Carbon Nanotube Networks Research Articles

High-Performance Shortwave Infrared Detector Based on Multilayer Carbon Nanotube Films.

Carbon nanotube (CNT) is an ideal candidate material for shortwave infrared (SWIR) detectors due to its large band gap tunability, strong infrared light absorption, and high mobility. Furthermore, the photodetectors based on CNT can be prepared on any substrate using a low-temperature process, which is conducive to three-dimensional (3D) integration. However, owing to the absorption limitation (<2%) of a single-layer network CNT film with low density, the photodetectors of CNT film show low photocurrent responsivity and detectivity. In this paper, we optimize the thickness of the high-purity semiconducting network CNT films to increase the photocurrent responsivity of the photodetectors. When the thickness of network CNT film is about 5 nm, the responsivity of the zero-bias voltage can reach 32 mA/W at 1800 nm wavelength. Then, using stacked CNT films and contact electrode design, the photodetectors exhibit a maximum responsivity of 120 mA/W at 1800 nm wavelength. The photodetectors with stacked CNT films and local n-type channel doping demonstrated a wide response spectral range of 1200-2100 nm, a peak detectivity of 3.94 × 109 Jones at room temperature, and a linear dynamic range over 118 dB. Moreover, the peak detectivity is over 2.27 × 1011 Jones when the temperature is 180 K. Our work demonstrates the potential of the CNT film for future SWIR imaging at a low cost.

Synergistic enhanced Zinc-ion battery performance achieving by atomic layer deposition of TiO2 on three-dimensional carbon nanotube network decorated Zn anode

Herein, we report a unique synergistic effect between carbon nanotube (CNT) network and atomic layer deposition (ALD) of TiO2, which not only enhances the ability to capture zinc ions but also suppresses Zn dendrite growth, resulting in uniform deposition of zinc ions during repeated cycles. The CNTs with luxuriant three-dimensional skeleton structure can provide plentiful deposition sites on Zn metal anode, which significantly reduces the nucleation overpotential and improves the reaction kinetics. Meanwhile, the TiO2 can repeatedly guide the uniform deposition of Zn owing to the excellent zincophilic. The deposition mechanism of zinc in the modified anode (TiO2CNT@Zn anode) is fully explained by comparing different carbon materials. The TiO2CNT@Zn anode shows a high Zn plating/stripping reversibility with an ultralow nucleation overpotential and achieves an ultralong lifespan over 2000 h with a voltage hysteresis of 22.5 mV compared to bare zinc (BZ) anode (63.7 mV) at a high current density of 5 mA cm−2. Moreover, the TiO2CNT@Zn anode maintains a highly stable Coulombic efficiency of 98.9% for more than 500 h. Moreover, the Zn-MnO2 battery with the TiO2CNT@Zn anode shows remarkably enhanced cycling stability.

Carbon Nanotube Diodes Operating at Frequencies of Over 50GHz.

Radiofrequency (RF)diodes used for fifth and sixth-generation (5G and 6G) mobile and wireless communication networks generally require ultrahigh cut-off frequencies and high integration densities of devices with different functions on a single chip and at low cost. Carbon nanotube diodes are promising devices for radiofrequency applications, but the cut-off frequencies are still far below the theoretical estimates. Here, a carbon nanotube diode that operates in the millimeter-wave frequency bands and is based on solution-processed, high-purity carbon nanotube network films is reported. The carbon nanotube diodes exhibit an intrinsic cut-off frequency over 100GHz and the as-measured bandwidth can exceed 50GHz at least. Furthermore, The rectification ratio of the carbon nanotube diode by approximately three times by using yttrium oxide for local p-type doping in the diode channel is improved.

Mid-Infrared Electrochromics Enabled by Intraband Modulation in Carbon Nanotube Networks.

Tuneable infrared properties, such as transparency and emissivity, are highly desirable for a range of applications, including thermal windows and emissive cooling. Here, we demonstrate the use of carbon nanotube networks spray-deposited onto an ionic liquid-infused membrane to fabricate devices with electrochromic modulation in the mid-infrared spectrum, facilitating control of emissivity and apparent temperature. Such modulation is enabled by intraband transitions in unsorted single-walled carbon nanotube networks, allowing the use of scalable nanotube inks for printed devices. These devices are optimized by varying film thickness and sheet resistance, demonstrating the emissivity modulation (from ∼0.5 to ∼0.2). These devices and the understanding thereof open the door to selection criteria for infrared electrochromic materials based on the relationship between band structure, electrochemistry, and optothermal properties to enable the development of solution-processable large-area coatings for widespread thermal management applications.

