Conductivity Of Carbon Nanotubes Research Articles

Conductive and Self-Healing Carbon Nanotube–Polymer Composites for Mechanically Strong Smart Materials

It is a great challenge to develop polymeric materials possessing multiple functionalities for their intrinsic properties. In our efforts to overcome this dilemma, we report a carbon nanotube (CNT)-doped polymer architecture design in this paper using a soft matrix synthesized from methacrylic acid and poly(ethylene glycol) methacrylate via reversible addition–fragmentation chain-transfer polymerization and further functionalized by 1-pyrenemethanol and doped with hard, stiff CNTs as fillers. The CNTs were dispersed evenly into the pyrene-functionalized copolymers obtained via the solution blending method. Our approach is simple, low-energy-consuming, facile in operation, and highly efficient. The developed composites demonstrate high mechanical strength, self-healing ability, and high electrical conductivity. To further maximize the potential of our CNT-filled composites, we introduced a simple but effective means to align CNTs by directional stretching at elevated temperatures and so achieved significant mechanical and electrical reinforcement. The multifunctional composites produced in this paper have desirable properties for future applications such as conductive bioskins, healthcare monitoring sensors, and other functional conductive electronics.

Processing of Composite Electrodes of Carbon Nanotube Fabrics and Inorganic Matrices via Rapid Joule Heating.

Composites of nanocarbon network structures are interesting materials, combining mechanical properties and electrical conductivity superior to those of granular systems. Hence, they are envisaged to have applications as electrodes for energy storage and transfer. Here, we show a new processing route using Joule heating for a nanostructured network composite of carbon nanotube (CNT) fabrics and an inorganic phase (namely, MoS2), and then study the resulting structure and properties. To this end, first, a unidirectional fabric of conductive CNT bundles is electrochemically coated with MoS2. Afterward, the conformally coated inorganic phase is crystallized via heat generated by direct current passing through the CNT ensemble. The Joule heating process is rapid (maximum heating rate up to 31.7 °C/s), enables accurate temperature control, and takes only a few minutes. The resulting composite material combines a high electrical conductivity of up to 1.72 (±0.25) × 105 S/m, tensile modulus as high as 8.82 ± 5.5 GPa/SG, and an axial tensile strength up to 200 ± 58 MPa/SG. Both electrical and mechanical properties are orders of magnitude above those of wet-processed nanocomposites of similar composition. The extraordinary longitudinal properties stem from the network of interconnected and highly aligned CNT bundles. Conductivity and modulus follow approximately a rule of mixtures, similar to a continuous fiber composite, whereas strength scales almost quadratically with the mass fraction of the inorganic phase due to the inorganic constraining realignment of CNTs upon stretching. This processing route is applicable to a wide range of nanocarbon-based composites with inorganic phases, leading to composites with specific strength above steel and electrical conductivity beyond the threshold for electronic limitations in battery electrodes.

Covalent Coupled Sulfur-Deficient MoS2 Nanosheets on Carbon Nanotubes toward Polysulfide Catalytic Conversion in a Lithium Sulfur Battery

The lithium sulfur battery is an attractive energy storage device because of its high theoretical capacity and energy density, but its lifetime is seriously limited by the shuttle effect of polysulfides. Herein, a rational design of vertical MoS2 nanosheets anchored on conductive carbon nanotubes through Mo–O–C covalent coupling is proposed. In this composite, the strong chemical interaction ensures rapid charge transfer at interfaces, while the sulfur-deficient and metallic 1T phase-containing MoS2 enhances the affinity with polysulfides and accelerates the reaction kinetics of polysulfide conversion. Benefitting from these merits, the composite serves as a coating layer on the separator in the lithium sulfur battery, leading to the impressive electrochemical performance of the initial capacities of 1291 mA h g–1 at 0.5 C and 1330 mA h g–1 at 0.2 C. The battery also shows an enhanced cycling stability with a low capacity fading rate of 0.089% per cycle after 500 cycles at 0.5 C.

