Growth Of Nitrogen-doped Carbon Nanotubes Research Articles

Neighboring Platinum Atomic Sites Activate Platinum-Cobalt Nanoclusters as High-Performance ORR/OER/HER Electrocatalysts.

The rational design of efficient and multifunctional electrocatalysts for energy conversion devices is one of the major challenges for clean and renewable energy transition. Herein, the local electronic structure of cobalt-platinum nanoclusters is regulated by adjacent platinum atomic site encapsulated in N-doped hollow carbon nanotubes (PtSA -PtCo NCs/N-CNTs) by pyrolysis of melamine-orientation-induced zeolite imidazole metal-organic frameworks (ZIF-67) with thimbleful platinum doping. The introduction of melamine can reactivate adjacent carbon atoms and initiate the oriented growth of nitrogen-doped carbon nanotubes. The systematic analysis suggests the significant role of thimbleful neighboring low-coordinated Pt─N2 in altering the localized electronic structure of PtCo nanoclusters. The optimized PtSA -PtCo NCs/N-CNTs-900 exhibit excellent hydrogen evolution reaction (HER)/oxygen evolution reaction (OER)/oxygen reduction reaction (ORR)/ catalytic performance reaching the current density of 10mA cm-2 in 1m KOH under the low 47 (HER) and 252mV (OER) overpotentials, and a high half-wave potential of 0.86 and 0.89V (ORR) in 0.1m KOH and 0.1m HClO4 , respectively. Remarkably, the PtSA -PtCo NC/N-CNT-900 also presents outstanding catalytic performances toward water splitting and rechargeable Zn-air batteries. The theoretical calculations reveal that optimal regulation of the electronic structure of PtCo nanoclusters by thimbleful neighboring Pt atomic reduces the reaction energy barrier in electrochemical process, facilitating the ORR/OER/HER performance.

Исследование влияния температуры роста на свойства легированных азотом углеродных нанотрубок для создания устройств нанопьезотроники

The regularities of the influence of the growth temperature on the geometrical parameters, the concentration of the dopant nitrogen and the type of defects formed in carbon nanotubes grown on a molybdenum sublayer are established in this paper. It is shown that the best piezoelectric and resistive properties are observed in nitrogen-doped carbon nanotubes (N-CNTs) grown at a temperature of 525 ºС, which is due to the highest concentration of dopant nitrogen and high aspect ratio of nanotubes. Based on the results of thermodynamic analysis, the dependence of the dopant nitrogen concentration and the defect type on the tendency to form molybdenum nitrides and carbides during the growth of N-CNTs is shown. The obtained results can be used in the development of nanopiezotronic devices based on arrays of vertically aligned N-CNTs: nanogenerators, strain sensors and memory elements.

Stepwise dispersion of nickel species for efficient coupling of electrocatalytic redox reactions

Advanced electrocatalysts are highly desirable to enhance energy conversion efficiency for properly coupling electrocatalytic redox reactions, but the fabrication of efficient bifunctional catalysts is still highly challenging. Herein, a self-feeding deposition strategy was demonstrated to disperse nickel species into single nickel atoms along with the growth of nitrogen-doped carbon nanotubes, thus inhibiting the thermal aggregation of nickel nanoparticles. The residual nickel nanoparticles are encapsulated among the bamboo-like carbon nanotubes and porous carbon matrix, which promotes the efficient electron transfer via the formation of heterojunctions. With the regulation of electronic and geometric structures between the single atom active sites and the isolated nickel nanoparticles, the unique nucleo- and electro-philic interfaces facilitate the targeted adsorption and activation of carbon dioxide and benzylamine molecules, respectively, thus narrowing the energy barriers to enhance electrocatalytic performances. The improved bifunctional electrocatalysis enables the carbon dioxide reduction into CO with an impressive Faraday efficiency (FE) up to 99.3 % and the highly efficient oxidation of benzylamine into benzonitrile (FE ∼ 98 %). This work not only reveals the fundamental understanding of the underlying structure–activity relationship, but also provides a new method for value-added chemicals production.

