MWCNT Network Research Articles

Constructing multiple interfaces in polydimethylsiloxane/multi-walled carbon nanotubes nanocomposites by the incorporation of cotton fibers for high-performance electromagnetic interference shielding and mechanical enhancement

Reflection of electromagnetic waves at multiple interfaces and then absorption in the matrices has been well demonstrated to efficiently improve electromagnetic interference (EMI) shielding of conductive polymer composites (CPC). In this study, a large number of multiple interfaces were constructed in polydimethylsiloxane/multi-walled carbon nanotubes (PDMS/MWCNT) nanocomposites by the incorporation of cotton fibers (CTF). The electromagnetic radiation was efficiently attenuated by the wave reflection at the multiple interfaces and then absorption at the interfaces of PDMS/CTF and CTF/MWCNT in the nanocomposites. The EMI shielding effectiveness (SE) of the PDMS/MWCNT nanocomposites with 2.0 and 3.0 vol% MWCNT increased from ∼16 to ∼30 dB, ∼20 to ∼41 dB by adding 15 vol% CTF, respectively. A relatively dense MWCNT network, which was also formed in the PDMS/MWCNT/CTF nanocomposites because of the volume occupation effect of CTF, resulted in the high electrical conductivity and low percolation threshold. For example, the electrical conductivity of the PDMS/MWCNT nanocomposites with 0.5 vol% MWCNT increased from 1.65 × 10-4 to 0.23 S/m, and the percolation threshold of the composites deceased from 0.44 to 0.2 vol% by the addition of 15 vol% CTF. In addition, the mechanical properties, especially the Young’s modulus and tensile strength, of PDMS/MWCNT nanocomposites were enhanced by the incorporation of CTF and the flexible property was maintained because of the high interfacial interaction between PDMS and CTF and the high aspect ratio of CTF. Furthermore, the samples exhibited highly reliable EMI SE even after bending 6000 times, suggesting the potential application in body protection and flexible electronic devices.

Unified equivalent circuit model for carbon nanotube-based nanocomposites

Carbon nanotubes form a complex network in nanocomposites. In the network, the configuration of the nanotubes is various. A carbon nanotube may be curled or straight, and it may be parallel or crossed to another. As a result, carbon nanotube-based composites exhibit integrated characteristics of inductor, capacitor and resistor. In this work, it is hypothesised that carbon nanotube-based composites all adhere to a RLC interior circuit. To verify the hypothesis, three different composites, viz multi-walled carbon nanotube/polyvinylidene fluoride (MWCNT/PVDF), multi-walled carbon nanotube/epoxy (MWCNT/EP), multi-walled carbon nanotube/polydimethylsiloxane (MWCNT/PDMS) were fabricated and tested. The resistances and the dielectric loss tangent (tanδ) of the materials were measured in direct and alternating currents. The measurement shows that the value of tanδ is highly affected by the volume fraction of MWCNT in the composites. The experimental results prove that the proposed RLC equivalent circuit model can fully describe the electrical properties of the MWCNT network in nanocomposites. The RLC model provides a new route to detect the inductance and capacitance of carbon nanotubes. Moreover, the model also indicates that the carbon nanotube-based composite films may be used to develop wireless strain sensors.

Metal-free, flexible triboelectric generator based on MWCNT mesh film and PDMS layers

We demonstrate a metal-free triboelectric energy harvester consisted of MWCNT mesh film and PDMS layer. Upon touch from a finger, the single electrode-mode energy harvester generates up to 27.0 W/m2 output power at 10 MΩ matched impedance. The device generates stable power upon touch by bare fingers or gloved fingers. Using copper counter electrode results in decreased power output, due to the weaker tendency in triboelectrification. The power output also scales with the pressure applied by the finger. The intertwined, condensed MWCNT network acts as a flexible yet effective current collector, with resistance across the device less than 10 Ω. This current collector possesses strong corrosion resistance and stability against potential oxidation, while its metal counterpart may undergo oxidation over extended exposure to air or frequent fracture upon straining. The flexible device form may be applied to various curved or irregular surfaces that undergo frequent human touches.

Controlled morphology of MWCNTs driven by polymer-grafted nanoparticles for enhanced microwave absorption

A simple and robust platform, based on polymer-grafted nanoparticles to facilitate a controlled morphology of nano-fillers, provides a route for strategically designing nanostructured EM wave absorbers with a percolated MWCNT network as well as a controlled NP arrangement.

