Carbon Nanotube Sheets Research Articles

Improvement of Electrical and Thermal Properties of Carbon Nanotube Sheets by Adding Silver Nanowire and Mxene for an Electromagnetic-Interference-Shielding Property Study.

Hybrid carbon nanotube (CNT) sheets were fabricated by mixing CNTs with silver nanowires (AgNWs) and MXene to study their electromagnetic-interference (EMI)-shielding properties. CNT/AgNW and CNT/MXene hybrid sheets were produced by ultrasonic homogenization and vacuum filtration, resulting in free-standing CNT sheets. Three different weight ratios of AgNW and MXene were added to the CNT dispersions to produce hybrid CNT sheets. Microstructure characterization was performed using scanning electron microscopy, and the Wiedemann-Franz law was used to characterize transport properties. The resulting hybrid sheets exhibited improved electrical conductivity, thermal conductivity, and EMI-shielding effectiveness compared to pristine CNT sheets. X-band EMI-shielding effectiveness improved by over 200%, while electrical conductivity improved by more than 1500% in the hybrid sheets due to a higher charge-carrier density and synergistic effects between nanomaterials. The addition of AgNW to CNT sheets resulted in a large improvement in electrical conductivity and EMI shielding; however, this may also result in increased weight and sample thickness. Similarly, the addition of MXene to CNT sheets may result in an increase in weight due to the presence of the denser MXene flakes.

Self-Supporting Microporous Layer for Polymer Electrolyte Fuel Cells Using Thin Carbon Mesh Gas Diffusion Layer

The gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs) are relatively thick compared with the electrocatalyst layer and electrolyte membrane. Reducing GDL thickness is expected to reduce gas transport resistance. Such thin GDLs with high electrical conductivity enable higher power density per volume of cell stacks. Here, thin MPL/GDLs are fabricated by printing a highly conductive microporous layer (MPL) on carbon meshes or carbon nanotube sheets as a substrate to create tailored self-supporting MPLs. The electrical conductivity was improved by optimizing the carbon black material used in the MPL, and carbon nanotubes were added to tailor a pore structure within the MPL. The thickness of the resulting MPL/GDLs is approaching 50 µm, which is not only thinner than the current MPL/GDL, but also results in lower gas transport resistance. The thinner MPL/GDLs are a promising solution to increase the power density of PEFC cell stacks.

Design Strategies for High Performance of Proton Exchange Fuel Cells with Ti‐Sputtered Carbon Nanotube Sheet Functional Layer

Design Strategies for High Performance of Proton Exchange Fuel Cells with Ti‐Sputtered Carbon Nanotube Sheet Functional Layer

Effect of Self‐Incandescent Heating on Superconducting NbN Nanowire Yarn

AbstractA flexible superconducting yarn composed of twisted niobium nitride (NbN) nanofibrils is developed and exhibited a superconducting transition temperature that met the reported record of ≈17 K. NbN is sputter‐deposited onto a template of aligned single‐layer carbon nanotube (CNT) sheets and subsequently processed by post‐Joule heat annealing following the insertion of twists. Considering self‐Joule heating approaches the level of incandescent light emission, the melting, reflow, and recrystallization of the NbN layer around each CNT template occurred, considerably enhancing the macroscopic superconducting properties of the NbN nanofibrillar yarn, including the critical current density and critical magnetic field. Furthermore, the superconducting performance, which degrades as a result of mechanical damage to the internal structure under excessive stress such as bending, can be restored by the reflow of the NbN during this process. Considering the melting point of NbN is higher than 2800 K, the proposed incandescent light‐emission‐driven Joule self‐heating process is considered an effective method for improving the properties of CNT‐templated metal hybrid yarns.

