Direct Growth Of Carbon Nanotubes Research Articles

(Invited) 3D Carbon-Based Hierarchical Electrodes for Energy Storage

: Carbon-based 3D hierarchical electrodes with appropriate spatial distributions of pores are expected to empower rapid and controllable electrochemical reactions. The ability to fabricate such an electrode, with tunable geometries comprised of continuous nano- and micro-conduits, allows simultaneous optimization of conversion capacity as well as reaction rate. Such manufacturability holds great potential to redefine the future of energy storage, electrocatalysis and chemical production for a sustainable future.In this presentation, I will outline two convergent strategies that involve the integration of additive manufacturing with several decades of advancements in nanomaterials synthesis, coupled with conventional pyrolysis – for creating such electrodes. The primary structure of 3D carbon-based electrodes was fabricated by either direct 3D writing, or the transition metal assisted pyrolysis of 3D-printed polymer templates. The secondary structure was established by employing bottom-up synthesis approaches: (a) SiO2 nanoparticle templates to create nanoscopic porous structures or (b) nanochannels formed through direct growth of carbon nanotubes. We have demonstrated that the primary and secondary structures can be formed by a single step. After monolithic integration of a tertiary structure to reveal sites for electrochemical conversion, these 3D architected electrodes offer impressive charge storage capacities while maintain excellent rate capability.By exploiting the short mass diffusion lengths, we have demonstrated that the new energy storage devices can operate at temperatures as low as -70°C without the requirement of a heater. Furthermore, the incorporation of a high loading of active materials in our 3D electrodes allows for concurrent enhancement of both energy density and power density. These scalable fabrication protocols address two critical challenges – sluggish mass transfer in 3D and the lack of accessible active sites, thereby offering a pathway to harness electrochemical reactions in 3D. This work offers an adaptable solution across a broad spectrum of industries.

Direct Growth of Carbon Nanotubes on Silver Substrate for Determination of Fluoroquinolone

Metallic electrodes modified with carbon nanotubes (CNTs) by direct growth have advantages over the ones modified through external connection methods. These advantages are: (i) reduced contact resistance between CNTs and metal substrate, which is required for electroanalytical determinations. (ii) Strong adhesion of the CNTs layer to the metal substrate which in turn prevents the detachment of CNTs from the electrode surface and stops the deterioration of the signal with time and use. This present work shows the use of carbon nanotubes-modified silver (CNTs-Ag) electrode prepared by direct growth of CNTs as indicator electrodes for differential electrolytic potentiometric (DEP) determination of the fluoroquinolone antibiotic, ciprofloxacin. Characterization of CNTs-Ag electrode by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy showed the growth of aligned, crystalline, and graphitized CNTs. Application of CNTs-Ag electrode for the determination of ciprofloxacin by sequential injection analysis (SIA) method exhibited fast and stable response, reproducible signals, and durability for long-term use. Ciprofloxacin has been quantified in the range of 60 – 1000 µmol/L with a good linear relationship. This work combined the advantages of Direct grown CNTs, SIA technique, and the square-wave DEP method. Figure 1

Ultrahigh-power all binder-free hybrid supercapacitors based on single-crystal hexagonal nanorods of molecular sieve VSB-5 hierarchical electrodes

BackgroundMolecular sieve Versailles Santa Barbara-5 (VSB-5) is a highly porous nanomaterial for electrochemical supercapacitor. MethodsA facile hydrothermal method is used to directly synthesize VSB-5 nanorods onto the Nickel Foam (NF). Significant findingsIn this work, one-dimensional single-crystal hydrogen nickel phosphate hydroxide hydrate (Ni20[(OH)12(H2O)6][(HPO4)8(PO4)4]·12H2O, also denotes as VSB-5, hexagonal nanorods arrays are successfully synthesized on NF via a hydrothermal method, and applied them as positive electrodes for hybrid supercapacitor (HSC). The resultant open framework of VSB-5 with unique nanochannels provides the synchronous advantages of a large surface area with numerous active sites for enhancing faradic redox reactions and abundant pathways for promoting electrolyte ions diffusion, thus leading to excellent energy storage behavior. Furthermore, the HSC is fabricated by paring the direct growth of carbon nanotubes (CNTs) on NF as the electrical-double-layer-capacitor negative electrode. Both the VSB-5/NF and CNTs/NF electrodes are binder-free hierarchical structures, owning the lowest interfacial resistivities between active materials and current collects, avoiding the aggregation issues to allow the facile diffusion of electrolyte for maximally utilizing the surface area. The resultant all binder-free VSB-5/NF//CNTs/NF HSC shows remarkable electrochemical performance, which delivers a maximum energy density of 46.9 W h kg−1 at a power density of 1225 W kg−1 with excellent capacity retention of 98.18% after 10,000 cycles.

