Carbon Carbon Nanotubes Research Articles

Defective 3D nitrogen-doped carbon nanotube-carbon fibre networks for high-performance supercapacitor: Transformative role of nitrogen-doping from surface-confined to diffusive kinetics

This work demonstrates hierarchical 3D nitrogen-doped carbon nanotube-carbon fibre (N-CNT@CF) networks obtained via a two-step synthetic technique: electrospinning and chemical vapour deposition (CVD) methods. Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM) reveal randomly entangled networks structure. Raman spectroscopy show structural defects, X-ray Diffraction spectroscopy (XRD) confirm the purity of the materials, while BET analysis show increase in surface area after nitrogen doping. Electrochemistry reveals that nitrogen-doping transforms surface-confined to diffusion-confined energy-storage mechanism (i.e., high power) even at low cycling rate, significantly increasing the specific capacitance of the symmetric device (155 F/g), specific energy (5.5 Whkg−1), specific power (254 W kg−1) and capacitance retention of 93% even after 10,000 cycles at 10 Ag−1. The N-CNT@CF-based symmetric cell exhibits higher fo value (ca. 82 Hz, response time,τ, of 12 ms) than the CNT@CF-based cell (ca. 25.1 Hz, 40 ms). The excellent performance of N-CNT@CF hybrid material is attributed to the Faradaic charge contribution arising from synergistic interaction between the nitrogen-doped carbon nanotubes and carbon nanofibers, high conductivity, high surface area coupled with enough accessible active sites for electrochemical reactions. This work underscores the importance of defect engineering and decoration of the vacant sites by nitrogen for enhanced supercapacitance.

Aligned carbon nanotube/carbon (CNT/C) composites with exceptionally high electrical conductivity at elevated temperature to 400 °C

To obtain a high electrical conductivity for aerospace and defense applications, in this paper, we investigated the electrical properties of carbon nanotube reinforced carbon (CNT/C) composites at elevated temperature up to 400 °C in air. The CNT/C composites were made of aligned CNT sheet and pyrolytic carbon (PyC) by chemical vapor infiltration (CVI) process. The electrical conductivity of the aligned CNT/C composites is 3.2 × 106 S · m−1 in room temperature and shows a positive temperature dependence as a function of the measuring temperature, and the conductivity reaches to the order of ∼107 S · m−1 at 400 °C. We concluded that the conduction in the aligned CNT/C composite is mainly dominated by the tunneling conductivity mechanism. These unique features are related to the structural change of composites by infiltrating amorphous PyC into the space in between of the CNT bundles. The exceptionally high conductivity might be contributed to the electron transport mechanism between the CNT bundles and the PyC matrix.

Aerosol-assisted synthesis of porous and hollow carbon-carbon nanotube composite microspheres as sulfur host materials for high-performance Li-S batteries

Spherical carbon materials with porous and hollow structures have been developed as efficient sulfur host materials for LiS batteries through various synthetic strategies. However, nanostructured carbon materials, generally synthesized by liquid solution processes, have disadvantages of low electrical conductivity as sulfur host materials. In this study, highly porous hollow carbon-carbon nanotubes (CNTs) composite microspheres, with a high loading rate of ultrafine S and high electrical conductivity, are designed and successfully synthesized by an aerosol-assisted process (ultrasonic spray pyrolysis) as efficient sulfur host materials. The carbon-CNTs composite microspheres, with a high sulfur loading rate of 70 wt%, exhibit superior electrochemical performance as a cathode compared to that of S-loaded CNTs balls for LiS batteries. The S-loaded carbon-CNTs composite microspheres exhibit a discharge capacity of 697 mA h g−1 for the 250th cycle at a current density of 1.0C and show high reversible discharge capacities of 685 mA h g−1, even at a high current density of 3.0C. The outstanding cycling and rate performance of S-loaded carbon-CNTs composite microspheres are attributed to the structural flexibility of the hollow structure, loading of ultrafine sulfur in micro- and mesopores of dextrin-derived carbon, and good electrical conductivity due to uniformly dispersed CNTs.

