Aerosol Chemical Vapor Deposition Research Articles

A new method for evaluation of nanotube growth kinetics in aerosol CVD

Aerosol chemical vapor deposition (CVD) – a particular case of floating catalyst CVD method with an extreme dilution of catalyst – has been demonstrated to be one of the most advanced one-stage and continuous techniques for the production of single-walled carbon nanotubes (SWCNTs) for various applications in electronics, optics, energy storage, etc. Nevertheless, rational scaling of the aerosol CVD reactor is often limited by a fundamental problem of tracking the growth kinetics, in particular, the nanotube growth rate and the catalyst deactivation rate. We propose a robust method for the assessment of nanotube growth kinetics (growth rate and catalyst lifetime) based on the analysis of the SWCNT film equivalent sheet resistance (R90) versus residence time (τ) dependencies. We have demonstrated identical trends of R90-vs-τ and length-vs-τ curves at different concentrations of CO2 used as a promoter in the Boudouard reaction- (CO-) based synthesis. As a result, we have revealed the mechanisms behind the CO2 effect on the catalyst deactivation rate not reported before. In particular, we observed an increase in CO2 concentration to provide a faster growth rate but an earlier catalyst deactivation. We believe this work might be useful for researchers from both academia and industry and facilitate more active development of aerosol CVD methods for the production of new materials.

Boosting CO-based synthesis of single-walled carbon nanotubes with hydrogen

Aerosol (floating catalyst) chemical vapor deposition method based on CO disproportionation (the Boudouard reaction) is one of the most promising techniques for the synthesis of single-walled carbon nanotubes (SWCNTs), especially in the form of thin films. However, despite its advantages (i.e., high quality of nanotubes, absence of double- or multi-walled nanotubes, and high controllability of the process), synthesis based on CO disproportionation fails to provide high-yield production. In this work, we examined the effect of hydrogen, admixed to the CO atmosphere as a growth promoter, on the synthesis and properties of SWCNTs. Using optical spectroscopy techniques, conductivity tests, TEM and SEM analysis, and thermodynamic calculations, we revealed hydrogen affects both catalyst activation and nanotube growth. We found a positive H2 effect in two different temperature regimes: the yield increased by a factor of ∼15 at a low temperature (880 °C), which, after doping, led to one of the lowest ratios of the equivalent sheet resistance (R90) and yield (i) and SWCNT lengthening by a factor of 2.4 leading to a 3-fold decrease in an R90 coupled with a noticeable increase in the yield at a high temperature (1000 °C) (ii). We believe the presented results are fruitful for the fundamental understanding of the mechanism for nanotube growth and practical opportunity to fine-tune the production rate of SWCNT films.

(Invited) Highly Transparent and Mechanically Robust Energy-Harvestable Piezocomposite with Embedded One-Dimensional P(VDF-TrFE) Nanofibers and Single-Walled Carbon Nanotubes

Here, highly transparent, flexible, and ultrathin piezocomposite, in which electrospun poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] nanofibers (NFs) and aerosol-synthesized single-walled carbon nanotubes (SWCNTs) are embedded in elastomer matrix, is fabricated. The P(VDF-TrFE) NF mat is exploited as a piezoelectric layer of the piezocomposite while the SWCNT film is applied as a transparent conductive electrode (TCE) thereof. The use of these one-dimensional (1D) nanomaterials allows the piezocomposite not only to have a high transparency along with low diffusivity, but also to exhibit enhanced mechanical properties. In addition, the coupling effect of piezo- and flexoelectricity exhibited from the electrospun NFs and the acid-doping effect conducted on the SWCNTs facilitate a significant improvement in kinetic energy-harvesting performance, leading to a maximum output voltage of 26.8 V. Moreover, electrospinning and aerosol chemical vapor deposition (CVD) methods employed here are facile, scalable, and cost-effective, thus are expected to accelerate the development of industrially feasible next-generation wearable electronics.