Highly Electrical Conductive PEDOT:PSS/SWCNT Flexible Thermoelectric Films Fabricated by a High-Velocity Non-solvent Turbulent Secondary Doping Approach.

Materials based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can be potentially employed as flexible thermoelectric generators (TEGs) to capture waste heat and generate electrical energy. Among various methods, secondary doping is an effective way to modulate its thermoelectric (TE) performance. Different from conventional measures such as dropping, soaking, and steam fumigation, strong shear is integrated with the doping process and termed high-velocity non-solvent turbulent secondary doping (HNTD). We systematically investigate the transformation of PEDOT:PSS during this procedure and the formation mechanism of its highly conductive pathway. It is illustrated that PEDOT:PSS experiences PSS swelling, the phase separation of PEDOT from PSS, the removal of isolated PSS, and the evolution of PEDOT to a linear conformation. These evolutions contribute to the substantial elevation of electrical conductivity (σ). Furthermore, by employing continuous single-walled carbon nanotube (SWCNT) networks as structural units, highly conductive flexible PEDOT:PSS/SWCNT TE thin films could be prepared without sacrificing the Seebeck coefficient (S). Additionally, the effect of HNTD and direct addition method on TE properties of composite films is also compared. Finally, the PEDOT:PSS composite film with 40 wt % SWCNTs by the HNTD method exhibits the maximized power factor (PF) of 501.31 ± 19.23 μW m-1 K-2 with σ of 4717.8 ± 41.51 S cm-1 and S of 32.6 ± 0.13 μV K-1 at room temperature. It is worth mentioning that the σ value 4717.8 ± 41.51 S cm-1 is the highest among the composites based on commercial carbon fillers and organic semiconductors. Finally, a 6-leg TEGs prototype is assembled and illustrates an output power of 4.416 μW under a temperature difference (ΔT) of 58 K. It is thought that such a strategy may provide some guidelines for manufacturing PEDOT:PSS-based functional materials.

A Damped Double Dipole Antenna for UHF RFID Sensing in the Frequency Domain

Ultrahigh frequency (UHF) radio frequency identification (RFID) tags provide an inexpensive framework for distributed sensing, yet for the most cost-effective implementation, it is necessary to consider antenna design in concert with the capabilities of responsive materials that can be coupled to the tag response. Materials, such as functionalized carbon nanotubes (CNTs), have been engineered to change in resistance when exposed to a variety of analytes and have been incorporated in RFID tags to create low-cost sensors that work at a fixed reader–tag separation distance. This article presents a damped double dipole antenna design enabling UHF RFID tags that are able to sense changes in resistance of a sensing element (with a conductivity similar to that of printed CNT networks) regardless of reader–tag distance within the far-field read range. Simulations of the proposed design show two methods of operation, either by comparing the damping between two resonant peaks or by shifting the resonant frequency of the RFID tag. The first method is validated experimentally with surface mount resistors, showing a relative change in the effective antenna transmission coefficient, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau _{e}$ </tex-math></inline-formula> , of 0.2 for a 35% change in resistance of the sensing element.

Damage progression monitoring using self-sensing capability and acoustic emission on glass fiber / epoxy composites and damage classification through principal component analysis

In this study, the synergistic combination of acoustic emission (AE) and self-sensing capability provided by the integration of carbon nanotube (CNT) networks was used to a better damage progression monitoring of glass fiber epoxy composites under flexural loading. The specimens were prepared with different stacking sequences ([06], [04], [0/90]S, and [90/0]S) using the vacuum assisted resin infusion procedure. The acoustic signals recorded during the tests were analyzed by a classification methodology which consists of the k-means method and principal component analysis (PCA), this analysis allowed the identification of the various damage mechanisms such as matrix cracking, fiber/matrix debonding, delamination and fiber breakage. The electromechanical response, through the change in electrical resistance signal, and some AE parameters such as the cumulative energy and/or strength cumulative were able to capture the occurrence of specific failure events during the composites damage evolution. Damage evaluation of failed specimens by means of scanning electron microscopy was performed, and it exhibited a less damage severity on specimens with CNT due to the reinforcement effect. This work demonstrates the complementarity of both non-destructive inspection techniques for monitoring damage progression in composite structures.