Free-standing compact cathodes for high volumetric and gravimetric capacity Li–S batteries

Free-standing compact Li–S cathodes with high volumetric/gravimetric capacities are prepared by embedding highly porous S-loaded carbon nanospheres into dense MWCNT networks.

Free-standing and flexible LiMnTiO4/carbon nanotube cathodes for high performance lithium ion batteries

A flexible, free-standing, and light-weight LiMnTiO4/MWCNT electrode has been prepared by vacuum filtration method for the first time. The as-prepared flexible LiMnTiO4/MWCNT electrode possesses a three-dimensional braiding structure in which LiMnTiO4 particles are well embedded in the twining CNT networks. The novel LiMnTiO4/MWCNT electrodes show tensile strength of 1.34 MPa and 2.04 MPa, when the percentages of MWCNTs reach to 30% and 50%, respectively. This novel flexible electrode exhibits a superior electrochemical property, especially at rate capability and cycling stability. The LiMnTiO4/MWCNT electrode can deliver capacity of 161 mAh g−1 (86.4% retention) after 50 cycles at 0.5C rate. Since the high conductivity from MWCNT networks, the LiMnTiO4/MWCNT electrode can still maintain a capacity of 77 mAh g−1 at 5C rate, which is much higher than that of the conventional electrode fabricated by slurry casting method on Al foil. The features of free-standing, light-weight, and excellent electrochemical performance indicate the potential of using the LiMnTiO4/MWCNT cathode in new-generation flexible lithium ion batteries.

Performance Enhancement and Side Reactions in Rechargeable Nickel–Iron Batteries with Nanostructured Electrodes

We report for the first time a solution-based synthesis of strongly coupled nanoFe/multiwalled carbon nanotube (MWCNT) and nanoNiO/MWCNT nanocomposite materials for use as anodes and cathodes in rechargeable alkaline Ni-Fe batteries. The produced aqueous batteries demonstrate very high discharge capacities (800 mAh gFe(-1) at 200 mA g(-1) current density), which exceed that of commercial Ni-Fe cells by nearly 1 order of magnitude at comparable current densities. These cells also showed the lack of any "activation", typical in commercial batteries, where low initial capacity slowly increases during the initial 20-50 cycles. The use of a highly conductive MWCNT network allows for high-capacity utilization because of rapid and efficient electron transport to active metal nanoparticles in oxidized [such as Fe(OH)2 or Fe3O4] states. The flexible nature of MWCNTs accommodates significant volume changes taking place during phase transformation accompanying reduction-oxidation reactions in metal electrodes. At the same time, we report and discuss that high surface areas of active nanoparticles lead to multiple side reactions. Dissolution of Fe anodes leads to reprecipitation of significantly larger anode particles. Dissolution of Ni cathodes leads to precipitation of Ni metal on the anode, thus blocking transport of OH(-) anions. The electrolyte molarity and composition have a significant impact on the capacity utilization and cycling stability.

Palladium decoration of hybrid carbon nanotubes/charcoal composite and its catalytic behavior in the hydrogenation of trans-cinnamaldehyde

In the present study, we addressed the palladium (Pd) decoration of multiwalled carbon nanotube (CNT)/activated carbon (AC) hybrid composites (MWCNT/AC), and examined the catalytic behavior of the composites in the hydrogenation of trans-cinnamaldehyde. The MWCNT/AC composites were prepared by growing CNT network on the surface of AC granules, using the chemical vapor deposition method. XPS analysis revealed that the MWCNT/AC and COOH–MWCNT/AC composites and isolated AC adsorbed Pd at different oxidation states when dipped into a Pd0 microemulsion: isolated AC and the COOH–MWCNT/AC composite adsorbed Pd nanoparticles at di- and tetravalent states (Pd2+/4+), while the MWCNT/AC composite adsorbed Pd nanoparticles at zero and tetravalent states (Pd0/Pd4+). The MWCNT/AC composite may thereby have hierarchical Pd adsorption properties dependent on the MWCNT network type grown onto the AC surface. Regarding the catalytic performance, the (Pd0/4+)-MWCNT/AC catalyst displayed higher selectivity to hydrocinnamaldehyde formation (95.9%) when compared with the (Pd2+/4+)-AC and (Pd2+/4+)-COOH–MWCNT/AC catalysts (72.1% and 91.4% selectivity, respectively). The catalytic performance of the (Pd0/4+)-MWCNT/AC catalyst with 2.8wt% of Pd loading was also superior than the catalytic performance of commercial catalysts with 5 and 10wt% of Pd loading and other Pd/CNTs catalysts reported in the literature.