Role of Hydrogen in Ethylene-Based Synthesis of Single-Walled Carbon Nanotubes.

We examined the effect of hydrogen on the growth of single-walled carbon nanotubes in the aerosol (a specific case of the floating catalyst) chemical vapor deposition process using ethylene as a carbon source and ferrocene as a precursor for a Fe-based catalyst. With a comprehensive set of physical methods (UV-vis-NIR and Raman spectroscopies, transmission electron microscopy, scanning electron microscopy, differential mobility analysis, and four-probe sheet resistance measurements), we showed hydrogen to inhibit ethylene pyrolysis extending the window of synthesis parameters. Moreover, the detailed study at different temperatures allowed us to distinguish three different regimes for the hydrogen effect: pyrolysis suppression at low concentrations (I) followed by surface cleaning/activation promotion (II), and surface blockage/nanotube etching (III) at the highest concentrations. We believe that such a detailed study will help to reveal the complex role of hydrogen and contribute toward the synthesis of single-walled carbon nanotubes with detailed characteristics.

Highly Transparent and Mechanically Robust Energy‐harvestable Piezocomposite with Embedded 1D P(VDF‐TrFE) Nanofibers and Single‐walled Carbon Nanotubes

AbstractHerein, highly transparent, flexible, and ultrathin piezocomposite, in which electrospun poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)] nanofibers (NFs) and aerosol‐synthesized single‐walled carbon nanotubes (SWCNTs) are embedded in elastomer matrix, is fabricated. The P(VDF‐TrFE) NF mat is exploited as a piezoelectric layer of the piezocomposite while the SWCNT film is applied as a transparent conductive electrode thereof. The use of these 1D nanomaterials allows the piezocomposite not only to be high transparency along with low diffusion of light (i.e., haze factor) but also to exhibit enhanced mechanical properties. In addition, the coupling effect of piezo‐ and flexoelectricity exhibited from the electrospun NFs and the acid‐doping effect conducted on the SWCNTs facilitates a significant improvement in kinetic energy‐harvesting performance, leading to a maximum output voltage of 26.8 V. Moreover, electrospinning and aerosol chemical vapor deposition methods employed here are facile, scalable, and cost‐effective, thus are expected to accelerate the development of industrially feasible next‐generation wearable electronics.

Machine learning methods for aerosol synthesis of single-walled carbon nanotubes

This work is devoted to the strategy towards the optimal development of multiparametric process of single-walled carbon nanotube (SWCNT) synthesis. Here, we examine the implementation of machine learning techniques and discuss features of the optimal dataset size and density for aerosol chemical vapor deposition method with a complex carbon source. We employ the dataset of 369 points, comprising synthesis parameters (catalyst amount, temperature, feed of carbon sources) and corresponding carbon nanotube characteristics (yield, quality, structure, optoelectrical figure of merit). Assessing the performance of six machine learning methods on the dataset, we demonstrate Artificial Neural Network to be the most suitable approach to predict the outcome of synthesis processes. We show that even a dataset of 250 points with the inhomogeneous distribution of input parameters is enough to reach an acceptable performance of the Artificial Neural Network, wherein the error is most likely to arise from experimental inaccuracy and hidden uncontrolled variables. We believe our work will contribute to the selection of an appropriate regression algorithm for the controlled carbon nanotube synthesis and further development of an autonomous synthesis system for an “on-demand” SWCNT production.

