Three-dimensional Carbon Nanotube Research Articles

High Strength Conductive Polyamide 6 Nanocomposites Reinforced by Prebuilt Three-Dimensional Carbon Nanotube Networks.

The rapidly growing fields of aerospace, energy, and electronic devices raise the demand for materials with ever-increasing mechanical properties and electrical and thermal conductivity. However, the combination of unusual high performance is difficult to attain. In this study, using prebuilt three-dimensional (3D) closely packed interconnected multiwalled carbon nanotube (MWNT) networks as a backbone for assembly of polymer matrix, a novel, green (solvent-free), and energy-saving method to prepare robust, highly electrical, and thermal conductive polyamide nanocomposites is reported. The as-prepared nanocomposites exhibit significant enhancements of 16 orders of magnitude in electrical conductivity and 505% in thermal conductivity, which mainly benefits from the contributions of closely packed 3D networks and conductive pathways of carbon nanotubes. In addition, even at a high MWNT loading of 25 wt %, the as-prepared nanocomposites still possess a high tensile strength of 99.4 MPa and Young's modulus of 5.3 GPa. The performance of the as-prepared nanocomposites exceeds that of most of the composites, which confirms the potential of the prebuilt MWNT network method for fabricating robust and highly conductive nanocomposites and the importance of good interconnectivity of nanofillers-nanofillers and nanofillers-matrix. The special fabrication method could open up a broad range of possibilities for aerospace, conducting elements, and structural nanomaterials, as well as electronic components with the requirements of heat dissipation, mechanical strength, thermal repair, corrosion resistance, and so on.

A high performance all-solid-state flexible supercapacitor based on carbon nanotube fiber/carbon nanotubes/polyaniline with a double core-sheathed structure

A new type of ternary carbon nanotube fiber (CNF)/three-dimensional (3D) porous carbon nanotubes (CNTs)/polyaniline (PANI) electrodes with a double core-sheathed architecture composed of CNF/CNTs and CNTs/PANI was fabricated via low-potential electrophoretic deposition of CNTs and subsequent electrochemical polymerization of PANI on the CNF surface. The resulting all-solid-state supercapacitor possesses a high specific capacitance of 67.31 mF cm−2 at the current density of 0.5 mA cm−2 and only a loss as less as 10% of its initial specific capacitance after 5000 charge-discharge cycles. Furthermore, it is capable of withstanding different bending deformations, and can maintain 99.8% capacitance, even after experiencing the bending of 180° for 500 times, which manifests a significant application potential in the field of flexible electronic devices.

Three-dimensional carbon nanotube yarn based solid state solar cells with multiple sensitizers exhibit high energy conversion efficiency

Fiber-type dye sensitized solar cells that are non-metallic, flexible, and thread-like in structure have many potential military and functional textile applications. With the use of quantum dots (QD), exciton transfer facilitators (Phenyl-C61-butyric acid methyl ester-PCBM) and Poly(3-hexylthiophene-2,5-diyl-P3HT), and careful preparation of the TiO2 oxide layer deposited on the carbon fiber working electrode, an optimized efficiency of 7.6% was obtained. Carbon nanotube yarn (CNTY) was used to prepare both the working and counter electrodes of the fabricated cells. TiCl4 annealing of the TiO2 layer was carried out and the resulting oxide layer morphology was found to be very uniform. The quantum dots, cadmium sulfide (CdS) and cadmium selenide (CdSe), were deposited directly onto the surface of the nanoporous oxide layer using chemical bath deposition (CBD). Also, the P3HT and PCBM were applied and deposited via CBD on the working electrode as a bulk heterojunction material. Potentiometric characterization of the prepared cells performed at different cell lengths and showed that the maximum efficiency was obtained for cells approximately 3.5 cm in length. Photovoltaic performance of these solid state three dimensional cells was also carried out for different cell configurations.