Solvent‐free synthesis of ZIF‐67 thin films as the catalyst for the direct growth of carbon nanotubes for the fabrication of electrical double‐layer capacitors

AbstractObjectiveThis work is focused on the direct growth of vertically aligned carbon nanotubes (CNTs) onto the flexible stainless‐steel mesh (SM) substrate using ZIF‐67 as the catalytic layer.Materials & MethodsThe CNTs/SM electrode is prepared by two‐step chemical vapor deposition (CVD) method using ZIF‐67 thin films as the catalytic layers. The time duration for the deposition of ZIF‐67 thin films by an atmospheric CVD process is controlled for direct, vertically aligned, dense and uniform growth of CNTs by a low‐pressure CVD process at a low temperature of 450 °C.Results & DiscussionThe electrochemical performance of CNTs/SM electrode is studied by cyclic voltammetry and galvanostatic charge/discharge measurements using KOH aqueous electrolyte which showed their better EDLC features and outstanding rate capability. The binder‐free directly grown CNTs/SM electrode displayed a low interfacial resistance between CNTs and SM substrate which comes from their synergistic effect of lower charge loss and better charge collection. Moreover, vertically aligned one‐dimensional CNTs could be rendered as the charge highway in the axial direction, which can promote the rapid charge transportation.ConclusionsThe directly grown CNTs on the commercial SM substrate using the ZIF‐67 catalytic layer fabricated via the solvent free technology can be regarded as a promising EDLC electrode for flexible super capacitors.

Facile and Rapid Electrochemical Conversion of Ni into Ni(OH)2 Thin Film as the Catalyst for Direct Growth of Carbon Nanotubes on Ni Foam for Supercapacitors

In this paper, a facile and rapid aqueous-based electrochemical technique was used for the phase conversion of Ni into Ni(OH)2 thin film. The Ni(OH)2 thin film was directly converted and coated onto the network surface of Ni foam (NF) via the self-hydroxylation process under alkaline conditions using a simple cyclic voltammetry (CV) strategy. The as-formed and coated Ni(OH)2 thin film on the NF was used as the catalyst layer for the direct growth of carbon nanotubes (CNTs). The self-converted Ni(OH)2 thin film is a good catalytic layer for the growth of CNTs due to the fact that the OH- of the Ni(OH)2 can be reduced to H2O to promote the growth of CNTs during the CVD process, and therefore enabling the dense and uniform CNTs growth on the NF substrate. This binder-free CNTs/NF electrode displayed outstanding behavior as an electric double-layer capacitor (EDLC) due to the large surface area of the CNTs, showing excellent specific capacitance values of 737.4 mF cm-2 in the three-electrode configuration and 319.1 mF cm-2 in the two-electrode configuration, at the current density of 1 mA cm-2 in a 6 M KOH electrolyte. The CNTs/NF electrode also displayed good cycling stability, with a capacitance retention of 96.41% after 10,000 cycles, and this the excellent cycling performance can be attributed to the stable structure of the direct growth of CNTs with a strong attachment to the NF current collector, ensuring a good mechanical and electrical connection between the NF collector and the CNTs.

