Formation Of Carbon Nanofibers Research Articles

Improving the Oxidation Resistance of Phenolic Resin Pyrolytic Carbons by In Situ Catalytic Formation of Carbon Nanofibers via Copper Nitrate.

Phenolic resin pyrolytic carbons were obtained by catalytic pyrolysis of phenolic resin at 500 °C, 600 °C, 700 °C, and 800 °C for 3 h in an argon atmosphere using copper nitrate as a catalyst precursor. The effects of copper salts on the pyrolysis process of phenolic resin as well as the structural evolution and oxidation resistance of phenolic resin pyrolytic carbons were studied. The results showed that copper oxide (CuO) generated from the thermal decomposition of copper nitrate was reduced to copper (Cu) by the gas generated from the thermal decomposition of the phenolic resin. Carbon nanofibers with tapered structures were synthesized by Cu catalysis of pyrolysis gas at 500-800 °C. The catalytic pyrolysis of phenolic resin with Cu increased the graphitization degree and reduced the pore volume of the phenolic resin pyrolytic carbons. The combined action improved the oxidation resistance of phenolic resin pyrolytic carbons.

Scalable One-Pot Fabrication of Carbon-Nanofiber-Supported Noble-Metal-Free Nanocrystals for Synergetic-Dependent Green Hydrogen Production: Unraveling Electrolyte and Support Effects.

Electrocatalytic hydrogen evolution reactions (HER) are envisaged as the most promising sustainable approach for green hydrogen production. However, the considerably high cost often associated with such reactions, particularly upon scale-up, poses a daunting challenge. Herein, a facile, effective, and environmentally benign one-pot scalable approach is developed to fabricate MnM (M═Co, Cu, Ni, and Fe) nanocrystals supported over in situ formed carbon nanofibers (MnM/C) as efficient noble-metal-free electrocatalysts for HER. The formation of carbon nanofibers entails impregnating cellulose in an aqueous solution of metal precursors, followed by annealing the mixture at 550 °C. During the impregnation process, cellulose acts as a reactor for inducing the in situ reductions of MnM salts with the assistance of ether and hydroxyl groups to drive the mass production (several grams) of ultralong (5 ± 1 μM) carbon nanofibers ornamented with MnM nanoparticles (10-14 nm in size) at an average loading of 2.87 wt %. For better electrocatalytic HER benchmarking, the fabricated catalysts were tested over different working electrodes, i.e., carbon paper, carbon foam, and glassy carbon, in the presence of different electrolytes. All the fabricated MnM/C catalysts have demonstrated an appealing synergetic-effect-dependent HER activity, with MnCo/C exhibiting the best performance over carbon foam, close to that of the state-of-the-art commercial Pt/C (10 wt % Pt), with an overpotential of 11 mV at 10 mA cm-2, a hydrogen production rate of 2448 mol g-1 h-1, and a prolonged stability of 2 weeks. The HER performance attained by MnCo/C nanofibers is among the highest reported for Pt-free electrocatalysts, thanks to the mutual alloying effect, higher synergism, large surface area, and active interfacial interactions over the nanofibers. The presented findings underline the potential of our approach for the large-scale production of cost-effective electrocatalysts for practical HER.

In situ transmission electron microscopy of temperature-dependent carbon nanofiber and carbon nanotube growth from ethanol vapor

