Carbon Nanotube–Multilayered Graphene Edge Plane Core–Shell Hybrid Foams for Ultrahigh‐Performance Electromagnetic‐Interference Shielding

Materials with an ultralow density and ultrahigh electromagnetic‐interference (EMI)‐shielding performance are highly desirable in fields of aerospace, portable electronics, and so on. Theoretical work predicts that 3D carbon nanotube (CNT)/graphene hybrids are one of the most promising lightweight EMI shielding materials, owing to their unique nanostructures and extraordinary electronic properties. Herein, for the first time, a lightweight, flexible, and conductive CNT–multilayered graphene edge plane (MLGEP) core–shell hybrid foam is fabricated using chemical vapor deposition. MLGEPs are seamlessly grown on the CNTs, and the hybrid foam exhibits excellent EMI shielding effectiveness which exceeds 38.4 or 47.5 dB in X‐band at 1.6 mm, while the density is merely 0.0058 or 0.0089 g cm^?3, respectively, which far surpasses the best values of reported carbon‐based composite materials. The grafted MLGEPs on CNTs can obviously enhance the penetration losses of microwaves in foams, leading to a greatly improved EMI shielding performance. In addition, the CNT–MLGEP hybrids also exhibit a great potential as nano‐reinforcements for fabricating high‐strength polymer‐based composites. The results provide an alternative approach to fully explore the potentials of CNT and graphene, for developing advanced multifunctional materials.     

Nanomanufacturing of RGO‐CNT Hybrid Film for Flexible Aqueous Al‐Ion Batteries

A highly electrically conductive film‐type current collector is an essential part of batteries. Apart from the metal‐based current collectors, lightweight and highly conductive carbon materials such as reduced graphene oxide (RGO) and carbon nanotubes (CNTs) show great potential as current collectors. However, traditional RGO manufacturing usually requires a long time and high energy, which decreases the product yielding rate and manufacturing efficiency. Moreover, the performance of the manufactured RGO needs to be further improved. In this work, CNT and GO are evenly mixed into GO‐CNT, which can be directly reduced into RGO‐CNT by Joule heating at 2936 K within less than 1 min. The fabricated RGO‐CNT achieves a high electrical conductivity of 2750 S cm^?1, and realizes a 10⁶‐fold increase. The assembled flexible aqueous Al‐ion battery with RGO‐CNT as the current collector exhibits impressive electrochemical performance in terms of superior cycling stability and exceptional rate capability, and excellent mechanical ability regarding the tolerance to mechanical damage such as bending, folding, piercing, and cutting without detrimental consequences.     

Single Carbon Fibers with a Macroscopic‐Thickness, 3D Highly Porous Carbon Nanotube Coating

Carbon fiber (CF) grafted with a layer of carbon nanotubes (CNTs) plays an important role in composite materials and other fields; to date, the applications of CNTs@CF multiscale fibers are severely hindered by the limited amount of CNTs grafted on individual CFs and the weak interfacial binding force. Here, monolithic CNTs@CF fibers consisting of a 3D highly porous CNT sponge layer with macroscopic‐thickness (up to several millimeters), which is directly grown on a single CF, are fabricated. Mechanical tests reveal high sponge–CF interfacial strength owing to the presence of a thin transitional layer, which completely inhibits the CF slippage from the matrix upon fracture in CNTs@CF fiber–epoxy composites. The porous conductive CNTs@CF hybrid fibers also act as a template for introducing active materials (pseudopolymers and oxides), and a solid‐state fiber‐shaped supercapacitor and a fiber‐type lithium‐ion battery with high performances are demonstrated. These CNTs@CF fibers with macroscopic CNT layer thickness have many potential applications in areas such as hierarchically reinforced composites and flexible energy‐storage textiles.     

Significantly Increased Solubility of Carbon Nanotubes in Superacid by Oxidation and Their Assembly into High‐Performance Fibers

This study demonstrates that small amount of oxygen incorporated into carbon nanotubes (CNTs) during the purification process greatly increases their solubility in chlorosulfonic acid (CSA). Using as‐purchased and unpurified CNT powders, the optimal purification process is established to significantly increase the solubility of CNTs in CSA, and spin CNT fibers with high mechanical strength (0.84 N tex^?1) and electrical conductivity (1.4 MS m^?1) from the CNT liquid crystal dope with high concentration of CNTs in CSA. The knowledge obtained here may guide development of a way to dissolve extremely long CNTs at high concentration and thereby to enable production of CNT fibers with ultimate properties.     