Defect-Induced Adsorption Switching (p- to n- Type) in Conducting Bare Carbon Nanotube Film for the Development of Highly Sensitive and Flexible Chemiresistive-Based Methanol and NO2 Sensor.

Lightweight and flexible gas sensors are essentially required for the fast detection of toxic gases to pass on the early warning to deter accident situations caused by gas leakage. In view of this, we have fabricated a thin paper-like free-standing, flexible, and sensitive carbon nanotube (CNT) aerogel gas sensor. The CNT aerogel film synthesized by the floating catalyst chemical vapor deposition method consists of a tiny network of long CNTs and ∼20% amorphous carbon. The pores and defect density of the CNT aerogel film were tuned by heating at 700 °C to obtain a sensor film, which showed excellent sensitivity for toxic NO2 and methanol gas in the concentration range of 1-100 ppm with a remarkable limit of detection ∼90 ppb. This sensor has consistently responded to toxic gas even after bending and crumpling the film. Moreover, the film heat-treated at 900 °C showed a lower response with opposite sensing characteristics due to switching of the semiconductor nature of the CNT aerogel film to n-type from p-type. The annealing temperature-based adsorption switching can be related to a type of carbon defect in the CNT aerogel film. Therefore, the developed free-standing, highly sensitive, and flexible CNT aerogel sensor paves the way for a reliable, robust, and switchable toxic gas sensor.

In situ N-doped carbon nanotubes modified NiS2 hierarchical hollow microspheres for boosting sodium storage performance

Engineering novel electrode materials with distinctive architectures has a significant influence on tuning the structural/electrochemical properties for boosting the sodium storage performance. Herein, starting from metal-organic framework (MOF), we report an in situ catalytic method with chemical transformation strategy to fabricate NiS2 hierarchical hollow microspheres (HMs) with continuous N-doped carbon nanotubes (NCNTs) networks (NiS2@NCNTs HMs). Benefitting from the hierarchical hollow structure and three-dimensional (3D) NCNTs networks as well as the robust structural stability, the prepared NiS2@NCNTs HMs indicates excellent Na+ storage performance. More specifically, the composite shows a high reversible capacity of 626.6 mA h g−1 at 0.2 A g−1 for Na+ storage and retains 333.3 mA h g−1 at 5.0 A g−1, remarkably higher than those of the previously reported NiS2-based anode materials. In particular, it maintains a stable reversible capacity of 343.0 mA h g−1 even at 3.0 A g−1 over 3000 cycles. The in situ catalytic NCNTs on MOF precursors strategy for hierarchical structural composites can be extended to other novel electrodes for high performance energy storage devices.

Ionic liquids self-assembly preparation of binder-free composites anode with well-dispersed Si nanoparticles on CNTs networks for lithium-ion batteries

Binder-free nano silicon/carbon nanotube composites anodes were synthesized by electrostatic self-assembly of ionic liquids (ILs) and annealing process. The addition of [Emim]Tf2N ILs successfully improved the dispersion of silicon nanoparticles (SiNPs) in the carbon nanotubes (CNTs). And the carbon nanotubes could be self-assembled into a 3D structure network through electrostatic gravitational force. Moreover, the wettability of electrode also be improved due to the heteroatoms of [Emim]Tf2N ILs doped in the CNTs during annealing. By integrating these advantages, the Si30%-CNTs anodes exhibit a high initial reversible discharge capacity of 2580.3 mAh g−1 at a current density of 0.4 A g−1. Even at a much higher current density of 10 A g−1, the Si30%-CNTs anodes can still deliver a high reversible discharge capacity of 871.1 mAh g−1. The outstanding performances compared to traditional coating method are assigned to that the ionic liquids self-assembly method improves the dispersion of SiNPs.

