Nanotube Sheets Research Articles

Localized Liquid Zones Assisted Highly Crystalline Single-Wall Carbon Nanotube Sheets: Implications for Conducting Shields in Coaxial Cables

The electrical conductivity of carbon nanotube (CNT) macro assemblies can be influenced by their crystallinity. Herein, we present the synthesis of high-quality SWCNT sheets for which an appropriate optimization parametric research of synthesis temperature, precursor flow rate, and H2 flow rate was carried out in this approach. It was found that highly crystalline SWCNT sheet (IG/ID = 180.3) was synthesized by floating catalyst chemical vapor deposition technique at 12 mL/h precursor flow rate and 1000 sccm H2 flow rate. Three distinct Raman laser wavelengths (514, 532, and 785 nm) were used to study the as-synthesized sheet, and the maximum calculated IG/ID ratio was found to be 180.3 (@ λ = 514 nm). Due to high concentration of H2 gas, the number of localized liquid zones or CNT nucleation sites increased which has an impact on both the quality as well as the diameter of CNTs. The I–V characteristics of CNT sheet were studied via four-probe technique, yielding a measured value of electrical conductivity of 9.21 × 106 S/m. Further, the R-T measurement showed the positive temperature coefficient up to the 108 K which indicates the metallicity of as produced CNT sheets. These highly conducting SWCNT sheets are the best solution for a wide range of applications in many fields, including conducting shields in coaxial cables, flexible and nano scale electrical and electronic devices, displays, biosensors, field-effect transistors and gas sensing materials.

Cathodic nanoporous CNT functional interlayer as a performance and durability boosting agent for proton exchange membrane fuel cells to operable at 120 °C

In proton exchange membrane fuel cells (PEMFCs), securing sufficient hydration in perfluorosulfonic acid (PFSA) membrane is considered an indicator of performance and durability. Here, we present a straightforward yet effective strategy that sandwiches the nanoporous carbon nanotube (CNT) sheet between the cathodic gas diffusion backing layer (GDBL) and bipolar plate (BP) of a conventional membrane electrode assembly (MEA). CNT sheets are synthesized through the cost-effective direct spinning method. The carbon source, winding rates, and the number of layers are varied to tailor the thickness and nanoporous morphology of the CNT sheets (5, 15, and 30 μm). CNT interlayer MEAs are evaluated for their performance in various temperature and relative humidity (RH), ranges of 80–120 °C and 25–100% RH. With these nanoporous CNT sheets, reactants disperse homogeneously, enhancing membrane hydration and interfacial contact, thereby fulfilling superior performance compared to conventional under entire conditions. Among CNT interlayers, the 30 μm records a 115.4% enhanced peak power density (0.28 W cm−2) and 89.2% extended durability (∼187 h) than conventional under 120 °C and 25% RH. Our strategy delivers a broader perspective of PEMFCs and other fuel cell types based on their ease of production and reproducibility.

Superior Stable, Highly Efficient, and Anisotropic Electrothermal Composite Heater in Various Directions with Fast Response Based on Aligned Carbon Nanotube Sheets

Flexible electrothermal heaters have a great potential for applications of warm‐keeping and thermotherapy. However, those common electrothermal heaters are so sensitive to strain that they are hard to resistant to deformation while still keeping the stable and outstanding electrothermal performance. Here, a flexible and elastic composite heater with a stable electrothermal property under varied strain with large deformation is developed by mimicking the wrinkle feature of human skin in a carbon nanotube (CNT)/polydimethylsiloxane (PDMS) bilayered structure. The created wrinkle feature of CNT film from the resilience of PDMS makes the electrothermal heater a stable electrothermal performance within 30–40% strain in different directions. The aligned preference of CNTs in the CNT film gives the electrothermal heater an ability that shows different electrothermal performance depending on different angles between the direction of CNT alignment and the long axis of the sample. This composite electrothermal heater also presents a highly efficient electrothermal performance that can reach 200 °C within 30s upon 2 V.

