Few-walled Carbon Nanotubes Research Articles

Lithium ion batteries made of electrodes with 99 wt% active materials and 1 wt% carbon nanotubes without binder or metal foils

Herein, we propose lithium ion batteries (LIBs) without binder or metal foils, based on a three-dimensional carbon nanotube (CNT) current collector. Because metal foils occupy 20–30 wt% of conventional LIBs and the polymer binder has no electrical conductivity, replacing such non-capacitive materials is a valid approach for improving the energy and power density of LIBs. Adding only 1 wt% of few-wall CNTs to the active material enables flexible freestanding sheets to be fabricated by simple dispersion and filtration processes. Coin cell tests are conducted on full cells fabricated from a 99 wt% LiCoO2-1 wt% CNT cathode and 99 wt% graphite-1 wt% CNT anode. Discharge capacities of 353 and 306 mAh ggraphite−1 are obtained at charge–discharge rates of 37.2 and 372 mA ggraphite−1, respectively, with a capacity retention of 65% at the 500th cycle. The suitability of the 1 wt% CNT-based composite electrodes for practical scale devices is demonstrated with laminate cells containing 50 × 50 mm2 electrodes. Use of metal combs instead of metal foils enables charge–discharge operation of the laminate cell without considerable IR drop. Such electrodes will minimize the amount of metal and maximize the amount of active materials contained in LIBs.

Selective Wrapping of Few-Walled Carbon Nanotubes by a Serpent-Like Heterobimetallic Coordination Polymer

In this work, selective interactions between the constituents of the composite CNT@MnCu (2) prepared using carbon nonotubes (CNTs) (1) and the heterobimetallic chain [MnCu(opba)]n (MnCu), opba = o-phenylenebis(oxamate), were studied mainly by resonance Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). An apparent interaction between CNTs and MnCu complex with the wrapping of the former by the heterobimetallic complex was observed in the microscopy images. The resonance Raman data suggest that the interations between MnCu complex and the CNTs are selective, occurring mainly with metallic CNTs independently of the diameter and excitation energy. However, for semiconducting CNTs, these interactions solely occur with tubes having diameters higher than ca. 1.47 nm.

Hybrid Gas Sensing and Transport Properties of Few-Walled CNTs Decorated with Discrete SnO₂ Nanoparticles.

CVD grown, few walled carbon nanotubes (FWCNTs) were quasi decorated with SnO₂nanoparticles (FWCNTs-SnO₂) and its gas sensing properties were analyzed with ammonia and ethanol. At room temperature FWCNTs-SnO₂show enhanced 'p type' gas sensing response than FWCNTs. Activation of SnO₂at high temperatures led to systematic changes in the sensing behavior towards 'n type' response. Temperature dependent transport behavior was found to be a one dimensional variable range hopping mechanism (1 D-VRH) for the FWCNTs and a 3D-VRH mechanism for the FWCNTs-SnO2. These temperature dependent gas transport and sensing properties elucidate the hybrid nature of the nanocomposite with novel characteristics. This also implies its importance as a potential gas sensor material.

Electrical behaviour of native cellulose nanofibril/carbon nanotube hybrid aerogels under cyclic compression.

Hybrid aerogels consisting of cellulose nanofibers (CNF) and modified few-walled carbon nanotubes (FWCNT) are investigated under cyclic mechanical compression to explore "electrical fatigue". For this purpose the FWCNTs were hydrophilized, thus promoting their aqueous dispersibility to allow FWCNT/CNF hybrid hydrogels, followed by freeze-drying to obtain hybrid aerogels. The optimized composition consisting of FWCNT/CNF 20/80 wt/wt showed conductivity of 10-5 S cm-1 as promoted due to double percolation, and showed only small changes in electrical and mechanical behaviour upon cycling 100 times. The electrical behaviour under cycled compression shows good stability and reversibility.

Biomass-derived carbonaceous positive electrodes for sustainable lithium-ion storage.

Biomass derived carbon materials have been widely used as electrode materials; however, in most cases, only electrical double layer capacitance (EDLC) is utilized and therefore, only low energy density can be achieved. Herein, we report on redox-active carbon spheres that can be simply synthesized from earth-abundant glucose via a hydrothermal process. These carbon spheres exhibit a specific capacity of ∼210 mA h gCS(-1), with high redox potentials in the voltage range of 2.2-3.7 V vs. Li, when used as positive electrode in lithium cells. Free-standing, flexible composite films consisting of the carbon spheres and few-walled carbon nanotubes deliver high specific capacities up to ∼155 mA h gelectrode(-1) with no obvious capacity fading up to 10,000 cycles, proposing to be promising positive electrodes for lithium-ion batteries or capacitors. Furthermore, considering that the carbon spheres were obtained in an aqueous glucose solution and no toxic or hazardous reagents were used, this process opens up a green and sustainable method for designing high performance, environmentally-friendly energy storage devices.