Facile Construction of Three-Dimensional Architectures of a Nanostructured Polypyrrole on Carbon Nanotube Fibers and Their Effect on Supercapacitor Performance

Conducting polymer and carbon nanotube hybrids have been researched intensively in recent years for electrodes of fiber-shaped supercapacitors (FSSCs) toward flexible and wearable energy storage devices. Here, three-dimensional (3D) hierarchical polypyrrole (PPy)/carbon nanotube fiber (CNTF) architectures have been prepared by a facial electrodeposition method for flexible FSSC electrodes. PPy nanoparticles, vertically aligned nanowire arrays (VANAs), and nanowire networks were synthesized on CNTFs, respectively, to construct three types of 3D architectures by controlling the electrodeposition condition of PPy. The influence of the 3D architectures of PPy/CNTF electrodes on the performance of the assembled quasi-solid-state FSSCs has been carefully studied. The FSSCs with PPy VANAs showed a much higher specific capacitance than that with PPy nanoparticles because the hierarchical porous structure of PPy VANAs provides a higher accessibility of electrolytic ions and a higher Coulombic efficiency than that with the PPy nanowire network. The PPy VANA-/CNTF-based FSSCs displayed high flexibility, stability, and a specific capacitance of 178.14 F g–1 at 0.4 A g–1, which is much higher than that based on common PPy cauliflower-like film/CNTF electrodes (92.06 F g–1) and pure CNTF electrodes (8.48 F g–1) under the same conditions, demonstrating the great advantages of the 3D hierarchical structure.

Ultrafine Pt nanoparticles decorated carbon nanotubes for enhanced electrocatalytic hydrogen evolution reaction

The ultrafine Pt nanoparticles (NPs) were decorated on carbon nanotubes (CNTs) via a simple hydrothermal process and the obtained Pt/CNTs composite shows excellent electrochemical HER activity in 0.5 M H2SO4 solution. Benefiting from the synergistic effects between high catalytic activity ultrafine Pt NPs and good conductivity of CNTs, Pt/CNTs catalyst has small overpotential of 24 mV at 10 mA cm−2 and low Tafel slope of 29 mV dec-1.

Nickel Hydroxide Nanoflake/Carbon Nanotube Composites for the Electrochemical Detection of Glutamic Acid using In Vitro Stroke Model

The significance of glutamic acid in healthcare as a neurotransmitter and food additive has prompted the scientific community to develop cost-effective non-enzymatic sensors with improved sensitivity, selectivity, and stability. Herein, we propose a non-enzymatic electrochemical sensor based on low-cost transition metal hydroxides to detect glutamic acid efficiently. An n-butanol/water interface-assisted synthesis strategy was employed as an initial step to tailor two-dimensional nickel hydroxide nanoflakes. To further improve electrical conductivity, nickel hydroxide nanoflakes were composited with a small amount of highly conductive multiwalled carbon nanotubes to form NH/MWCNT composite. The NH/MWCNT composite-modified sensor demonstrated excellent detection of glutamic acid with a detection limit of 72 nM, even in the presence of many interfering groups. The practicality of the sensor in medical technology was established by its ability to detect glutamic acid released by SH-SY5Y neural cells in both normal and oxygen–glucose deprivation-stressed conditions. As an extended application, the proposed sensor was also demonstrated to detect monosodium glutamate, a food additive found in commercially available food products. Finally, as a proof of concept, an in-house flexible sensor was fabricated to monitor glutamic acid released by human neural cells and monosodium glutamate in food samples. We anticipate that the present work will contribute to the development of cutting-edge third-generation non-enzymatic sensors for glutamic acid monitoring.

Nitrogen-doped carbon confined NiFe–NiFeP nanocubes immobilized on carbon nanotube as an efficient electrocatalyst for oxygen evolution reaction

The future sustainable energy related application, especially Zn-air batteries (ZABs) and electrochemical water splitting to produce hydrogen, are limited by oxygen evolution reaction (OER). Transition metal phosphides have excellent catalytic activity for OER, but their poor conductivity and bad stability still require to be solved. Herein, the nitrogen-doped carbon (NC) confined NiFe–NiFeP nanocubes immobilized on carbon nanotube (CNT) (NiFe–NiFeP@NC/CNT) is fabricated by employing NiFe-Prussian Blue Analogs (NiFe–PBAs) nanocubes and CNT composite as precursor, and subsequent polydopamine (PDA) coating, carbonization and partial phosphorization. Profiting from its unique “nanonecklaces” structure with conductive CNT and ordered NiFe–NiFeP@NC nanocubes, NiFe–NiFeP@NC/CNT provides an efficient electron transfer path and uniformly dispersed active sites for OER process. The optimized NiFe–NiFeP@NC/CNT exhibits a low overpotential of 228 (328) mV at 10 (100) mA cm−2 and high durability. Furthermore, the NiFe–NiFeP@NC/CNT || Pt/C requires 1.51 V to realize 20 mA cm−2 for overall water spitting. And the ZAB assembled with NiFe–NiFeP@NC/CNT shows excellent discharge-charge stability for 240 h.