Synthesis of MWCNTs from xylenes for fabrication of highly electrically conductive and gas-sensitive polymer composites

For Multi-Walled Carbon Nanotubes (MWCNTs), high quality, purity, and low cost are very desirable. Therefore, in this reported research work, qualitative and pure MWCNTs were synthesized using a cheap and affordable carbon source-xylenes (a mixture of isomers) by the Aerosol Chemical Vapor Deposition Method (A-CVD). The high quality, purity, and homogeneity of the synthesized material have been verified by Raman spectroscopy, EDX, XRD, and SEM results. In the present study, Polystyrene/xMWCNT, Polyvinyl acetate/xMWCNT, and Polyvinyl alcohol/xMWCNT composites with different MWCNT contents of (x = 1, 2, 4, 8, and 16) wt% were prepared by an optimized technique for irreversible dispersion of MWCNTs inside polymers, which was developed by our research group. SEM analysis results revealed that the MWCNTs are well incorporated inside all three polymer matrices, and a highly dispersed distribution of MWCNTs has been obtained inside all three matrices due to this technique. Also, the electrical conductivity of the prepared composites was measured, and the prepared nanocomposites show high electrical conductivity for all concentrations of MWCNTs. Based on the maximum dispersion of MWCNTs inside the PS polymer matrix, the highest electrical conductivity is observed for this composite, which once more proves that the dispersion technique as well as the nature of the polymer play an important role in the preparation of highly electroconductive nanocomposites (1%-0.136 S/m; 2%-1.053 S/m; 4%-5.376 S/m; 8%-71.48 S/m; 16%-933.71 S/m). Comparison of electrical conductivity results of these composites with literature results demonstrates the advantages of this technique in substitution of the another dispersion methods. The nanocomposites prepared by our research group also show a sensor effect (change of resistivity) under different gases (methane, propane, carbon monoxide). It is interesting that, for analyzed gases, the resistivity of some nanocomposites increased, whereas for others it decreased. This effect can be explained by the different nature of the adsorption interaction between the analyzed gas and the polymer composite, and this depends on the chemical composition and properties of both gases and polymer matrices.

High-yield microplasma synthesis of monodisperse sub-3 nm diameter metal nanoparticles explained by a charge-mediated formation mechanism

The size and composition of nanoparticles are instrumental to many catalytic processes; for example, their controlled synthesis is key to achieving high yield and quality in aerosol chemical vapor deposition (CVD) of carbon nanotubes (CNTs). Using a custom-built atmospheric pressure DC microplasma reactor, we synthesize sub-3 nm iron nanoparticle aerosols at high number concentration (>109 #/cm3) with narrow size distribution (σg<1.3) from a ferrocene vapor precursor. We demonstrate precise diameter control down to 1.1 nm and maximum yield near unity. We invoke a charge-mediated formation mechanism to show that the ∼ 10 μs plasma residence time is sufficient to dissociate the precursor and partially ionize the resulting iron vapor, yet too short for the aggregation of clusters beyond 10 atoms. Thus, particle growth occurs primarily downstream of the plasma domain through aggregation of neutral and ionized vapor and clusters. This model closely reproduces the observed particle size distributions with the selection of an appropriate fractional ionization, yet is insufficient to entirely explain the rapid growth rate observed experimentally. This mechanism is different from that of existing microplasma processes, which have a longer residence time allowing particle formation to occur within the plasma, and may explain the demonstrated capability to co-optimize nanoparticle yield, throughput, and diameter control at a level exceeding the performance of previously published thermal and microplasma methods.

Residence time effect on single-walled carbon nanotube synthesis in an aerosol CVD reactor

