Катализаторы электровосстановления кислорода в щелочной среде на основе углеродных нанотрубок, модифицированных мочевиной, фталоцианинами железа, кобальта и палладием

Facile and controllable route for nitrogen doping of carbon nanotubes composite membranes by catalyst-free chemical vapour deposition

A facile method prepared nitrogen and boron doped carbon nano-tube based catalysts for oxygen reduction

It is essential to build the models of carbon nanotubes when their mechanical characteristics are studied by using molecular dynamics or other numerical methods. The approach of computer simulation on structures of single walled carbon nanotubes was studied in this paper based on the analysis of different structures of carbon nanotubes. The detail steps and the corresponding formulas are given. Moreover, a program for simulating different structures of single walled carbon nanotubes was developed. The program has some advantages such as high speed, good stability and so on. It provides essential foundations for analysis of mechanical characteristics of carbon nanotubes.

Nitrogen-doping effects on the growth, structure and electrical performance of carbon nanotubes obtained by spray pyrolysis method

This paper presents an experimental study of flow boiling heat transfer from carbon nanotube (CNT) structures in a two-phase cooling facility. Multi-walled CNT (MWCNT) structures of dimensions 80 mm × 60 mm were applied to a horizontal flow boiling channel. Two CNT structures with different properties viz. NC-3100 and MERCSD were tested with a dielectric liquid FC-72. The height of the CNT structures was fixed at 37.5 μm and tests were conducted at coolant mass fluxes of 35, 50, and 65 kg/m2·s under saturated flow boiling conditions. The experimental results show that the CNT structures enhance the boiling heat transfer coefficients by up to 1.6 times compared to the smooth aluminum surface. The results also show that the CNT structures increase significantly the Critical Heat Flux (CHF) of the smooth aluminum surface from 66.7 W/cm2 to 100 W/cm2.

In this study, the thermal behaviour of small-sized single-atom CNTs was examined. CNTs are composed of crystals that form a nanostructure with different geometric shapes by arranging them in different ways according to the length-diameter ratio. Due to the mechanical, electrical, and thermal properties of CNTs, the thermal conduction of CNT materials is critical in controlling the performance and stability of CNTs. CNTs, which are low-dimensional materials with a single atomic layer thickness, have excellent thermal conductivity. According to the simulation technique in ANSYS, CNTs containing the same number of atoms and bonds were developed. The heat transfer of different structures of CNTs in armchairs (6,6) and zig-zag (12,0) were compared. A comparison of zig-zag and armchair CNTs thermal behaviour shows that zig-zag CNTs lattice structure has more advantages than armchair CNTs lattice structure by heat transfer. Highlights In this study, finite element-based thermal analysis of single and double-walled armchair and zig-zag carbon nano-tubes (CNTs) using the lattice method was investigated. A simulation technique was developed and applied in the ANSYS program for single and double-walled carbon nanotubes (CNTs). Armchairs (6,6) and zig-zag (12,0) CNTs in different lattice structures with equal atomic numbers and bond numbers are modelled according to different diameters and length ratios. The CNTs, which have the same material properties as the trays placed at both open ends of the pipes, are kept at different temperature values, and conduction heat transfer behaviour is investigated for certain temperature values. According to the investigated heat conduction behaviour of zig-zag and armchair CNTs, the lattice structure of the zig-zag carbon nano-tubes is more advantageous in terms of heat conduction than the cage structure of armchair CNTs, and it transmits heat faster than the armchair CNTs.

The effect of gas pressure on the structure of carbon nanotubes (CNTs) has been systematically investigated in the chemical vapor deposition process. The yield of CNTs (defined as the weight ratio of CNTs vs. catalyst) increases significantly with the gas pressure, reaches 600% at 600 Torr, then decreases with further increase of gas pressure. At low reacting gas pressure the CNTs have completely hollow cores, whereas at high pressure the CNTs have a bamboo structure. The density of the compartments in the bamboo-structured CNTs increases dramatically with the increase of the gas pressure. This result shows that the structure and yield of carbon nanotubes are strongly affected by the growth gas pressure.