Biscrolled hierarchical hybrid structure of PEDOT:PSS/CNTs-NMP yarn based solid state linear supercapacitor for wearable e-textile

The environmental friendly flexible solid state linear supercapacitor (FSLSc) based on the hierarchical hybrid yarn with core-shell type structure of poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) and hydrophilic carbon nanotubes (CNTs) sheet, fabricated using novel biscrolling technique is proposed. The hierarchical hybrid yarn structure of the electrode establishes the improved electrochemical interface of PEDOT:PSS with the both the hydrophilic CNTs and an aqueous PVA/H3PO4 gel electrolyte. The exterior surface of the yarn electrode rich in PEDOT:PSS which interact with ions from electrolyte and stores charges faradaically while the core region with dense CNTs yarn contributes with its multifunctional capabilities such as EDLC type capacitor, current collector and mechanical support. The observed two-fold decrease in ESR value (∼49Ω) and two-fold increase in capacitance (∼112.76 F/g) for hybrid yarn electrode with N-methyl-2-pyrrolidone (NMP) treated hydrophilic CNTs compared to the one with pristine CNTs, confirms the improved interface of PEDOT:PSS formed with hydrophilic CNTs and aqueous electrolyte. The FSLSc devices with NMP treated CNTs hybrid yarn electrodes exhibited excellent electrochemical performance in terms of the maximum power and energy density of 980 W/kg and 3.799 Wh/kg, respectively. The FSLSc displayed remarkable cycling performance upto 5000 cycles of charge-discharge and a robust bending stability after 1000 bending cycles, making it promising for practical application of the next-generation flexible solid state electrochemical energy storage in e-textiles.

Nano-welded carbon nanotube sponges for efficient oil spill remediation

Carbon nanotube (CNT) sponges are valuable for oil spill cleanup, yet their scalable production poses a notable challenge. This research presents an innovative and an energy efficient method to create CNT sponges from CNT sheets, enhancing their oil absorption capacity and mechanical durability. The method involves a direct foaming approach employing hydrazine hydrate and ethanol to induce porosity within densely arranged CNT films. Use of hydrazine generates voids in the CNT network and functions to reduce any surface oxygen functionalities, which impart it superhydrophobicity, as depicted by water contact angle of 142°. To enhance the mechanical properties of the CNT sponge, nanoscale welding is implemented using amorphous carbon, which resulted in 109% and 113% improvement in the ultimate compressive strength and modulus, respectively. The sponge demonstrated a remarkable oil absorption capacity exceeding 200 times its weight, along with an impressive absorption capability of 130 times for organic solvents like dichloromethane and chloroform, marking a substantial enhancement compared to existing alternatives. Moreover, the sponge's reusability was assessed through oil squeezing tests, retaining its performance across five cycles. The material's unique properties make it a promising solution for various environmental and industrial applications.

Unique correlation between electrical, structural properties and electromagnetic shielding properties of carbon nanotube sheets

Correlation between electrical, structural properties and electromagnetic shielding efficiency (EMI SE) of carbon nanotube sheets (CNTSs) was investigated. Solvent densification of CNTSs led to enhancements of carbon nanotube (CNT) bundling behavior and densification in the thickness direction while maintaining the areal density of the CNTSs. These structural modifications resulted in enhanced electrical properties and reduced sheet thickness by modifying the microstructure and bundling characteristics. Remarkably, contrary to conventional EMI shielding materials, the sheet resistance which reflects bundling behavior and microstructure of CNTSs, is the critical factor affecting the EMI SE of the CNTSs rather than electrical conductivity. The findings provide fundamental insights essential for the design of EMI shielding films incorporating CNTs.