Responsive Polymer Composite Fiber

Comprehensive SummaryWearable devices are a mainstream for our future daily life, where responsive polymer composite fibers represent one of the key components. However, their practical applications are hampered by several challenges, including poor responsive reversibility, poor controllability and low stability as well as single function. Herein, we share our recent studies on overcoming the above challenges for achieving novel responsive polymer composite fibers, especially focusing on chromatic fibers, deformational fibers and their integrations. Furthermore, we introduce a type of novel materials for these responsive fiber materials, i.e., aligned carbon nanotube sheets and fibers simultaneously with excellent electrical, optical and mechanical properties. For the future development, we further highlight the possible directions in this field. What is the most favorite and original chemistry developed in your research group?The conception and realization of display textile. Displays are the basic building blocks of electronics. Integrating displays into textiles offers exciting opportunities for smart electronic textiles, which are believed to change the future life of the human being. For instance, display textiles serve to bridge human‐machine interactions, and a real‐time communication tool may become true for individuals with voice or speech disorders. After hard work for over ten years, we have finally achieved this goal at lab and further produced such display textiles at large scale at industry.How do you get into this specific field? Could you please share some experiences with our readers?When I started to do research independently at Fudan University, I tried to do something unique. I just did not hope to simply follow the available direction. I majored at chemical fibers during my undergraduate study and later made research on electronic devices, so it was natural for me to combine fibers and electronics together. I do not remember the detail time I figured out the idea. In my mind, it should be very interesting and must be very cool. I did not know and even had not thought whether they were useful or not. After the paper was published in 2021, so many people contacted us for the use of display textiles for a spectrum of applications. During the study on the display textiles that have been also investigated for smart systems, we started to explore new smart fibermaterials almost at the same time. These smart fiber materials are discussed in this article.How do you supervise your students?First, it is important for me to understand them as every student is unique. Second, according to their characteristics, I may choose specific research projects, often following their interests. Third, I fully respect them when they start the research. They are totally free to decide the work time and work style. I trace the process mainly aiming at solving problems for them. Of course, I keep asking them to enhance their scientific tastes and make the first‐class research, not only so‐called original science or technology. I will try my best to help them to publish their results at top journals, which is important for their future development. During the whole training process, the most important thing I hope to achieve is enjoying science, at least feel successful. It is obviously not easy. Sometimes we make it, and sometimes we fail. We always work for the better full of hope. I sincerely hope that every student, after graduation, will have a good memory at my lab.What is the most important personality for scientific research?I think there are two very important characteristics. One is brave. A scientist should be brave to solve the most difficult problem in the field. The other is imagination. Science is pretty similar to arts in many aspects. We may fix the gap sometimes through imagination. However, it is particularly challenging to train scientists for good imagination in science.

Exploring the possibility of using MWCNTs sheets as an electrode for flexible room temperature NO2 detection

In the last few years, significant progress has been made in nanotechnology, especially in the fabrication of sensors. Generally, metal electrodes are used in devices. Here, carbon nanotubes sheet has been used as an electrode and tin oxide nanoparticles made by the sol-gel method as the sensing material. The combination was used for sensing NO2 in the atmosphere at room temperature. For the MWCNT ​+ ​SnO2 (modified MWCNT) case, there was no immediate recovery for 14 ​ppm gas, and for 28 ppm and 56 ​ppm, recovery times were 13 ​s and 6 ​s, respectively. Using modified MWCNTs sheets as an electrode for flexible devices is the novelty of this work.

Electroconductive and Anisotropic Structural Color Hydrogels for Visual Heart-on-a-Chip Construction.

Heart‐on‐a‐chip plays an important role in revealing the biological mechanism and developing new drugs for cardiomyopathy. Tremendous efforts have been devoted to developing heart‐on‐a‐chip systems featuring simplified fabrication, accurate imitation and microphysiological visuality. In this paper, the authors present a novel electroconductive and anisotropic structural color hydrogel by simply polymerizing non‐close‐packed colloidal arrays on super aligned carbon nanotube sheets (SACNTs) for visualized and accurate heart‐on‐a‐chip construction. The generated anisotropic hydrogel consists of a colloidal array‐locked hydrogel layer with brilliant structural color on one surface and a conductive methacrylated gelatin (GelMA)/SACNTs film on the other surface. It is demonstrated that the anisotropic morphology of the SACNTs could effectively induce the alignment of cardiomyocytes, and the conductivity of SACNTs could contribute to the synchronous beating of cardiomyocytes. Such consistent beating rhythm caused the deformation of the hydrogel substrates and dynamic shifts in structural color and reflection spectra of the whole hybrid hydrogels. More attractively, with the integration of such cardiomyocyte‐driven living structural color hydrogels and microfluidics, a visualized heart‐on‐a‐chip system with more consistent beating frequency has been established for dynamic cardiomyocyte sensing and drug screening. The results indicate that the electroconductive and anisotropic structural color hydrogels are potential for various biomedical applications.