Electrochemical Performance of FeF3·0.33H2O/MWCNTs Composite Cathode Synthesized by Solvothermal Process

This paper reports a FeF3·0.33H2O/multi-walled carbon nanotubes (MWCNTs) composite for energy storage applications. The composite material is prepared by solvothermal reaction with FeF3·3H2O and MWCNTs as precursors, and FeF3·3H2O was removed of crystalliferous water and converted to FeF3·0.33H2O during solvothermal treatment. Structural characterizations show that FeF3·0.33H2O that crystalline with a diameter of about 30 nm were distributed in the network of MWCNTs. As a cathode material for lithium ion batteries, FeF3·0.33H2O/MWCNTs was superior to pure FeF3·0.33H2O in terms of high capacity (an initial capacity of 181 mAh g-1 in 2.0-4.3 V at 20 mA g-1), good cycleability (50% capacity retension at 50th cycle) and good rate capability (116 mAh g-1 at 100 mA g-1). The enhanced performances were attributed to the conductive MWCNT network which improved the electron transport ability and buffered volume change of the cathode.

A New Free Standing ZnO/MWCNT Nanocomposite Anode Produced By Sol-Gel Spin Coating Method for Li-Ion Batteries

Lithium-ion batteries (LIBs) are one of the most popular types of rechargeable battery for portable electronics, with one of the best energy densities, and also the choice power source for electric and hybrid vehicles [1]. Zinc oxide is an attractive material as a potential substitute for the conventional graphite anode in lithium-ion batteries, because the theoretical capacity of ZnO (978 mAhg-1) has been estimated to be superior to that of graphite (372 mAhg−1) [2]. High capacity anodes such as zinc based usually suffer severe capacity fading, stemming from both the quick aggregation of zinc particles and the huge volume expansion during Li+ insertion/extraction cycles, which cause pulverization of the anodes and electrical detachment of active materials [3]. MWCNT buckypaper substrate is considered as a buffer material to prevent mechanical disintegration of anode material during the battery applications. In this work, ZnO/MWCNT buckypaper nanocomposite films were prepared as free-standing anode materials by sol–gel spin coating method. To the best of our knowledge there is no work to be published by using highly porous MWCNT buckypapers to be infiltrated with ZnO sol by spin coating. It was aimed to accommodate the stresses arisen from the volume increase during charging process by using highly porous MWCNT network that coated with a thin layer of the ZnO. The structural properties and electrochemical performance of free standing ZnO/MWCNT buckypaper composite film anodes of CR2016 type Li-ion batteries were investigated. SEM (Scanning Electron microscopy), EDS (Energy-dispersive X-ray spectroscopy), XRD (X-ray diffraction) analyses and electrochemical performance tests were performed to characterize the nanocomposites. The cells were charged and discharged at 25 °C between fixed voltage limits (2.5 V to 0.2 V) on an MTI model of BST8-MA battery tester.[1] Y. Wang, F. Su, J.Y. Lee, X.S. Zhao, Chem. Mater., 18, 1347-1353 (2006).[2] M.O. Guler, T. Cetinkaya, U. Tocoglu, H. Akbulut, Microelectronic Engineering, doi:10.1016/j.mee.2013.12.029 (2014).[3] X.H. Huang, X.H. Xia, Y.F. Yuan, F. Zhou, Electrochim. Acta, 56, 4960-4965 (2011).

Comparison of Vapor Sensing Properties of Pristine and Hexamethylene Diamine-Treated MWCNT Networks to Primary, Secondary and Tertiary Alcohols

The sensing properties of pristine and hexamethylene diamine (HDA)-treated multiwall carbon nanotube networks (MWCNT-Ns) to selected primary, secondary (sec-) and tertiary (ter-) alcohols were examined by resistance measurements. It was seen that sensor responses, S (%), of MWCNT (HDA)-N to these alcohols were much higher than those of the pristine network. An increase in the S (%) values per mm Hg of both networks was observed from propanol to butanol, when their values from primary alcohols to sec-/tert-ones decreased due to the change in the interaction area of these alcohols with the MWCNT-Ns.