Porous Carbon-Carbon Nanotubes Composites with Different Structures (CNTs/PC, CNTs@PC) as Catalysts for ORR

Background: Non-precious metal based catalysts have become a hot research material due to their easy availability, low cost and outstanding electrochemical performance. Among them, carbon-based materials like carbon nanotubes and porous carbon with their own characteristics are especially favored by researchers in the field of catalyzing oxygen reduction. Therefore, rational construction of combining porous carbon with carbon nanotubes attracts great research attention on the object to utilize the excellent porosity, large specific surface area of porous carbon and the good electronic conductivity, high stability of carbon nanotubes to catalyze oxygen reduction. In this work, we synthesized two catalysts with different structure of coating carbon nanotubes with porous carbon by paralyzing a mixture of pre-prepared porous carbon, Co3O4 nanoparticles and melamine/ glucosamine hydrochloride. Then, the composites were applied to fuel cells as cathodic oxygen reduction reaction catalysts, which both exhibited good onset potential and excellent stability. Objective: Briefly, the porous carbon was prepared by heating the mixture of glucosamine hydrochloride and Co(NO3)26H2O under N2 flowing. Co3O4 nanoparticles were prepared by pyrolyzing cobalt nitrate-impregnated cotton wool. The CNTs/PC was synthesized by pyrolyzing the mixture of porous carbon, Co3O4 nanoparticles and melamine. The CNTs@PC was synthesized by pyrolyzing the mixture of porous carbon, Co3O4 nanoparticles and glucosamine hydrochloride. The cyclic voltammetry, liner sweep voltammetry and chronoamperometry measurements were analyzed to obtained the catalysis performance for oxygen reduction. Results: Through the rational design of catalyst structure, porous carbon and carbon nanotubes with different structures were constructed to expose more active sites on the surface of the sample. As a result, the onset potential of CNTs/PC and CNTs@PC are all at 0.9 V. After 20,000s chronoamperometry measurement, the current holding rate of CNTs/PC reached 95%, CNTs@PC was 94%, while Pt/C was only 77%. This shows that the prepared catalysts possess outstanding stability compared to Pt/C. Conclusion: In this work, we synthesized two catalysts with different structure by paralyzing a mixture of pre-prepared porous carbon, Co3O4 nanoparticles and melamine/glucosamine hydrochloride, growing carbon nanotubes on the surface (CNTs/PC) and inside (CNTs@PC) of the porous carbon framework. The catalytic property of prepared CNTs/PC and CNTs@PC all possess good onset potential and excellent stability toward ORR. Therefore, a reasonable design of the catalyst structure is required to expose more active sites on the sample surface.

Cobalt sulfide @ CNT-CNF for high-performance asymmetric supercapacitor

A cobalt sulfide encapsulated within carbon nanotube-carbon nanofiber (Co9S8@CNT-CNF) nanohybrid electrode is designed and prepared. The physicochemical characterization such as X-ray diffraction (XRD) and electron microscopy revealed the formation of Co9S8@CNT-CNF. The specific capacitance of Co9S8@CNT-CNF is 1656 F g−1 at 1 A g−1 with good electrochemical cycle stability (92.6% up to 10,000 cycles). The Co9S8@CNT-CNF electrode exhibits a maximum power density of 8.83 kW kg−1 with an energy density of 65 Wh kg−1, while a maximum energy density of 175 Wh kg−1 is attained at a power density of 463 W kg−1. This impressive electrochemical performance of the Co9S8@CNT-CNF composite indicated significant potential for application in high-power and energy-storage devices.

Coconut‐Shell‐Derived Carbon/Carbon Nanotube Composite for Fluoride Adsorption from Aqueous Solution

Devastating effect of fluoride in drinking water on human health is a great concern and defluoridation is essential to make groundwater suitable for drinking. The aim of this study is to evaluate the dissolved fluoride removal efficiency of a novel and low‐cost carbon/carbon nanotube (CNT) composite under batch conditions. CNTs are coated on the coconut‐shell charcoal surface at 450 °C by using plasma‐enhanced chemical vapor deposition. Thereafter, processed charcoal samples are ball milled and used for the fluoride removal from aqueous medium. The amount of fluoride removal is found to be ≈65% of the initial concentration of 4.4 mg L−1 in 3 h contact time at the adsorbent dose of 10 g L−1. The linear forms of three isotherm models (Langmuir, Freundlich, and Temkin) and two kinetic models (pseudo‐first order and pseudo‐second order) are applied to the adsorption data to determine the best fit for equilibrium expression. Isotherm data fit the Langmuir model while the adsorption kinetics is represented by the pseudo‐second‐order kinetic model. The fluoride adsorption process onto prepared carbon/CNT composite occurred spontaneously (ΔG° = −1.656 kJ mol−1) in an endothermic nature (ΔH° = 11.07 kJ mol−1) with increased randomness (ΔS° = 41.69 J mol−1 K−1). To validate the performance further, the as‐prepared adsorbent is successfully used to treat groundwater samples with excess fluoride concentration collected from Nalgonda district, Telangana, India.