Flexible high-capacity and long-cyclability hydrogel batteries enabled by polyvalent vanadium ion redox chemistry

Aqueous secondary batteries based on nonflammable electrolytes are attracting extensive attention due to high safety, fast reaction kinetics, and low cost. Herein, we report the development of flexible hydrogel batteries based on polyvalent vanadium ion redox chemistry. In this battery, symmetrical composite hydrogel electrodes used as both cathode and anode are prepared by in-situ fabrication of highly porous 3D poly(N-isopropylacrylamide) scaffold alongside conductive multi-walled carbon nanotube networks and swollen with redox-active vanadium ion electrolyte. The abundant nanoscale porosity and channels in the hydrogel matrix are conducive to the infiltration/diffusion of vanadium ions and H+ ions, thus enabling high areal loading mass (13 mgv cm−2) and large areal capacity (0.99 mAh cm−2). The active materials in the flexible electrodes exist in the form of composite hydrogel state, which is beneficial to facilitate ion transport and electrochemical kinetics, delivering an impressive power density of 11 mW cm−2 at 10 mA cm−2. Moreover, the flexible vanadium ion hydrogel batteries also exhibit excellent mechanical properties and long-term durability of 1000 cycles. These merits make them promising for the applications in wearable and smart electronics.

MOF-derived carbon/ZnS nanoparticle composite interwoven with structural and conductive CNT scaffolds for ultradurable K-ion storage

This study reports MOF-derived carbon/ZnS nanoparticle composite interwoven with CNT scaffolds for ultradurable K-ion storage. Metal–organic framework (MOF)-derived carbons possess in situ generated metal particles, which are subsequently utilized to prepare metal compounds. In MOF derivatives, the original morphology of MOF is rarely maintained due to the collapse of the framework and pyrolysis of organic ligands at high temperature. Accordingly, metal nodes aggregate, resulting in coarsening and non-uniform distribution of metal particles, which degrades their electrochemical properties. Moreover, the collapse dwindles micropore volume, decreases interparticle porosity and hinders diffusion of ions. Despite the importance in energy storage materials, however, these issues have been largely overlooked in MOF-assisted nanoparticle synthesis. We report a novel strategy for synthesizing robust MOF grown in situ on and interwoven with structural and conductive scaffolds of carbon nanotube networks (MOF-5@ACNT), which effectively stabilize the structure and morphology of the MOFs by preventing them from collapsing, thereby suppressing the aggregation and coarsening of metal particles during carbonization. To synthesize ZnS nanoparticles embedded in MOF-derived carbon (ZnS/C@CNT), MOF-5@ACNT and sulfur are mixed and heat-treated to prepare ZnS/C@CNT, wherein the initial cubic morphology of MOF-5 is retained and ∼15 nm ZnS nanoparticles are uniformly distributed without aggregation. ZnS/C@CNT exhibits a highly reversible conversion–alloying reaction with a high specific capacity (410 mA h g−1) and excellent cycling performance (87 % retention after 1000 cycles). The intimate contact between the ZnS nanoparticles and carbon through chemical interactions and structural and morphological stability make ZnS/C@CNT a promising anode material for KIBs.

Impact of Dielectric Environment on Trion Emission from Single-Walled Carbon Nanotube Networks.

Trions are charged excitons that form upon optical or electrical excitation of low-dimensional semiconductors in the presence of charge carriers (holes or electrons). Trion emission from semiconducting single-walled carbon nanotubes (SWCNTs) occurs in the near-infrared and at lower energies compared to the respective exciton. It can be used as an indicator for the presence of excess charge carriers in SWCNT samples and devices. Both excitons and trions are highly sensitive to the surrounding dielectric medium of the nanotubes, having an impact on their application in optoelectronic devices. Here, the influence of different dielectric materials on exciton and trion emission from electrostatically doped networks of polymer-sorted (6,5) SWCNTs in top-gate field-effect transistors is investigated. The observed differences of trion and exciton emission energies and intensities for hole and electron accumulation cannot be explained with the polarizability or screening characteristics of the different dielectric materials, but they show a clear dependence on the charge trapping properties of the dielectrics. Charge localization (trapping of holes or electrons by the dielectric) reduces exciton quenching, emission blue-shift and trion formation. Based on the observed carrier type and dielectric material dependent variations, the ratio of trion to exciton emission and the exciton blue-shift are not suitable as quantitative metrics for doping levels of carbon nanotubes.