Microwave-Assisted Direct Growth of Carbon Nanotubes at Graphene Oxide Nanosheets to Promote the Stereocomplexation and Performances of Polylactides

Microwave-Assisted Direct Growth of Carbon Nanotubes at Graphene Oxide Nanosheets to Promote the Stereocomplexation and Performances of Polylactides

Effect of HF wet-etching and H2-plasma polishing on the low-temperature growth of carbon nanotubes on stainless-steel substrates

Direct growth of carbon nanotubes (CNTs) on 316 stainless-steel (SS) substrates could facilitate versatile commercial applications. For the successful synthesis of CNTs on SS substrate, hydrofluoric acid (HF) etching renders suitable surface roughness to promote CNT growth. For catalyst preparation and also subsequent CNT growth, H2-plasma treatment plays essential roles. Reversing the aging effect of Fe/Ni from its unwanted oxides of reduced catalytic activity and formation of Fe nanoparticles from the sheet are accomplished using H2-plasma. High-density plasma, along with specific gas precursors with its energetic ions, required for uniform CNT growth is attained by microwave plasma-enhanced chemical vapor deposition. By using CO2, providing suitable oxidizer precursors, in (CH4 + H2) diffuse plasma, necessary ambience for low-temperature nucleation (300 °C) and high-yield CNT growth is obtained. Reduction in the deposition rate by highly-energetic ion collisions in high-power plasma is resolved by introducing remote plasma configuration using a specially designed mask assembly. Considering the optimum magnitudes of the intensity ratios of D- and 2D-peaks to the G-peak in the Raman spectra of CNTs, a time span of 2 h of HF-etching appears optimum for proper functioning of the Fe/Ni nanoparticle catalyst. Furthermore, H2-plasma polishing is effectively utilized as the last step of pretreatment, leading to the growth of lower-diameter CNTs. Finally, using a shadow mask assembly and weak oxidizing gas, low-temperature growth of CNTs is successfully accomplished on SS substrates, pretreated by optimum HF-etching and H2-plasma polishing on the Fe-nanoparticle catalyst layer, avoiding the conventional steps of high-temperature annealing for catalyst nanoparticle formation as well as high-temperature nucleation for CNT growth. Even without the use of a separate Fe-catalyst layer, CNT growth is accomplished directly on HF-etched and H2-plasma polished SS substrates, utilizing mostly Fe/Ni nano-grains that originate from the intrinsic composition of SS as the nucleation sites. Use of limited action-steps and of a low-temperature (~300 °C) distinguish this as a realistic avenue for commercial production of CNTs.

Влияние параметров метода PECVD на рост углеродных нанотрубок для устройств нанопьезотроники

The results of experimental studies of the influence of the growth temperature and the thickness of the catalytic layer on the geometric and structural parameters of carbon nanotubes (CNTs) are presented. It is shown that the use of a TiN-based sublayer makes it possible to provide a low resistivity during the direct growth of CNTs on a conducting contact. It was found that for the formation of the best piezoelectric response, it is necessary to form the most defective CNTs. It is shown that the degree of defectiveness of CNTs can be controlled during their growth. A relationship has been established between the geometric and structural parameters of CNTs that affect the piezoelectric response. The potential applicability of CNTs for the creation of nanopiezotronic devices (nanogenerators, energy nanocarvesters) on their basis is shown.

Direct Growth of Carbon Nanotubes on Aluminum Foil by Atmospheric Pressure Microwave Plasma Chemical Vapor Deposition

This paper is about the research that carbon nanotubes (CNTs) grow on aluminum foils without additional catalysts by atmospheric pressure microwave plasma chemical vapor deposition (AMPCVD) with the precursor of argon-hydrogen-ethanol. At different temperatures, a series of experiments that CNTs grow on aluminum foils were done with and without the alumina layer. The EDS results showed that iron impurities in aluminum foils catalyze the growth of CNTs. By measurements of SEM and HRTEM, tens of microns long and multi-walled CNTs are grown. The CNTs’ content in the sample changes more with the increase in temperature. The Raman measuring shows that CNTs have fewer defects with higher temperature. Finally, by measurements of EDS mapping and XRD on aluminum foil, the growth mechanism of CNTs was discussed.