• Residence time in aerosol CVD was tuned while nanotube nucleation maintained. • Carbon nanotube length and I G /I D ratio increase with a higher residence time. • The increase in length and defectiveness drops equivalent sheet resistance. • Effect of vortices, diffusion, and thermophoresis on nanotube yield was shown. • SWCNT/HAuCl 4 thin films with equivalent sheet resistance of 51 Ω/□ were obtained. We examine an effect of residence time on the growth of single-walled carbon nanotubes (SWCNTs) in an aerosol (floating catalyst) chemical vapor deposition (CVD) process using CO as a carbon source and ferrocene as a catalyst precursor. The key feature of aerosol CVD reactors, namely stabilization of fine nanoparticles by an extreme dilution, limits the method for catalyst evolution studies. We show an approach to examine the role of the residence time while maintaining all the processes preceding the nanotube growth (catalyst formation, nanotube nucleation). Using the diameter distribution of nanotubes as a fingerprint of the SWCNT nucleation stage, we have proven the latter to be unaffected by changes in the residence time. Using SEM observations, we have revealed a quite intuitive but inspiring correlation between the carbon nanotube length and residence time. We have also found a decrease in the SWCNT yield caused by the drop in the aerosol concentration, which could be attributed to the gas-phase losses as well as the shift in the catalyst activation degree. Nevertheless, the trends observed allowed us to reach a tenfold decrease in an equivalent sheet resistance (sheet resistance of a film with 90% transmittance at 550 nm) by a threefold increase in the residence time at optimal CO 2 concentration. SWCNT films with the equivalent sheet resistance as low as 245 Ω/□ and 51 Ω/□ (for pristine and doped carbon nanotubes, correspondingly) ensure the promising future of the proposed strategy for optimization of both aerosol CVD reactors and SWCNT-based films for optoelectronic applications.

Room temperature gas sensing mechanism of SnO2 towards chloroform: Comparing first principles calculations with sensing experiments

Herein, room temperature sensing of chloroform (CHCl3) gas using SnO2 nanostructured thin films synthesized via a single-step aerosol chemical vapor deposition (ACVD) process is demonstrated. The sensing mechanism is investigated by means of dispersion-corrected density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations of chloroform’s adsorption on the (110) facet of rutile SnO2. Theoretical calculations demonstrate that direct adsorption of chloroform on the stoichiometric and the oxygen defective SnO2 surface is thermodynamically favorable. Upon adsorption, chloroform molecules donate charge to the surface inducing a drop in the surface resistance, thus promoting a sensing response. Calculated adsorption energies are in the range of (0.7–1.0 eV) per chloroform molecule, which is noticeably larger than the previously calculated adsorption energies on graphene and graphene oxide (0.2–0.4 eV), suggesting a stronger binding on metal-oxides compared to carbon-based materials. Long-range dispersive interactions are found to account for>50% of the calculated adsorption energies. AIMD simulations in the canonical ensemble at room temperature show that chloroform molecules minimally interact with the ionosorbed oxygen species (O2-) suggesting that the room temperature sensing mechanism is mainly attributed to the direct binding of chloroform molecules on the sensor surface.

Transparent and Freestanding Single-Walled Carbon Nanotube Films Synthesized Directly and Continuously via a Blown Aerosol Technique.

Single-walled carbon nanotube (SWCNT) films are promising materials as flexible transparent conductive films (TCFs). Here, inspired by the extrusion blown plastic film technique and the SWCNT synthesis approach by floating catalyst chemical vapor deposition (FCCVD), a novel blown aerosol chemical vapor deposition (BACVD) method is reported to directly and continuously produce freestanding SWCNT TCFs at several hundred meters per hour. The synthesis mechanism, involving blowing a stable aerosol bubble and transforming the bubble into an aerogel, is investigated, and a general phase diagram is established for this method. For the SWCNT TCFs via BACVD, both carbon conversion efficiency and SWCNT TCF yield can reach three orders of magnitude higher than those with the conventional FCCVD. The film displays a sheet resistance of 40ohmsq-1 at 90% transmittance after being doped, representing the record performance based on large-scale SWCNT films. Transparent, flexible, and stretchable electrodes based on BACVD films are demonstrated. Moreover, this high-throughput method of producing SWCNT TCFs can be compatible with the roll-to-roll process for mass production of flexible displays, touch screens, solar cells, and solid-state lighting, and is expected to have a broad and long-term impact on many fields from consumer electronics to energy conversion and generation.