Strengthening sandwich composites by laminating ultra-thin oriented carbon nanotube sheets at the skin/core interface

Strong, tough, and lightweight composites are increasingly needed for diverse applications, from wind turbines to cars and aircraft. These composites typically contain sheets of strong and high-modulus fibers in a matrix that are joined with other materials to resist fracture. Coupling these dissimilar materials together is challenging to enhance delamination properties at their interface. We herein investigate using a trace amount of carbon nanotube sheets to improve the coupling between composite skins and core in a composite sandwich. Ultra-thin (∼100 nm) forest-drawn multi-walled carbon nanotube (MWNT) sheets are interleaved within the skin/core interphase, with MWNTs aligned in the longitudinal direction. The mechanical behavior is characterized by end-notched flexural testing (ENF). With two MWNT sheets placed in the skin/core interphase, the following performance enhancements are achieved: 36.8 % increase in flexural strength; 127.3 % and 125.7 % increases in mode I & II fracture toughness values, respectively; and 152.8 % increase in interfacial shear strength (IFSS). These are achieved with negligible weight gain of the composite sandwich (0.084 wt% increase over the baseline sandwich without MWNT sheets). The finite element simulation results show that MWNT sheets enhance the skin/core coupling by reducing stress concentration, enabling the transition from catastrophic brittle failure to a stable ductile failure mode. The MWNT sheets interleaved sandwich composites are thus demonstrated to be stronger and tougher while providing electrical conductivity (4.3 × 104S/m) at the skin/core interface for potential de-icing, electromagnetic interference shielding, and structural health monitoring.

Simulating lightning effects on carbon fiber composite shielded with carbon nanotube sheets using numerical methods

The demand for lightweight aircraft structures has shifted from traditional metals like aluminum to composite materials such as carbon fiber reinforced polymers (CFRP) to achieve weight reduction. However, this transition has led to decreased lightning strike protection efficiency due to the dielectric nature of CFRP. To address this problem, two CFRP samples—one unprotected and the other shielded with carbon nanotube (CNT) sheets—were subjected to artificial lightning strike testing. The research employed a coupled thermal-electrical finite element analysis method to investigate the lightning strike's impact and damage mechanisms on both samples. The numerical results closely aligned with published experimental data, validating the simulation. Unprotected CFRP sustained damage through the thickness direction up to 8 composite plies and in-plane direction over a length of 110 mm. In contrast, the sample protected with CNT sheets exhibited damage limited to the surface of the first 4 plies, with in-plane damage reduced to 24 mm. Notably, the damage area in the CFRP protected with CNT sheets showed a substantial 78.1 % reduction compared to the unprotected CFRP sample. This suggests that CNT can enhance the electrical conductivity of CFRP when incorporated between interlayers in both in-plane and thickness directions. The study enhances understanding of CFRP damage behavior and failure modes under lightning strike conditions, emphasizing CNT sheets as an improved and viable lightning strike protection system for aerospace applications, warranting further investigation.

Underwater Thermoacoustic Generation by a Hierarchical Tetrapodal Carbon Nanotube Network.

Solid-state fabricated carbon nanotube (CNT) sheets have shown promise as thermoacoustic (TA) sound generators, emitting tunable sound waves across a broad frequency spectrum (1-105 Hz) due to their ultralow specific heat capacity. However, their applications as underwater TA sound generators are limited by the reduced mechanical strength of CNT sheets in aqueous environments. In this study, we present a mechanically robust underwater TA device constructed from a three-dimensional (3D) tetrapodal assembly of carbon nanotubes (t-CNTs). These structures feature a high porosity (>99.9%) and a double-hollowed network of well-interconnected CNTs. We systematically explore the impact of different dimensions of t-CNTs and various annealing procedures on sound generation performance. Furnace-annealed t-CNTs, in contrast to directly resistive Joule heating annealing, provide superior, continuous, and homogeneous hydrophobicity across the surface of bulk t-CNTs. As a result, the t-CNTs-based underwater TA device demonstrates stable, smooth, and broad-spectrum sound generation within the frequency range of 1 × 102 to 1 × 104 Hz, along with a weak resonance response. Furthermore, these devices exhibit enhanced and more stable sound generation performance at nonresonance frequencies compared to regular CNT-based devices. This study contributes to advancing the development of underwater TA devices with characteristics such as being nonresonant, high-performing, flexible, elastically compressible, and reliable, enabling operation across a broad frequency range.

