Carbon Nanotube Fibers Research Articles

Statistical Analysis of Intertube Tunneling Contacts in the Macroscopic Electrical Conductivity of Carbon Nanotube Fibers

Statistical Analysis of Intertube Tunneling Contacts in the Macroscopic Electrical Conductivity of Carbon Nanotube Fibers

Optimized Thermal Oxidation Strategy for Amorphous Carbon Removal in Wet-Spun Carbon Nanotube Fibers

Optimized Thermal Oxidation Strategy for Amorphous Carbon Removal in Wet-Spun Carbon Nanotube Fibers

An optical carbon nanotube fibre probe for measurement of nano structures with large aspect ratio

An optical carbon nanotube fibre probe for measurement of nano structures with large aspect ratio

Versatile and Fast Electrochemical Activation Method for Carbon Nanotube Fibers with Diverse Active Materials.

In this study, the challenge of non-electrochemical activity in carbon nanotube fibers (CNTFs) is addressed by developing a modified chlorosulfonic acid (CSA) densification process specifically developed for directly spun CNTFs. This post-treatment method, well-known for enhancing the physical properties of CNTFs, utilizes the double diffusion phenomenon to efficiently integrate a diverse range of active materials, from conductive polymers like polyaniline (PANI) to metal oxides like nickel oxide (NiO), into the fibers. This universal and cost-effective approach not only simplifies the integration process but also significantly boosts both the electrochemical and physical properties of the fibers. For instance, the PANI@CNTF composite exhibited a remarkable 17-fold increase in specific capacitance and a two-fold increase in load value compared to its pristine counterparts. This method proves straightforward, efficient, and versatile, making it suitable for developing fiber-shaped electrodes that advance the capabilities of wearable energy storage systems.

(Invited) Fabricating High Performance Fiber-Shaped Supercapacitor from the State-of-the-Art Carbon Nanotube Fiber

Fiber shaped supercapacitors are being actively developed as one of the most robust power supplies available for wearable and portable applications [1,2]. The development of fiber shaped current collector with excellent flexibility, light weight, chemical stability and good conductivity has become very important. CNT fibers (CNTF) has been highlighted as a superior core component, with highly densified and aligned structure [3]. Newly developed state-of-the-art CNTF exhibits unprecedentedly high performance, such as high strength (100 cN tex-1), electrical conductivity (2 MS m-1) and excellent flexibility (50% knot efficiency), which could not be realized in the previous version of CNTF [4]. Therefore, novel strategy must be developed to be applied for this utmost CNTF with low surface area and very smooth surface with few functional groups.In this talk, we introduce a simple and efficient strategy to construct a hybrid 3D structure on a fiber-shaped support material for a high-performance FSSC [5]. A state-of-the-art liquid crystal spun CNTF with a highly densified structure and high electrical conductivity was utilized as the basic core component of FSSC. To fabricate a stereoscopic hybrid 3D structure, GO and/or Mxene, which are the most representative 2D materials, were vertically attached to CNTF by electrophoretic deposition as a hierarchical scaffold for further hybridization. It was very important to further deposit pseudocapacitive active materials immediately after the deposition of GO to solidify and maintain the 3D structure of GO, which is simple but highly efficient. The prepared Ni-Co oxide/VG@CNTF (NC/VG@CNTF) hybrid electrode exhibits prominent specific capacitance (1724 F g-1 at 1 A g-1, total electrode weight) and mechanical durability (93.1% capacitance retention at 5,000 bending cycles). Remarkably, FCCSs fabricated with asymmetric configurations show unprecedentedly high energy and power densities, demonstrating the superiority of our proposed strategy (energy density of 65 Wh kg-1 at a power density of 100 kW kg-1). This demonstrates that state-of-the-art CNTF can be an excellent candidate suitable for various wearable and flexible applications. Acknowledgements This research was supported by Korea Institute of Science and Technology (KIST) Institutional Program and Open Research Program (ORP), and grants from the National Research Foundation of Korea government (NRF, 2019R1A5A8080326).