Due to their unusual electrical conductivity, carbon nanotubes as the ideal candidates for making future electronic components have extensive application potentiality. In order to meet the requirements in space electronic components for carbon nanotubes, effect of 170 keV proton irradiation on structure and electrical conductivity of multi-walled carbon nanotubes (MWCNTs) film is investigated in this paper. Surface morphologies and microstructure of the carbon nanotube films are examined by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy, respectively. Electrical conductivities of the carbon nanotube films before and after 170 keV proton irradiation are measured using four-point probe technique. SEM analysis reveals that when proton irradiation fluence is greater than 51015 p/cm2, the surface of the carbon nanotube film becomes rough and loose, and obvious bending, shrinkage, and entanglement of nanotubes are observed. Moreover, the shrinkage phenomenon of MWCNTs caused by proton irradiation is found the first time so far as we know. Based on Raman and XPS analyses, it is confirmed that 170 keV protons can improve the ordered structure of the MWCNTs, and irradiation fluence plays a key role in reducing the disorder in the MWCNTs. Improvement of the irradiated MWCNTs by 170 keV protons can be attributed to restructuring of defect sites induced by knock-on atom displacements. On the other hand, carbon impurities on surface of the MWCNT film are reduced due to the effect of sputtering by the 170 keV proton irradiation, which is also helpful to the improvement of the structure of carbon nanotubes. EPR spectra show that the electrons delocalized over carbon nanotubes decrease with increasing irradiation fluence, implying that the carbon nanotube film is not sensitive to ionizing radiation induced by the 170 keV protons, and the electrical conductivities of the MWCNTs films may be decreased. Four-point probe technical analysis shows that with increasing irradiation fluence, electrical properties of the carbon nanotubes film deteriorate, which can be attributed to the changes in electronic properties and morphology of the MWCNT films induced by 170 keV protons. Acquired results could be beneficial to tailoring of structure and properties for the carbon nanotubes film irradiated by protons to develop nanoelectronics of radiation-resistant systems.

Changes in the local atomic and electronic structure and the chemical state of the surface of multiwalled carbon nanotubes (MWCNTs) irradiated with continuous and pulsed ion beams are studied using transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy. It is demonstrated that changes in the structure and the chemical state of MWCNTs under continuous irradiation with argon ions are attributable to the radiation-induced defect formation. When a pulsed carbon–proton beam is used, thermal effects exert a considerable influence on the structure of carbon nanotubes. The obtained results suggest that continuous and pulsed ion beams are suitable for targeted functionalization of physical and chemical properties of MWCNTs.

The structure of individual multi-wall carbon nanotubes exposed to irradiation by a argon ions and electron flux, as well as subsequent heat processing in an inert medium has been studied using transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that irradiation with argon ions and electrons leads to the formation of defects in the structure of carbon nanotubes, changes in the interlayer distance in the walls of nanotubes, and the fixing of functional oxygen-containing groups on their surface. Annealing of pre-irradiated nanotubes in an inert atmosphere causes a partial restoration of the multi-wall carbon nanotube structure. At the same time, in the case of irradiation with argon ions, the nanotube structure is being recovered and the oxygen concentration decreases. In the case of electron irradiation after annealing, extended multi-vacancy defects occur, on which functional groups containing a double chemical bond of carbon and oxygen (C=O) are formed. Using calculations carried out within the framework of density functional theory, the coupling energy values and optimized geometry for various configurations of vacancy clusters in the graphene plane have been obtained.

Carbon nanotube based electrocatalysts have been expected to be the alternative catalysts for the Oxygen Reduction Reaction (ORR) due to their competitively high activity and low cost compared with the conventional Pt/C catalysts. Although pristine carbon nanotubes are known to exhibit poor ORR activity, doping heteroatoms, introducing transition metals and controlling carbon structure can be applied to enhance their ORR activity extensively.[1-4] Nevertheless, the origin of the ORR activity is still not well understood. The Metal-Nitrogen-Carbon complex (MNC) and Nitrogen containing carbon (CNx) related sites have been proposed to be the possible active sites in nitrogen doped carbon materials. In both MNC and CNx structures, it is widely accepted that pyridinic nitrogen plays an important role in the ORR. To further verify the ORR mechanism, in this study, we conduct durability tests to study the relationship between ORR activity and nitrogen structures. The LSV of HA-N900, HA-N900 after durability test (Dur-HA-N900) and re-nitrogen doping of Dur-HA-N900 (Re-N900) in 0.1M HClO4 were shown in Figure 1. As pyridinic nitrogen is always related to the high ORR activity, it is reasonable that along with the ORR activity decreases after the durability test, the pyridinc nitrogen concentration also decreases. Indeed, this phenomenon was confirmed by conducting XPS measurements for the samples. On the other hand, interestingly, we found that even though by introducing pyridinc nitrogen to the same level as that before the durability test through re-nitrogen doping, the ORR activity could not return to the initial state. The ORR activity, along with the role of different kind of nitrogen composition and the metal impurities’ effect will be discussed further on the conference through detailed characterizations with X-ray Photoelectron Spectroscopy (XPS), Temperature Programed Desorption (TPD) and Raman Spectroscopy. The MWCNTs used were provided by Showa Denko KK Japan (VGCF-X, diameter: 15nm, approximate length: 3μm; containing Fe impurities <1 wt%). As a precursor, functionalized and purified MWCNT was obtained by heat and acid treatment in the mixture of H2SO4/HNO3 (HA). [5] Then HAMWCNTs were nitrogen doped in 10% NH3/ Argon gas at 900℃(HA-N900). The durability test was conducted by cycling the catalysts under Ar gas bubbling in 0.1M HClO4 with a scan rate of 500mV/s, voltage window [1.0-1.5] V vs. RHE for 1600 cycles. Acknowledgements This work partially was supported by the Center for Low Carbon Society Strategy (LCS) and Shin-Etsu Chemical Co. Ltd. , Japan. Their contribution is greatly appreciated. Reference [1] Waki, Keiko. "Nitrogen Doped Defective Carbon Nanotube Electrocatalyst for Oxygen Reduction Reaction." PRiME 2016/230th ECS Meeting (October 2-7, 2016). Ecs, 2016. [2] Waki, Keiko, et al. "Non-nitrogen doped and non-metal oxygen reduction electrocatalysts based on carbon nanotubes: mechanism and origin of ORR activity." Energy & Environmental Science 7.6 (2014): 1950-1958. [3] Li, Yanguang, et al. "An oxygen reduction electrocatalyst based on carbon nanotube-graphene complexes." Nature nanotechnology 7.6 (2012): 394-400. [4]Tao, Li, et al. "Edge-rich and dopant-free graphene as a highly efficient metal-free electrocatalyst for the oxygen reduction reaction." Chemical Communications 52.13 (2016): 2764-2767. [5] Oktaviano, Haryo S, et al. "Nano-drilled multiwalled carbon nanotubes: characterizations and application for LIB anode materials." Journal of Materials Chemistry 22.48 (2012): 25167-25173. Figure 1