Lithium-Sulfur Batteries: The Effect of High Sulfur Loading on the Electrochemical Performance

Sulfur as a cathode material is a well-known candidate for next generation Li metal-based batteries. However, the intrinsic limitations associated with low conductivity of sulfur and instability of Li metal anode prevents the commercialization of lithium sulfur batteries. Many researches have studied the cathode design to improve the electrochemical performance. However, not many have emphasized on the high sulfur and minimal electrolyte loadings to compete against the currently available Li-ion batteries. Here, we use binder-free three-dimensional carbon nanotubes (3D CNTs)/sulfur (S) as a cathode material to test different electrolyte to sulfur ratios (E/S ratio of 6 to 10). We also pair the cathode against the MoS2-protected Li anode for enhanced electrochemical performance and cycling stability. Thus, we obtain a reversible specific capacity of ~930 mAh g-1 for up to 1000 cycles.

Three-Dimensional Carbon Nanotube/Transition-Metal Oxide Sponges as Composite Electrodes with Enhanced Electrochemical Performance

Innovative three-dimensional (3D) carbon nanotube (CNT)/transition-metal oxide (TMO) sponge electrodes are synthesized by freeze-drying and calcination processes. The high specific surface area and...

Stretchable and compressible strain sensor based on carbon nanotube foam/polymer nanocomposites with three-dimensional networks

In this study, a flexible strain sensor based on nanocomposites filled with three-dimensional carbon nanotube (CNT) foam was developed. CNT sample was prepared by using melamine-formaldehyde foam as a template, and the prepared material showed hydrophobic properties and the ability to spontaneously adsorb uncured polymer (polydimethylsiloxane) with excellent structural stability, thus ultimately eliminating the problems associated with the dispersion and re-agglomeration of CNTs in a polymer matrix. The flexible nanocomposite sensor showed excellent piezoresistivity under both compression and tension strain with high sensitivity and could be sustained with outstanding stability under the cyclic runs. The principle verification results demonstrated that the developed sensor could monitor the motion of a finger and serve as an electronic skin to display the distribution of pressure, suggesting its great potential for applications in wearable and flexible electronics.

Palladium Nanoparticles Anchored on Three-Dimensional Nitrogen-Doped Carbon Nanotubes as a Robust Electrocatalyst for Ethanol Oxidation

Palladium nanoparticles were uniformly anchored on nitrogen-doped carbon nanotubes with a three-dimensional network structure (denoted as Pd/3DNCNTs) through a facile, surfactant-free, and green approach with ethanol as the reducing agent. As a robust catalyst for the ethanol electrocatalytic oxidation reaction (EOR), Pd/3DNCNTs exhibit superior improved electrocatalytic activity, accelerated kinetics, and robust stability, mainly attributed to the unique architecture features of the 3DNCNTs. The results of this part of the work reveal that the Pd/3DNCNTs with an infusive electrochemical property for EOR are promising for direct ethanol fuel cells (DEFCs) and various other applications in electrochemistry. Additionally, the green approach probably provides some new ideas for the design of other new catalysts for fuel cells.

Lithium-Sulfur Batteries: The Effect of High Sulfur Loading on the Electrochemical Performance

It is no secret that sulfur as a cathode material is a promising candidate for next generation Li metal-based batteries. However, the intrinsic limitations associated with low conductivity of sulfur and instability of sulfur based composite prevents the commercialization of lithium sulfur batteries. For the past years of Li-S batteries research, many research has been carried out on the cathode design to improve the electrochemical performance. However, it has been mathematically determined that even with high sulfur loading amount and effective sulfur utilization, the true value of energy density cannot outperform the currently available LIBs. That is, other inactive materials must be utilized to address the inherent sulfur issues which would only add more weight. Thus, we propose a novel and facile synthesis of binder-free three-dimensional carbon nanotubes (3D CNTs)/sulfur (S) hybrid composite as an electrode material, where 3D CNTs provide a high conduction path and short diffusion length for Li-ions, while providing ample amount of space for higher sulfur loading. In addition to sulfur loading, the amount of electrolyte also determines the electrochemical performance of Li-S cell in terms of sulfur utilization and cycling stability. However, the statistical analysis shows that more than 90% of reported publications have neglected this E/S ratio. This is important parameter for determining sulfur utilization and energy density of the cell. Here, we report the performance of three-dimensional carbon nanotubes/sulfur hybrid composite with different sulfur loading amounts from 1 to 9 mg/cm2 while tuning the electrolyte/sulfur (E/S) ratio from 12 to 1. The results have demonstrated the E/S ratio of 7 (60 µL electrolyte to 8.5 mg cm-2 sulfur) with reversible specific capacity of ~1068 mAh g-1 at 0.1C rate (~1.4mA cm-2) for up to 150 cycles.