Hierarchical networks of redox-active reduced crumpled graphene oxide and functionalized few-walled carbon nanotubes for rapid electrochemical energy storage.

Crumpled graphene is known to have a strong aggregation-resistive property due to its unique 3D morphology, providing a promising solution to prevent the restacking issue of graphene based electrode materials. Here, we demonstrate the utilization of redox-active oxygen functional groups on the partially reduced crumpled graphene oxide (r-CGO) for electrochemical energy storage applications. To effectively utilize the surface redox reactions of the functional groups, hierarchical networks of electrodes including r-CGO and functionalized few-walled carbon nanotubes (f-FWNTs) are assembled via a vacuum-filtration process, resulting in a 3D porous structure. These composite electrodes are employed as positive electrodes in Li-cells, delivering high gravimetric capacities of up to ∼170 mA h g(-1) with significantly enhanced rate-capability compared to the electrodes consisting of conventional 2D reduced graphene oxide and f-FWNTs. These results highlight the importance of microstructure design coupled with oxygen chemistry control, to maximize the surface redox reactions on functionalized graphene based electrodes.

Molecular Beacon CNT-based Detection of SNPs

An fluorescence quenching effect due to few-walled carbon nanotubes chemically modified by carboxyl groups has been utilized to discriminate Single Nucleotide Polymorphism (SNP). It was shown that the complex obtained from these nanotube and singlestranded primer DNA is formed due to stacking interactions between the hexagons of the nanotubes and aromatic rings of nucleotide bases as well as due to establishing of hydrogen bonds between acceptor amine groups of nucleotide bases and donor carboxyl groups of the nanotubes. It has been demonstrated that these complexes may be used to make highly effective DNA biosensors detecting SNPs which operate as molecular beacons.

Highly Stretchable Conductive Fibers from Few-Walled Carbon Nanotubes Coated on Poly(m-phenylene isophthalamide) Polymer Core/Shell Structures.

A core/shell stretchable conductive composite of a few-walled carbon nanotube network coated on a poly(m-phenylene isophthalamide) fiber (FWNT/PMIA) was fabricated by a dip-coating method and an annealing process that greatly enhanced interactions between the FWNT network and PMIA core as well as within the FWNT network. The first strain-conductivity test of the as-prepared FWNT/PMIA fiber showed a stretching-induced alignment of nanotubes in the shell during the deformation process and a good conductivity stability with a slight conductivity drop from 109.63 S/cm to 98.74 S/cm (Δσ/σ0 = 10%) at a strain of ∼150% (2.5 times the original length). More importantly, after the first stretching process, the fiber can be recovered with a slight increase in length but a greatly improved conductivity of 167.41 S/cm through an additional annealing treatment. The recovered fiber displays a similarly superb conductivity stability against stretching, with a decrease of only ∼13 S/cm to 154.49 S/cm (Δσ/σ0 = 8%) at a strain of ∼150%. We believe that this conductivity stability came from the formation and maintaining of aligned nanotube structures during the stretching process, which ensures the good tube-tube contacts and the elongation of the FWNT network without losing its conductivity. Such stable conductivity in stretchable fibers will be important for applications in stretchable electronics.

Efficient photo-thermionic emission from carbon nanotube arrays

Electron emission from well-aligned, few-walled carbon nanotube arrays was triggered by a low power (<110 mW), continuous-wave, 650 nm light. Significant electron emission was obtained at low bias voltage. Photo-thermionic emission was found to be the mechanism of emission since the local temperature was measured to be higher than 2000 K, and the emission was consistent with the Richardson Law. A high thermionic emission current of ∼300 μA was obtained under a low electric field of 0.45 V/μm. The space-charge-limited emission was observed during the current–voltage testing, which obeyed the Child Law. Under high bias voltage, thermal-assisted field emission was also observed. The emission exhibited high stability (<5%), fast response (<1.8 ms), and low emittance (∼2°).