Nature of improved double-layer capacitance by KOH activation on carbon nanotube-carbon nanofiber hierarchical hybrids

Carbon nanotubes (CNTs) and their related hybrids grown by chemical vapor deposition (CVD) method have been frequently used as energy-storage electrode materials. In most cases, the tips of CNTs are almost well closed, which often limits the utilization efficiency of their tubular structure in storage of charges. In this work, the authors have designed a type of tip-open CNT/CNF hierarchical hybrids via KOH activation on the CVD-grown Al/Fe-catalyzed CNT/CNF precursors. Results showed that the CNT hierarchies' tips can be fully opened via KOH activation at 700–750 °C for 90 min. As expected, the tip-open CNT-CNF hybrids show a highly improved specific capacitance, which increases by 3.3 times that of the pristine ones. Moreover, sweep analysis indicated that the diffusion-type capacitance increases by 3.7 times while the Helmholtz-type capacitance increases only by 1.5 times, indicating that the tip-open CNTs contribute to ∼30% of the increase in double-layer capacitance. Further optimization on activation time and temperature indicated that activation at 700 °C for 90 min is suitable for opening the tips of CNT hierarchies and protecting the CNTs’ tubular structure. This research would give some useful advice for the preparation of high-performance CNT-related electrode materials for energy storage.

Robust carbon nanotube composite fibers: Strong resistivities to protonation, oxidation, and ultrasonication

Carbon nanotube (CNT) fibers have great potential in the field of high performance fibers. However, poor inter-tube coupling between bundles resulting in low structural and mechanical stability under strong acid, ultrasonication and high-temperature oxidation limited the practical applications of CNT fibers in extreme environment. Here we report the preparation of robust carbon nanotube/carbon (CNT/C) composite fibers with highly aligned and dense structure utilizing an ultrafast Joule heating tension-annealing approach. CNT fibers prepared by floating catalytic chemical vapor deposition were infiltrated by polyacrylonitrile (PAN) solution, followed by programable tension annealing in argon for 10 s. Such a short process carbonized infiltrated PAN, resulting in the formation of CNT/C fibers within which CNTs were bonded by pyrolytic carbon. Due to the carbon-bonded structure, the composite fibers exhibited improved resistivity against structure damages when exposed to strong acid, ultrasonication, and high-temperature oxidation. Comparing with the pristine CNT fibers, such composite fibers showed 320% improvement in breaking load, 354% increase in strength (2.3 GPa) and 667% increase in modulus (60 GPa), respectively. Moreover, such composite fibers have low densities (1.48 g/cm3) and excellent flexibility and toughness. These combined features could broaden the application of the CNT/C composite fibers in many areas.

Influence of Multiwalled Carbon Nanotubes as Additives in Biomass-Derived Carbons for Supercapacitor Applications.

Glucose-derived carbon/carbon nanotube (CNT) hybrid materials were prepared by hydrothermal carbonization of glucose in the presence of CNTs and subsequent carbonization, physical activation, or chemical activation. The proportion of CNTs added during the hydrothermal polymerization of glucose was varied to ascertain the optimum dose to maximize the performance of the carbon hybrids in supercapacitor applications. Both the thermal treatment applied and the addition of CNTs lead to changes in the textural and chemical properties of the activated carbons. It was observed that samples bearing CNTs exhibit higher number of nucleation centers for glucose oligomers to polymerize, and consequently, the behavior of the hydrothermal carbon toward activation differs according to the activating agent employed. Moreover, the initial chemical speciation dominated by acidic groups shifts to more basic functionalities (quinones and carbonyl groups) with the addition of CNTs. The effect of the different physicochemical properties of the prepared carbons on their electrochemical behavior was evaluated. The addition of 2 wt % of CNTs and subsequent chemical activation leads to electrode materials yielding 206 F g-1 and 78% of capacitance retention up to 0.8 V and 20 A g-1 and high rate cyclability (97% after 5000 cycles). The outstanding performance is ascribed to the high surface area, narrow mesopores, and phenol/carbonyl surface functionalities, which enhance molecular diffusion, the amount of stored energy, and electronic transportation, respectively.

