Growth Of Multi-walled Carbon Nanotubes Research Articles

Supercapacitor electrodes by direct growth of multi-walled carbon nanotubes on Al: a study of performance versus layer growth evolution

Supercapacitor electrodes were fabricated by direct growth of multi-walled carbon nanotubes (CNTs) on Al current collectors via a chemical vapor deposition process in the presence of a spin-coated Co-Mo catalyst. A detailed study of the dependence of the CNT layer structure and thickness on growth time set the basis for the assessment of supercapacitors assembled with the CNTs/Al electrodes. As the main features of the layer growth evolution, an increase in the population of finer CNTs and a shift from a random entanglement to a rough vertical alignment of nanotubes were noted with proceeding growth. The growth time influence on the performance of supercapacitors was in fact apparent. Particularly, the specific capacitance of CNTs/Al electrodes in 0.5MK2SO4 aqueous electrolyte increased from 35 to 80Fg−1 as the CNT layer thickness varied from 20 to 60μm, with a concurrent loss in rate capability (knee frequency from 1kHz to 60Hz). The latter was excellent in general, arguably due to both a fast ion transport through the interconnected CNT network and a negligible contribution of the active layer/current collector contact to the equivalent series resistance (0.15–0.22mΩg), a distinct advantage of the direct growth fabrication method. Overall, a relatively simple process of direct growth of CNTs on Al foils is shown to be an effective method to fabricate supercapacitor electrodes, notably in the absence of special measures and processing steps finalized to a tight control of nanotubes growth and organization.

Discovery of wall-selective carbon nanotube growth conditions via automated experimentation.

Applications of carbon nanotubes continue to advance, with substantial progress in nanotube electronics, conductive wires, and transparent conductors to name a few. However, wider application remains impeded by a lack of control over production of nanotubes with the desired purity, perfection, chirality, and number of walls. This is partly due to the fact that growth experiments are time-consuming, taking about 1 day per run, thus making it challenging to adequately explore the many parameters involved in growth. We endeavored to speed up the research process by automating CVD growth experimentation. The adaptive rapid experimentation and in situ spectroscopy CVD system described in this contribution conducts over 100 experiments in a single day, with automated control and in situ Raman characterization. Linear regression modeling was used to map regions of selectivity toward single-wall and multiwall carbon nanotube growth in the complex parameter space of the water-assisted CVD synthesis. This development of the automated rapid serial experimentation is a significant progress toward an autonomous closed-loop learning system: a Robot Scientist.

Effect Of Catalyst Concentration On The Synthesis Of MWCNT By Single Step Pyrolysis

Multiwall carbon nanotubes (MWCNT) are synthesised by cost effective method of pyrolysing xylene (as hydrocarbon, precursor) in the presence of ferrocene (as catalyst) at 750 o C. The so obtained MWCNTs has a length ranging from 90 µm to 300 µm and diameter ranging from 20 nm to 200 nm depending on the amount of ferrocene added to the xylene for the synthesis. The diameter of the MWCNT’s increased with the increase in ferrocene content in the precursor solution. Bigger agglomerates of iron particle lead to the growth of larger diameter MWCNTs. These MWCNTs with higher concentration of iron nanoparticles in it are useful for catalytic applications. X-ray diffraction (XRD) of the as-synthesised MWCNTs showed a graphitic-like peak (002). Field emission scanning electron microscope (FESEM) is utilized for its morphological analysis, Raman analysis showed the presence of D band (about 1350 cm -1 ) and G band (about 1580 cm -1 ) indicating high crystalline graphitic layers. Fourier transform infrared (FTIR) studies in the transmission mode were carried out in the range 400 - 4000 cm -1 (peaks at 1386, 1639, 2363, 3434, 3747 cm -1 etc.) for bond stretching analysis. All the characterization processes were carried out before and after purification process. The MWCNT’s diameter and their distribution are studied with the help of ImageJ software using the FESEM micrographs.

Carbon nanotubes on nanoporous alumina: from surface mats to conformal pore filling.

Control over nucleation and growth of multi-walled carbon nanotubes in the nanochannels of porous alumina membranes by several combinations of posttreatments, namely exposing the membrane top surface to atmospheric plasma jet and application of standard S1813 photoresist as an additional carbon precursor, is demonstrated. The nanotubes grown after plasma treatment nucleated inside the channels and did not form fibrous mats on the surface. Thus, the nanotube growth mode can be controlled by surface treatment and application of additional precursor, and complex nanotube-based structures can be produced for various applications. A plausible mechanism of nanotube nucleation and growth in the channels is proposed, based on the estimated depth of ion flux penetration into the channels.PACS63.22.Np Layered systems; 68. Surfaces and interfaces; Thin films and nanosystems (structure and non-electronic properties); 81.07.-b Nanoscale materials and structures: fabrication and characterization

Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth

The low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalyst particles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are “replaced” by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering the mechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality.