In Situ Growth of Nitrogen-Doped Carbon Nanotubes Based on Hierarchical Ni@C Microspheres for High Efficiency Bisphenol A Removal through Peroxymonosulfate Activation.

N-doped carbon nanotubes (NCNTs) are promising metal-free heterogeneous catalysts toward peroxymonosulfate (PMS) activation in advanced oxidation processes for wastewater remediation. However, conventional CNTs always suffer from serious agglomeration and low N content, which renders their design synthesis as an important topic in the related field. With hierarchical Ni@C microspheres as a nutritious platform, we have successfully induced in situ growth of NCNTs on their surface by feeding melamine under high-temperature inert atmospheres. These as-grown NCNTs with a small diameter (ca. 20 nm) are firmly rooted in Ni@C microspheres and present loose accumulation on their surface, and their relative content can be tailored easily by manipulating the mass ratio of melamine to Ni@C microspheres. The investigation on bisphenol A (BPA) removal reveals that the loading amount of NCNTs affects the catalytic performance greatly, and the optimum ratio of melamine to Ni@C microspheres is 5.0 because the corresponding MNC-5.0 possesses sufficient surface N sites and moderate electron transfer, resulting in powerful PMS activation and sufficient utilization of reactive oxidative species (ROS). MNC-5.0 also addresses its advantages as compared with other NCNTs from post treatment and spontaneous growth strategies. The primary ROS responsible for BPA degradation are identified as hydroxyl radical, sulfate radical, superoxide radical, and singlet oxygen through quenching experiments and electron paramagnetic resonance, and the corresponding catalytic mechanism is also put forward based on these results.

ZIF-67 derived nitrogen doped CNTs decorated with sulfur and Ni(OH)2 as potential electrode material for high-performance supercapacitors

Herein we report the synthesis of nitrogen-doped carbon nanotubes (NC) based sulfide (S) and nickel hydroxide (NH) supported on nickel foam as a novel electrode material for the supercapacitors (abbreviated as Co/NC/S@NH). A class of zeolitic imidazolate frameworks, ZIF-67 (Co), is initially grown to synthesize nanotubes directly on the nickel foam (NF). The anion exchange reactions are performed for the growth of sulfide and nickel hydroxide on ZIF-67 (Co) derived carbon nanotubes. In the structural analysis, X-ray diffraction confirmed the successful in-situ growth of carbon nanotubes. Transmission electron microscopy was employed to confirm the formation of NC-based sulfide and nickel hydroxide. The Co/NC/S@NH, hierarchical hybrid electrode, exhibited improved capacitance of 1636 F/g at 1 A/g (982 C/g or 273 mA/h) with exceptional cyclic stability. The Co/NC/S@NH showed capacity retention of 94% over 5,000 cycles. The enhanced electrochemical performance of the synthesized electrode is due to the improved redox reactions and direct growth of nitrogen-doped carbon nanotubes on 3D nickel foam which act as "superhighways" for electron transportation. Moreover, the sulfur ions could hinder the collapse of a structure by the intercalation among layers, whereas the extremely hydroxylated surface of Ni(OH)2 nanosheets could promote accessibility of ions to the electrolyte which decreases the resistance of electrodes which agreed with the finding from electrochemical impedance spectroscopy.

Growth of nitrogen-doped carbon nanotubes using Ni/La2Zr2O7 as catalyst: Electrochemical and magnetic studies

The combination of different nanomaterials to achieve particular applications is a topic with an increasing impact on diverse areas of nanotechnology. In particular, the material of La2Zr2O7 (LZO) and NiO could be employed as a source of catalyst for carbon nanotube fabrication. In this work, the Ni/LZO material was utilized to fabricate nitrogen-doped multiwalled carbon nanotube (N-MWCNTs). The N-MWCNTs were produced at 850 °C by the aerosol assisted catalytic chemical vapor deposition method using benzylamine as the sole carbon and nitrogen precursor. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and vibrating sample magnetometry. Before the synthesis of N-MWCNTs, NiO was reduced to Ni to act as a catalyst and LZO as support. N-MWCNTs exhibited the typical feature bamboo shape morphology with small nanoparticles anchored inside and on its surface. The electrochemical studies show interesting results about charge capacity and a hydroquinone/quinone redox process of oxygen functionalities. The magnetic properties of N-MWCNTs showed a ferromagnetic behavior with a saturated magnetization of 43 emu/g at 0.2 T.