Low-temperature selective catalytic reduction of NO x with NH3 over an activated carbon-carbon nanotube composite material prepared by in situ method.

Ce-supported activated carbon–carbon nanotube composite (Ce/AC-CNTs) catalyst was prepared by in situ formation of CNTs on AC and then modified by Ce. This Ce/AC-CNTs catalyst was subsequently used for low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR). The NO conversion of Ce/AC-CNTs was 1.41 times higher than that of Ce/AC at 150 °C with good SO2 tolerance. The catalysts were analyzed by N2 physisorption, SEM, XRD, NH3-TPD, XPS, and Raman technologies. The results showed that the introduction of CNTs could form new mesopores and increase the amount of surface chemisorbed oxygen and acid sites, which all contribute to the high NH3-SCR activity.

Carbon nanotube/carbon composite fiber with improved strength and electrical conductivity via interface engineering

Carbon nanotube/carbon (CNT/C) composites show potential for lightweight structural materials and non-metal electrical conductors for aerospace, military, and other industries where the combination of lightweight, high strength and excellent conductivity are required. Most research attempts have been reported to fabricate CNT/C composite focusing on the high CNT alignment and dense carbon matrix. However, simultaneous improvement of strength and electrical conductivity in materials still presents a great challenge. In this study, pyrolyzed polydopamine (py-PDA) with selected surface treatments is introduced as an interface enhancer between CNTs and the carbon matrix. Due to the presence of py-PDA, the effective physical interlocking and conductive pathways are rebuilt at the interface area between CNTs and carbon matrix, resulting in better load transfer and electron transport. The CNT/py-PDA/C composite fibers demonstrated remarkable improvements in electrical conductivity (2.1 × 103 S cm−1 or 228 S m2 kg−1) and tensile strength (up to 727 MPa or 790 MPa/(g·cm−3)), which should prove to be vastly advantageous as compared to the previously reported CNT/C composites. The outstanding thermal stability of fully carbonized materials is also an attractive feature. Coupled with scalable manufacturing methods, these integrated characteristics of CNT/py-PDA/C composite fiber can potentially have broad applications for lightweight structural materials and non-metal conductors.

Bifunctional Electrocatalysts for Overall Water Splitting from an Iron/Nickel-Based Bimetallic Metal-Organic Framework/Dicyandiamide Composite.

Pyrolysis of a bimetallic metal-organic framework (MIL-88-Fe/Ni)-dicyandiamide composite yield a Fe and Ni containing carbonaceous material, which is an efficient bifunctional electrocatalyst for overall water splitting. FeNi3 and NiFe2 O4 are found as metallic and metal oxide compounds closely embedded in an N-doped carbon-carbon nanotube matrix. This hybrid catalyst (Fe-Ni@NC-CNTs) significantly promotes the charge transfer efficiency and restrains the corrosion of the metallic catalysts, which is shown in a high OER and HER activity with an overpotential of 274 and 202 mV, respectively at 10 mA cm-2 in alkaline solution. When this bifunctional catalyst was further used for H2 and O2 production in an electrochemical water-splitting unit, it can operate in ambient conditions with a competitive gas production rate of 1.15 and 0.57 μL s-1 for hydrogen and oxygen, respectively, showing its potential for practical applications.