Growth and morphology of carbon nanostructures on nickel oxide nanoparticles in catalytic chemical vapor deposition

The present study explores the conditions favorable for the growth of cylindrical carbon nanostructures such as multi-walled carbon nanotube (MWCNT) and carbon nanofiber by catalytic chemical vapor deposition (CCVD) method using nickel oxide-based catalyst nanoparticles of different average sizes as well as different levels of doping by copper oxide. The role of doping and the average size have been related to the observed melting behavior of nanoparticles of nickel oxide by thermal and diffraction analysis, and the importance of melting has been highlighted in the context of growth of cylindrical nanostructures. In the reducing environment prevailing in the CCVD chamber due to decomposition of flowing acetylene gas at elevated temperature, there is extensive reduction of oxide nanoparticles. Lack of melting and faster flow of carbon-bearing gases favor the formation of a carbon deposit cover over the catalyst nanoparticles giving rise to the formation of nanobeads. Melting allows rapid diffusion of carbon from the surface to inside catalyst particles, and reduced flow of gas lowers the rate of carbon deposit, both creating conditions favorable for the formation of cylindrical nanostructures, which grows around the catalyst particles. Smaller particle size and lower doping favor growth of MWCNT, while growth of fiber is commonly observed on larger particles having relatively higher level of doping.

Growth and microstructural investigation of multiwall carbon nanotubes fabricated using electrodeposited nickel nanodeposits and chemical vapor deposition method

This study proposes a common approach for growing multiwall carbon nanotubes (MWCNTs) on nickel nanodeposits. MWCNT growth was performed in two separate stages. In the first stage, nickel nanodeposits were electrodeposited on n-Si(111):H substrate in the presence of sulfuric acid. Based on atomic force microscopy (AFM) observations, the nickel deposits had a fairly polygonal morphology and were distributed on the prepared n-Si(111):H substrate. In the second stage, acetylene gas was decomposed on the surfaces of the nickel nanodeposits using chemical vapor deposition method at 700°C. When carbon is saturated in a catalyst, it acts as a primary nucleating element for MWCNT growth. The structure of the MWCNTs was also investigated using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Results showed that the synthesized MWCNTs had a small wall thickness and were formed under the experimental conditions applied to the system.

Plasma Enhanced Chemical Vapor Deposition Time Effect on Multi-Wall Carbon Nanotube Growth Using C<sub>2</sub>H<sub>2</sub> and H<sub>2</sub> as Precursors

Multi-wall carbon nanotube (MWCNT) structures were grown on cobalt catalyst layer through Plasma Enhanced Chemical Vapor Deposition (PECVD) process. Acetylene (C2H2) and hydrogen (H2) are used as precursors during the PECVD process. The morphology structures of the MWCNTs grown under different PECVD time were investigated and characterized using Scanning Electron Microscope (SEM). The effect of the PECVD time on the MWCNT growth is studied by varying the PECVD time at 45 sec and 600 sec. The morphology structures suggest that the growth rate is proportional to the PECVD time under the similar setting condition of pressure, acetylene flow-rate and temperature.

The Field Emission Properties of Multi-Wall Carbon Nanotubes on Flexible Carbon Cloth Substrate with Different Interlayers

This paper examines the field emission synthesis of multi-walled carbon nanotubes (MWCNTs) grown on various interlayers on carbon cloth (CC) substrates, such as Ni/CC, Ni/Ti/CC, and Ni/Al/CC, by thermal chemical vapor deposition using ethylene (C2H4) as the carbon source and nickel (Ni) as the catalyst. The Al interlayer activates the substrate for MWCNTs growth on carbon cloth with Ni as the active catalyst. Field emission SEM was utilized to study the morphology of the catalyst and MWCNTs, and a Raman spectrometer was used to characterize the quality of CNTs. As a result, catalyst particles initiate the nanotube growth and the tube diameters were found to be governed by the size of the associated particles. In our experiment, the smallest size and highest density of catalyst nanoparticles was formed on Al/CC substrate, so that the MWCNTs have a smaller diameter and higher density on this than on Ni/CC and Ni/Ti/CC substrate. Therefore, MWCNTs grown on flexible carbon cloth with an Al interlayer have the best quality and field emission characteristics of the materials examined in this paper. Keywords: Carbon nanotubes, carbon cloth, interlayer effect.