Identification of catalytic sites for cerium redox reactions in a metal-organic framework derived powerful electrocatalyst

The development of N-doped carbon materials with highly catalytic activity for catalyzing electrode reactions as alternatives to noble metal is of great importance for the practical implementation of redox flow batteries (RFBs). However, in addition to C-Nx sites, the high structural heterogeneity of N-doped carbon materials often contains metal-Nx sites and graphene encapsulated metal nanoparticle simultaneously, as a result of their metal-assistant synthesis method. Thus it is challenging to identify the predominant active structure within N-doped carbon catalysts for RFBs, which normally receives far less attention in the field of RFB research. Herein, we report a general metal-organic frameworks assisted approach to high-yield growth of nitrogen-doped carbon nanotubes (NCNTs) onto 3D graphite felt (GF) substrates without the requirement of any additional C and N sources or costly and complex CVD systems. The obtained NCNTs-modified GF (NCNT-GF) exhibits high electrocatalytic activity and stability toward cerium redox reactions. Based on the moderate and selective NH4Cl-purification process and the electrochemical poison experiments, we definitely elucidate the spectator role of atomically dispersed metal-Nx sites and graphene encapsulated metal nanoparticles, and the pivotal role of C-Nx sites in the NCNT-GF materials for cerium redox reactions.

Cobalt boride modified with N-doped carbon nanotubes as a high-performance bifunctional oxygen electrocatalyst

An excellent electrocatalyst for reversible oxygen reduction and oxygen evolution synthesized by direct growth of nitrogen-doped carbon nanotubes on cobalt boride nanoparticles.

Perovskite-based bifunctional electrocatalysts for oxygen evolution and oxygen reduction in alkaline electrolytes

Due to the high cost of precious metal-based electrocatalysts for oxygen reduction and oxygen evolution, the development of alternative low cost and efficient catalysts is of high importance for energy storage and conversion technologies. Although non-precious catalysts that can efficiently catalyze oxygen reduction and oxygen evolution have been developed, electrocatalysts with high bifunctional activity for both oxygen evolution and reduction are needed. Perovskites based on modified lanthanum cobaltite possess significant activity for the oxygen evolution reaction. We describe the synthesis of a bifunctional oxygen electrode with simultaneous activity for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline media by direct growth of nitrogen-doped carbon nanotubes on the surface of a perovskite containing Co and Fe by means of chemical vapor deposition. The difference in the overvoltage between ORR (at 1mA/cm2) and OER (at 10mA/cm2) was below 880mV in 0.1M KOH. The formation of H2O2 during the ORR was reduced by at least three fold when using the bifunctional catalyst as compared to the non-modified perovskite. Long-term durability tests indicate stable performance for at least 37h during the OER and 23h during the ORR.

Preparation of nitrogen-doped carbon nanotubes with different morphologies from melamine-formaldehyde resin.

We report a facile method for the synthesis of nitrogen-doped carbon nanotubes (NCNTs) from melamine-formaldehyde (MR) resin using FeCl3 or supported FeCl3 as catalysts. The growth of NCNTs follows a decomposition-reconstruction mechanism, in which the polymer precursor would totally gasify during pyrolysis process and then transformed into carbon nanotubes. The morphology of the NCNTs could be adjusted via applying different catalyst supports and three kinds of carbon nanotubes with outer-diameter of 20-200 nm and morphologies of either bamboo-like or hollow interiors were obtained. Nitrogen atoms in the materials were mainly in the form of pyridinic and quaternary form while the formation of iron species strongly depended on the interaction between iron precursor and organic carbon/nitrogen sources. All MR resin derived NCNTs are efficient toward oxygen reduction reaction (ORR). NCNTs prepared using FeCl3 as catalyst showed the highest ORR activity with half-wave potentials of -0.17 V, which is comparable with commercial Pt/C. This is probably because of a close contact between MR resin and iron precursor could enhance the iron-ligand coordination strength and thus steadily improve the performance of the catalyst.