High-temperature magnetic coercivity of CNTs filled with multi-phase Fe-based nanoparticles

A system of Fe-filled multiwall carbon nanotubes (MWCNT) was grown by aerosol chemical vapor deposition with three different concentrations of ferrocene as precursor catalyst. The obtained samples were thoroughly analyzed from the point of view of their morphological, microstructural and magnetic properties. It was found that ferrocene concentration did not change the MWCNTs morphology. However, it increases the number of MWCNTs containing Fe and the Fe amount in each MWCNT. The Fe is located either in form of nanorods within the inner channel of the MWCNTs or as nanoparticles of various sizes, sometimes aggregated in clusters. The magnetic results indicate the presence of different phases, identified as α-Fe, Fe3C and Fe3O4, mostly in form of single-domain particles. A simple model of single domain non-interacting particles allows explaining the observed temperature behavior of coercivity and remanence over a wide temperature range, up to 950 K. The different ferrocene concentrations affect only the saturation magnetization but not the coercivity of the samples. As a further result, MWCNT/epoxy nanocomposites, with possible application as electromagnetic shields, were prepared by the “two factor mechanical method”. The nanocomposites exhibit the same magnetic properties of the Fe-filled MWCNTs, in terms of both coercivity and hysteresis loop shape.

Growth and functionalization of carbon nanotubes for nitroaromatic explosive detection

Abstract This paper presents the synthesis and functionalization of carbon nanotubes (CNTs) with amino groups to prepare sensors for detecting explosives, in particular nitroaromatic explosives such as TNT. CNTs have been grown by aerosol-chemical vapor deposition (A-CVD) technique and analyzed by SEM, TEM Raman and IR spectroscopy methods. Very smooth and long CNTs with good electrical conductive properties have been obtained. Two steps of functionalization process have been performed, oxidation and amidation. Infrared absorption and elemental analysis confirmed the successful functionalization of the CNTs.

Single-walled carbon nanotube membranes for optical applications in the extreme ultraviolet range

In this paper, we explore the possibility of using free-standing thin films from single-walled carbon nanotube (SWCNT) material in optics of the extreme ultraviolet (EUV) range. Test samples were fabricated using an aerosol chemical vapor deposition method. Synchrotron radiation was used to record the transmittance spectra of samples in the EUV range. The measured transmittance for a film 40 nm thick almost monotonously increases from 76% at a wavelength of 20 nm–99% at a wavelength of 1 nm. The measured stress-strain curve for the test samples shows that the SWCNT-based thin films have rather high ductility as opposite to fragile films made of conventional solid state materials. We use numerical simulations to demonstrate that the film strain occurs mainly by straightening and sliding of the nanotubes past each other without forming of strain localization responsible for fragile behavior. The combination of high radiation transmittance and unique mechanical properties makes the SWCNT-based thin films very promising for use in the EUV optics. In particular, such films can be used to protect delicate optical elements for EUV lithography from their contamination with debris particles.

Heat Exchange Structures Based on Copper/CNT Composite

In this study different types of multi-walled carbon nanotubes (MWCNT) were produced by the fixed bed and aerosol chemical vapor deposition (CVD) method. Nanocomposite materials were prepared by incorporation of different MWCNTs in copper matrix using powder metallurgy methods. By using hot pressing in combination with hot extrusion, the orientation of the carbon reinforcement was tuned from 3D to 1D alignment. After a selective etching process the carbon reinforcement is partially free-standing at the composite surface, but still embedded in the metal matrix. The engineered surface acts almost like a black body. The spectral evaluation of the surface functionalization will be shown for wavelengths from 200 nm to 20 µm. These results are compared to bulk copper. The free-standing MWCNT also behave like fins/pins in heat exchanger structures or surface enhancement in pool boiling. The experimental setup will be explained and the measurement described for pure copper. The theoretical heat transfer coefficient of the engineered surface is calculated depending on diameter and length of the free-standing MWCNTs. The results are compared to bulk copper.