High Surface Area Carbon Electrodes for the Bromine Reactions in H2-Br2 Fuel Cells

The H2-Br2 system is considered as one of the viable options for large scale electrical energy storage due to faster H2 and Br2 reaction kinetics, low cost, and high round-trip efficiency. In order to improve the performance of the H2-Br2 fuel cell, carbon electrodes with high active surface area are needed. A preliminary study was conducted to synthesize and characterize the carbon nanotube based electrodes. Based on the results obtained from SEM, TEM, and EDX analysis, multi-wall carbon nanotube growth is confirmed. Also, the results from the multi-step chronoamperometry study have shown that the active areas of carbon nanotube electrodes are significantly higher than a plain carbon electrode.

Influence of Methane Gas on Growth of Multi-Walled Carbon Nanotubes by Arc Discharge Process

The influence of methane (CH4) gas as feedstock and ambient pressures on growth of multi-walled carbon nanotube (MWCNT) and carbon nano structures is studied by arc discharge process. The discharge is produced between graphite rods at different 100, 300 and 500 torr ambient pressures. Plasma kinematics such as density and temperature is determined by optical emission spectroscopy to investigate the contribution of ambient environment and pressure towards the growth of MWCNT and nano structures. The samples of synthesized MWCNT are analyzed transmission electron microscope, scanning electron microscope, Raman spectroscope and X-ray diffraction analysis. An increase in the growth of the carbon nanotubes with increase in the ambient pressure of the CH4 gas is observed. The CH4 molecules serve as feed stock and enhance the growth of carbon nanotubes. An increase in the growth of other carbon nanostructures such as graphene are also observed with increase in pressure.

Preparation and characterization of multi-walled carbon nanotubes grown on transition metal catalysts

Abstract Transition metal catalysts (mainly: iron, cobalt and nickel) on various supports are successfully used in a largescale production of carbon nanotubes (CNTs), but after the synthesis it is necessary to perform very aggressive purification treatments that cause damages of CNTs and are not always effective. In this work a preparation of unsupported catalysts and their application to the multi-walled carbon nanotubes synthesis is presented. Iron, cobalt and bimetallic iron-cobalt catalysts were obtained by co-precipitation of iron and cobalt ions followed by solid state reactions. Although metal particles were not supported on the hard-to-reduce oxides, these catalysts showed nanometric dimensions. The catalysts were used for the growth of multi-walled carbon nanotubes by the chemical vapor deposition method. The syntheses were conducted under ethylene - argon atmosphere at 700°C. The obtained catalysts and carbon materials after the synthesis were characterized using transmission electron microscopy (TEM), X-ray diffraction method (XRD), Raman spectroscopy and thermogravimetric analysis (TG). The effect of the kind of catalyst on the properties of the obtained carbon material has been described.

Effect of Carrier Gas on the Growth and Characteristics of Spin-Capable Multiwalled Carbon Nanotubes

Multiwalled carbon nanotube (MWCNT) sheets that can be spun directly from a spin-capable MWCNT forest promise novel applications that utilize the unique and outstanding characteristics of this material. The growth of spin-capable MWCNT forests will be achieved through the understanding of the important factors affecting the forest growth, since the precise conditions necessary for effective spin-capability are extremely sensitive. In this paper, we discuss the effect of carrier gas, the initial catalyst thickness, and the roles of the hydrogen. These factors were investigated in order to assess and understand these critical parameters and thereby develop a repeatable and reliable spin-capable MWCNT growth process.

High Growth Yield of Single Multiwall Carbon Nanotube With Different Length Effect

Vertically aligned single multiwalled carbon nanotube (MWCNT) is quite an interesting nanostructure due to its high probability of nanodevice realization with an ultrahigh integration density. Although ~200 nm catalyst diameter size and plasma-enhanced chemical vapor deposition (PECVD) method have been known as key parameters to grow a single MWCNT, the details and the phenomenon of below 200 nm catalyst size have not been studied or published well. Here, we report the details of catalyst size effect below 200 nm. One-hundred-nanometer diameter Ni catalyst on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer shows 95% yield of single MWCNT growth. Surface roughness of substrate makes a large deviation in the yield and the critical catalyst size for single MWCNT. The various catalyst sizes result in the different growth rate of carbon nanotube (CNT) at the same growth condition. The change of diffusion surface area induces such a difference. From the results, single MWCNTs with various lengths are successfully grown on the same substrate by a one-step growth process.