Temperature dependence of water structure in carbon nanotubes

Nitrogen-doped non-precious metal catalysts show high oxygen reduction reaction (ORR) activity, which are considered as possible alternatives for fuel cell catalysts. It has been reported that the transition metals and nitrogen doped carbon complex shows outstanding performance of ORR activity, suggesting that metal impurities in carbon nanotube play a very important role to the ORR activity. [1] On the other hand, recently the ORR active sites in N—doped carbon materials are carbon atoms with Lewis basicity next to pyridinic N was proposed. [2] However, the mechanism and the ORR active site are still in controversy. In our previous work, we reported that annealing multi-walled carbon nanotubes (MWCNT) with nano-drilled defective structure in Argon atmosphere could reach high ORR activity. [3] We suggest that the edge of defects is essential for the formation of active site. In order to clarify the active site and further enhance the ORR activity, here, by making defective edges on the MWCNT structure accompanied with nitrogen doping, we showed that the ORR activity has been improved with onset potential reached up to 1.1V vs RHE in 0.1M KOH and 0.88V vs RHE in 0.1M HClO4. The MWCNT used were provided by Showa Denko KK Japan (VGFX-XA, diameter: 15nm, approximate length: 1μm; containing Fe impurities <1 wt%). As a precursor, functionalized and purified MWCNT was obtained by heat and acid treatment in the mixture of H2SO4/HNO3. [3] Defective MWCNTs were then prepared following our previous report by nano-drilling purified MWCNT using CoOx as oxidation catalyst. [3,4] Then defective MWCNTs were nitrogen doped in 10% NH3/ Argon at 900℃. The ORR activity of nitrogen doped defective MWCNT in acid was shown in Fig.1 and in alkaline was shown in Fig.2. We found that nitrogen doped defective MWCNTs show very high ORR activity and efficiently doping nitrogen to the defective edge is essential for the enhancement of ORR activity. The optimization of nitrogen doping process and the nitrogen contain along with the role of defect structure on the ORR activity will be discussed further through detailed characterizations with X-ray photoelectron spectroscopy, Temperature Programmed Desorption and Raman Spectroscopy. Acknowledgement This work partially was supported by COI STREAM from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Shin-Etsu Chemical Co. ,Ltd. Japan. Their contribution is greatly appreciated. Reference [1] Li, Yanguang, et al. "An oxygen reduction electrocatalyst based on carbon nanotube-graphene complexes." Nature nanotechnology 7.6 (2012): 394-400. [2] Guo, Donghui, et al. "Active sites of nitrogen-doped carbon materials for oxygen reduction reaction clarified using model catalysts." Science 351.6271 (2016): 361-365. [3] K. Waki, R. A. Wong, H. S. Oktaviano, T. Fujio, T. Nagai, K. Kimoto and K. Yamada, Energy Environ. Sci., 2014, 7, 1950-1958. [4] Oktaviano, Haryo S., Koichi Yamada, and Keiko Waki. "Nano-drilled multiwalled carbon nanotubes: characterizations and application for LIB anode materials." Journal of Materials Chemistry 22.48 (2012): 25167-25173. Figure 1

In the last ten years carbon nanotube composites are in the focus of the researchers. Concentration series were prepared using carbon nanotube containing master blend by IDMX mixer. In the experiments polypropylene, polycarbonate and ABS polymers were used as matrix materials. The prepared materials were characterised by scanning electron microscopy. The carbon nanotubes can be seen on the fractured surfaces. We did not find any sign of agglomerates in the materials. The nanocomposites were investigated by LP-FTIR method. The specimens were irradiated with 1 W for 1 minute by CO2 laser. The polymer matrix was burnt or charred by the CO2 laser; the structure of the carbon nanotubes in the matrix was studied. The carbon nanotubes create a physical network in the polymers we used.

Investigation of sol-derived Co-phenylene diamine/carbon materials as oxygen reduction catalysts in alkaline media