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs), which have been known for decades, recently gained significant commercial interests for various applications. However, the controlled synthesis of CNF/CNT has been hindered by the lack of nanoscale experimental evidence on how the growth temperature affects the growth process under real growth environment. We report the in situ transmission electron microscopy (TEM) experiments to directly observe Ni catalyzed CNF/CNT growth from alcohol precursor at near atmospheric pressure using a homebuilt bubbler system for the introduction of ethanol vapor. Using real time imaging, we revealed the active state of the Ni catalyst during the temperature-dependent CNF/CNT growth (600–800 °C). We observed the formation of CNFs starting from 600 °C and CNTs were formed at higher temperatures. The lattice parameter measurements pointed to an expansion of the Ni lattice as the temperature was increased, which we attribute to increased carbon solubility. The as-grown CNFs and CNTs were further characterized by XPS, Raman spectroscopy, and EELS, that allowed to have a highly reliable overall view of the structure changes with temperature. Results revealed that the change in structure with temperature was caused by the combined effects of increased carbon solubility and graphitization of the walls of the growing nanostructure. This increased carbon solubility in turn affected carbon diffusion and could be the reason for the change in structure from CNF to CNT at high temperature. Using in situ TEM we clearly revealed the effect of growth temperature on the structural changes.

Effect of CNF in-situ growth on microstructure and mechanical properties evolution of RMI-deriver C/C–SiC composites

The present paper investigates the effect of carbon nanofibers (CNFs) on the microstructure and mechanical properties of Carbon fiber reinforced carbon and silicon carbide binary matrix (C/C–SiC) composite prepared by using the reactive melt infiltration technique. The CNFs used in this paper were generated through in-situ reaction in the pores of C/C preforms using the chemical vapor deposition. Results indicate introducing additional carbon sources in the form of CNFs in the C/C preform can remarkably improve the permeability of molten Si, resulting in higher density and more uniform microstructure of the RMI-deriver C/C–SiC composites. Consequently, the in-situ formation of CNFs reduces the residual Si content by 64.71% and increases the mechanical strength and modulus at room temperature by [22.31% and 17.89%] and after heat treatment at 1500 °C by [35.6% and 47.48%] with respect to no-CNF containing composites due to a lower amount of residual Si content and additional reinforcement effect of the unreacted CNFs.

Effect of sodium promoters on Ni/Al2O3 catalyst for CO2 hydrogenation: The carbon fixation as carbon nanofiber and reverse-water gas reactions

Reducing CO2 emissions has become a critical priority in addressing the environmental impact of carbon dioxide. Technologies for CO2 fixation primarily involve carbon capture storage and utilization (CCSU) and chemical conversion, typically pursued along independent tracks. In our research, we have focused on developing a catalytic reaction for CO2 hydrogenation that integrates the benefits of both CCSU and chemical conversion. The use of sodium-promoted Ni/Al2O3 catalyst (NiNax/Al2O3) in the CO2 hydrogenation process exhibits a synergistic effect, leading to the simultaneous production of CO, CH4, and carbon nanofibers (CNFs). Notably, the conversion of CO2 into CNFs represents a novel approach for carbon fixation, in addition to the formation of CO and CH4. Importantly, the formation of CNFs on the NiNax/Al2O3 catalyst does not compromise its catalytic activity for CO2 hydrogenation to CO and CH4, which is a noteworthy finding. This bifunctional catalyst has the potential to offer significant advantages, including high CO production and the generation of valuable carbon materials. The CNFs are predominantly formed at the interfacial sites between NiNax and Al2O3. The formation process involves the reaction between H2 bound to Ni and adsorbed CO2, leading to the formation of hydrogen carbonate species, which subsequently give rise to CNFs. The reduction of CO2 to CNFs is facilitated by the transfer of electrons from Al3+ species to the interfacial sites between NiNax and Al2O3.

Non-destructive estimation of conductive network constructed by 1D fillers in polymer composites via small angel X-ray scattering

Efficient and non-destructive estimation of conductive network in conductive polymer composites is now becoming an urgent issue than ever owing to the rapid rise of modern electronic industry. Nevertheless, traditional observation and estimation method inevitably cause damage and distortion to sample, demanding urgent development of a non-destructive fidelity detection methodology. In this study, the degree of network formation of carbon nano-fibers in polymer matrix was calculated based on small-angle X-ray diffraction (SAXS). The degree of fiber network construction based on the power law coefficient (A) has been proved to be valid and effective in comparison with other testing methods. Moreover, a mathematical model was established to predict the electrical conductivity of the conductive polymer composite. This study not only solves the problem of non-destructive testing of fiber network construction, but also provides theoretical guidance for the design of conductive polymer composites.