Active Material-Free Continuous Carbon Nanotube Fibers with Unprecedented Enhancement of Physicochemical Properties for Fiber-Type Solid-State Supercapacitors

The continuous evolution of wearable and flexible devices has driven the need for resilient energy storage systems that can uphold their power and energy density amidst varying mechanical deformations. Among the diverse energy storage mediums, fiber-type solid-state supercapacitors (FSSCs) have been spotlighted for their potential in wearable energy storage, thanks to their inherent capability to blend into diverse structural forms, mirroring the versatility of traditional fibers [1]. In this context, Carbon nanotube fibers (CNTFs) produced through a wet-spinning process based on the liquid crystalline (LC) phase emerge as an ideal electrode material, given their remarkable electrical conductivity, mechanical robustness, and unmatched flexibility [2].While the excellent physical properties of CNTFs is undeniably compelling, their electrochemical inactivity has been a persistent hurdle in realizing their full potential in FSSC applications. Most prior studies have aimed to circumvent this by modifying the fiber’s surface with active materials, such as metal oxides [3] and conductive polymers [4], to serve as energy storage sites. Despite its successes, this approach has been plagued by issues like active material detachment during long-term usage and, more importantly, increasing processing costs due to the need for additional materials and process.In this study, we have pioneered a new approach to enhance the electrochemical activity of LC spun CNTFs without the need for additional post-processing or active materials, addressing the challenge of the sp2 carbon surface's limitations. Through strategic surface functionalization and subsequent LC phase development of CNTs, an unprecedented high-concentration dope (i.e., 160 mg/mL) for wet-spinning was realized. Leveraging high-concentration dope, the as-spun functionalized CNTF (F-CNTF) exhibits more aligned and densely packed structures compared to raw CNTF, resulting in significantly improved mechanical and electrical properties. While the raw CNTF exhibited a specific capacitance of 4.2 F/g at 0.5 A/g, the electrochemically activated F-CNTF, bearing enhanced physicochemical properties, demonstrated a high specific capacitance of 139.4 F/g at the same charge-discharge rate, all without any active materials or post-processing. For practical application, we integrated symmetric FSSCs using F-CNTFs into a textile and used it as a power source for a 1.5 V digital clock, which was operating effectively for over 15 minutes. Additionally, wrist straps integrated with F-CNTF FSSCs could function effectively as a power source even when folded, rolled, or worn on the wrist. This study not only highlights the potential for efficient, mass-produced fiber-type energy storage electrodes but also marks a significant departure from the conventional, non-economical sheath-core strategy, paving the way for more sustainable and efficient energy storage solutions in wearable technology.[1] A. Fakharuddin, H. Li, F. Di Giacomo, T. Zhang, N. Gasparini, A. Y. Elezzabi, A. Mohanty, A. Ramadoss, J. Ling, A. Soultati, M. Tountas, L. Schmidt-Mende, P. Argitis, R. Jose, M. K. Nazeeruddin, A. R. B. Mohd Yusoff, M. Vasilopoulou, Fiber-Shaped Electronic Devices, Advanced Energy Materials (2021) 11, 2101443[2] N. Behabtu, C. C. Young, D. E. Tsentalovich, O. Kleinerman, X. Wang, A. W. K. Ma, E. A. Bengio, R. F. Ter Waarbeek, J. J. De Jong, R. E. Hoogerwerf, S. B. Fairchild, J. B. Ferguson, B. Maruyama, J. Kono, Y. Talmon, Y. Cohen, M. J. Otto, M. Pasquali, Strong, Light, MultifunctionalFibers of Carbon Nanotubes with Ultrahigh Conductivity, Science (2013) 339, 182[3] J.-G. Kim, D.-M. Lee, J. Y. Jung, M. J. Kim, M.-S. Khil, H. S. Jeong, N. D. Kim, Hybrid polyaniline/Liquid Crystalline CNT Fiber Composite for Ultimate Flexible Supercapacitors, ACS Applied Energy Materials (2021) 4, 1130[4] J.-G. Kim, H. Yu, J. Y. Jung, M. J. Kim, D.-Y. Jeon, H. S. Jeong, N. D. Kim, 3D Architecturing Strategy on the Utmost Carbon Nanotube Fiber for Ultra-High Performance Fiber-Shaped Supercapacitor, Advanced Functional Materials (2022) 32, 2113057

