherent thermal conductivity of the carbon nanotubes during the actual testing process. Additionally, we analyzed the relationship between the output voltage and output current (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eg, and tested the variation of output power with output current at different temperatures (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eh), the results indicated that the maximum output power reached 10.7uW, the FTEGs wristband demonstrated stable thermoelectric conversion performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Methods","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Preparation of carbon nanotube dispersions\u003c/h2\u003e \u003cp\u003eSWCNTs and PVP (polyvinylpyrrolidone) dispersant were purchased from Suqian NCT Materials Co., Ltd. A solution was prepared by dissolving 0.2 g of SWCNTs and 0.3 g of PVP dispersant in 50 milliliters of deionized water. The mixture was stirred at 300 rpm for 2 hours, yielding a uniform dispersion with a conductive agent content of 0.4 wt% and a dispersant content of 0.6 wt%. Subsequently, the dispersion underwent ultrasonic treatment in an ice bath for 30 minutes to prevent changes due to overheating during the ultrasonication process. Finally, the processed carbon nanotube dispersion was stored in a suitable container. Then, a certain amount of the dispersion was drawn using a syringe and spin-coated onto a PI substrate with dimensions of 20 mm by 5 mm. During the spin-coating process, care was taken to ensure uniform thickness. The coated substrate was subsequently dried on a heating plate at 100\u0026deg;C for 1 hour and then subjected to a vertical pressure of 2 MPa using a press for 10 minutes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Simulation of thermoelectric models\u003c/h2\u003e \u003cp\u003eA three-dimensional model of the FTEGs was created utilizing COMSOL Multiphysics 6.1, which can be accessed at \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.comsol.com\u003c/span\u003e\u003cspan address=\"https://www.comsol.com\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Initially, the performance of a single thermoelectric element was tested within the COMSOL multiphysics environment. Subsequently, 120 Legs were integrated in series, and steady-state simulations were conducted using the thermoelectric effect and circuit modules. Circuit nodes were utilized to connect the ammeter, external load, FTEGs, and voltmeter, thus constructing the circuit simulation model. By varying the resistance of the external load, data were collected from the ammeter and voltmeter.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Design of the FTEGs-based wearable wristband\u003c/h2\u003e \u003cp\u003eBased on the simulation results, we designed a FPC board made of PI material and applied gold plating to the copper electrodes to enhance their conductivity. To ensure better spin-coating results and improve efficiency, we first designed a mask and placed it over the FPC board. The SWCNTs dispersion was then applied to the FPC board using a syringe for spin-coating, ensuring a uniform coating to avoid thickness variations. The coated FPC board was subsequently placed in an oven and dried at 100\u0026deg;C for 1 hour. After drying, the FPC board was subjected to heat-pressing with a vertical pressure of 2 MPa for 10 minutes to enhance the density of the SWCNTs film and to ensure tight bonding with the flexible FPC board.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Performance evaluation of the FTEGs wearable wristband\u003c/h2\u003e \u003cp\u003eTo evaluate the performance and practical application of the FTEGs wearable wristband, a temperature-difference-controllable test platform was established. A thermally conductive aluminum box filled with water at a specific temperature was utilized. The FTEGs wearable wristband was then tightly attached to the outer sides of the aluminum box, while a hydrogel was applied to the middle section of the wristband to serve as the cold end for thermal insulation and cooling. Temperature data were collected using a UNI-T contact thermometer probe. By controlling the temperature, the actual performance of the device was measured. The FTEGs wearable wristband was tested with external resistors of different values, and the relationships between voltage, current, and output power were recorded by varying the external load resistance. During the performance testing, the measured data were processed to calculate both the mean and variance, as shown in Equations (\u003cspan refid=\"Equ7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) and (\u003cspan refid=\"Equ8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Therefore, each data point in the graphs represents the average of the measured data, and a smaller variance indicates that the data set deviates less from the mean, making the data more reliable.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e.\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e\n$$\\:\\mu\\:=\\frac{{x}_{1}+{x}_{2}+\\cdots\\:{x}_{n}}{n}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ8\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ8\" name=\"EquationSource\"\u003e\n$$\\:\\delta\\:=\\sqrt{\\frac{1}{n}\\sum\\:_{i=1}^{n}{({x}_{i}-\\mu\\:)}^{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this study, we presented a FTEGs wearable wristband based on SWCNTs. Through a meticulous fabrication process, a uniformly dispersed carbon nanotube film with excellent electrical conductivity was obtained. Utilizing COMSOL Multiphysics for simulation and optimization, the thermoelectric wristband demonstrated promising thermoelectric conversion performance. By fabricating a thermoelectric wristband and conducting tests, it was shown that the maximum output power of the wristband reached 10.7 \u0026micro;W at a temperature difference of 36.5 K. This thermoelectric wristband proposes an effective solution in the field of carbon-based thermoelectric wearable devices. Future research will focus on further optimizing the material composition and device structural design, aiming to enhance the output power and improve long-term durability.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e6.\u003c/strong\u003e \u003cstrong\u003eContributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eX.D.S. nvestigation,Methodology,Writing – original draft, Y.Z.Q.