Temperature optimization in a gas reactor for the synthesis of carbon nanofibers: A numerical approach

The synthesis of carbon nanofibers (CNF) in a gas reactor requires specific thermal conditions. The temperature at which the process is carried out determines the final structure of the CNF, being 600 °C (873.15 K) the optimal temperature. In this work we address the modeling and numerical simulation of flow and temperature for a mixture of gases in a 0.09 m of diameter and 1 m long reactor to optimize the temperature inside it. The study is focused on determining appropriate temperatures at the reactor shell, to assure optimal temperatures at the catalyst support device where the reaction of formation of CNF takes place. Different locations of the support device are considered: the position on the left is at 17 cm from the reactor entrance; the central position is in the middle of the reactor, at 44 cm from both, the entrance and the outlet of the reactor; and the position at the right is at 17 cm from the outlet. We show that the location on the left is not suitable as it requires an impracticable temperature at the reactor shell. Optimal temperatures at the reactor shell can be found when the support device is located at the center of the reactor or closer to the outlet, being the latter more convenient for energy efficiency, as it requires a lower temperature at the shell. Simulations are performed using COMSOL Multiphysics. Results are interesting for laboratory experiments in order to control the temperature required for the optimal formation of these important industrial nanomaterials.

Carbon nanofiber growth from methane over carbon-supported NiCu catalysts: Two temperature regimes

An alternative route towards COx-free production of hydrogen is the thermal catalytic decomposition of methane. In addition to hydrogen, valuable carbon nanomaterials can be formed. Carbon nanofiber formation from methane decomposition over carbon supported NiCu catalysts was studied in-situ using a Thermogravimetric analyzer. We especially investigated how the carbon yield is influenced by reaction parameters. Based on experiments with varying temperature (450–600 °C), two distinct temperature regimes were identified. Different kinetic parameters were derived for the two regimes. Activation energies of 86 and 45 kJ/mol, and reaction orders in methane of close to 1 and 1.5, were found in the low and high temperature regimes, respectively. We postulate that at lower temperature the methane dissociation is rate limiting, while at higher temperature the carbon formation plays a more critical role. At low temperatures mostly full fishbone fibers are formed, whereas at higher temperatures mainly hollow fibers are formed. The maximum carbon yield is obtained at the transition between the two regimes, when the carbon supply and carbon nanostructure formation are balanced.

Efficient Production of Segmented Carbon Nanofibers via Catalytic Decomposition of Trichloroethylene over Ni-W Catalyst.

The catalytic utilization of chlorine-organic wastes remains of extreme importance from an ecological point of view. Depending on the molecular structure of the chlorine-substituted hydrocarbon (presence of unsaturated bonds, intermolecular chlorine-to-hydrogen ratio), the features of its catalytic decomposition can be significantly different. Often, 1,2-dichloroethane is used as a model substrate. In the present work, the catalytic decomposition of trichloroethylene (C2HCl3) over microdispersed 100Ni and 96Ni-4W with the formation of carbon nanofibers (CNF) was studied. Catalysts were obtained by a co-precipitation of complex salts followed by reductive thermolysis. The disintegration of the initial bulk alloy driven by its interaction with the reaction mixture C2HCl3/H2/Ar entails the formation of submicron active particles. It has been established that the optimal activity of the pristine Ni catalyst and the 96Ni-4W alloy is provided in temperature ranges of 500-650 °C and 475-725 °C, respectively. The maximum yield of CNF for 2 h of reaction was 63 g/gcat for 100Ni and 112 g/gcat for 96Ni-4W catalyst. Longevity tests showed that nickel undergoes fast deactivation (after 3 h), whereas the 96Ni-4W catalyst remains active for 7 h of interaction. The effects of the catalyst's composition and the reaction temperature upon the structural and morphological characteristics of synthesized carbon nanofibers were investigated by X-ray diffraction analysis, Raman spectroscopy, and electron microscopies. The initial stages of the carbon erosion process were precisely examined by transmission electron microscopy coupled with elemental mapping. The segmented structure of CNF was found to be prevailing in a range of 500-650 °C. The textural parameters of carbon product (SBET and Vpore) were shown to reach maximum values (374 m2/g and 0.71 cm3/g, respectively) at the reaction temperature of 550 °C.