A Miniaturized Flexible Patch Based on CNT Fiber Sensors and Highly Integrated SoC for Analysis of Sweat

A Miniaturized Flexible Patch Based on CNT Fiber Sensors and Highly Integrated SoC for Analysis of Sweat

Innovative fabrication of CNT/SiC composite fibers via impregnation-wet twisting-pyrolysis: Advancements in strength, conductivity, and EMI shielding

Floating catalyst chemical vapor deposition (FCCVD) is a key method for synthesizing high-strength, electrically conductive carbon nanotube (CNT) fibers. However, the high porosity of FCCVD CNT fibers limits the full utilization of the intrinsic performance of CNTs. It remains a challenge to assemble and continuous fabricate high-performance CNT fibers. Herein, this study proposed an impregnation-wet twisting-pyrolysis process to fabricate continuous CNT/SiC composite fibers to enhance the mechanical and electrical properties by reducing pore sizes and improving the interaction between CNTs. The resulting compact structure and enhanced interfacial interactions of the CNT/SiC fibers exhibited both high strength (2015.27 MPa) and high electrical conductivity (7.2 × 105 S/m), representing increases of 130.8 % and 69.9 % compared to pristine CNT fibers. The unidirectional laminates assembled by continuous CNT/SiC fibers demonstrated high electromagnetic interference (EMI) shielding effectiveness of 66.33 dB. This innovative continuous process holds significant potential for the industrial utilization of CNT/SiC fibers.

The effects of CNT type, alignment and dopants on piezoresistance in CNT fibres

Carbon nanotube fibres (CNTF) are piezoresistive, hence heralded as deformation sensors in applications ranging from flexible touch sensors to artificial skins and robotics. This work studies the piezoresistive behaviour of a wide range of CNT fibres from different sources, processing routes and microstructures. It provides a unifying view of the factors controlling piezoresistance in CNT fibres and related nanocarbon networks. We clarify the role of alignment and concentration of dopants and the constituent CNT type, demonstrating that the origin of piezoresistance in aligned fibres is the direct deformation of the constituent nanotubes, therefore, it is governed by the bulk modulus and thus the degree of CNT alignment. Doping through intercalation, which does not affect modulus or CNT separation, is detrimental to piezoresistive sensing, reducing the gauge factor proportionally to its decrease in resistivity. Aligned fibres show a quasi-linear piezoresistive response, with a positive change in resistance for all deformation modes applied: axial tension, axial or transverse compression. The axial gauge factor is shown to be proportional to fibre Young's modulus, with values of 2–9 for fibres spun from aerogels and above 30 for undoped fibres spun from liquid crystal solutions, respectively. Piezoresistance is attributed to the formation of internal barriers for conduction between metallic regions, which arise from the heterogeneous stress distribution along individual CNTs inherent in shear lag-type stress transfer. Commercial multifilament CNT yarns with a high degree of alignment and a format amenable for integration in large structures have demonstrated the piezoresistive gauge factors of 4 and sufficient sensitivity at strains below 1 % suitable for structural health monitoring of engineering structural composites.

Investigation into shear-thinning behavior in wet spinning of carbon nanotube fibers modeled by power law viscosity model

The wet spinning of carbon nanotube (CNT) fibers, a representative solution processing of CNTs, has been advanced through the integration of well-established polymer sciences into their field. However, the flow behavior of CNT dispersions in the narrow spinning line, where its characteristics undergo changes due to the high-shear rate regime, has not been utilized to determine their spinnability, despite being a commonly employed method in the wet spinning of polymer fibers. Herein, we employed the power law viscosity model to investigate the correlation between flow behavior and the spinnability of CNT dispersion through the power law index which approaches to 0 as the shear-thinning behavior strengthens. We suggest that the spinnability of CNT dispersion is proportional to the degree of shear-thinning behavior of the dispersion. We ascribe this correlation to the integrity of CNT fibers which predominantly rely on the strong van der Waals forces between CNTs. These findings offer new insights into the role of fiber integrity in spinnability and provide a framework for optimizing the wet spinning process of CNT fibers through detailed analysis of dispersion flow behavior.