Effects of midplane carbon nanotube sheet interleave on the strength and impact damage resistance of carbon fiber reinforced polymer composites

AbstractThe effects of embedding a midplane carbon nanotube (CNT) sheet on the impact damage resistance, tensile strength and propensity for interlaminar shear failure in a carbon fiber reinforced polymer matrix composite is experimentally evaluated. External and internal damage in the impacted composite laminates were characterized via surface profilometry and ultrasonic C‐scan, respectively. The external dent areas and dent depths were greater for impacted laminates without the CNT sheet interleave, while the planar internal damage areas were greater for the impacted laminates with the CNT sheet. Destructive evaluation of the impacted laminates showed significant delaminations and matrix cracks in the vicinity of the midplane for the laminates with the CNT sheet, while damage was more distributed through the thickness in the non‐CNT sheet ones. While a single CNT sheet interleave did not significantly affect the tensile strength of the laminate, residual strength after impact and the corresponding strain to failure was higher because of the CNT sheet interleave. The propensity for interlaminar shear failure was greater for laminates without the CNT sheet than those with the CNT sheet.

Thermal Burst Synthesis of High-Performance Si Nanotube Sheets for Lithium-Ion Batteries

One of the drawbacks of Si-based battery anodes is poor cycle stability due to volume expansion of the anode material. To overcome this limitation, we propose a novel strategy of Si nanotube sheet synthesis using the thermal burst method. Herein, SiO2 nanotubes are prepared using the hard template method; subsequently, Si nanotube sheets are produced during the thermal burst caused by magnesiothermic reduction, which occurs because nanotubes are broken by ZnO with a larger thermal expansion coefficient. The electrochemical test results indicate that the Si nanotube sheets possess excellent electrochemical properties. The discharge specific capacity can reach 712.7 mAh g–1 even at the current density of 5 A g–1. Moreover, after carbon coating, a discharge capacity of 695.9 mAh g–1 is retained after 400 cycles at 1 A g–1 and the capacity retention of full batteries can reach 81.78% after 50 cycles at a rate of 0.5 C. Thus, the Si-based anode electrode with excellent electrochemical performance can be prepared by the thermal burst process, and this strategy can be applied to the preparation of other anode materials.

Effect of a Metallocene Catalyst Mixture on CNT Yield Using the FC-CVD Process

This work studies synthesis of carbon nanotube (CNT) sheet using the high temperature (1400 °C) floating catalyst chemical vapor deposition (FC-CVD) method. Three metallocenes—ferrocene, nickelocene, cobaltocene—and their combinations are used as precursors for metal catalysts in the synthesis process. For the carbon source, an alcohol fuel, a combination of methanol and n-hexane (9:1), is used. First, the metallocenes were dissolved in the alcohol fuel. Then, the fuel mixture was injected into a tube furnace using an ultrasonic atomizer with Ar/H2 carrier gas in a ratio of about 12/1. The synthesis of CNTs from a combination of two or three metallocenes reduces the percentage of metal catalyst impurity in the CNT sheet. However, there is an increase in structural defects in the CNTs when using mixtures of two or three metallocenes as catalysts. Furthermore, the specific electrical conductivity of the CNT sheet was highest when using a mixture of ferrocene and cobaltocene as the catalyst. Overall, the multi-catalyst method described enables tailoring certain properties of the CNT sheet. However, the standard ferrocene catalyst seems most appropriate for large-scale manufacturing at the lowest cost.