NixMnyCozO Nanowire/CNT Composite Microspheres with 3D Interconnected Conductive Network Structure via Spray‐Drying Method: A High‐Capacity and Long‐Cycle‐Life Anode Material for Lithium‐Ion Batteries

The combination of high‐capacity and long‐term cycling stability is an important factor for practical application of anode materials for lithium‐ion batteries. Herein, Ni_xMn_yCo_zO nanowire (x + y + z = 1)/carbon nanotube (CNT) composite microspheres with a 3D interconnected conductive network structure (3DICN‐NCS) are prepared via a spray‐drying method. The 3D interconnected conductive network structure can facilitate the penetration of electrolyte into the microspheres and provide excellent connectivity for rapid Li⁺ ion/electron transfer in the microspheres, thus greatly reducing the concentration polarization in the electrode. Additionally, the empty spaces among the nanowires in the network accommodate microsphere volume expansion associated with Li⁺ intercalation during the cycling process, which improves the cycling stability of the electrode. The CNTs distribute uniformly in the microspheres, which act as conductive frameworks to greatly improve the electrical conductivity of the microspheres. As expected, the prepared 3DICN‐NCS demonstrates excellent electrochemical performance, showing a high capacity of 1277 mAh g^?1 at 1 A g^?1 after 2000 cycles and 790 mAh g^?1 at 5 A g^?1 after 1000 cycles. This work demonstrates a universal method to construct a 3D interconnected conductive network structure for anode materials     

Cover Picture: Direct Growth of Flexible Carbon Nanotube Electrodes (Adv. Mater. 3/2008)

Entangled networks of multiwalled carbon nanotubes (CNTs) integrated into a highly conducting carbon layer can be grown on a range of substrates including glassy carbon and metal foils. On p. 566, Gordon Wallace and co‐workers report the fabrication of a continuous flexible CNT electrode with high surface area and conductivity. The electrode demonstrates a stable battery capacity of 572 mAh g^–1. This discovery provides a direct route for the generation of large‐scale flexible CNT electrode materials.     

State of the Art of Carbon Nanotube Fibers: Opportunities and Challenges

The superb mechanical and physical properties of individual carbon nanotubes (CNTs) have provided the impetus for researchers in developing high‐performance continuous fibers based upon CNTs. The reported high specific strength, specific stiffness and electrical conductivity of CNT fibers demonstrate the potential of their wide application in many fields. In this review paper, we assess the state of the art advances in CNT‐based continuous fibers in terms of their fabrication methods, characterization and modeling of mechanical and physical properties, and applications. The opportunities and challenges in CNT fiber research are also discussed.     

Micromechanics modeling of the electrical conductivity of carbon nanotube (CNT)–polymer nanocomposites

A mixed micromechanics model was developed to predict the overall electrical conductivity of carbon nanotube (CNT)–polymer nanocomposites. Two electrical conductivity mechanisms, electron hopping and conductive networks, were incorporated into the model by introducing an interphase layer and considering the effective aspect ratio of CNTs. It was found that the modeling results agree well with the experimental data for both single-wall carbon nanotube and multi-wall carbon nanotube based nanocomposites. Simulation results suggest that both electron hopping and conductive networks contribute to the electrical conductivity of the nanocomposites, while conductive networks become dominant as CNT volume fraction increases. It was also indicated that the sizes of CNTs have significant effects on the percolation threshold and the overall electrical conductivity of the nanocomposites. This developed model is expected to provide a more accurate prediction on the electrical conductivity of CNT–polymer nanocomposites and useful guidelines for the design and optimization of conductive polymer nanocomposites.     

Hierarchical 3D All‐Carbon Composite Structure Modified with N‐Doped Graphene Quantum Dots for High‐Performance Flexible Supercapacitors

Flexible supercapacitors have shown enormous potential for portable electronic devices. Herein, hierarchical 3D all‐carbon electrode materials are prepared by assembling N‐doped graphene quantum dots (N‐GQDs) on carbonized MOF materials (cZIF‐8) interweaved with carbon nanotubes (CNTs) for flexible all‐solid‐state supercapacitors. In this ternary electrode, cZIF‐8 provides a large accessible surface area, CNTs act as the electrical conductive network, and N‐GQDs serve as highly pseudocapactive materials. Due to the synergistic effect and hierarchical assembly of these components, N‐GQD@cZIF‐8/CNT electrodes exhibit a high specific capacitance of 540 F g^?1 at 0.5 A g^?1 in a 1 m H₂SO₄ electrolyte and excellent cycle stability with 90.9% capacity retention over 8000 cycles. The assembled supercapacitor possesses an energy density of 18.75 Wh kg^?1 with a power density of 108.7 W kg^?1. Meanwhile, three supercapacitors connected in series can power light‐emitting diodes for 20 min. All‐solid‐state N‐GQD@cZIF‐8/CNT flexible supercapacitor exhibits an energy density of 14 Wh kg^?1 with a power density of 89.3 W kg^?1, while the capacitance retention after 5000 cycles reaches 82%. This work provides an effective way to construct novel electrode materials with high energy storage density as well as good cycling performance and power density for high‐performance energy storage devices via the rational design.     