A Binder-Free Carbon-RuO2 Composite Cathode for Rechargeable Li-O2 Batteries

A rechargeable lithium–oxygen (Li–O2) battery is considered as a promising technology for electrochemical energy storage systems, because its theoretical energy density is about ten times higher than those of state-of-the-art Li-ion batteries. The cathode (positive electrode) for Li–O2 batteries is made of carbon and polymeric binders; however, these constituents undergo parasitic decomposition reactions during battery operation, which in turn causes considerable performance degradation. Therefore, the rational design of the cathode is necessary for building robust and high-performance Li–O2 batteries. Here, a binder-free carbon nanotube (CNT) electrode surface-modified by atomic layer deposition (ALD) of dual acting RuO2 as an inhibitor–promoter is proposed for rechargeable Li–O2 batteries. The electrode architecture was designed and fabricated by taking the following features of CNT and ALD into consideration. (i) A free-standing sheet of CNTs can be prepared via a simple filtration procedure without using any binders. (ii) Given that the surface of multi-walled CNTs is very inert, the ALD process yields preferential nucleation–growth of isolated nanoparticles on defect sites rather than producing continuous films on the entire CNT surface. With its proven activity, therefore, RuO2 anchored preferentially to defect sites can play a dual role as an inhibitor (passivating structural defects on CNTs) and a promoter (facilitating electrochemical Li2O2 decomposition). (iii) The ALD process based on sequential, self-limiting reactions allows for the deposition of highly uniform RuO2 nanoparticles within the three-dimensional CNT electrode, which leads to decreased Ru loading while maintaining high catalytic performance. The binder-free RuO2/CNT cathode shows outstanding electrochemical performance as characterized by small voltage gaps (~0.9 V) as well as excellent cyclability without any signs of capacity decay over 80 cycles. The excellent electrochemical performance could be explained by the unique features of the electrode: (i) the absence of polymeric binders with high reactivity with Li2O2 and (ii) the dual function of RuO2 nanoparticles to inhibit carbon decomposition on CNT defects and to promote electrochemical Li2O2 decomposition.

Morphological control of three-dimensional carbon nanotube anode for high-capacity lithium-ion battery

In this paper, we report the results of modulating the processing conditions (mainly, temperature) of a two-step method consisting of sputtering deposition of a Ni catalytic layer and chemical vapor deposition (CVD) of carbon nanotubes (CNTs) on a three-dimensional (3D)-structured Cu mesh to control the morphology of CNTs for advanced Li-ion battery (LIB) applications. We disclosed that CNT growth at a low temperature (700 °C) produced small-diameter CNTs (CNT_S) with an average diameter of ∼20 nm, while that at a high temperature (750 °C) produced large-diameter CNTs (CNT_L) with an average diameter of 200–300 nm. The high-resolution transmission electron microscopy (HR-TEM) and Raman analyses manifested poorly crystalline CNTs for both samples. CNT_S showed a specific capacity of 476 mAh g−1, which is ∼176% superior to that of CNT_L (271 mAh g−1) and ∼128% higher than the theoretical capacity of the state-of-the-art graphites and recently reported nanostructured carbon-based anode materials.

Thermal conductivity characterization of three dimensional carbon nanotube network using freestanding sensor-based 3ω technique

A novel three-dimensional (3D) carbon nanotube (CNT) network, composed of vertically aligned CNT array (primary CNT) bridged with randomly oriented secondary CNT, is synthesized in this work. We report the first data for the thermal properties of this new structure using freestanding sensor-based 3ω technique. Introducing freestanding sensor to conventional 3ω system enables the nondestructive characterization for samples with rough surfaces. The thermal conductivities of CNT films, as well as the contact resistance between the sensor and sample surfaces, are extracted numerically by a finite-element thermal model. The thermal conductivities of 3D CNT network under different array densities range from 9.3 to 19.8 W/mK. It is found that at lower CNT array density of 5.6 × 108/cm2, the growth of secondary CNT enhances the thermal conductivity of primary CNT array by 55.9%. This significant improvement in thermal conductivity can be attributed to the additional thermal pathway provided by the secondary CNTs in the primary CNT forest. However as the density of primary CNT array increases beyond 7.2 × 108/cm2, the growth of secondary CNTs on primary CNT forest reduces its thermal conductivity. This reduction in thermal conductivity can possibly be caused by the excessive thermal resistance from the CNT-CNT connection points within 3D CNT network.