Plasmonic Bridge Sensor Enabled by Carbon Nanotubes and Au–Ag Nano-Rambutan for Multifunctional Detection of Biomechanics and Bio/Chemical Molecules

Wearable, noninvasive, and simultaneous sensing of subtle strains and eccrine molecules on human body is essential for future health monitoring and personalized medicine. However, there is a huge chasm between biomechanics and bio/chemical molecule detections. Here, a wearable plasmonic bridge sensor with multiple abilities to monitor subtle strains and molecules is developed. Hollow Au-Ag nano-rambutans and carbon nanotubes (CNTs) are adsorbed in the nonwoven fabrics (NWFs) conjointly, where the gap between the conducting network of CNTs is bridged by the Au-Ag nano-rambutans during the subtle strain sensing, and the detection sensitivity for stress is improved at least 1 order of magnitude compared to that with the only CNTs. In order to acquire the accurate human action recognition, a machine learning algorithm (support vector machines) based on output biomechanics data is designed. The average accuracy of our plasmonic bridge sensor reaches 89.0% for human action recognition. Moreover, due to the hollow structure and high nanoroughness, the single Au-Ag nano-rambutan particle has strong localized surface plasmon resonance effect and high surface-enhanced Raman scattering (SERS) activity. Based on their unique SERS spectra introduced by the hollow Au-Ag nano-rambutan adsorbed in the NWFs, noninvasive extraction and "fingerprint" recognition of bio/chemical molecules could be realized during the wearable sensing. In sum, the NWFs/CNTs/Au-Ag sensor bridges the barrier between the bodily strain detection and molecule recognition during the wearable sensing. Such integrated and multifunctional sensing strategy for universal biomechanics and bio/chemical molecules means to assess human health to be of importance.

Gallic Acid-Reduced Graphene Oxide Deposited with Carbon Nanotubes for Transparent Film Heaters

The flexible transparent film heater described in this research was based on graphene, carbon nanotubes (CNTs), and polyethylene terephthalate (PET). Natural polyphenols gallic acid (GA) was chosen as the “green” reducing agent of graphene oxide (GO) to prepare the GA-functionalized GO (GGO). Then, the GGO nanosheets were introduced into the CNT network, and the GGO/CNT-PET composite films were successfully prepared by a simple spraying method. This type of transparent conductive film (TCF) possesses an excellent optoelectronic performance (Rs = 49.1 Ω/sq., T = ca. 80% at 550 nm) and a very low RMS roughness (approximately 6.89 nm). The sheet resistance of the films changed slightly after the 1000 bending cycles and 100 h of air exposure time, which indicated that the film has good mechanical properties and environmental stability. The composite TCFs were further applied to fabricate transparent film heaters (TFHs) and showed excellent Joule heating performance, fast response speed, good cycling stability, long-term stability, and controllable operating temperature (the power density of the TFHs shows an approximate linear behavior), which satisfy the requirements of TFHs in practical applications, such as safe voltage and temperature in wearable devices, the stable controlling temperature in smart windows, fast heating in defoggers, and so on.

Optimized Heat Transfer Rate in Cu/CNT Nano Composite Prepared by Electrodeposition Technique

The Cu/CNT nanocomposites are prepared by reinforcing Carbon Nanotubes (CNT) in a copper matrix through the electrodeposition technique. These nanocomposites are prepared by varying the diameter and concentrations of the CNT and are characterized by heat transfer rate. This study describes the overall heat transfer phenomena of Cu/CNT nanocomposite due to the preferential deposition of CNTs in the Cu matrix. The heat transfer rate is optimized and increased by 41.08% and 46.91% in natural and forced convection respectively compared to pure Cu coating. The reason is attributed to the better alignment, the optimum concentration of CNT in the composite, and the homogenously placed CNTs network in the composite.