Fracture toughness enhancement of fuzzy CNT-glass fiber reinforced composites with a combined reinforcing strategy

Low interlaminar mechanical properties is the foremost drawback of glass fiber reinforced composites (GFRPs). Hierarchical nanoparticles on fibers (e.g. carbon nanotubes (CNTs)) can improve interlaminar properties of composites with negligible weight increase because of excellent mechanical properties, and low density. Interlaminar properties of composites can be enhanced with the well-dispersed CNTs in polymer matrices as it facilitates load transfer from matrix to fibers. This paper investigates the mechanical properties of CNT-reinforced GFRPs. Two reinforcing strategies were studied as dispersion of CNTs in epoxy matrix and direct growth of CNTs onto glass fibers (GFs), simultaneously. The former is referred to as nanotube-reinforced composites (NRCs) while the latter is known as fuzzy architectures. Furthermore, the combination of NRCs and fuzzy glass fibers (F-GFs), also known as fuzzy nano-reinforced composites (F-NRCs), is used to fabricate composites and identify the reinforcing capabilities through both methods. Mechanical properties are investigated by Mode-I fracture toughness and unidirectional (UD) composite tensile tests. Even though NRCs and F-NRCs yield similar enhancements in the propagation fracture toughness as 113% and 119%, respectively, the tensile strength of F-NRCs is decreased by 24% due to heat treatment during the CNT synthesis.

Enhanced magnetic properties of aluminum oxide nanopowder reinforced with carbon nanotubes

Magnetic carbon nanotubes (CNTs)/alumina (Al2O3) nanocomposites were synthesized by the direct growth of CNTs on alumina by chemical vapor deposition (CVD) process. X-ray diffraction studies show that the crystalline structure of alumina nanoparticles remains preserved during the CVD process. Electron microscopy studies reveal the uniform distribution of CNTs within the alumina matrix. CNTs of average diameter 20 nm are spread around alumina particles of size 120 nm. The proportion of CNTs in alumina composites is determined to be approximately 10% from the thermogravimetric analysis. CNT-reinforced alumina nanocomposites demonstrate a significant improvement of the magnetic properties as compared with pristine alumina powder. The diamagnetic property of alumina nanopowder is transformed into a strongly pronounced ferromagnetic response upon the incorporation of CNTs. The saturation magnetization increased by ~ 2500%, and a pronounced coercivity of 68 Oe was observed in the nanocomposites. It is suggested that the encapsulation of cobalt inside the CNTs constrains the magnetic moments to result in higher saturation magnetization. Hence, the CNTs/Al2O3 system synthesized in this work can be employed to engineer novel ceramic composites with enhanced magnetic properties.

Direct growth of carbon nanotubes on basalt fiber for the application of electromagnetic interference shielding

This paper reported the preparation of a hierarchical structure consisting of micro-scale basalt fiber fabric and nano-scale carbon nanotubes (CNTs). The developed fabric was employed as reinforcement to develop nanocomposites with multi-layer structures for electromagnetic interference shielding. Different techniques were employed to study the morphologies and properties of the fabric and corresponding nanocomposites. The results showed that by optimizing the experimental conditions, CNTs with controlled content and quality were grown on the surface of basalt fiber. These properties significantly affected the electromagnetic interference shielding performance of corresponding nanocomposites. The novelty of this study lies in the direct growth of nanotubes on basalt fiber by utilizing the in-situ generated mineral nanoparticles on fiber surface as a catalyst, and a spontaneous infusion of uncured polymer into the fabric, which eliminates the problems associated with the dispersion and re-agglomeration of CNTs during the preparation of nanocomposites.