Super-aligned carbon nanotubes and GelMA hydrogel composite scaffolds promote spiral ganglion neuron growth and orientation

Sensorineural hearing loss caused by the damage and degeneration of spiral ganglion neurons (SGNs) is a common disease. So, the regeneration and directional growth of spiral ganglion neurons (SGNs) is vital for the treatment of sensorineural hearing loss. In this study, we combined methacrylated gelatin (GelMA) hydrogel and super-aligned carbon nanotubes sheets (SACNTs) to form a composite material (GelMA-SACNT) that combined the good biocompatibility of GelMA hydrogel with the conductivity of carbon nanotubes. The prepared composite material retained the topological structure of SACNTs and thus provided a suitable platform for neural cell culture. SGNs grown on GelMA-SACNT showed well orientation, increased length of neurites and filopodia and increased area of the axon growth cone. Furthermore, neural network activity on the GelMA-SACNT was increased. These results clearly show that the prepared GelMA-SACNT can promote the growth of SGNs and the formation of anisotropic neural networks and thus has potential for the treatment of sensorineural hearing loss.

Highly flexible all-solid-state microsupercapacitors for on chip applications using a transfer-free fabrication process

Recent research efforts in flexible electronics focus on developing lightweight, thin, and flexible micro scale supercapacitor devices integratable on a chip as power source devices. The key requirements for such devices are high performance, 2D form factor, and compatibility with thin-chip technology. We report the fabrication of an ultra-thin flexible microsupercapacitor (fMSC) based on a highly aligned horizontal array of carbon nanotube (HACNT) sheet with in-plane interdigitated configuration using a facile, single-step and scalable fabrication process. The devices exhibited, excellent flexibility under various bending states, and outstanding bending durability up to 10,000 cycles under bending angle of 180°. A representative fMSC with resolution of 40 μm showed a high peak energy density of 54 mWh cm−3. It was observed that the electrolyte deposition technique (drop-cast vs. spin-coating) affects the performance of fMSC devices. Drop-cast devices showed a higher specific capacitance (almost double) compared to spin-coated devices, but at the expense of flexibility. To demonstrate on-board integration, an array of these fMSCs was used as an energy storage unit in a vibrational energy-harvesting device, powered by a piezoelectric disk. This work demonstrates the potential of HACNT sheet based fMSCs with spin-coat electrolytes as ultra-thin microsupercapacitor devices for portable and wearable electronics.

Recyclable aligned carbon nanotube-sheet-based particulate air filter with high filtration efficiency and low pressure drop

There is an increasing demand for particulate matter filters to primarily block viruses and fine particulate matter floating in the air from entering the human body. The most commonly used microfiber-based filter has a technical flaw in which the filtration efficiency cannot be maximized as there is a trade-off in terms of performance; the pressure drop increases when the filtration efficiency increases. Here, we report the development of a recyclable macroscopic carbon nanotube (CNT)-based filter consisting of unidirectionally arranged multi-walled carbon nanotube sheets. Owing to the uniform arrangement of the 10–20 nm carbon nanotubes, uniform nanopores are formed. As a result, the CNT-sheet-based particulate matter filter exhibited low pressure drop characteristics, even at a high filtration efficiency. In addition, it was confirmed that the collected particulate matter could rapidly be removed through heat generated by applying a voltage to the conductive CNT sheet.

CNT sheet as a cathodic functional interlayer in polymer electrolyte membrane fuel cells

Carbon nanotube (CNT) sheet was sandwiched between the cathodic GDBL and a bipolar plate of polymer electrolyte membrane fuel cells (PEMFCs). The CNT sheets were synthesized through the direct spinning method and investigated their morphological characteristics. The electrochemical performances of MEA with CNT interlayer were measured via polarizations, iR-free, and electrochemical impedance spectra (EIS) compared to the conventional MEA under elevating backpressure. The performance of the MEA with CNT interlayer at 1.0 barg was enhanced by 91.8% (364 mW cm−2 at 0.7 V), which was higher than the peak power density improvement of 13.0% (850 mW cm−2 at 0.48 V). We also identified that corresponding ohmic and charge-transfer resistances were reduced. Especially, the ohmic resistance was decreased by up to 42.2% with increasing operating pressure compared to the conventional MEA due to better hydration and interfacial contact. Notwithstanding that the performance was ameliorated with increased pressure, we found that the mass transport loss tends to become more sensitive at the high current density region, and thus optimum operating conditions were proposed. We concluded that the CNT sheet as a functional interlayer would be advantageous in improving the performance of commercialized PEMFCs.