Processability, structural evolution and properties of melt processed biaxially stretched HDPE/MWCNT nanocomposites

The HDPE/MWCNT nanocomposites show a structural evolution of MWCNT networks from 3D to 2D during biaxial stretching.

Highly Enhanced Vapor Sensing of Multiwalled Carbon Nanotube Network Sensors by n‐Butylamine Functionalization

The sensing of volatile organic compounds by multiwall carbon nanotube networks of randomly entangled pristine nanotubes or the nanotubes functionalized by n‐butylamine, which were deposited on polyurethane supporting electrospinned nonwoven membrane, has been investigated. The results show that the sensing of volatile organic compounds by functionalized nanotubes considerably increases with respect to pristine nanotubes. The increase is highly dependent on used vapor polarity. For the case of highly polar methanol, the functionalized MWCNT network exhibits even more than eightfold higher sensitivity in comparison to the network prepared from pristine nanotubes.

Deformable strain sensors based on patterned MWCNTs/polydimethylsiloxane composites

ABSTRACTPatterned MWCNT/polydimethylsiloxane (PDMS) nanocomposite strain sensors were achieved by a microelectromechanical system assisted electrophoretic deposition (EPD) technique. With the combined effect of superior intrinsic piezoresistivity of the individual MWCNT and the tunneling effect of the MWCNT network, the stretchable composite demonstrates high sensitivity to the tensile strain. The gauge factor shows a strong dependence on both the initial resistance of the CNT/PDMS composite and the applied strain level. The mechanism is elucidated by analyzing the structure‐property‐function of patterned CNT networks. When the entanglement of a MWCNT network allows effective load transfer, the sensitivity is primarily dominated by the intrinsic piezoresistivity of individual MWCNTs. Conversely, when the MWCNTs interpenetrate loosely, the tunneling effect prevails. The sensitivity of the device can be tailored by the proposed technique since MWCNT film thickness/density can be readily controlled by means of the patterning parameters of the EPD process. The work provides useful guidance for design and development of strain/stress sensors with targeted sensitivity for flexible electronics applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1505–1512

Facile scalable synthesis of Co3O4/carbon nanotube hybrids as superior anode materials for lithium-ion batteries

In this report, Co3O4/multiple-wall carbon nanotube (MWCNT) hybrid materials were synthesized via strong ultrasonication-assisted shaking and magnetic stirring processes. The prepared samples were well characterized by utilizing powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy techniques. Results indicated that the resulting Co3O4 nanoparticles were highly dispersed in the MWCNT network backbone and further form Co3O4/MWCNT hybrid materials. The obtained Co3O4/MWCNT hybrids can be employed as anode electrode in Lithium-ion batteries and deliver as high as discharge capacity of 1250mAhg−1 at a current density of 0.2C, additionally, 81% of the discharge capacity for sample 2 with 20wt.% MWCNT loading could be retained after 70 cycles, which could be associated with the specific hybrid structure of the electrode as well as the addition of MWCNT. Most importantly, the present synthetic approach is facile, controllable, and scalable, which allowing it more easily adapted to prepare other hybrid materials with specific architectures.

Percolated pore networks of oxygen plasma-activated multi-walled carbon nanotubes for fast response, high sensitivity capacitive humidity sensors

We report on the preparation of capacitive-type relative humidity sensors incorporating plasma-activated multi-wall carbon nanotube (p-MWCNT) electrodes and on their performance compared with existing commercial technology. Highly open porous conductive electrodes, which are almost impossible to obtain with conventional metal electrodes, are fabricated by spray-depositing MWCNT networks on a polyimide layer. Oxygen plasma activation of the MWCNTs is also explored to improve the water adsorption of the MWCNT films, by introducing oxygen-containing functional groups on the CNT surface. Polyimide humidity sensors with optimized p-MWCNT network electrodes exhibit exceptionally fast response times (1.5 for adsorption and 2 s for desorption) and high sensitivity (0.75 pF/% RH). These results may be partially due to their percolated pore structure being more accessible for water molecules, expending the diffusion of moisture to the polyimide sensing film, and partially due to the oxygenated surface of p-MWCNT films, allocating more locations for adsorption or attraction of water molecules to contribute to the sensitivity.