Effect of Nitrogen Modified Carbon Nanotube Supports on the Properties of Direct Ethanol Fuel Cell Catalyst

Direct alcohol fuel cells are viewed as a promising candidate for powering portable electronics due to the high volumetric energy density of alcohols. Methanol is often used as the fuel because its electro-oxidation is relatively simple. However, ethanol is more preferable as it is non-toxic and has higher energy density but on the other hand, its full electro-oxidation is difficult due to the strong carbon-carbon bonds in its structure. It is clear that new electrocatalysts are needed for the efficient oxidation of ethanol. Generally, there are two components in an alcohol oxidizing fuel cell catalyst: an active metallic nanoparticle (commonly platinum or its alloy) and a carbon support, which is used to disperse and minimize the agglomeration of the nanoparticles. The stabilizing effect is further increased with doping of carbon with heteroatoms (e.g. nitrogen, boron, sulphur), which creates local charges to anchor nanoparticles on the support due to the different electronegativity of the atoms [1]. In this study, the use of PtRu supported on nitrogen modified few-walled carbon nanotubes (FWNT) [2] is studied for the electro-oxidation of ethanol in alkaline electrolyte at rotating disc electrode in temperature range relevant to direct ethanol fuel cells (0-60°C) and also in actual fuel cell conditions. The catalysts with 30% PtRu(1:1) loading have been prepared with following supports: FWNT, nitrogen-doped FWNT (N-FWNT) and aniline-covered FWNT (A-FWNT). The catalyst layer structure of the different catalysts is studied with scanning electron microscopy. Electrochemical characterization shows that PtRu/A-FWNT has significantly lower electrochemically active surface area based on CO stripping than PtRu/FWNT and PtRu/N-FWNT indicating that covering the FWNT support reduces its surface area. However, nitrogen modification reduces the CO oxidation overpotential by approximately 20 mV. In Fig. 1, ethanol electro-oxidation currents are presented at 0.5 V vs RHE at 0 and 2000 s. It can be seen that PtRu/A-FWNT is very active but suffers from high poisoning rate, while PtRu/N-FWNT is not as active but has high tolerance from catalyst poisoning. The activity of the nitrogen-modified catalysts increase relatively compared to PtRu/FWNT when the temperature is raised from 0 to 60°C. Fuel cell electrode polarization tests in actual alkaline fuel cell with Fumatech FAA3 membrane indicate that PtRu/N-FWNT does not perform very well at low temperature (30°C). However, as temperature is raised to 50°C, it shows the best performance followed by PtRu/A-FWNT and then by PtRu/FWNT. Furthermore, when constant current test for 40 h were performed, the PtRu/N-FWNT was most stable, while voltages with PtRu/A-FWNT and PtRu/FWNT quickly decreased to zero. Studying the electrode structure with SEM showed very dense layer structure for PtRu/A-FWNT and PtRu/FWNT contrasting very porous structure formed with PtRu/N-FWNT. This indicates that in addition to enhanced reaction kinetics also better mass transfer in the catalyst layer can be achieved with N-FWNT support. Larger pores facilitate the transport of ethanol to active PtRu nanoparticles and the transport of poisoning reaction products away from the electrode. Similar porous structure was seen in our previous study with N-FWNT catalyst for oxygen reduction reaction [3]. 1. Pylypenko et al., Energy Environ. Sci. 6 (2013) 2957-2964. 2. Rakov et al., Russ. J. Phys. Chem 78 (2004) 1966-1971 3. Kanninen et al., Appl. Cat. B: Environ. 156-157 (2014) 341-349. Figure 1

Ordered wrapping of poly(methyl methacrylate) on single wall carbon nanotubes

A unique crystalline signature not reported previously for atactic poly(methyl methacrylate) PMMA was observed in the X-ray diffraction of single wall carbon nanotubes (SWNT)/PMMA bucky papers indicating ordered PMMA wrapping on SWNT. This ordered PMMA wrapping was not observed in few wall carbon nanotubes (FWNT)/PMMA and multiwall carbon nanotube (MWNT)/PMMA bucky papers.

Scalable nanomanufacturing of surfactant-free carbon nanotube inks for spray coatings with high conductivity

Spray-coated carbon nanotube films offer a simple and printable solution for fabricating low cost, lightweight, and flexible thin-film electronics. However, current nanotube spray inks require either a disruptive surfactant or destructive surface functionalization to stabilize dispersions at the cost of the electrical properties of the deposited film. We demonstrate that high-purity few-walled carbon nanotubes may be stabilized in isopropanol after surface functionalization and that optimizing the ink stability dramatically enhances the conductivity of subsequent spray-coated thin films. We consequently report a surfactant-free carbon nanotube ink for spray-coated thin films with conductivities reaching 2,100 S/cm. Zeta-potential measurements, used to quantify the nanotube ink dispersion quality, directly demonstrate a positive correlation with the spraycoated film conductivity, which is the key metric for high-performance printed electronics.