Tribological Properties of Carbon Nanotube and Carbon Nanofiber Blended Polyvinylidene Fluoride Sheets Laminated on Steel Substrates

Nanostructured carbon dispersed polymer nanocomposites are promising materials for tribological applications. Carbon nanofiber (CNF) and carbon nanotube (CNT) dispersed polyvinylidene fluoride (PVDF) nanocomposite was prepared by chemical synthesis route. Morphology and microstructure of well-dispersed CNF and CNT in PVDF were specified by scanning electron microscope and X-ray diffraction, respectively. Moreover, chemical and functional characteristics were examined by Raman spectroscopy and FTIR investigation. The friction coefficient of PVDF nanocomposite laminated on steel substrate decreased with an increase in the dispersed quantity of CNF and CNT. The friction coefficient of PVDF is approximately 0.27; however, the addition of carbon nanomaterial in PVDF will further decrease the friction coefficient between 0.24 and 0.17. This value was significantly less in CNT dispersed PVDF nanocomposite. This could be explained by easy shearing and rolling action contact interfaces.

Improved thermoacoustic sound projectors by vibration mode modification

The problem of coupled panel-cavity vibrations is addressed by studying the resonance modes in high power, low frequency, encapsulated thermoacoustic sound projectors using scanning laser vibrometry and sound pressure measurements. We fabricated and analyzed the performance of large area thermoacoustic sound projectors based on freestanding carbon nanotube sheets, encapsulated between a heat sink and various rigid vibrating plates. For thin, simply-supported vibrating plates we observed a strong deviation of resonance frequency and sound intensity from theoretical prediction for in vacuo plates. The domination of symmetric, odd modes for thin plates, with substantially improved sound radiation, is attributed to the coupled panel-cavity modes produced by harmonically varying pressure within the cavity. The observed modified mode shapes result from a minimum energy principle, wherein the potential energy stored in the entrained gas is minimized by reducing the overall change of the cavity gas volume. The effect of plate and cavity thickness on thermoacoustic projector performance in air is described for various devices. The optimized ultralight, low volume sound projectors can generate a remarkably high sound pressure level in air of over 120 dB re 20 μPa @ 1 m in a frequency range of 500 - 3000 Hz.

Highly Oriented Carbon Nanotube Supercapacitors

The demand for supercapacitors (SCs) with high capacitance, high charge–discharge rate, and long lifespan has been increasing because of the rapid development of wearable devices. In particular, flexible and durable SCs are essential for applications in wearable devices. A reasonable strategy to achieve such SCs involves the design and fabrication of SCs with flexible materials. In this study, we present a flexible SC with highly oriented carbon nanotube (CNT) sheets, which exhibit all the component functions of SCs: activated materials, conductive materials, and current collectors. Repeated bending tests validated the robustness of the flexible SCs. The SCs demonstrated extremely high durability with >99.9% capacitance retention after 50 000 bending cycles. Furthermore, we observed that the orientation angle of the CNT sheets with respect to the current flow direction (θ) was crucial for determining the performance of SCs. The SCs with CNT sheets oriented in the current flow direction (θ = 0°) showed a higher scan rate and robustness than those with other CNT sheet orientations (θ = 45 or 90°), because of the ease of access of charge carriers to the electrodes of the entire CNT sheet. Well-designed flexible and durable CNT-SCs can drastically improve the performance of future flexible devices.

Hierarchically porous, biaxially woven carbon nanotube sheet arrays for next-generation anion-exchange membrane water electrolyzers

A hierarchically porous, biaxially woven carbon nanotube sheet was proposed in a cathode of anion-exchange membrane water electrolysis to increase surface area and enhance transports.