Thermal Annealing Induced Enhancements of Electrical Conductivities and Mechanism for Multiwalled Carbon Nanotubes Filled Poly(Ethylene-co-Hexene) Composites

Thermal annealing-induced enhancements of electrical conductivities at the temperature higher than the melting point of poly(ethylene-co-hexene) matrix for multiwalled carbon nanotubes filled poly(ethylene-co-hexene) (MWCNTs/PEH) composites were investigated by electrical conductivity measurements. Two types of MWCNTs with low and high aspect ratios (4 and 31) were added as fillers into PEH matrix, respectively for comparison study purpose. The morphological changes due to annealing for MWCNTs/PEH composites were observed by SEM. The formation of MWCNT networks in the composites were clearly demonstrated by rheological measurements. It is surprisingly found that the electrical conductivity for MWCNTs/PEH composites with high MWCNT concentrations increases obviously with annealing time of 40 min and the maximum increment approaches about 3 orders of magnitude with annealing time of 120 min. The increase of electrical conductivity of MWCNTs/PEH composites depends on MWCNT content, MWCNT aspect ratio and annealing time. SEM results clearly reveal that micrometer-sized MWCNT aggregates are broken down and more loosely packed MWCNT networks form due to annealing. Different types of networks in the composites are responsible for the evolutions of rheological (MWCNT network and PEH chain-MWCNT combined network) and electrical conductivity properties (tube-tube contacting MWCNT network). The reconstruction of MWCNT network during annealing is attributed to rotational diffusion of MWCNTs in PEH matrix at high temperature and the length of MWCNTs shows significant effect on this. The obvious enhancements of electrical conductivities can be ascribed to the thermal annealing-induced formation of loosely packed more homogeneous networks through non-Brownian motions.

MWCNT‐Based Ag2S‐TiO2 Nanocomposites Photocatalyst: Ultrasound‐Assisted Synthesis, Characterization, and Enhanced Catalytic Efficiency

Multiwalled carbon nanotube based nanoscale Ag2S and TiO2 composites have successfully synthesized via a facile ultrasound‐assisted method. The nanocomposites were characterized by Fourier transform infrared (FT‐IR) spectroscopy, UV‐vis absorption spectra, BET surface area measurements, X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The Ag2S‐TiO2/CNT nanocomposites exhibited much higher photocatalytic activity than pure TiO2 for the degradation of Rhodamine B (Rh.B) under UV and visible light. The improved photocatalytic activities may be attributed to increased adsorbability of Rh.B molecules and increased charge transfer rate in the presence of a one‐dimensional MWCNT network.

A binder-free Ge-nanoparticle anode assembled on multiwalled carbon nanotube networks for Li-ion batteries

Germanium (Ge) nanoparticle-multiwalled carbon nanotube (MWCNT) anodes are fabricated through the anchoring of Ge on the surface of electrophoretically pre-deposited MWCNT networks via a thermal evaporation process. This Ge-MWCNT nanocomposite displays a large reversible capacity of over 800 mA h g(-1) at 1 C even after 200 cycles.

Porous graphene/carbon nanotube composite cathode for proton exchange membrane fuel cell

Porous Pt-graphene/multiwalled carbon nanotube (MWCNT) composite cathodes were fabricated for proton exchange membrane fuel cells and their electro-chemical performances were examined. Rod-like MWCNTs with a high aspect ratio induced a porous network structure and Pt-graphene was bound homogeneously to the porous network structure of MWCNTs in the form of a very rough surface, which facilitated simultaneous access between the Pt electro-catalyst and reactant. In addition, the porous MWCNT network enabled the Pt-graphene electrode to overcome the deficiency induced by high electrical resistance by providing an electrical pathway for the oxygen reduction reaction (ORR). Therefore, the ORR charge transfer resistance of the Pt-graphene/MWCNT composite cathode was much smaller than that of the Pt-graphene cathode, and the maximum power density of the Pt-graphene/MWCNT composite cathode was four times higher than that of the Pt-graphene cathode.