Novel three-dimensional carbon nanotube networks as high performance thermal interface materials

Vertically aligned carbon nanotube (VACNT) arrays are considered as promising thermal interface materials (TIMs) due to their superior out-of-plane thermal conductivities. However the air gaps between adjacent CNTs within the CNT array hinder the in-plane heat transfer, thus significantly degrading the thermal performance of VACNT-based TIMs. To improve the in-plane thermal conduction of VACNT arrays, we propose a novel three dimensional CNT (3D CNT) network structure, where VACNTs are cross-linked by randomly-oriented secondary CNTs. Three different catalyst preparation methods for the secondary CNT growth are compared in terms of their ability to produce a dense network of secondary CNTs. The 3D CNT network grown using the chemical impregnation method shows a denser network structure, and thus is chosen for further thermal characterization. The temperature fields of the corresponding 3D CNT network under different heating powers are recorded using a 15 μm-resolution infrared thermal imaging system. The in-plane thermal conductivity is then derived from these fields using numerical fitting with a 3D heat diffusion model. We find that the in-plane thermal conductivity of the 3D CNT network is 5.40 ± 0.92 W/mK, at least 30 times higher than the thermal conductivity of the primary VACNT array used to grow the 3D CNT network.

Polyaniline-encapsulated silicon on three-dimensional carbon nanotubes foam with enhanced electrochemical performance for lithium-ion batteries

Seeking free volume around nanostructures for silicon-based anodes has been a crucial strategy to improve cycling and rate performance in the next generation Li-ion batteries. Herein, through a simple pyrolysis and in-situ polymerization approach, the low cost commercially available melamine foam as a soft template converts carbon nanotubes into highly dispersed and three-dimensionally interconnected framework with encapsulated silicon/polyaniline hierarchical nanoarchitecture. This unique core-sheath structure based on carbon nanotubes foam integrates a large number of mesoporous, thus providing well-accessible space for electrolyte wetting, whereas the carbon nanotubes matrix serves as conductive thoroughfares for electron transport. Meanwhile, the outer polyaniline coated on silicon nanoparticles provides effective space for volume expansion of silicon, further inhibiting the active material escape from the current collector. As expected, the PANI-Si@CNTs foam exhibits a high initial specific capacity of 1954 mAh g−1 and retains 727 mAh g−1 after 100 cycles at 100 mA g−1, which can be attributed to highly electrical conductivity of carbon nanotubes and protective layer of polyaniline sheath, together with three-dimensionally interconnected porous skeleton. This facile structure can pave a way for large scale synthesis of high durable silicon-based anodes or other electrode materials with huge volume expansion.

Three-dimensional macroporous CNTs microspheres highly loaded with NiCo2O4 hollow nanospheres showing excellent lithium-ion storage performances

Three-dimensional macroporous carbon nanotubes microspheres highly loaded with phase-pure NiCo2O4 hollow nanospheres are synthesized by the spray pyrolysis process and are characterized for potential use in lithium-ion batteries. Polystyrene nanobead template and the nanoscale Kirkendall diffusion process are first combined and are applied to the spray pyrolysis process to form macroporous NiCo2O4/carbon nanotubes composite microspheres with extremely high rate performance as anode materials for lithium-ion batteries. Metallic NiCo2/carbon nanotubes composite microspheres—formed as intermediate products—are transformed into composite microspheres of phase-pure NiCo2O4 hollow nanospheres and carbon nanotubes by the nanoscale Kirkendall diffusion process. The mean size of the hollow NiCo2O4 nanospheres decorated on the carbon nanotubes backbone is 28 nm. The macroporous NiCo2O4/carbon nanotubes composite microspheres have discharge capacities of 840, 748, 677, 591, 514, 451, 391, 337, and 289 mA h g−1 at current densities of 0.5, 1, 2, 5, 10, 15, 20, 25, and 30 A g−1, respectively. The discharge capacity of the macroporous NiCo2O4/carbon nanotubes microspheres for the 500th cycle at a current density of 3 A g−1 is 572 mA h g−1. The uniquely structured hollow NiCo2O4 nanosphere/carbon nanotubes composite microspheres have superior cycling and rate performances for lithium-ion storage.