Fuel Cell Electrocatalyst Using Polybenzimidazole‐Modified Carbon Nanotubes As Support Materials

Toward the next generation fuel cell systems, the development of a novel electrocatalyst for the polymer electrolyte fuel cell (PEFC) is crucial to overcome the drawbacks of the present electrocatalyst. As a conductive supporting material for the catalyst, carbon nanotubes (CNTs) have emerged as a promising candidate, and many attempts have been carried out to introduce CNT, in place of carbon black. On the other hand, as a polymer electrolyte, polybenzimidazoles (PBIs) have been recognized as a powerful candidate due to the high proton conductivity above 100 °C under non‐humid conditions. In 2008, we found that these two materials have a strong physical interaction and form a stable hybrid material, in which the PBIs uniformly wrap the surfaces of the CNTs. Furthermore, PBIs serve as effective binding sites for the formation of platinum (Pt) nanoparticles to fabricate a ternary composite (CNT/PBIs/Pt). In this review article, we summarize the fundamental properties of the CNT/PBIs/Pt and discuss their potential as a new electrocatalyst for the PEFC in comparison with the conventional ones. Furthermore, potential applications of CNT/PBIs including use of the materials for oxygen reduction catalysts and reinforcement of PBI films are summarized.     

Hydrothermal Coating of Patterned Carbon Nanotube Forest for Structured Lithium‐Ion Battery Electrodes

Controlling the arrangement and interface of nanoparticles is essential to achieve good transfer of charge, heat, or mechanical load. This is particularly challenging in systems requiring hybrid nanoparticle mixtures such as combinations of organic and inorganic materials. This work presents a process to coat vertically aligned carbon nanotube (CNT) forests with metal oxide nanoparticles using microwave‐assisted hydrothermal synthesis. Hydrothermal processes normally damage delicate CNT forests, which is addressed here by a combination of lithographic patterning, transfer printing, and reduction of the synthesis time. This process is applied for the fabrication of structured Li‐ion battery (LIB) electrodes where the aligned CNTs provide a straight electron transport path through the electrode and the hydrothermal coating process is used to coat the CNTs with conversion anode materials for LIBs. These nanoparticles are anchored on the surface of the CNTs and batteries fabricated following this process show a fourfold longer cyclability. Finally, this process is used to create thick electrodes (350 µm) with a gravimetric capacity of over 900 mAh g^?1.     

A Solid‐State Fibriform Supercapacitor Boosted by Host–Guest Hybridization between the Carbon Nanotube Scaffold and MXene Nanosheets

Fiber‐shaped supercapacitors with improved specific capacitance and high rate capability are a promising candidate as power supply for smart textiles. However, the synergistic interaction between conductive filaments and active nanomaterials remains a crucial challenge, especially when hydrothermal or electrochemical deposition is used to produce a core (fiber)–shell (active materials) fibrous structure. On the other hand, although 2D pseudocapacitive materials, e.g., Ti₃C₂T _x (MXene), have demonstrated high volumetric capacitance, high electrical conductivity, and hydrophilic characteristics, MXene‐based electrodes normally suffer from poor rate capability owing to the sheet restacking especially when the loading level is high and solid‐state gel is used as electrolyte. Herein, by hosting MXene nanosheets (Ti₃C₂T _x ) in the corridor of a scrolled carbon nanotube (CNT) scaffold, a MXene/CNT fiber with helical structure is successfully fabricated. These features offer open spaces for rapid ion diffusion and guarantee fast electron transport. The solid‐state supercapacitor based on such hybrid fibers with gel electrolyte coating exhibits a volumetric capacitance of 22.7 F cm⁻³ at 0.1 A cm⁻³ with capacitance retention of 84% at current density of 1.0 A cm⁻³ (19.1 F cm⁻³), improved volumetric energy density of 2.55 mWh cm⁻³ at the power density of 45.9 mW cm⁻³, and excellent mechanical robustness.     