In-situ construction of interconnected N-doped porous carbon-carbon nanotubes networks derived from melamine anchored with MoS2 for high performance lithium-ion batteries

Three-dimensional (3D) interconnected N-doped porous carbon-carbon nanotubes networks derived from melamine anchored with MoS2 (MoS2/NPC-NCNTs) composite is successfully synthesized through a simple two-step method. The NPC-NCNTs hybrid is fabricated via simultaneous in-situ carbonization and catalytic growth using melamine formaldehyde polymer as the carbon and nitrogen precursors and SiO2 nanoparticles as the mesoporous template. MoS2 nanoflowers are anchored into the NPC-NCNTs by a hydrothermal method. In the composite, the NPC and NCNTs are entwined and interconnected each other, as a reinforced concrete structure to form a robust skeleton and an excellent 3D conductive network; MoS2 nanoflowers consisting of several nanosheets are closely incorporated with the NPC-NCNTs hybrid. Benefiting from the unique features such as abundant porosity, enhanced electrical conductivity and superb buffering capability, the MoS2/NPC-NCNTs composite electrode delivers a high specific capacity (1218.7 mA h g−1 at 200 mA g−1), a superior rate capability (452.2 mA h g−1 at 4000 mA g−1) and an excellent cyclic stability (capacity retention of 526.1 mA h g−1 after 400 cycles at 1000 mA g−1).

Effects of Carbon Nanotube-Carbon Fiber Cementitious Conductive Anode for Cathodic Protection of Reinforced Concrete

Abstract Carbon nanotube-carbon fiber/cement-based composites used as auxiliary anode for cathodic protection of reinforced concrete were explored in this paper. Cathodic protection was applied with impressed current and its efficiency was verified by corrosion potential, corrosion current, and AC impedance spectroscopy. Results showed that cement composites containing 0.4 wt. % carbon fiber and 0.5 wt. % carbon nanotubes exhibit the optimum electrical and mechanical properties. Effective protection on steel re-bars can be expected due to a sufficient negative potential shift by the applied electric current. Compared with a carbon fiber cementitious conductive anode system, a decrease of corrosion current of steel re-bars was observed for the carbon nanotube-carbon fiber cementitious conductive anode system. During cathodic protection, both capacitive loop radius of a Nyquist plot in the intermediate frequency region and the charge transfer resistance increased with time. A detailed mechanism analysis of the efficiency of cathodic protection using the carbon nanotube-carbon fiber cementitious conductive anode is also included.

Silicon-multi-walled carbon nanotubes-carbon microspherical composite as high-performance anode for lithium-ion batteries

Silicon-multi-walled carbon nanotubes-carbon (Si-MWNTS-C) microspheres have been fabricated through the ball milling and spray drying method followed by the carbonization process. The as-prepared composite microspheres are confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The specific capacity of the as-prepared microspherical composite as anode in lithium-ion batteries (LIBs) is about 1100 mAh g−1 at the current density of 0.2 A g−1 (based on the total weight of the composite). At the high current density of 6 A g−1, the Si-MWNTS-C microspheres exhibit reversible capacity of 415 mAh g−1. Through the ex situ SEM, we observed that the Si-MWNTS-C microspherical composite particles have no extinct change on the electrode surface except for the growth of the spherical particles after 100 cycles. The excellent electrochemical performance is ascribed to the synergistic effect between Si nanoparticles (Si NPs) and MWNTS-C microspheres. The as-prepared Si-MWNTS-C microspheres can effectively accommodate large volume changes and provide a 3D conductive network during the lithiation–delithiation processes.

Macroporous carbon nanotube-carbon composite electrodes

Macroporous carbon nanotube-carbon composite electrodes (CNT-C) have been fabricated and characterized. CNT/polystyrene beads assembly was first prepared by electrophoretic co-deposition. Polypyrrole (PPy) was then polymerized electrochemically in the pore volume generated by the CNT assembly. After removal of the polystyrene template and pyrolysis of the conductive polymer between 650 and 950 °C, a macroporous composite material made of CNT and an amorphous carbon binder (quoted as C) was obtained. Increasing the amount of PPy allowed to improve the mechanical properties of the composite, as measured by the Young's modulus extending from 7 (CNT alone) to 663 GPa (CNT-C composite). CNT-C composite was characterized by Raman and X-ray photoelectron spectroscopies. Its surface area was dramatically enhanced, as evidenced by the increase in capacitance from 6 mF cm−2 to 199 mF cm−2 in the presence of the largest content of amorphous carbon. The influence of the amount of deposited carbon was discussed regarding the VO2+/VO2+ electrochemistry (i.e., the most critical redox couple in vanadium redox flow batteries). A 50 μm thick macroporous CNT-C composite gave rise to 5 times enhancement of the electrochemical response compared to a nonmacroporous CNT-layer).