Diameter-dependent ultrafast lithium-ion transport in carbon nanotubes.

Ion transport in solids is a key topic in solid-state ionics. It is critical but challenging to understand the relationship between material structures and ion transport. Nanochannels in crystals provide ion transport pathways, which are responsible for the fast ion transport in fast lithium (Li)-ion conductors. The controlled synthesis of carbon nanotubes (CNTs) provides a promising approach to artificially regulating nanochannels. Herein, the CNTs with a diameter of 5.5 Å are predicted to exhibit an ultralow Li-ion diffusion barrier of about 10meV, much lower than those in routine solid electrolyte materials. Such a characteristic is attributed to the similar chemical environment of a Li ion during its diffusion based on atomic and electronic structure analyses. The concerted diffusion of Li ions ensures high ionic conductivities of CNTs. These results not only reveal the immense potential of CNTs for fast Li-ion transport but also provide a new understanding for rationally designing solid materials with high ionic conductivities.

Enhancing supercapacitor performance using nanosheet-covered nanotube structures Co3S4/Ni0.96S@CNTs with carbon nanotubes as conductive substrates.

Transition metal sulfides have broad application prospects as supercapacitor electrode materials. However, their poor structural stability and conductivity hinder improvements in their electrochemical performance. Therefore, the introduction of highly conductive carbon nanotubes (CNTs) as sulfide growth substrates is considered to improve the microstructure and electrochemical performance of electrode materials. In this study, a highly conductive CNT solution was sprayed onto a nickel foam current collector, and Co3S4/Ni0.96S was successfully constructed on a CNT conductive substrate using a combination of hydrothermal and electrochemical deposition methods, forming a unique nanosheet-covered nanotube structure Co3S4/Ni0.96S@CNTs. The addition of an appropriate concentration of CNTs can not only serve as a substrate for the growth of Co3S4/Ni0.96S, but also effectively maintain the overall nanosheet structure. Thus, the Co3S4/Ni0.96S@CNTs (2-CSNS@CNTs) have a stable structure and a wide range of electrochemical reaction sites, ensuring excellent conductivity and cycling stability. The electrode material 2-CSNS@CNTs exhibited a specific capacity of 1427.05 C g-1 at 1 A g-1. Additionally, the asymmetric supercapacitor 2-CSNS@CNTs exhibited a high energy density of 53.76 W h kg-1 at 800 W kg-1 and a capacity retention rate of 68.5% at 10 A g-1 after 1000 cycles.

Extending conducting channels in Fe-N-C by interfacial growth of CNTs with minimal metal loss for efficient ORR electrocatalysis.

Achieving a high electrocatalytic performance using a completely metal-free electrocatalyst, preferably based on only carbonaceous materials, remains a challenge. Alternatively, an efficient composite of a carbon nanostructure and a non-noble metal with minimum dependence on a metal holds immense potential. Although single-atom catalysis brings superior performance, its complex synthetic strategy limits its large-scale implementation. Previous investigation has shown that atomic dispersion (Fe-Nx-C) is accompanied by higher metal-loss compared to nanoparticle formation (Fe-NPs-N-C). Therefore, to achieve minimum metal loss, we first incorporated iron nanoparticles (Fe NPs) to N-doped carbon (N-C) and then exposed them to a cheap carbon source, melamine at high temperature, resulting in the growth of carbon nanotubes (CNTs) catalysed by those Fe NPs loaded on N-C (Fe-NPs-N-C). Thermogravimetric analysis showed that the metal-retention in the composite is higher than that in the bare carbon nanotube and even the atomically dispersed Fe-active sites on N-C. The composite material (Fe-NPs-N-C/CNT) shows a high half-wave potential (0.89 V vs. RHE) which is superior to that of commercial Pt/C towards the oxygen reduction reaction (ORR). The enhanced activity is attributed to the synergistic effect of high conductivity of CNTs and active Fe-sites as the composite exceeds the individual electrocatalytic performance shown by Fe-CNTs & Fe-NPs-N-C, and even that of atomically dispersed Fe-active sites on N-C.