Enhanced mechanical and electrical properties of single-walled carbon nanotube fibers via electric field-assisted wet spinning

Researchers have been working on creating fibers from single-walled carbon nanotubes (SWCNTs) that have optimal properties at the molecular level. However, the prepared SWCNT fibers have showed much lower properties than the ones predicted by theory because the interactions between SWCNTs and SWCNT bundles were not strong enough due to the poor alignment of SWCNTs in the fibers. In this study we improved the mechanical and electrical properties of the SWCNT fibers by using an electric field during the wet spinning process. The electric field, which was applied to the top of the syringe plunger and the tip of the spinneret, oriented the SWCNTs in the chlorosulfonic acid dope solution in a nozzle system, and made them more compact. The SWCNT fibers produced through our process exhibited a significant improvement in their properties. Specifically, we observed a 117.5 % increase in tensile strength and a 140.5 % increase in electrical conductivity. Importantly, these enhancements were achieved without the need for any additional post-treatments. This clearly demonstrates the effectiveness of our current wet spinning method.

Carbon‐Nanotube Microelectrodes for Electrochemical Determination of Melatonin

AbstractVoltammetric methods hold promise for the rapid and sensitive quantification of melatonin. This study reports the direct electrochemical quantification of melatonin using carbon nanotube (CNT) fiber cross‐sections as microelectrodes. Six identical highly densified CNT fiber cross‐sections were employed to quantify melatonin in the range of 0.05–100 μM. The limit of detection and quantification were 10 and 35 nM, respectively, with a sensitivity of 0.1322 nA/μM. Interference studies with uric acid, hypoxanthine, and ascorbic acid demonstrate its performance. Real‐world application was highlighted by measuring melatonin in food, pharmaceutical, and human urine samples.

Cobalt-Based Ferrite Modified Carbon Nanotubes Fibers for Flexible and Disposable Microelectrode Toward Electrochemical Glucose Sensing.

Glucose detection is critical in clinical health and the food industry, particularly in the diagnosis of blood sugar levels. Carbon-based fiber materials have recently featured prominently as non-enzymatic electrochemical glucose detectors. Herein, cobalt-based ferrite (CoFe2O4) in the form of nanoparticles has been successfully fabricated over the carbon nanotubes (CNTs) fiber via a simple hydrothermal process. Fabricated microelectrode (CoFe2O4@CNTs) was investigated as an electrocatalyst toward the non-enzymatic electrochemical glucose sensors. The structure and morphology of the modified fiber were studied by scanning electron microscopy including energy-dispersive X-ray spectroscopy. The electrochemical capability of the microelectrode was analyzed by using different electrochemical techniques including cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The proposed sensors exhibited a superb sensitivity of 0.21 µAcm-2 mM-1, a good linear range from 1 to 9mM, and a lower detection limit of 1.7mM. Further investigation via EIS indicated the low charge transfer resistance as compared to the bare CNTs-based fiber. Outcomes revealed that the material can potentially prove promising for the disposable microelectrode toward electrochemical glucose sensing.

Dual-Hydrogen Bond Donor-Functionalized Carbon Nanotube Fibers: Enhancing Anion-Sensing Performance Through Functionalization Approaches.

In this study, chemiresistive anion sensors are developed using carbon nanotube fibers (CNTFs) functionalized with squaramide-based dual-hydrogen bond donors (SQ1 and SQ2) and systematically compared the sensing properties attained by two different functionalization methods. Model structures of the selectors are synthesized based on a squaramide motif incorporating an electron-withdrawing group. Anion-binding studies of SQ1 and SQ2 are conducted using UV-vis titrations to elucidate the anion-binding properties of the selectors. These studies revealed that the chemical interaction with acetate (AcO-) induced the deprotonation of both SQ1 and SQ2. Selectors are functionalized onto the CNTFs using either covalent or non-covalent functionalization. For covalent functionalization, SQ1 is chemically formed on the surface of the CNTFs, whereas SQ2 is non-covalently functionalized to the surface of the CNTFs assisted by poly(4-vinylpyridine). The results showed that non-covalently functionalized CNTFs exhibited a 3.6-fold higher sensor response toward 33.33mm AcO- than covalently functionalized CNTFs. The selector library is expanded using diverse selectors, such as TU- and CA-based selectors, which are non-covalently functionalized on CNTFs and presented selective AcO--sensing properties. To demonstrate on-site and real-time anion detection, anion sensors are integrated into a sensor module that transferred the sensor resistance to a smartphone via wireless communication.