Biomimetic vertically aligned aerogel with synergistic photothermal effect enables efficient solar-driven desalination

Taking sustainable solar energy for efficient rapid clean water production is eagerly desired to overcome the water shortage issue. However, great challenges remain in constructing short water transport channels and enhancing sunlight utilization efficiency. Herein, a biomimetic solar-driven interfacial evaporator with rapid water transport and high photothermal conversion efficiency inspired by natural-trees was successfully developed, via engineer vertically aligned hydrophilic sodium alginate (SA) aerogels while hierarchically assembled MXene interwoven carbon nanotube (CNT) networks as micro/nano light absorb layer. Due to the synergistic photothermal effect between 2D MXene nanosheets and 1D CNT with multiple reflective nanostructure and strong light-absorption over a broad spectrum, and super-hydrophilic SA with highly oriented water transport channels, which enables fast water/vapor transport while utilizing solar energy efficiently. Vertically aligned aerogel exhibits an excellent water evaporation performance which as high as 2.416 kg m−2 h−1 (deducting dark conditions) and remarkable solar energy utilizing efficiency of 90.56 %, which are extremely higher than that of most reported desalination devices. Furthermore, the solar-driven evaporator also exhibits strong antibacterial properties and long-term operation stability. The biomimetic vertically aligned aerogel with excellent water evaporation and light utilization efficiency holds great promise for high-performance water purification and desalination applications. Synopsis statementResearch on the rapid clean water production from wastewater/seawater with high solar energy utilization efficiency has become a hot topic, and solar-driven desalination offers a sustainable solution to meet water demands. This study reports a biomimetic solar-driven interfacial evaporator with oriented water transport nanochannel and multi-reflective solar absorber for efficient clean water production.

Improved Performance of Composite Bipolar Plates for PEMFC Modified by Homogeneously Dispersed Multi-Walled Carbon Nanotube Networks Prepared by In Situ Chemical Deposition

Composite bipolar plates with excellent performance play a crucial role in improving the overall performance of proton-exchange-membrane fuel cells. However, for graphite/resin composite bipolar plates, their electrical conductivity and mechanical properties are often too complex to meet the needs of users at the same time. Although nanoconductive fillers can alleviate this problem, the performance improvement for composite bipolar plates is often limited due to problems such as agglomeration. In this study, a uniformly dispersed multi-walled carbon nanotube network was prepared by in situ vapor deposition on the surface and pores of expanded graphite, which effectively avoided the problem of agglomeration and effectively improved the various properties of the composite BPs through the synergistic effect with graphite. With the addition of 2% in situ deposited carbon nanotubes, the modified composite bipolar plate has the best conductivity (334.53 S/cm) and flexural strength (50.24 MPa), and all the properties can meet the DOE requirements in 2025. Using the in situ deposition of carbon nanotubes to modify composite bipolar plates is a feasible route because it can result in multi-walled carbon nanotubes in large quantities and avoid the agglomeration phenomenon caused by adding nanofillers. It can also significantly improve the performance of composite bipolar plates, achieving the high performance of composite bipolar plates at a lower cost.

Enhanced thermal conductivity of polyamide nanocomposites involving expanded graphite–carbon nanotube network structure using supercritical CO2

In this study, supercritical carbon dioxide (scCO2) was used to form a network structure of expanded graphite (EG) and multi-walled carbon nanotube (MWCNT) to achieve high thermal conductivity. Continuous processes, such as supercritical drying and rapid expansion of supercritical solutions were applied to pristine graphite and MWCNT. Polyamide 6 (PA6) nanocomposites with scCO2-treated EG and MWCNT were prepared by twin-screw extruder-based melt compounding. In the PA6 nanocomposites, the EG sheets were homogenously dispersed, while the MWCNTs were located between the EG sheets, thereby acting as a bridge for the EG. Subsequently, the 35 wt.% imbedding in PA6 nanocomposite had an effective heat transfer pathway and high thermal conductivity (2.12 W m−1 K−1). It was observed that supercritical fluid processing is a facile and effective strategy to improve the thermal conductivity of polymer nanocomposites.

Modeling of thermal conductivity for disordered carbon nanotube networks

Several theoretical models have been developed so far to predict the thermal conductivities of carbon nanotube (CNT) networks. However, these models overestimated the thermal conductivity significantly. In this paper, we claimed that a CNT network can be considered as a contact thermal resistance network. In the contact thermal resistance network, the temperature of an individual CNT is nonuniform and the intrinsic thermal resistance of CNTs can be ignored. Compared with the previous models, the model we proposed agrees well with the experimental results of single-walled CNT networks.