Ionic EAP Actuators with Electrodes Based on Carbon Nanomaterials.

Flexible polymer-based actuators, often also called artificial muscles, are an essential part of biomimetic systems that mimic the movement principles of animal world creatures. The most used electrode material to force the actuator move is an ensemble of noble metal nanoparticles in the electroactive polymer surface. Noble metal electrodes have enough electrical conductivity and elasticity and are not subjected to oxidation. However, high cost of such electrodes and their tendency to cracking dictate the need for searching other materials, primarily carbon ones. The review considers several options for this search. For example, carbon nanotubes and graphene have excellent properties at the level of a single individually taken nanotube or graphene sheet. However, conservation of these properties in structurally imperfect film electrodes requires a separate study. In addition, there are problems of compatibility of such electrodes with the polymers that requires cumbersome technologies, e.g., hot pressing, which complicates the production of the actuator as a whole. The review concerns the technology options of manufacturing actuators and the results obtained on their basis, both including hot pressing and avoiding this procedure. In particular, the required level of the graphene oxide reduction in hydrazine provides sufficient adhesion at rather high electrical conductivity of the graphene film. The ability to simultaneous achieving these properties is a nontrivial result, providing the same level of actuation as with expensive noble metal electrodes. Actuators that additionally require greater lifetime resource should be obtained in other ways. Among them are using the graphdiyne electrodes and laser processing of the graphene electrodes.

Directional, Low-Energy Driven Thermal Actuating Bilayer Enabled by Coordinated Submolecular Switching.

The authors reveal a thermal actuating bilayer that undergoes reversible deformation in response to low‐energy thermal stimuli, for example, a few degrees of temperature increase. It is made of an aligned carbon nanotube (CNT) sheet covalently connected to a polymer layer in which dibenzocycloocta‐1,5‐diene (DBCOD) actuating units are oriented parallel to CNTs. Upon exposure to low‐energy thermal stimulation, coordinated submolecular‐level conformational changes of DBCODs result in macroscopic thermal contraction. This unique thermal contraction offers distinct advantages. It's inherently fast, repeatable, low‐energy driven, and medium independent. The covalent interface and reversible nature of the conformational change bestow this bilayer with excellent repeatability, up to at least 70 000 cycles. Unlike conventional CNT bilayer systems, this system can achieve high precision actuation readily and can be scaled down to nanoscale. A new platform made of poly(vinylidene fluoride) (PVDF) in tandem with the bilayer can harvest low‐grade thermal energy and convert it into electricity. The platform produces 86 times greater energy than PVDF alone upon exposure to 6 °C thermal fluctuations above room temperature. This platform provides a pathway to low‐grade thermal energy harvesting. It also enables low‐energy driven thermal artificial robotics, ultrasensitive thermal sensors, and remote controlled near infrared (NIR) driven actuators.

Highly-porous Super-Growth carbon nanotube sheet cathode develops high-power Lithium-Air Batteries

Lithium-Air Battery (LAB) is expected to develop ultra-high energy density batteries, but the low rate performance and poor cycle life of present LAB cells hinder practical development. Here we report that a highly porous carbon nanotube (CNT) cathode dramatically enhances the rate capability of LAB. Single-walled CNTs (SWCNTs) with wavy patterns prepared from the Super-Growth (SG) method successfully provided CNT sheets with high porosity of up to 94%. The pore structure was characterized by two distinct pores in size, namely, highly extended mesoscale (approximately 5–200 nm) pores formed inside CNT bundles that provide large surface area for oxygen reduction reaction (ORR) and inter-bundle gaps in a micrometer scale that works for oxygen diffusion path. This porous CNT sheet cathode significantly increased the discharge rate of LAB cells, specifically enabling a high discharge current density of 3.0 mA/cm2 securing practical cell capacity of 3.3 mAh/cm2, which is comparable to the current LiB technology that provides ∼3 mAh/cm2 cell capacity at ∼1C rate (∼3 mA/cm2) discharge. Furthermore, this highly porous cathode was also effective for extending the cycle life of LAB cells. Such bimodal pore architecture of the CNT sheet cathode paves the new strategy for developing high-power energy-dense LAB.