Evaluating the electrocatalytic activity of flower-like Co-MOF/CNT nanocomposites for methanol oxidation in basic electrolytes.

Efficient electrocatalysts, with high tolerance to methanol oxidation, good stability, and acceptable cost are the main requisites for promising direct methanol fuel cell (DMFC) electrode materials. This target can be achieved by the integration of different active materials with unique structures. In this work, a cobalt metal-organic framework (Co-MOF) flower structure was prepared by a hydrothermal method, and then a simple ultrasonication method was employed to anchor carbon nanotubes (CNTs) in between the MOF flower petals and fabricate a Co-MOF/CNT hybrid composite. Different ratios of CNTs were used in the composite preparations, namely 25, 50, and 75 wt% of the composite. The nanocomposites were entirely investigated using different characterization techniques, such as XRD, FTIR, SEM, TEM, and XPS. Comparative electrochemical measurements confirmed that due to the integration of highly conductive CNTs with the porous active fascinating structure of Co-MOF, Co-MOF/50% CNTs exhibited improved electrocatalytic activity with a current density of 35 mA cm-2 at a potential of 0.335 V and a scan rate of 50 mV s-1. The excellent electrochemical activity and stability could be due to the synergy between Co-MOF and the CNTs that conferred adequate active sites for methanol electro-oxidation and a lower equivalent series resistance, as revealed from the electrochemical impedance spectroscopy study. This study opens a new avenue to decrease the utilization of platinum and increase the methanol oxidation activity using low-cost catalysts.

Geometrically-controlled evaporation-driven deposition of conductive carbon nanotube patterns on inclined surfaces.

Controllable accumulation of carbon nanotubes in self-assembly techniques is of critical importance in smart patterning and printed electronics. This study investigates how inclining the substrate and inhibiting the droplet spreading by sharp solid edges can affect the droplet contact angle and pinning time to improve the electrical conductivity and uniformity of the deposited patterns. Rectangular and circular pedestals were employed to investigate the effect of geometry on the deposition characteristics and to incorporate the gravitational effect by varying the substrate inclination angle. The results indicate that confining the droplet contact line to remain pinned to the pedestal edge can significantly alter the width, uniformity, and precision of the deposited patterns. These improvements correspond to the enhancement of the droplet pinning time (due to the edge effect) and to the further increase of the local evaporation rate near the contact line (due to the droplet elevation). By conducting experiments on different rectangular pedestals with varying solid-liquid interfacial areas and comparing their deposition characteristics, a rectangular pedestal with specific dimensions is selected in terms of pattern consistency and material usage efficiency. It is also shown that higher inclination angles further increase the deposited line accumulation density. Combining confinement and inclination techniques yields promising deposited patterns with high consistency and low resistivity, ranging from 8.75 kΩ mm-1 to a minimum of 0.63 kΩ mm-1 for a 3 × 6 mm2 rectangular pedestal.

Constructing metal-organic framework-derived carbon incorporated V2O5 nanowire-bundle arrays on carbon nanotube fiber as advanced cathodes for high-performance wearable zinc-ion batteries

Fiber-shaped energy storage devices with light weight, superflexibility, and weavability demonstrate promising prospects for application in wearable and portable electronics. Especially, fiber-shaped aqueous rechargeable zinc ion batteries (FARZIBs), which can facilitate the development of wearable electronic products owing to their high safety, low cost, environmental friendliness. Nevertheless, it is very challenging to achieve high rate capability, energy density, and cycling performance simultaneously for the FARZIBs. Herein, a high-performance FARZIB is created from vanadium-based metal-organic frameworks (MOFs) derived vanadic oxide (V2O5) nanowire-bundle arrays (NBAs) grown on highly conductive carbon nanotube fibers (CNTFs) directly as the binder-free cathode. Profiting from high specific area and porous structure of MOFs, as well as arrays structure and binder-free features, our as-assembled FARZIBs exhibited a high capacity of 0.71 mAh cm−2 at a current density of 2 mA cm−2, and demonstrated outstanding rate capability and prominent cycling performance. Moreover, the FARZIBs delivered an extremely high energy density of 215 mWh cm−3 at a power density of 600 mW cm−3. Therefore, our work brings new prospects for the next generation of wearable electronics.