Fabrication and characterization of MWCNT/natural Azerbaijani bentonite electroconductive ceramic composites

Multi-walled carbon nanotubes have been synthesized by Aerosol-Chemical Vapor Deposition method. Carbon nanotubes firstly have been used as filler in affordable and prevalent natural Azerbaijani bentonite clays for fabrication electroconductive ceramic composites. In this paper, multi-walled carbon nanotubes/natural Azerbaijani bentonite ceramic composites were prepared by two-factor mechanical method and followed by calcination at 1050℃ in an inert atmosphere. The ceramic composites were characterized by scanning electron microscope, atomic force microscope, X-ray diffraction and thermogravimetric-differential-thermal analysis. X-ray diffraction analysis confirmed the presence of two principal components – multi-walled carbon nanotube and bentonite in composites. From the thermogravimetric-differential-thermal data, it was revealed that multi-walled carbon nanotube/ bentonite ceramic composites demonstrate thermo-oxidative stability up to 580–640℃. Scanning electron microscope images demonstrated a sufficiently high dispersibility of carbon nanotubes and satisfactory homogeneity in the composites. Experimental results demonstrated that by increasing the mass fraction of multi-walled carbon nanotubes from 1% to 8% in multi-walled carbon nanotube/bentonite ceramic composites, the electrical conductivity enhances substantially. The enhancement of electrical conductivity of the composites explained the mass fraction of multi-walled carbon nanotubes, as well as the uniform dispersion of multi-walled carbon nanotubes in the bentonite clays. Compared with other 8% multi-walled carbon nanotubes/bentonite ceramic composites, the electrical conductivity of heptane-multi-walled carbon nanotube/Gobu bentonite (σ = 397 S·m−1) and heptane-multi-walled carbon nanotubes/Atyali (σ = 305 S·m−1) composites is 2–5 times higher than the conductivity of composites obtained with cyclohexane carbon nanotubes- cyclohexane-multi-walled carbon nanotube/Atyali (σ = 78 S·m−1), cyclohexane-multi-walled carbon nanotube/Gobu (σ = 111,5 S·m−1). These results can be explained with the structure, the number of layers, purity and diameter distribution, as well as the type and amount of defects in internal and external layers of Hep-multi-walled carbon nanotubes which cause better dispersion in bentonite clays. Due to the high conductivity and high temperature stability, these composites can be used as promising material for fabrication heating elements, electrodes, substrates for microelectronic devices, etc.

SnO2 Nanostructured Thin Films for Room-Temperature Gas Sensing of Volatile Organic Compounds.

We demonstrated room-temperature gas sensing of volatile organic compounds (VOCs) using SnO2 nanostructured thin films grown via the aerosol chemical vapor deposition process at deposition temperatures ranging from 450 to 600 °C. We investigated the film's sensing response to the presence of three classes of VOCs: apolar, monopolar, and biopolar. The synthesis process was optimized, with the most robust response observed for films grown at 550 °C as compared to other temperatures. The role of film morphology, exposed surface planes, and oxygen defects were explored using experimental techniques and theoretical calculations to improve the understanding of the room-temperature gas sensing mechanism, which is proposed to be through the direct adsorption of VOCs on the sensor surface. Overall, the improved understanding of the material characteristics that enable room-temperature sensing gained in this work will be beneficial for the design and application of metal oxide gas sensors at room temperature.

Aerosol Chemical Vapor Deposition of One-Dimensional Cu-Doped TiO2 Nanostructured Anodes for High-Rate Lithium Ion Batteries