Fabrication of Highly Stretchable Conductors via Morphological Control of Carbon Nanotube Network

Stretchable conductors, which can keep their excellent electrical conductivity while highly stretched, have been investigated extensively due to their wide range of applications in flexible and stretchable electronics, wearable displays, etc.; however, their preparation is often complicated and expensive. Herein, an efficient method to prepare high performance stretchable conductors through morphological control of conductive networks formed with carbon nanotubes (CNTs) in an elastomer matrix is reported. It is observed that an interface‐mediated method could be used to align randomly oriented filler during stretching and to induce buckling of CNTs during relaxation. Further morphological studies indicate the possible formation of a wavy CNT structure induced by cyclic pre‐straining. Subsequent thermal annealing is observed to collapse the oriented network and improve the local contacts between conductive networks. Through such a simple procedure, a conductivity of nearly 1000 S m^?1 and a stretchability of 200% can be achieved for composites containing 20 wt% CNTs. CNTs are observed to buckle over a large area in polymer bulk, and the combination of pre‐straining and thermal annealing modifies the conductive network in the elastomer matrix. As a general method, this could be used for easy fabrication of high‐performance stretchable conductors for arbitrary‐shaped objects on a large scale.     

碳纳米管在超级电容器中的应用研究进展

超级电容器是近年来发展起来的一种新型储能装置。碳纳米管由于具有独特的中空结构，良好的导电性和高的比表面积，被认为是超级电容器理想的电极材料之一，引起了广泛的关注。通过介绍碳纳米管在超级电容器中的应用研究进展，评述了碳纳米管、活化碳纳米管、碳纳米管／金属氧化物复合物以及碳纳米管／导电聚合物复合物用做超级电容器电极材料的特点和性能。认为单纯的碳纳米管由于比表面积小，比容量偏低。化学活化可以显著提高碳纳米管的比表面积，增大其比电容。将碳纳米管与准电容材料金属氧化物或导电聚合物复合。可以发挥各自的优势，从而得到低成本、高性能的复合电极材料，将是今后发展的一个方向。     

Physical characterization of functionalized spider silk: electronic and sensing properties

Abstract

This work explores functional, fundamental and applied aspects of naturally harvested spider silk fibers. Natural silk is a protein polymer where different amino acids control the physical properties of fibroin bundles, producing, for example, combinations of β-sheet (crystalline) and amorphous (helical) structural regions. This complexity presents opportunities for functional modification to obtain new types of material properties. Electrical conductivity is the starting point of this investigation, where the insulating nature of neat silk under ambient conditions is described first. Modification of the conductivity by humidity, exposure to polar solvents, iodine doping, pyrolization and deposition of a thin metallic film are explored next. The conductivity increases exponentially with relative humidity and/or solvent, whereas only an incremental increase occurs after iodine doping. In contrast, iodine doping, optimal at 70 °C, has a strong effect on the morphology of silk bundles (increasing their size), on the process of pyrolization (suppressing mass loss rates) and on the resulting carbonized fiber structure (that becomes more robust against bending and strain). The effects of iodine doping and other functional parameters (vacuum and thin film coating) motivated an investigation with magic angle spinning nuclear magnetic resonance (MAS-NMR) to monitor doping-induced changes in the amino acid-protein backbone signature. MAS-NMR revealed a moderate effect of iodine on the helical and β-sheet structures, and a lesser effect of gold sputtering. The effects of iodine doping were further probed by Fourier transform infrared (FTIR) spectroscopy, revealing a partial transformation of β-sheet-to-amorphous constituency. A model is proposed, based on the findings from the MAS-NMR and FTIR, which involves iodine-induced changes in the silk fibroin bundle environment that can account for the altered physical properties. Finally, proof-of-concept applications of functionalized spider silk are presented for thermoelectric (Seebeck) effects and incandescence in iodine-doped pyrolized silk fibers, and metallic conductivity and flexibility of micron-sized gold-sputtered silk fibers. In the latter case, we demonstrate the application of gold-sputtered neat spider silk to make four-terminal, flexible, ohmic contacts to organic superconductor samples.     