Polymer/Carbon Composites with Versatile Interfacial Interactions for High Performance Carbon‐Based Thermoelectrics: Principles and Applications

AbstractThe urgent demand for renewable energy has attracted widespread interest in polymer‐based thermoelectric materials due to easy fabrication, high flexibility, low toxicity, low thermal conductivity, and great potential in industrial applications. However, the power factors of the polymers are still quite low compared with those of their inorganic counterparts, resulting in a low energy conversion efficiency. Highly conductive carbon materials, including graphene and carbon nanotubes, have recently been incorporated into the polymer matrix through intrinsic chemical intimacy, providing new opportunities to tune the thermoelectric properties. In particular, the characteristic π‐π coupling and other interactions between the two components have contributed to unique mechanisms for better thermoelectric performance beyond the simple rule of mixtures. This paper aims to review the up‐to‐date progress in polymer/carbon nanocomposites along with various compositions and novel synthetic strategies. The salient aspects of this review are characteristic interactions and various mechanisms, which might result in enhanced thermoelectric properties and subsequent potential applications in energy harvesting, wearable electronics, photo‐thermoelectrics, and other devices.

Scalable, flexible, and hierarchical porous conductive nanocomposites for self-powered and pressure sensing dual-mode integration

Multimodal sensing is promising in applications of fast responses to multi-source stimulus under complex tasks like intelligent robot perception and human motion monitoring. In this work, a flexible piezoresistive carbon nanotubes (CNTs) nanocomposites-based triboelectric nanogenerator (PC-TENG) dual-modal sensor is presented. Such hierarchical porous structures based on CNTs/polydimethylsiloxane (PDMS) nanocomposites were prepared by a facile scalable template sacrifice method. The dual-modal PC-TENG sensor can achieve decoupling responses of self-powered and self-sensing by optimizing conductive and dielectric properties of nanocomposites, via integrating elastic porous PDMS structures embedded with percolating conductive CNTs networks. The PC-TENG sensor exhibits high performances of triboelectric output with an open-circuit voltage of 120 V, a short-circuit current of 8 μA, and an output power of up to 139.5 μW, as well as low hysteresis and highly sensitive piezoresistive effect. The excellent electromechanical property of PC-TENG sensor enables it to be used as a self-powered and piezoresistive dual-mode flexible sensor. We further demonstrated that PC-TENG sensor has a dualmodal sensing precision and rapid response capability that facilitates detections of wearable devices operation, health monitoring devices in complex environments without being interfered by a single signal.

Highly Stretchable Composite Foams via Sustainable Utilization of Waste Tire Rubbers for Temperature-Dependent Electromagnetic Wave Absorption.

Recently, the sustainable utilization of waste resources has become a low-cost and effective strategy to design high-performance functional materials to solve the increasingly serious environmental pollution problem. Herein, the flexible and highly stretchable polyurethane (PU) composite foams assisted by one-dimensional carbon nanotubes (CNTs) and zero-dimensional Fe3O4 were fabricated using waste tire rubbers (WTRs) as reinforcements during a simple self-foaming process. The collaborative introduction of conductive CNTs, magnetic Fe3O4, and WTRs with three-dimensional cross-linked structures enabled the construction of an efficient electronic transmission path and heterointerfaces inside the composite foam. The resulting composite foam possessed a desired minimum reflection loss (RLmin) of −47.43 dB, and also exhibited superior mechanical properties with a tensile strength of >3 MPa and multiple tensile deformation recovery abilities. In addition, increasing the temperature could significantly improve the electromagnetic wave absorption performance of the composite foam. This comprehensive composite foam derived from WTRs has shown a promising development potential for using waste materials to relieve electromagnetic pollution.

The Use of Electrochemical Impedance Spectroscopy as a Tool for the In-Situ Monitoring and Characterization of Carbon Nanotube Aqueous Dispersions.