Electrochemical polymerization of pyrene derivatives on functionalized carbon nanotubes for pseudocapacitive electrodes.

Electrochemical energy-storage devices have the potential to be clean and efficient, but their current cost and performance limit their use in numerous transportation and stationary applications. Many organic molecules are abundant, economical and electrochemically active; if selected correctly and rationally designed, these organic molecules offer a promising route to expand the applications of these energy-storage devices. In this study, polycyclic aromatic hydrocarbons are introduced within a functionalized few-walled carbon nanotube matrix to develop high-energy, high-power positive electrodes for pseudocapacitor applications. The reduction potential and capacity of various polycyclic aromatic hydrocarbons are correlated with their interaction with the functionalized few-walled carbon nanotube matrix, chemical configuration and electronic structure. These findings provide rational design criteria for nanostructured organic electrodes. When combined with lithium negative electrodes, these nanostructured organic electrodes exhibit energy densities of ∼350 Wh kg−1electrode at power densities of ∼10 kW kg−1electrode for over 10,000 cycles.

Electrically conducting nanobiocomposites using carbon nanotubes and collagen waste fibers

Electrically conducting hybrid biocomposite films were prepared using a simple and cost-effective method by incorporating different types of carbon nanotubes (XCNTs) viz., few walled carbon nanotube (FWCNT) and boron doped carbon nanotube (BCNT) into biopolymers. Collagen extracted from animal skin wastes was blended with guar gum and XCNTs in varying proportions to form flexible and electrically conducting hybrid films. We found that the electrical conductivity of both types of hybrid films increases radically as the XCNT loading increases. BCNT incorporated hybrid films show better electrical conductivity (3.0 × 10−1 S/cm) than their FWCNT loaded counter parts (4.8 × 10−4 S/cm) at a dosage of 2 wt.%. On the other hand, mechanical and other physical properties such as transparency, flexibility and surface smoothness of the developed hybrid films were affected as a function of XCNT concentration. We also demonstrated that the developed hybrid films lit up a LED lamp when inserted between batteries and the brightness of the emitted light depended on the XCNT loading. These results suggest a new way to transform an industrial biowaste into innovative advanced materials for applications in fields related to biomedicine, biosensors and electronics.

Conductive graphene fibers for wire-shaped supercapacitors strengthened by unfunctionalized few-walled carbon nanotubes.

Graphene fibers are a promising electrode material for wire-shaped supercapacitors (WSSs) that can be woven into textiles for future wearable electronics. However, the main concern is their high linear resistance, which could be effectively decreased by the addition of highly conductive carbon nanotubes (CNTs). During the incorporation process, CNTs are typically preoxidized by acids or dispersed by surfactants, which deteriorates their electrical and mechanical properties. Herein, unfunctionalized few-walled carbon nanotubes (FWNTs) were directly dispersed in graphene oxide (GO) without preoxidation or surfactants, allowing them to maintain their high conductivity and perfect structure, and then used to prepare CNT-reduced GO (RGO) composite fibers by wet-spinning followed by reduction. The pristine FWNTs increased the stress strength of the parent RGO fibers from 193.3 to 385.7 MPa and conductivity from 53.3 to 210.7 S cm(-1). The wire-shaped supercapacitors (WSSs) assembled based on these CNT-RGO fibers presented a high volumetric capacitance of 38.8 F cm(-3) and energy density of 3.4 mWh cm(-3). More importantly, the performance of WSSs was revealed to decrease with increasing length due to increased resistance, revealing a key issue for graphene-based electrodes in WSSs.

Super growth of vertically aligned carbon nanotubes on pulsed laser deposited catalytic thin films

Efficient and reproducible growth of vertically aligned carbon nanotube (CNT) forests by catalytic chemical vapor deposition (CVD) requires precise setting of the properties of the catalyst thin films and CVD conditions. In this work, super growth of vertically aligned CNTs onto Al2O3 support and Fe–Co catalyst layer system is presented. The layers were grown by pulsed laser deposition (PLD) onto silicon wafer pieces. Their thickness and optical properties were controlled by spectroscopic ellipsometry. The effect of heat treatment at 750 °C in nitrogen and in hydrogen of these PLD layers was compared. High-resolution electron microscopic images showed that treatment of catalyst layers in H2 resulted in finer and denser catalytic particles. As a result, well-aligned, dense and few-walled CNT forests with 1–1.5 mm height were deposited by water-vapor-assisted CVD on the hydrogen-treated films, while without hydrogen treatment defected CNT structures were grown. According to these observations, Raman spectroscopy showed a higher degree of crystallinity in case of CNT-s, where reduction by hydrogen influenced the oxidation state of the metallic catalytic particles in a beneficial way.