Mechanical properties of epoxy composites filled with multi-walled carbon nanotube, Nanoaluminum particles and glass fibers at elevated temperatures

The present work investigates the mechanical properties of a composite material composed of multi-walled carbon nanotubes (MWCNTs), nano-aluminum powder (NAP), and glass fibers (GF) for five different compositions. The study further investigated how MWCNTs contribute to maintaining the mechanical properties of nanocomposites when exposed to elevated temperatures, up to 180 °C. The evaluation of impact strength revealed that the nanocomposite, composed of 2 % MWCNTs, 15 % NAP, and 10 % GF, demonstrated the greatest impact strength. At room temperature, the composite containing 2 % MWCNTs, 5 % NAP, and 20 % GF exhibited the highest ultimate tensile strength (UTS). Conversely, at elevated temperatures reaching up to 180 °C, the highest UTS was observed in the composition with 2 % MWCNTs, 10 % NAP, and 15 % GF. The hardness of the nanocomposite was influenced by its composition; at room temperature, the maximum hardness was observed in the mixture containing 2 % MWCNTs, 20 % NAP, and 5 % GF. In contrast, at elevated temperatures, the composition with 2 % MWCNTs, 5 % NAP, and 20 % GF exhibited the highest hardness. Overall, the study found that incorporating GF and NAP improved the mechanical properties of the composite. These results indicate that the composite's performance could be further optimized for specific applications through the addition of filler materials.

Flexible and air-stable n-type oleylamine/carbon nanotube hybrid yarns for high-performance wearable thermoelectric generators

Wearable thermoelectric generators (TEGs), envisioned to harness the temperature gradient (ΔT) between the human body and the environment into electricity, hold great promise for powering wearable electronics. However, their practical application has been hampered by the scarcity of flexible n-type thermoelectric (TE) materials boasting both high performance and long-term air stability. Here, we introduce a significant advancement by developing an n-type TE material through immersing carbon nanotube yarn (CNTY) into an oleylamine (OAm)/ethanol solution, followed by drying under atmospheric conditions. The resulting OAm/CNTY exhibits a Seebeck coefficient of -80.48 μV K-1, an electrical conductivity of 1353.18 S cm-1 and a power factor of 876.25 μW m-1 K-2, all while exhibiting exceptional mechanical flexibility. Notably, this hybrid yarn maintains stable n-type behavior even after enduring exposure to air for over 370 days, surpassing previous n-type TE materials based on CNT fibers and CNTY. Leveraging this advancement, we construct a prototype wearable TEG by alternately embroidering pristine p-type CNTY and n-type OAm/CNTY into a polyester spacer fabric, electrically connecting them in series using conductive silver paint. The resulting wearable TEG, featuring with 150 p-n couples, yields an output voltage of 705.94 mV and a maximum output power of 44.34 μW at a ΔT of 40 K. This groundbreaking work opens new avenues for the development of high-performance, air-stable, and flexible n-type TE material, ushering in a new era for wearable TEGs.