Lanthanum nickel alloy catalyzed growth of nitrogen-doped carbon nanotubes by chemical vapor deposition

CNTs doped with large amounts of nitrogen were produced on a LaNi5 alloy catalyst by CVD and its growth mechanism discussed on the basis of dissolution and precipitation mechanisms.

Nitrogen-Doped Carbon Nanotubes Prepared at Different Temperatures for Oxygen Reduction Reaction

The nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor deposition using a solution containing ethanediamine and ferrocene with the four selected reacting temperatures of 800 ºC, 850 ºC, 900 ºC and 950 ºC. The temperature-dependent morphologies, microstructures, compositions and electrocatalytic activities of the CNTs were examined by SEM, TEM, XPS, Raman and electrochemical measurements. The excellent catalytic activity toward oxygen reduction reaction (ORR) in sodium hydroxide solutions was obtained with the N-CNTs prepared at 800 ºC due to the largest amount of nitrogen being doped into CNTs mainly in the form of pyridinic type nitrogen, while poorer with the N-CNTs prepared at 900 ºC as it is close to the crystal phase transformation temperature of iron. The yield of the N-CNTs increased with the increase of temperature. The growth of N-CNTs was affected by the amounts of nitrogen aggregated within the bamboo joints.

Growth of nitrogen-doped carbon nanotubes and fibers over a gold-on-alumina catalyst

Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor decomposition of a N,C-precursor over a supported Au catalyst. Large quantities of carbon nanotubes with a compartmentalized structure containing ca. 5 at.% N were produced over a 1.5% Au/δ-Al 2O 3 catalyst with a mean diameter of Au particles equal to 2.8 nm under continuous flow conditions at 800 °С and 1 bar of the reaction gas mixture containing pyridine (Py) vapor (5 vol.%), Н 2 (10–20 vol.%) and Ar (balance). The majority of the N-CNTs obtained after 10 min have outer diameters (ODs) of 13–45 nm and closed tips without any encapsulated gold particles of the catalyst which indicates the “base-growth” mechanism of N-CNT formation. Carbon deposits synthesized for 30–135 min contain carbon fibers with OD values up to several micrometers, formed by self-assembling of N-CNTs, and individual N-CNTs. X-ray photoelectron spectra provide evidence for various chemical states of nitrogen (pyridinic, “quaternary” (graphitic) and pyrrolic nitrogen) in the N-CNTs, and these are discussed.

Growth of Vertically Aligned Nitrogen-Doped Carbon Nanotubes: Control of the Nitrogen Content over the Temperature Range 900−1100 °C

Nitrogen-doped carbon nanotubes were grown vertically aligned on the iron nanoparticles deposited on silicon substrates, by thermal chemical vapor deposition of methane/ammonia and acetylene/ammonia mixtures in the temperature range 900−1100 °C. The concentration of the nitrogen atoms has been controlled in the range 2−6 atomic %, by the flow rate of ammonia. All nanotubes exhibit a bamboo-like structure over this temperature range. The growth rate is insensitive to this nitrogen content, but the structure is strongly dependent on it. As the nitrogen content increases, the thicker compartment layers form uniformly at a regular distance and the relative amount of crystalline graphitic sheets is notably reduced. Electron energy-loss spectroscopy reveals the higher nitrogen concentration and the lower crystallinity for the compartment layers compared to the wall. The growth of nitrogen-doped carbon nanotubes has been explained using a base growth mechanism proposed for carbon nanotubes. We suggest that the nitrogen doping would produce more flexible compartment layers connecting the wall under a less strain.