Energy storage has become increasingly important in recent years due to the rapidly increasing number of electric vehicles (EVs) in use and expanded utilization of intermittent renewable energy sources. Improvements in longevity, energy density, and high rate capability are needed for the next generation of batteries. Lithium-ion batteries (LIBs), the most widely commercialized rechargeable batteries are being used in EVs and some pilot grid-scale storage facilities. One avenue for enhancing the performance of LIBs is the development of novel electrode materials. One such material, titanium dioxide (TiO2) exhibits very high stability during cycling and is capable of ultra-high rate charging and discharging. However, a major drawback to TiO2 is its relatively low electrical conductivity, which limits its performance. Using nanostructured, one-dimensional morphologies the issue of low conductivity can be mitigated. Additionally, metal-doping of TiO2 with various metallic cations such as zinc, copper, or niobium has been shown to increase conductivity as well. Aerosol chemical vapor deposition (ACVD) is an atmospheric pressure technique used to deposit nanostructured metal oxide thin films. In ACVD, a vapor phase organometallic precursor is fed to a reactor and undergoes thermal degradation forming metal oxide monomers. The monomers nucleate to form particles which undergo condensational growth before depositing onto a heated substrate, where the particles sinter into various morphologies. Controlling the rates of these processes using various system parameters leads to the deposition of one-dimensional, columnar structures. Additionally, by introducing two precursors simultaneously doped materials can be synthesized, with the composition controlled by the relative flowrates into the reactor. In this work, we aim to investigate the effect of Cu-doping on the properties and performance of nanostructured TiO2 negative electrodes in LIBs. To achieve this, Cu-doped TiO2 films with compositions between 0-10 at% are synthesized on stainless steel using ACVD and directly utilized as anodes in LIBs. In order to determine the effect of Cu-doping on battery performance a rate capability test is performed by cycling the batteries at progressively higher rates. Additionally, long-term cycling is performed to determine the stability of the electrodes. Additionally, characterization of the lithium diffusion coefficient is performed using both cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). Finally, density function theory (DFT) simulations are performed in order to validate the experimentally measured values for the lithium diffusion coefficient and the electrical conductivity.

Oriented, One‐Dimensional Tin Dioxide–Titanium Dioxide Composites as Anode Materials for Lithium‐Ion Batteries

AbstractHighly oriented columnar nanostructures of tin dioxide (SnO2) and a composite tin dioxide material with a thin titanium dioxide coating (SnO2–TiO2) are fabricated using aerosol chemical vapor deposition (ACVD) and are utilized as high‐capacity anode materials in lithium‐ion batteries. The SnO2 nanostructures exhibit a specific capacity of 445 mAh g−1 after 100 cycles at a rate of 1 C, but experience substantial capacity fade at a charge rate of 2 C, and a capacity of 251 mAh g−1 after 100 cycles. To enhance the capacity retention a coating of TiO2 is applied to the electrodes. Comparatively, the SnO2–TiO2 electrode exhibits a capacity of 497 mAh g−1 after 100 cycles at a charge rate of 2 C. Diffusion measurements indicate that no inhibition of lithium diffusion occurs due to a thin TiO2 coating. The superior capacity retention of the composite electrode may be attributed to the protection of SnO2 from irreversible reactions using a TiO2 coating.

Effect of gaseous and condensate products of ethanol decomposition on aerosol CVD synthesis of single-walled carbon nanotubes

In this study, the gaseous and condensate products of ethanol decomposition during the synthesis of single-walled carbon nanotubes (SWCNTs) by aerosol chemical vapor deposition (floating catalyst CVD) method were investigated. To determine the conditions for perfect and clean SWCNT formation the products synthesized at different temperatures and collected inside and outside the reactor were studied by transmission electron microscopy, Raman, Fourier transform infrared (FT-IR) and optical absorption spectroscopy. The individual and bundled SWCNTs of a predominantly small diameter (∼1 nm) were revealed. The obtained tubes exhibit a stable distribution of chiral indices in a wide range of the set temperature (750–1000 °C), which is promising for the development of controlled synthesis methods. The FT-IR analysis results show that the main gaseous products of thermal ethanol decomposition in our CVD system are methane and carbon monoxide. Acting as carbon source, the mixture of CO and CH4 makes possible to produce pure SWCNTs, as those obtained in the catalytic CO disproportionation method, with higher yield, taking into account twice the amount of carbon release during CH4 catalytic pyrolysis. The carbon deposit on the reactor wall is found to play important role in maintaining an optimal regime of CNT synthesis.