Electrochemical investigation on high-rate properties of graphene nanoplatelet-carbon nanotube hybrids for Li-ion capacitors

Li-ion capacitors (LICs) are considered a bridging electrochemical energy device between Li-ion batteries and supercapacitors. Graphene nanoplatelet (GNP)‑carbon nanotube (CNT) hybrid materials can be a good candidate for negative electrode materials used in LICs. The rate performance of LIC negative electrodes plays a key role in increasing the power density of LICs. In this study, the Li storage kinetics of a GNP-CNT hybrid electrode was investigated. CNTs were directly grown on the GNP surfaces through chemical vapor deposition via transition metal oxide seeding. Natural graphite, GNP, and mixture (GNP and CNT) electrodes were used as the control electrodes. The kinetics was evaluated using electrochemical analysis tools such as galvanostatic charge-discharge cycling at various current densities, cyclic voltammetry, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy. The results revealed that the direct growth of CNTs on the GNP surfaces led to strong contact between these materials. This contact could play a pivotal role in the improvement of reversible Li storage kinetics characterizing negative electrodes for high-power LICs.

Fe‐N‐C Catalysts: Direct Growth of Carbon Nanotubes Doped with Single Atomic Fe–N4 Active Sites and Neighboring Graphitic Nitrogen for Efficient and Stable Oxygen Reduction Electrocatalysis (Adv. Funct. Mater. 49/2019)

Fe‐N‐C Catalysts: Direct Growth of Carbon Nanotubes Doped with Single Atomic Fe–N₄ Active Sites and Neighboring Graphitic Nitrogen for Efficient and Stable Oxygen Reduction Electrocatalysis (Adv. Funct. Mater. 49/2019)

Direct Growth of Carbon Nanotubes Doped with Single Atomic Fe–N4 Active Sites and Neighboring Graphitic Nitrogen for Efficient and Stable Oxygen Reduction Electrocatalysis

AbstractSingle atomic Fe–Nx moieties embedded on a high surface area carbon (Fe–N/C) represents one of the most promising nonprecious metal electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. While significant progress has been made in the preparation of Fe–N/C catalysts with high‐density Fe–Nx sites, key structural descriptors determining the intrinsic activity of the Fe center remain elusive, and effective ways to enhance the intrinsic activity are still lacking. Moreover, most Fe–N/C catalysts developed to date are built on carbons with rather low graphitization degree, which suffer from relatively severe carbon corrosion and thereby poor stability. The direct growth of carbon nanotubes doped with high‐density Fe–Nx sites neighbored with graphitic‐nitrogen‐rich environment is reported here, which are successfully applied as a both active and stable ORR electrocatalyst in fuel cells. Combining both experiments and density functional theory calculations, it is revealed that the neighboring graphitic nitrogen can effectively induce higher filling degree of d‐orbitals and simultaneously decrease on‐site magnetic moment (namely, lowered spin) of the Fe center, which can optimize the binding energies of ORR intermediates and thereby substantially enhance intrinsic ORR activity.

Direct growth of flexible carbon nanotube interconnects during polymer-ceramic conversion reaction for release of thermal stress

Polymer-derived ceramics, which are a class of emerging ultrahigh-temperature semiconductor materials, face challenges when it comes to the semiconductor–metal interconnects. High thermal stress produced at the semiconductor–metal interface during ultrahigh-temperature applications (>1000 °C), owing to the mismatch in the coefficients of thermal expansion of the two materials, can readily lead to the mechanical failure of the semiconductor–metal interconnection. Herein, flexible carbon nanotube (CNT) interconnects were formed from Ni alloy (Ni95AlSiMn) wires to the SiCN semiconductor through the direct growth of CNT on the Ni alloy wires during the synthesis of SiCN itself by a polymer-ceramic conversion reaction. The catalytic Ni nanoparticles and the gaseous carbon sources needed for the growth of CNT were generated during the polymer-ceramic conversion reaction. Flexible CNT interconnects exhibited outstanding electrical characteristics and excellent interfacial strength. Further, the temperature dependence of the resistance of SiCN could be measured at temperatures of up to 1000 °C without significant mechanical failure or a decrease in the interfacial strength because the thermal stress was readily released by the flexible CNT interconnects. Thus, the fabricated CNT interconnects with excellent electrical, thermal, and thermo mechanical properties are highly suited for various ultrahigh-temperature applications.