Investigating the Effects of Synthesis Parameter on the Yield and Structural Health of In-Situ Grown Carbon Nanotubes

Investigating the Effects of Synthesis Parameter on the Yield and Structural Health of In-Situ Grown Carbon Nanotubes Carbon nanotubes have proved to be very unique and versatile reinforcing agent for the development of nanocomposites in recent times. In this study, CNTs were grown on cobalt based nano particles by Alcoholic Catalytic Chemical Vapor Deposition process for the fabrication and promotion of hard metallic in-situ nanocomposites materials. Alcoholic (ethanol) precursor was preferred as it minimizes defects on CNTs surfaces. Besides in-situ growth of CNTs, other main objective of this study was to optimize a reaction temperature (among several), which offered better yield and quality of grown CNTs. Yield and quality index of CNTs were better at 900oC. Influence of synthesis reaction temperatures on quality of grown CNTs was investigated by Raman Spectroscopic technique. CNTs graphitic hexagonal crystal planes were confirmed by XRD spectra.

Multi-scale alignment construction for strong and conductive carbon nanotube/carbon composites

Carbon nanotube/carbon (CNT/C) composites derived from entangled CNT network and different precursors, phenolic or pitch, were fabricated in this work. Multi-step mechanical stretching, repeated polymer infiltration pyrolysis and graphitization were subsequently performed for the preparation. CNT alignment was accomplished in CNT/C derived from both phenolic and pitch precursors, while aligned carbon matrix could be only found in CNT/pitch derived CNT/C composites. Such phenomenon provided direct evidence for the promoting effect of CNT alignment on the graphitization of the carbon matrix. Mechanisms for the stretching induced alignment and the formation of aligned carbon matrix were proposed and discussed. The planar configuration of pitch molecules and its Pi–Pi stacking with CNT walls were considered beneficial for the stress induced graphitization, thus the carbon matrix could be aligned along the CNT walls. Based on the tensile and electrical conductivity measurements, we believed that CNT alignment dominated both mechanical and conducting performances of cured (stabilized) and carbonized CNT/C composites; while the alignment of carbon matrix played the decisive role in graphitized CNT/C. In addition, the carbonized composites could exhibit tensile strength as high as 1.2GPa, while the electrical conductivity of graphitized samples was in the scale of 105S/m.

Synthesis of Carbon Nanotube-Carbon Nanosphere on the CF Surface by CVD

In the current work, the synthesis of carbon nanotubes (CNTs) and carbon nanospheres (CNS’s) has been investigated by applying the chemical vapor deposition method in a one-step sample preparation. In this method, iron nitrate non-hydrate (Fe(NO3)3.9H2O) and acetylene (C2H2) have been used as the catalyst source and carbon source, respectively, to grow CNT directly on the CF surface at 700°C and then CNS’s were synthesized on the CNT layers at 900°C under a 250sccm gas flow rate (40%N2, 40%H2, 20% C2H2). According to the SEM and TEM micrographs from the resultant carbon nanoparticles, the diameters of the CNTs and CNS’s have been estimated about 30-50nm and 300-400nm, respectively.

An Aligned and Laminated Nanostructured Carbon Hybrid Cathode for High-Performance Lithium-Sulfur Batteries.

An aligned and laminated sulfur-absorbed mesoporous carbon/carbon nanotube (CNT) hybrid cathode has been developed for lithium-sulfur batteries with high performance. The mesoporous carbon acts as sulfur host and suppresses the diffusion of polysulfide, while the CNT network anchors the sulfur-absorbed mesoporous carbon particles, providing pathways for rapid electron transport, alleviating polysulfide migration and enabling a high flexibility. The resulting lithium-sulfur battery delivers a high capacity of 1226 mAh g(-1) and achieves a capacity retention of 75% after 100 cycles at 0.1 C. Moreover, a high capacity of nearly 900 mAh g(-1) is obtained for 20 mg cm(-2), which is the highest sulfur load to the best of our knowledge. More importantly, the aligned and laminated hybrid cathode endows the battery with high flexibility and its electrochemical performances are well maintained under bending and after being folded for 500 times.