Large-area and high-efficiency carbon nanotube/silicon heterojunction solar cells enabled by self-similar fiber electrodes and solid-state gel electrolytes

Carbon nanotube/silicon (CNT/Si) Van der Waals heterojunction solar cells have attracted increasing attention due to their low-cost, easy-fabrication process and potential use in next generation photovoltaics. Herein, we reported a high-performance and large-area solar cell fabricated using high-quality CNT films, self-similar CNT fibers and solid-state gel electrolytes. The power conversion efficiency of the fabricated device reached 13.1 % in an active area of 1 cm2, which is much higher than that of the pristine CNT/Si device (7.19 %). In this system, small-bundled and carbon-welding structure at inter-tube junctions enable the CNT film with excellent conductivity. The CNT fiber electrodes were adopted as front contact grids to further reduce the resistance of the CNT film owing to their high conductivity and self-similar microstructure. The solid-state gel electrolyte functions as a p-type dopant to enhance the conductivity of CNTs and the built-in potential at the heterojunction, meanwhile its antireflection property contributes to a significant improved photocurrent of the solar cells. This simple and effective way provides a facile route for developing high-performance, large-area CNT/Si Van der Waals heterojunction solar cells.

Multilayer Core-Shell Fiber Device for Improved Strain Sensing and Supercapacitor Applications.

1D fiber devices, known for their exceptional flexibility and seamless integration capabilities, often face trade-offs between desired wearable application characteristics and actual performance. In this study, a multilayer device composed of carbon nanotube (CNT), transition metal carbides/nitrides (MXenes), and cotton fibers, fabricated using a dry spinning method is presented, which significantly enhances both strain sensing and supercapacitor functionality. This core-shell fiber design achieves a record-high sensitivity (GF ≈ 4500) and maintains robust durability under various environmental conditions. Furthermore, the design approach markedly influences capacitance, correlating with the percentage of active material used. Through systematic optimization, the fiber device exhibited a capacitance 26-fold greater than that of a standard neat CNT fiber, emphasizing the crucial role of innovative design and high active material loading in improving device performance.

Stretchable and Self-Powered Mechanoluminescent Triboelectric Nanogenerator Fibers toward Wearable Amphibious Electro-Optical Sensor Textiles.

Flexible electro-optical dual-mode sensor fibers with capability of the perceiving and converting mechanical stimuli into digital-visual signals show good prospects in smart human-machine interaction interfaces. However, heavy mass, low stretchability, and lack of non-contact sensing function seriously impede their practical application in wearable electronics. To address these challenges, a stretchable and self-powered mechanoluminescent triboelectric nanogenerator fiber (MLTENGF) based on lightweight carbon nanotube fiber is successfully constructed. Taking advantage of their mechanoluminescent-triboelectric synergistic effect, the well-designed MLTENGF delivers an excellent enhancement electrical signal of 200% and an evident optical signal whether on land or underwater. More encouragingly, the MLTENGF device possesses outstanding stability with almost unchanged sensitivity after stretching for 200%. Furthermore, an extraordinary non-contact sensing capability with a detection distance of up to 35cm is achieved for the MLTENGF. As application demonstrations, MLTENGFs can be used for home security monitoring, intelligent zither, traffic vehicle collision avoidance, and underwater communication. Thus, this work accelerates the development of wearable electro-optical textile electronics for smart human-machine interaction interfaces.

Advanced doping method for highly conductive CNT fibers with enhanced thermal stability

Abstract Due to the inherent limitations of metals, such as their poor performance at high temperatures caused by thermo-oxidation and expansion, carbon nanotube yarns (CNTFs) have emerged as promising alternatives because of their high electrical conductivity and thermal stability. Doping of CNTFs has been widely studied because it significantly increases electrical conductivity through a simple process. Despite these advantages, doped CNTFs are not suitable for extreme environments, especially high temperatures. This is due to the weak interaction between dopants and CNTFs, along with the low thermal stability of the dopants themselves, leading to dopant decomposition and oxidation at high temperatures. Herein, we present doped CNTFs that are covalently functionalized with a nitrogen compound composed of imide and nitro groups, which are renowned for good thermal stability. The electron-withdrawing effect of this nitrogen compound polarizes the CNTFs to a positive charge, inducing p-type doping effects and enhancing electrical conductivity from 2989 to 4008 S cm−1. The strong covalent bonding between the nitrogen compound and CNTFs, along with the thermal stability of the dopants, ensures that the electrical conductivity of our doped CNTFs is maintained even after annealing at 300 °C for 12 h. Our proposed doped CNTFs offer a guideline for expanding the practical applications of doped CNTFs to a wider range of high-temperature environments.