Catalytic growth of multi-wall carbon nanotubes on carbon cloth using powdery ferrous sulfate heptahydrate as catalyst precursor

Multi-wall carbon nanotubes (MWCNTs) were synthesized on carbon fiber cloth by chemical vapor deposition using natural gas as the carbon source and FeSO 4 · 7H 2 O powder as the catalyst precursor. Scanning and transmission electron microscopy and Raman spectroscopy were used to characterize the product. Small catalyst particles were observed on the top of the tubes. The MWCNTs were dispersed uniformly and aligned perpendicular to the cloth. They had a high crystallinity, and few impurities and defects. The density and structure of the MWCNTs on the cloth can be controlled by deposition temperature and time. [New Carbon Materials 2013, 28(6): 421–427]

Growth of small diameter multi-walled carbon nanotubes by arc discharge process

Multi-walled carbon nanotubes (MWCNTs) are grown by arc discharge method in a controlled methane environment. The arc discharge is produced between two graphite electrodes at the ambient pressures of 100 torr, 300 torr, and 500 torr. Arc plasma parameters such as temperature and density are estimated to investigate the influences of the ambient pressure and the contributions of the ambient pressure to the growth and the structure of the nanotubes. The plasma temperature and density are observed to increase with the increase in the methane ambient pressure. The samples of MWCNT synthesized at different ambient pressures are analyzed using transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. An increase in the growth of MWCNT and a decrease in the inner tube diameter are observed with the increase in the methane ambient pressure.

Cr as a key factor for direct synthesis of multi-walled carbon nanotubes on industrial alloys

Six kinds of industrial alloys, SUS316, FCH2, Invar, Permalloy, Inconel, and Nichrome, and three kinds of pure metals, Fe, Ni, and Cr, were used for substrates on which multi-walled carbon nanotubes (MWCNTs) were directly synthesized from ethylene. To activate their surfaces for the MWCNT formation, their surfaces were modified by two steps, (1) oxidation step in Ar–O2 mixture gas and (1) following reduction step in Ar–H2 mixture gas. It was discovered that Cr is a key component to realize the catalytic growth of MWCNTs on Fe and Ni emerged from the alloys. Using SUS316 to observe the influence of oxidation duration on MWCNT diameter, it was seen that increasing the oxidation duration resulted in the increase of the MWCNT diameter. This tendency can be explained by diffusion of Fe through Cr-rich layer, which causes the increase of catalyst particle diameters. The excess Fe diffusion through the Cr-rich layer resulted in the formation of a unique mushroom structure. These effects seen in the observation on the oxidation duration did not appear when reduction duration was prolonged because the Cr-rich layer could inhibit the Fe diffusion. Instead, the length of the MWCNTs can became maximum by employing an appropriate reduction duration.

Effect of Metal Catalysts on Synthesis of Carbon Nanomaterials by Alcohol Catalytic Chemical Vapor Deposition

Carbon nanomaterials (CNMs) were synthesized by alcohol catalytic chemical vapor deposition (CVD) at atmospheric pressure using different metal catalysts (Ni, Co and Fe) at growth temperature of 700◦C. Ni and Fe exhibited as active catalysts for multi-walled carbon nanotubes (MWNTs) growth, while Co acted as an active catalyst for bamboo-like MWNTs and carbon nanofibers (CNFs). The CNMs synthesized from Ni catalyst showed the highest crystallinity with a small amount of byproducts. These results imply that metal catalyst is key parameter to the structure, morphology and crystallinity of CNMs. The different effect of metal catalyst on growth of CNMs can be described in term of the difference in the change in Gibbs free energy for metal carbide formation.

Catalytic growth of multi-wall carbon nanotubes on carbon cloth using powdery ferrous sulfate heptahydrate as catalyst precursor

Multi-wall carbon nanotubes (MWCNTs) were synthesized on carbon fiber cloth by chemical vapor deposition using natural gas as the carbon source and FeSO4·7H2O powder as the catalyst precursor. Scanning and transmission electron microscopy and Raman spectroscopy were used to characterize the product. Small catalyst particles were observed on the top of the tubes. The MWCNTs were dispersed uniformly and aligned perpendicular to the cloth. They had a high crystallinity, and few impurities and defects. The density and structure of the MWCNTs on the cloth can be controlled by deposition temperature and time.

Fabrication of 3D carbon nanotube/porous carbon hybrid materials

Three dimensional hybrid carbon materials have been prepared using different biomass-derived porous carbons as catalyst supports for growing multi-walled carbon nanotubes (MWCNTs) via a chemical vapor deposition method. The nickel catalyst-loaded supports before and after growing MWCNTs were characterized by scanning and transmission electron microscopy, Fourier transform infrared spectroscopy spectra, and mercury porosimetry. The results show that the grown MWCNTs microstructures are closely related to the porous structures and surface conditions of the carbon supports. By using bamboo as template, a porous carbon support with a large total pore volume, appropriate pore size, and abundant favorable surface functional groups is obtained, which is found to be an ideal support for growing the MWCNTs. Investigation of growth mechanism demonstrated that the combination of appropriate porous structures and surface conditions plays an essential role in catalyst distribution and MWCNTs growth.