Honeycomb-like NiCo2O4@Ni(OH)2 supported on 3D N−doped graphene/carbon nanotubes sponge as an high performance electrode for Supercapacitor

In order to increase the energy density of supercapacitor, a new kind electrode material with excellent structure and outstanding electrochemical performance is highly desired. In this article, a new type of three-dimensional (3D) nitrogen-doped single-wall carbon nanotubes (SWNTs)/graphene elastic sponge (TRGN−CNTs−S) with low density of 0.8mgcm−3 has been successfully prepared by pyrolyzing SWNTs and GO coated commercial polyurethane (PU) sponge. In addition, high performance electrode of the honeycomb-like NiCo2O4@Ni(OH)2/TRGN-CNTs-S with core-shell structure has been successfully fabricated through hydrothermal method and then by annealing treatment and electrochemical deposition method, respectively. Benefited from 3D structural feature, the compressed NiCo2O4@Ni(OH)2/TRGN-CNTs-S electrode exhibits high gravimetric and volumetric capacitance of 1810Fg−1, 847.7Fcm−3 at 1Ag−1. The high rate performance and long-term stability was also obtained. Furthermore, an asymmetric supercapacitor using NiCo2O4@Ni(OH)2/TRGN-CNTs-S cathode and NGN/CNTs anode delivered high gravimetric and volumetric energy density of 54Whkg−1 at 799.9Wkg−1 and 37WhL−1 at 561.5WL−1. In summary, an excellent electrochemical electrode with new elastic 3D SWNTs/graphene supports and binder free pseudocapacitive materials was introduced.

Three-Dimensional Porous Carbon Nanotube Papers as Current Collector and Buffer for SnO2 Anodes

A novel three-dimensional porous conductive papers have been successfully synthesized via a simple physical route. Multi-walled carbon nanotubes (MWCNTs)@SnO2 composite anode materials are embedded in porous conductive papers. The peculiar structure can accommodate the huge volume expansion of MWCNTs@SnO2 composite anode materials during charge–discharge process. The framework formed by MWCNTs and cellulose can greatly improve the strength, stability and flexibility of the electrode. In addition, the structure successfully prevent the aggregation of SnO2 nanoparticles and collapse of MWCNTs@SnO2 composite electrode, leading to the improvement in electrochemical utilization and stable cyclability. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The electrochemical properties and application were evaluated by galvanostatic discharge–charge testing and cycling voltammetry. As a result, the MWCNTs@SnO2 composite electrode showed excellent rate performance. The discharge capacity remains about 680[Formula: see text]mAh g[Formula: see text] after 100 cycles at 200[Formula: see text]mA g[Formula: see text], and even around 300[Formula: see text]mAh g[Formula: see text] at 1000[Formula: see text]mA g[Formula: see text].

Electrodeposition of Metals and Their Oxides on Electrochemically Modified Three-Dimensional Carbon Nanotubes

The change in the qualitative and quantitative composition of oxygen-containing surface groups on the fibers of carbon-fibrous and nanocarbon materials is studied as a result of their electrochemical modification in solutions of indifferent electrolytes. The effect of preliminary electrode treatment on the efficiency of electrodeposition of metals on carbon-fibrous and nanocarbon materials is shown by the example of electrodeposition of cadmium, copper, nickel, and platinum, and that of metal oxides by the example of precipitation of manganese oxide. Preliminary electrochemical treatment of these carbon materials allows obtaining precipitates in the form of nanosized particles and in the form of continuous coating with good adhesion to the surface of the fibers of carbon materials.