Integrated Electrostimulation Cell Culture Systems Driven by Chemically Modified Twistron Mechanical Energy Harvesting Electrodes

AbstractDeveloping mechanical energy harvesters for electrical stimulation (ES) needed to augment cell behavior is a burgeoning area of interest. Mechanical energy harvesters that can generate electrical energy in electrolyte‐containing aqueous environments offer a unique solution for delivering ES to cells. In this work, a fully integrated ES assembly (FESA) is introduced that comprises coiled polydopamine (PDA) containing carbon nanotube yarn (CNT) harvesters, serving as ES generators, and poly(3,4‐ethylenedioxythiophene) coated carbon nanotube (PEDOT/CNT) sheets employed as a conductive scaffold. The PDA containing CNT (PDA/CNT) yarn, a novel twistron electrode, achieves an enhanced electrical power at a lower matching impedance than coiled CNT yarn to efficiently transfer ES to the conductive scaffold. The PEDOT used for the scaffold provides a suitable surface for cell adhesion and low resistance for effective ES transmission. In addition, the upscaled array of coiled PDA/CNT yarns provides an ES current density range up to 75.4 µA cm−2, which is much higher than for ES systems using different mechanical energy harvesters. This FESA is designed to provide an optimal level of ES for the proliferation and differentiation of chondrocytes. The findings illuminate the potential of chemically modified twistron energy harvesters as an innovative and effective strategy to promote biological response.

Facile and Nondestructive Transformation of Intrinsic Hydrophobic Behavior of a Carbon Nanotubes Sheet to Hydrophilic.

It is imperative to induce hydrophilicity in intrinsically hydrophobic carbon nanotubes (CNTs) without losing their superior properties for applications that specifically deal with aqueous media. A method for transforming a CNTs sheet from hydrophobic to hydrophilic by treatment with N-methyl-2-pyrrolidone (NMP) is explored. The NMP-treated CNT sheets are assessed based on complementing characterization, and it is concluded that the binding of NMP to a CNTs surface is through noncovalent interaction without the incorporation of defects in CNTs. The induced hydrophilicity in the CNTs sheet is stable for water exposure over a longer duration while it displays a semireversible nature upon heat treatment. The mechanical and electrical properties of the NMP-treated CNTs sheet revealed enhancement in the tensile strength from 221 to 421 MPa while maintaining a good electrical conductivity of ∼1.22 × 104 S/m because of the improved interfacial properties. The hydrophilic CNTs exhibited excellent adsorption capacity for methylene blue dye. The NMP-treated CNTs sheets demonstrated their suitability in flexible hybrid supercapacitor (FHSC) devices with improved electrochemical performance with enhancement in the capacitance from 5.4 to 7.6 F/g and a decrease in the equivalent series resistance from 53 to 34 Ω compared to pristine CNTs-based devices. These solid-state FHSC devices displayed excellent cyclic charge-discharge performance along with robust behavior over thousands of bending cycles without significant performance degradation. The excellent dye removal capability and superior electrochemical performance of the NMP-treated CNTs sheet is a consequence of their improved interface with aqueous media, which is governed by the hydrophilic nature of the CNTs sheet.

Pristine and Coated Carbon Nanotube Sheets—Characterization and Potential Applications

A carbon nanotube (CNT) sheet is a nonwoven fabric that is being evaluated for use in different textile applications. Several properties of pristine CNT sheets and CNT sheets coated with a polysilazane sealant and coating were measured and compared in the paper. The polysilazane coating is used to reduce the shedding of CNT fibers from the sheet when the sheet is in contact with surfaces. Most fabrics show some shedding of fibers during the washing or abrasion of the fabric. This study showed that the coating reduces the shedding of fibers from CNT fabric. The coating also increased the flame resistance of the fabric. The pristine and coated sheets both have low strength but high strain to failure. The pristine and coated CNT sheet densities are 0.48 g/cc and 0.65 g/cc, respectively. The pristine CNT sheet is approximately 27 μ thick. The coated sheet is approximately 24 μ thick. The coating may have densified the sheet, making it thinner. The thickness of the compliant sheets was difficult to measure and is a source of error in the properties. Characterization results are given in this paper. The results are for comparison purposes and not to establish material properties data. Possible applications for CNT sheets are briefly discussed.