Synthesis of Multi-Walled Carbon Nanotube by using Ethanol as a Carbon Source

The challenges associated with synthesis carbon nanotubes are still the main causes [1,2] which limit the use in many application [3,4] in spite of the amazing physiochemical properties and variety of types of single walled carbon nanotubes (SWNTs), few walled carbon nanotubes (FWCNTs), and multi walled carbon nanotubes (MWNTs) [5]. The prediction for the near future is the possibility of removing all the obstacles that prevent or hinder the manufacturing process of this carbon-polymer distinguished in all the specifications [6]. The methods which commonly depend on the synthesis of carbon nanotubes include arc discharge [7], chemical vapor deposition [8,9], and laser ablation [10] which represent physical, chemical, or miscellaneous methods. Chemical vapor deposition techniques are the simplest, cheapest, and most flexible methods as compared with the other types for this purpose [11]. This technique generally depends on making a precipitation process at high temperatures for the clouds of precursor, vapor which mainly contains an appropriate percentage of carbon atoms [12]. The process of synthesis can be done in two ways: the first by using a catalyst, and the second without a catalyst [13], which acts as center for the growth of the tubular structures of carbon nanotubes, thus increasing the diameter of these centers and leading to the process of building carbon atoms towards more than one wall [14,15]. In this regard, chemical vapor deposition was used to synthesis MWNTs by using ethanol alcohol as a sources of carbon at temperature of 750800 C without using a catalyst. Figure 1 shows a diagram for the process of synthesis in the schematic below.

Size-controlled large-diameter and few-walled carbon nanotube catalysts for oxygen reduction.

We demonstrate a new strategy for tuning the size of large-diameter and few-walled nitrogen-doped carbon nanotubes (N-CNTs) from 50 to 150 nm by varying the transition metal (TM = Fe, Co, Ni or Mn) used to catalyze graphitization of dicyandiamide. Fe yielded the largest tubes, followed by Co and Ni, while Mn produced a clot-like carbon morphology. We show that morphology is correlated with electrocatalytic activity for the oxygen reduction reaction (ORR). A clear trend of Fe > Co > Ni > Mn for the ORR catalytic activity was observed, in both alkaline media and more demanding acidic media. The Fe-derived N-CNTs exhibited the highest BET (∼870 m(2) g(-1)) and electrochemically accessible (∼450 m(2) g(-1)) surface areas and, more importantly, the highest concentration of nitrogen incorporated into the carbon planes. Thus, in addition to the intrinsic high activity of Fe-derived catalysts, the high surface area and nitrogen doping contribute to high ORR activity. This work, for the first time, demonstrates size-controlled synthesis of large-diameter N-doped carbon tube electrocatalysts by varying the metal used in N-CNT generation. Electrocatalytic activity of the Fe-derived catalyst is already the best among studied metals, due to the high intrinsic activity of possible Fe-N coordination. This work further provides a promising route to advanced Fe-N-C nonprecious metal catalysts by generating favorable morphology with more active sites and improved mass transfer.

Directly correlating the strain-induced electronic property change to the chirality of individual single-walled and few-walled carbon nanotubes.

We fabricate carbon nanotube (CNT)-field effect transistors (FETs) with a changeable channel length and investigate the electron transport properties of single-walled, double-walled and triple-walled CNTs under uniaxial strain. In particular, we characterize the atomic structure of the same CNTs in the devices by transmission electron microscopy and correlate the strain-induced electronic property change to the chirality of the CNTs. Both the off-state resistance and on-state resistance are observed to change with the axial strain following an exponential function. The strain-induced band gap change obtained from the maximum resistance change in the transfer curve of the ambipolar FETs is quantitatively compared with the previous theoretical prediction and our DFTB calculation from the chirality of the CNTs. Although following the same trend, the experimentally obtained strain-induced band gap change is obviously larger (57%-170% larger) than the theoretical results for all the six CNTs, indicating that more work is needed to fully understand the strain-induced electronic property change of CNTs.

Important factors for effective use of carbon nanotube matrices in electrochemical capacitor hybrid electrodes without binding additives

Activated carbon (AC) provides surface while carbon nanotubes (CNTs) provide conductive matrix. Ethanol, removable from AC pores, is suitable as dispersant. Few-wall CNTs, dispersible in ethanol, is suitable as CNTs.