Facile assembly of Ni(OH)2 nanosheets on nitrogen-doped carbon nanotubes network as high-performance electrocatalyst for oxygen evolution reaction

Developing non-noble metal-based electrocatalysts with cost-effective materials for water splitting is critical to clean energy generation and storage. However, the process of water splitting is greatly hindered by the oxygen evolution reaction (OER), which is kinetically sluggish and requires large overpotentials. Herein, we report an active and stable OER catalyst by electrodeposition of ultrathin Ni(OH)2 nanosheets on three-dimensional interwoven nitrogen-doped carbon nanotubes (N-CNTs). The Ni(OH)2 nanosheets grown on the N-CNTs afforded a current density of 10 mA cm−2 at the overpotential of only 254 mV, smaller than the commercial IrO2 catalyst. Moreover, the as-prepared catalyst shows long-term durability almost without degradation over 100 h. The excellent OER activity can be ascribed to the unique layered structure of Ni(OH)2, the ultrathin and interconnected features of the nanosheets, and the three-dimensional (3D) porous conducting network of the N-CNTs. The rational design strategy can be extended to the preparation of other non-precious metal catalysts with enhanced OER performance.

Encased Copper Boosts the Electrocatalytic Activity of N-Doped Carbon Nanotubes for Hydrogen Evolution.

Nitrogen (N)-doped carbons combined with transition-metal nanoparticles are attractive as alternatives to the state-of-the-art precious metal catalysts for hydrogen evolution reaction (HER). Herein, we demonstrate a strategy for fabricating three-dimensional (3D) Cu-encased N-doped carbon nanotube arrays which are directly grown on Cu foam (Cu@NC NT/CF) as a new efficient HER electrocatalyst. Cu nanoparticles are encased here instead of common transition metals (Fe, Co, or Ni) for pursuing a well-controllable morphology and an excellent activity by taking advantage of its more stable nature at high temperature and in acidic or alkaline electrolyte. It is discovered that metallic Cu exhibits strong electronic modulation on N-doped carbon to boost its electrocatalytic activity for HER. Such a nanostructure not only offers plenty of accessible highly active sites but also provides a 3D conductive open network for fast electron/mass transfer and facilitates gas escape for prompt mass exchange. As a result, the Cu@NC NT/CF electrode exhibits superior HER performance and durability, outperforming most of the reported M@NC materials. Furthermore, the etching experiments together with X-ray photoelectron spectroscopy (XPS) analysis reveal that the electronic modulation from encased Cu significantly enhances the HER activity of N-doped carbon. These findings open up opportunities for exploring other Cu-based nanomaterials as efficient electrocatalysts and understanding their catalytic processes.

Construction of Hierarchical CNT/rGO-Supported MnMoO4 Nanosheets on Ni Foam for High-Performance Aqueous Hybrid Supercapacitors.

Rationally designed conductive hierarchical nanostructures are highly desirable for supporting pseudocapacitive materials to achieve high-performance electrodes for supercapacitors. Herein, manganese molybdate nanosheets were hydrothermally grown with graphene oxide (GO) on three-dimensional nickel foam-supported carbon nanotube structures. Under the optimal graphene oxide concentration, the obtained carbon nanotubes/reduced graphene oxide/MnMoO4 composites (CNT/rGO/MnMoO4) as binder-free supercapacitor cathodes perform with a high specific capacitance of 2374.9 F g-1 at the scan rate of 2 mV s-1 and good long-term stability (97.1% of the initial specific capacitance can be maintained after 3000 charge/discharge cycles). The asymmetric device with CNT/rGO/MnMoO4 as the cathode electrode and the carbon nanotubes/activated carbon on nickel foam (CNT-AC) as the anode electrode can deliver an energy density of 59.4 Wh kg-1 at the power density of 1367.9 W kg-1. These superior performances can be attributed to the synergistic effects from each component of the composite electrodes: highly pseudocapacitive MnMoO4 nanosheets and three-dimensional conductive Ni foam/CNTs/rGO networks. These results suggest that the fabricated asymmetric supercapacitor can be a promising candidate for energy storage devices.