Assessment of carbon nanotube sheet densification level

Assessment of carbon nanotube sheet densification level

Highly stretchable conductor with elastomeric passivation sheath enabling applications in harsh conditions

The rapid development of robotics requires stretchable electrical conductors capable of large deformations and having high operational stability in terms of electrical and mechanical characteristics. Carbon nanotubes (CNT) have been considered as the primary component of stretchable conductors, and mechanically drawn CNT sheets have shown their functionality when combined with various elastomeric materials in the shape of yarns. Herein, an electrically passivated stretchable conductor with an elastomer sheath and a spandex–CNT coiled-yarn core structure is reported. Based on the proven performance of spandex–CNT coiled-yarn, the electrical insulation by the Ecoflex elastomer enhances its applicability in an actual situation without degrading the stretchable conductor functionality. The experimental results show a substantial working deformation range (up to 350%), high durability, and low resistance variation during repetitive stretch and release cycles. Additionally, its stability is confirmed over a wide temperature range (up to 150 °C) and even inside an acidic liquid environment where the elastomeric sheath protects the conducting core. The perfect cooperation between the Ecoflex sheath and spandex–CNT core opens the possibility of deploying this stretchable conductor technology under harsh conditions.

Direct-spun carbon nanotube sheet: A flexible, ultralight, stackable three-dimensional current collector for high-performance lithium-ion batteries

Among the key components of a battery electrode, current collectors hold significant importance for the energy density of lithium ion batteries (LIBs) as metal foils account for a significant proportion of the total mass. Carbon nanotube sheet (CNTS) has garnered considerable attention because of its fascinating material features such as high electrical conductivity, low density, and excellent flexibility. In this study, we demonstrate the utilization of a direct-spun CNTS as a current collector in order to enhance the electrochemical performance and replace the conventional current collector, that is, aluminum (Al) foil, in LIBs. When the CNTS coated with NCM811 (NCM811/CNTS) is evaluated in LIBs, it delivers superior rate capability and cycle stability compared with Al foil-based and buckypaper-based NCM811 electrodes. It is because the CNTS with a large surface area and high electrical conductivity establishes a number of electronic pathways to the cathode electrode. In addition, the porous structure of the CNTS efficiently enhances the adhesive properties of the electrodes. Due to the synergistic benefits of CNTS, cells with stacked NCM811/CNTS electrodes are successfully fabricated. Electrode stacking with multiple NCM811/CNTS electrodes exhibits improved areal capacity and stable cycle stability, suggesting a new strategy to replace the concept of conventional thick electrodes. Moreover, pouch cells with LTO/CNTS as an anode and NCM811/CNTS as a cathode display stable electrochemical performance even under mechanical deformation (e.g., folding/unfolding)

Investigation of carbon nanotube sheet for lunar dust shielding

Carbon nanotubes (CNT) sheet is a new type of nonwoven fabric that is being evaluated for different applications. This article presents the first friction-based investigation of the use of CNT sheet as a dust shield. The focus application is for shielding future machinery on the moon from lunar dust. Lunar dust is strongly abrasive; it adheres to all surfaces and causes wear. The absence of an atmosphere and water on the moon, along with its low gravity, and electrostatic adhesion exacerbates the issue of lunar dust, which affects all surfaces, including machinery and human apparel. Friction testing was performed to represent the effect of abrasion occurring on a garment surface while astronauts are working on the moon. The coefficients of static and sliding friction between two CNT sheets, held against each other by a weight, were 0.6 and 0.45, respectively. The presence of lunar regolith simulant reduced the friction coefficients between the two CNT sheets by 33% and 22% for static and sliding friction, respectively. The dust in the sheets was easily cleaned with dry wiping and compressed air, showing no requirement to use water for cleaning in space applications. However, the CNT sheets experienced wear after repeated friction tests. The CNT sheets passed the flammability test standards ASTM D6413/D6413M-15 and NPFA 1971 for applications under extreme heat conditions. Thus, CNT sheet can be considered as a multi-functional material for lunar applications, with shielding protection against dust and electromagnetic waves, and resistance to high temperatures.