Grown Carbon Nanotubes on Electrospun Carbon Nanofibers as a 3D Carbon Nanomaterial for High Energy Storage Performance

AbstractCarbon hierarchical nanostructures have been widely applied because of their outstanding properties and large surface area. Future energy materials for applications, such as Li‐ion, Li‐sulfur, Li‐air batteries, and supercapacitors require materials with high energy density and power capability. The preparation of three‐dimensional (3D) carbon nanotubes (CNTs)‐carbon nanofibers (CNFs) nanomaterials through a multi‐step process has many difficulties. The aggregation, the high expense of CNTs, and the difficult conditions for synthesizing CNTs have pushed researchers to consider new methods. The direct growth of CNTs on CNFs via one‐step electrospinning and a combined pyrolysis process is an efficient method for preparing 3D CNTs‐CNFs, as demonstrated in the literature. Herein, the importance of the hybrid 3D CNTs‐CNFs nanomaterials is reviewed, as well as their growth mechanisms, and the parameter influence on the morphology of grown CNTs. Moreover, the performance of the electrochemical energy storage for the hybrid CNTs grown on CNFs in the literature is reviewed and explained. Finally, the nanomaterials form the CNTs grown CNFs have great potential for various applications.

Low turn-on and uniform field emission from structurally engineered carbon nanotube arrays through growth on metal wire mesh substrates

A simple and novel approach to improve the field emission properties from carbon nanotube (CNT) arrays is presented through the direct growth of CNTs onto metal wire mesh substrates. We utilized the curvilinear profiles of the wires to create a cleaved CNT array structure, which was uniformly distributed throughout the entire emitter array area. Investigation of the factors governing the emission properties showed that increased wire diameter, increased CNT array height, and decreased catalyst thickness led to decreased turn-on fields (TOFs) within our experimental range. In addition, we found that the underlying mechanism explaining these empirical results stemmed from the creation of sharp edges which were sufficiently spaced and homogeneously distributed throughout the emitter array. Through this method, a low TOF of ~0.95 V µm−1 for a 10 µA cm−2 emission current density was achieved, which is among the lowest values reported for field emission arrays.

Protective effect of ultrathin alumina film against diffusion of iron into carbon fiber during growth of carbon nanotubes for hierarchical composites investigated by ptychographic X-ray computed tomography

Composite materials based on carbon fiber (CF) are prone to failure at the fiber-matrix interface upon compression or stress transverse to the fiber axis. The direct growth of carbon nanotubes on CF constitutes a novel approach to enhance the mechanical properties of the interface. However, the challenge is that, during the growth, tensile properties of the fiber are altered due to the diffusion effect of iron nanoparticles used in the process, leading to CF surface defect formation. In this work, we deliver and discuss an analysis methodology on ptychographic X-ray computed tomography (PXCT) images in order to assess the iron nanoparticle abundance within CFs. PXCT provides 50 nm - resolved 3D electron density maps of the CFs. We evidence the protective effect of an ultrathin alumina film against iron infiltration into CF during the CNT growth. This method potentially allows to evaluate the efficiency of other diffusion-minimizing approaches. The conclusions of the PXCT examination are validated by energy-dispersive X-ray spectroscopy and scanning transmission electron microscopy carried out on thin sample slices cut with a focused ion beam. The results provide a new insight into the mechanical performance of CFs and therefore constitute valuable knowledge for the development of hierarchical composites.

Effects of the Growth Time and the Thickness of the Buffer Layer on the Quality of the Carbon Nanotubes

Direct growth of carbon nanotubes (CNTs) array onto silicon substrate by the chemical vapor deposition (CVD) is reported. Experimental results show that the thickness of the buffer layer has a significant effect on the morphology and defects of the array, and when the buffer layer is about 15 nm, the best array on the silicon substrate can be obtained. Moreover, when the growth time is less than the threshold time (70 minutes), the array height will increase with the increase of the time. Importantly, when the growth time is higher than this threshold time, the growth of array will stop, but when the growth is continuing, the amorphous carbon and carbon can cluster, which will affect the structure of the array. These results provide a good material basis for the device, thermal, and conductivity technology.