\u0026nbsp;,\u0026nbsp;Y.R.W\u0026nbsp;and Y.W.S\u0026nbsp;Writing – review \u0026amp; editing,\u0026nbsp;M.Z.Y., D.Y.C.\u0026nbsp;Methodology,\u0026nbsp;G.S.\u0026nbsp;Funding acquisition,Methodology,Project administration,Resources,Supervision,Writing – review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e7.\u003c/strong\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research is supported by the National Natural Science Foundation of China, China under Grant 62334006, Grant 62271275, Grant 62131010 and Grant U22A2013 in part by the Zhejiang Provincial Natural Science Foundation of China, China under Grant LR22F010001, the Project of Scientific and Technological Plan of Zhejiang Province, China under Grant 2024C01, and the Project of Jiaxing Science and Technology , Grant 2023AY11027,Project of the Zhejiang Provincial Department of Education, Grant Y202250242.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e8.\u003c/strong\u003e\u003cstrong\u003eDeclaration of Competing interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e9.\u003c/strong\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data supporting the plots in this paper are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e10.\u003c/strong\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespondence\u003c/strong\u003e and requests for materials should be addressed to Ge Shi or Yizhou Qi.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReprints and permissions information\u0026nbsp;\u003c/strong\u003eis available at www.nature.com/reprints.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePublisher’s note\u0026nbsp;\u003c/strong\u003eSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institu-tional affiliations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOpen Access\u0026nbsp;\u003c/strong\u003eThis article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permit-ted by statutory regulation or exceeds the permitted use, you will need toobtain permission directly from the copy-right holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eVan Toan, N., Tuoi, K., Ono, T. \u0026amp; T. T. \u0026amp; High-performance flexible thermoelectric generator for self-powered wireless BLE sensing systems. \u003cem\u003eJ. 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Integration of tau-shaped fins and perforated polyimide substrate for enhanced power output in flexible thermoelectric generator for human body heat harvesting. (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHong, M. et al. Advances in printing techniques for thermoelectric materials and devices. \u003cem\u003eSoft Sci.\u003c/em\u003e \u003cb\u003e3\u003c/b\u003e, (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eContributions.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003envestigation, X. D. S. Methodology,Writing \u0026ndash; original draft, Y.Z.Q., Y.R.W and Y.W.S Writing \u0026ndash; review \u0026amp; editing, M.Z.Y., D.Y.C. Methodology, G.S. Funding acquisition,Methodology,Project administration,Resources,Supervision,Writing \u0026ndash; review \u0026amp; editing.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6259525/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6259525/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSingle-walled carbon nanotubes (SWCNTs) have attracted increasing attention in wearable thermoelectric devices due to their extremely high strength and toughness. Here we introduce a flexible thermoelectric wearable wristband based on SWCNTs. High-performance SWCNTs films were successfully fabricated through ultrasonic dispersion and heat-pressing processes, exhibiting a Seebeck coefficient of 42.5\u0026micro;V/K and a maximum electrical conductivity of 3503 S/cm. The flexible films showed excellent bending durability with less than 9.5% Seebeck coefficient loss after 400 cycles\u0026zwnj;. The width and length of the thermoelectric legs were optimized, and a wearable thermoelectric wristband was simulated by connecting the legs in series, thereby analyzing its total output power. Furthermore, a thermoelectric wristband was fabricated by spin-coating onto a flexible printed circuit (FPC) substrate, and it achieved a maximum output power of 10.7\u0026micro;W under a temperature difference of 36.5 K. This research provides an efficient and feasible energy harvesting pathway for utilizing carbon-based materials as thermoelectric materials.\u003c/p\u003e","manuscriptTitle":"A Thermoelectric Wristband Based on Single-Walled Carbon Nanotubes for Energy Harvesting","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-14 17:04:33","doi":"10.21203/rs.3.rs-6259525/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-30T10:02:06+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-26T18:10:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"218990000657962332721042006460953768474","date":"2025-06-12T23:27:42+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-01T06:03:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"115877367369761907974842342010435128395","date":"2025-03-31T09:26:40+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-27T00:21:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-27T00:17:02+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-03-26T16:56:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-25T07:23:28+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-03-25T07:22:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"46e77200-4aa5-4d70-89dd-bd2d5422851d","owner":[],"postedDate":"April 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":46880586,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials/Carbon nanotubes and fullerenes"},{"id":46880587,"name":"Physical sciences/Energy science and technology/Energy harvesting/Devices for energy harvesting"}],"tags":[],"updatedAt":"2025-07-28T16:03:08+00:00","versionOfRecord":{"articleIdentity":"rs-6259525","link":"https://doi.org/10.1038/s41598-025-12751-8","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-07-23 15:58:00","publishedOnDateReadable":"July 23rd, 2025"},"versionCreatedAt":"2025-04-14 17:04:33","video":"","vorDoi":"10.1038/s41598-025-12751-8","vorDoiUrl":"https://doi.org/10.1038/s41598-025-12751-8","workflowStages":[]},"version":"v1","identity":"rs-6259525","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6259525","identity":"rs-6259525","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}