Improved Performance of High‐Temperature Proton Exchange Membrane Fuel Cells by Purified CNT Nanoporous Sheets

AbstractGiven environmental friendliness, high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) can be the alternative power source for clean power generation. However, neither developments nor strategies of diffusion media are actively conducted yet to achieve high‐performance HT‐PEMFCs. Herein, a nanoporous carbon nanotube (CNT) sheet, a new anode diffusion layer between the gas diffusion layer|bipolar plate interface that improves fuel cell performance and durability by CNT purification for facilitating fuel accessibility with uniform interfacial contact for reducing acid loss, is reported. Configuration of the optimal CNT‐inserted fuel cell is examined and proposed under the operating temperature of 140–200 °C. The underlying mechanism of this new diffusion layer with multiphysics simulation elucidates that the nanoporous nature induces gas‐wall collision, enabling uniform dispersion within adjacent diffusion media. These fuel cells outperform performance over two times higher and have a voltage decay rate nearly two times lower than conventional HT‐PEMFC.

Transition of Carbon Nanotube Sheets from Hydrophobicity to Hydrophilicity by Facile Electrochemical Wetting

The present study delves into the transformative effects of electrochemical oxidation on the hydrophobic-to-hydrophilic transition of carbon nanotube (CNT) sheets. The paper elucidates the inherent advantages of CNT sheets, such as high electrical conductivity and mechanical strength, and contrasts them with the limitations posed by their hydrophobic nature. A comprehensive investigation is conducted to demonstrate the efficacy of electrochemical oxidation treatment in modifying the surface properties of CNT sheets, thereby making them hydrophilic. The study reveals that the treatment not only is cost-effective and time-efficient compared to traditional plasma treatment methods but also results in a significant decrease in water contact angle. Mechanistic insights into the hydrophilic transition are provided, emphasizing the role of oxygen-containing functional groups introduced during the electrochemical oxidation process.

Electrochemically Oxidized Carbon Nanotube Sheets for High-Performance and Flexible-Film Supercapacitors.

The development of flexible, high-performance supercapacitors has been a focal point in energy storage research. While carbon nanotube (CNT) sheets offer promising mechanical and electrical properties, their low electrical double-layer capacitance significantly limits their practicability. Herein, we introduce a novel approach to address this challenge via the electrochemical oxidation treatment of CNT sheets stacked on a polyethylene terephthalate substrate. This introduces oxygen-containing functional groups onto the CNT surface, thereby dramatically enhancing the pseudocapacitive effect and improving ion adsorption. Consequently, using the material in a two-electrode system increased the capacitance by 54 times compared to pristine CNT. The results of electrochemical performance characterization, including cyclic voltammograms, galvanostatic charge/discharge curves, and capacitance retention testing data, confirm the efficacy of the electrochemical oxidation approach. Furthermore, the mechanical flexibility of the electrochemically wetted CNT sheets was validated through resistance and discharge retention testing under repetitive bending (98% capacitance retention after 1000 bending cycles). The results demonstrate that electrochemically wetted CNT sheets retain their intrinsic mechanical and electrical properties while significantly enhancing the electrochemical performance (0.59 mF/cm2 or 97.8 F/g). This work represents a significant advancement in the development of flexible, high-performance supercapacitors with potential applicability to wearable electronics, flexible displays, and next-generation energy storage solutions.