Hybrid network structure and thermal conductive properties in poly(vinylidene fluoride) composites based on carbon nanotubes and graphene nanoplatelets

A small quantity of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were introduced into the poly(vinylidene fluoride) (PVDF)/GNP and PVDF/CNT composites, respectively, to prepare the corresponding ternary PVDF/CNT/GNP and PVDF/GNP/CNT composites. The results demonstrated that adding CNTs into the PVDF/GNP composites greatly promoted the formation of the hybrid network structure of fillers. This was much different from the scenario that adding GNPs into the PVDF/CNT composites. GNPs and CNTs exhibited excellent nucleation effects for the crystallization of PVDF matrix; however, the variation of the PVDF crystallinity was small. Adding CNTs into the PVDF/GNP composites greatly enhanced the electrical conductivity of the PVDF/CNT/GNP composites. This was also different from the scenario of the PVDF/GNP/CNT composites. Furthermore, the PVDF/CNT/GNP composites exhibit higher thermal conductivity and higher synergistic efficiency compared with the PVDF/GNP/CNT composites. The conductive mechanisms and the synergistic effects of the ternary composites were then analyzed.     

Carbon nanotube films as a platform to transduce molecular recognition events in metalloporphyrins

Porphyrins have been widely used for many years as functional materials for chemical sensors. Their outstanding chemical features are balanced by some restrictions in terms of transduction techniques. In particular, porphyrin layers are barely conductive, with the consequence that the fabrication of porphyrin based chemiresistors is not possible, except in few rare cases. On the other hand, carbon nanotubes (CNTs) have superior electric properties ranging from metallic to semiconductor in character. Although the conductivity of CNTs is very sensitive to adsorbed molecules, it should be considered that the adsorption onto carbon structures is also scarcely selective and cannot be modified unless other molecular recognition systems are coupled with the CNTs. Following this approach, in this paper we investigated the sensing properties of hybrid CNT-porphyrin films to explore the possibility of transducing the adsorption events occurring in a porphyrin layer into resistance changes of the CNT layers. The results obtained indicate that the presence of the porphyrin films increases the sensitivity of the electric resistance of the CNTs to the concentration of volatile compounds. This enhancement is probably due to the catalytic effect of the metalloporphyrin in conveying the charge transfer from the adsorbate molecule to the CNTs substrate. This property of metalloporphyrins may introduce a further differentiation between porphyrin based sensors that could be positively utilized in sensor array configurations.     

Aligning Solution‐Derived Carbon Nanotube Film with Full Surface Coverage for High‐Performance Electronics Applications

The main challenge for application of solution‐derived carbon nanotubes (CNTs) in high performance field‐effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution‐derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on‐state current I_on of 290 µA µm^?1 (V_ds = ?1.5 V and V_gs = ?2 V) and peak transconductance g_m of 150 µS µm^?1, which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT‐based electronics.     

Highly Conductive Ti3C2Tx MXene Hybrid Fibers for Flexible and Elastic Fiber‐Shaped Supercapacitors

Fiber‐shaped supercapacitors (FSCs) are promising energy storage solutions for powering miniaturized or wearable electronics. However, the scalable fabrication of fiber electrodes with high electrical conductivity and excellent energy storage performance for use in FSCs remains a challenge. Here, an easily scalable one‐step wet‐spinning approach is reported to fabricate highly conductive fibers using hybrid formulations of Ti₃C₂T_x MXene nanosheets and poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate. This approach produces fibers with a record conductivity of ≈1489 S cm^?1, which is about five times higher than other reported Ti₃C₂T_x MXene‐based fibers (up to ≈290 S cm^?1). The hybrid fiber at ≈70 wt% MXene shows a high volumetric capacitance (≈614.5 F cm^?3 at 5 mV s^?1) and an excellent rate performance (≈375.2 F cm^?3 at 1000 mV s^?1). When assembled into a free‐standing FSC, the energy and power densities of the device reach ≈7.13 Wh cm^?3 and ≈8249 mW cm^?3, respectively. The excellent strength and flexibility of the hybrid fibers allow them to be wrapped on a silicone elastomer fiber to achieve an elastic FSC with 96% capacitance retention when cyclically stretched to 100% strain. This work demonstrates the potential of MXene‐based fiber electrodes and their scalable production for fiber‐based energy storage applications.     

Macroscopic fibers of well-aligned carbon nanotubes by wet spinning

A simple process to spin fibers consisting of multi-walled carbon nanotubes (CNTs) directly from their lyotropic liquid-crystalline phase is reported. Ethylene glycol is used as the lyotropic solvent, enabling a wider range of CNT types to be spun than previously. Fibers spun with CNTs and nitrogen-doped CNTs are compared. X-ray analysis reveals that nitrogen-doped CNTs have a misalignment of only +/-7.8 degrees to the fiber axis. The tensile strength of the CNT and nitrogen-doped CNT fibers is comparable but the modulus and electrical conductivity of the are lower. The electrical conductivity of both types of CNT fibers is found to be highly anisotropic. The results are discussed in context of the microstructure of the CNTs and fibers.