So far, there is no validated technology for characterizing the dispersion and morphology state of carbon nanotubes (CNTs) aqueous dispersions during sonication. Taking advantage of the conductive nature of CNTs, the main hypothesis of the current study is that Electrochemical Impedance Spectroscopy (EIS) is an appropriate technique for the in-situ monitoring and qualification of the dispersion state of CNTs in aqueous media. To confirm our hypothesis, we monitored the Impedance |Z| during the sonication process as a function of type CNTs/admixtures used for the preparation of the aqueous solutions and of crucial process parameters, such as the applied sonication power and duration (i.e., sonication energy). For dispersions above the percolation threshold, a drop of |Z| by approximately seven orders of magnitude was observed, followed by a linear reduction. The dramatic change in |Z| is regarded as an indication of the formation of a conductive path or destruction of an existing one during sonication and can be used to characterize the dispersion and morphology state of CNTs. The results of the EIS provide, straightforwardly and reliably, the required information to create an optimum dispersion protocol for conductive CNT suspensions. The produced dispersions are part of research focusing on the manufacturing of cement-based composite materials with advanced thermoelectric functionalities for energy harvesting. Such dispersions are not only limited to energy harvesting applications but also to applications where functionalities are introduced through the use of conductive-based suspensions.

Rheological, Thermal and Mechanical Characterization of Toughened Self-Healing Supramolecular Resins, Based on Hydrogen Bonding.

This paper proposes the design of toughened self-healing supramolecular resins able to fulfill functional and structural requirements for industrial applications. These new nanocomposites are based on compounds acting as promotors of reversible self-healing interactions. Electrically conductive carbon nanotubes, selected among those allowing to reach the electrical percolation threshold (EPT) with a very low amount of nanofiller, were dispersed in the self-healing polymeric matrix to contrast the electrical insulating properties of epoxy matrices, as required for many applications. The formulated supramolecular systems are thermally stable, up to 360 °C. Depending on the chemical formulation, the self-healing efficiency η, assessed by the fracture test, can reach almost the complete self-repairing efficiency (η = 99%). Studies on the complex viscosity of smart nanocomposites highlight that the effect of the nanofiller dominates over those due to the healing agents. The presence of healing compounds anchored to the hosting epoxy matrix determines a relevant increase in the glass transition temperature (Tg), which results in values higher than 200 °C. Compared to the unfilled matrix, a rise from 189 °C to 223 °C is found for two of the proposed formulations.

Outside Front Cover: Volume 3 Issue 4

Outside front cover image: A customizable and multi-functional electronic conductive organogel is proposed by combining conductive carbon nanotube clusters and flexible adhesive organogels. Based on customizable conductive networks and entropy-driven organogel actuation, the conductive organogels can sense various strain and stress signals and imitate natural organisms with muscle actuation and neurofeedback. This strategy for preparing electronic conductors can enhance the rational design of soft robotics and flexible sensors, facilitating further progress of artificial intelligent systems. (DOI: https://doi.org/10.1002/smm2.1108)

Wearable ultraviolet sensing fibers embedded with carbon nanotubes and zinc oxide nanowires

Owing to the increasing interest in personal health, the real-time measurement of the exposure to ultraviolet (UV) rays during outdoor activities is a key technology that could be widely applied in the field of smart healthcare. Although wearable sensors that respond to UV intensity are being investigated, the development of sensors with stable durability and excellent sensing characteristics, despite movements, such as bending and exposure to external factors, including sweat and rain, is insufficient. In this study, we fabricated a wearable UV fiber sensor by embedding conductive carbon nanotubes (CNTs) and UV-sensitive zinc oxide nanowires (ZnO NWs) into highly elastic spandex fiber via a simple dipping-drying procedure. The ZnO NWs and CNTs coated in the form of a network inside the strands that constitute the spandex fiber enhanced the stability of the UV sensing measurements despite external changes, such as bending. In addition, by coating hydrophobic (3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)phosphonic acid onto the ZnO NWs, the current distortion of the UV sensing channel due to contact with liquid could be prevented. It was confirmed that the fiber-based UV sensor, in which ZnO NWs and CNTs are networked, responds sensitively to UV in an environment with exposure to water or sweat.