Comparative Study on Carbon Erosion of Nickel Alloys in the Presence of Organic Compounds under Various Reaction Conditions.

The processes of carbon erosion of nickel alloys during the catalytic pyrolysis of organic compounds with the formation of carbon nanofibers in a flow-through reactor as well as under reaction conditions in a close volume (Reactions under Autogenic Pressure at Elevated Temperature, RAPET) were studied. The efficiency of the ferromagnetic resonance method to monitor the appearance of catalytically active nickel particles in these processes has been shown. As found, the interaction of bulk Ni-Cr alloy with the reaction medium containing halogenated hydrocarbons (1,2-dichloroethane, 1-iodobutane, 1-bromobutane) results in the appearance of ferromagnetic particles of similar dimensions (~200-300 nm). In the cases of hexachlorobenzene and hexafluorobenzene, the presence of a hydrogen source (hexamethylbenzene) in the reaction mixture was shown to be highly required. The microdispersed samples of Ni-Cu and Ni-Mo alloys were prepared by mechanochemical alloying of powders and by reductive thermolysis of salts-precursors, accordingly. Their interaction with polymers (polyethylene and polyvinyl chloride) under RAPET conditions and with ethylene and 1,2-dichloroethane in a flow-through reactor are comparatively studied as well. According to microscopic data, the morphology of the formed carbon nanofibers is affected by the alloy composition and by the nature of the used organic substrate.

SnSe nanoplates swallowed in carbon nanofibers as the self-standing anode for lithium-ion and sodium batteries with enhanced performance

SnSe is a promising anode candidate for both lithium-ion and sodium batteries (LIBs and SIBs) with high theoretic capacities, low toxicity and abundant resources. However, it suffers a short cycling life due to the poor conductivity and volume expansion when used as anode material. To improve its Li/Na storage properties, SnSe nanoplates are encapsulated in carbon nanofibers formation a 3D conductive network via a moderate electrostatic spinning and heat treatment. The modified SnSe anode exhibits textile-like feature with extensively mechanical flexibility, and was directly used as anode without and additives for both LIBs and SIBs. It delivers an excellent cycle performance with a high capacity (598 mA h g−1 after 400 cycles for LIBs and 240 mA h g−1 after 250 cycles for SIBs), which are modify enhanced comparing with reported works. The effective strategy can provide an available approach to build self-standing and flexible architecture, which is beneficial for the design of electrode materials for SIBs.

Effect of hydrogen flow rate on the synthesis of carbon nanofiber using microwave-assisted chemical vapour deposition with ferrocene as a catalyst

Carbon nanostructure materials are becoming of considerable commercial importance, with interest growing rapidly over the decade since the discovery of carbon nanofibers. In this study, a new novel method is introduced to synthesize the carbon nanofibers by gas-phase, where a single-stage microwave-assisted chemical vapour deposition approach is used with ferrocene as a catalyst and acetylene and hydrogen as precursor gases. Hydrogen flow rate plays a significant role in the formation of carbon nanofibers, as being the carrier and reactant gas in the floating catalyst method. The effect of process parameters such as microwave power, radiation time and gas ratio of C2H2/H2 was investigated statistically. The carbon nanofibers were characterized using scanning and transmission electron microscopy and thermogravimetric analysis. The analysis revealed that the optimized conditions for carbon nanofibers production were microwave power (1000 W), radiation time (35 min) and acetylene/hydrogen ratio (0.8). The field emission scanning electron microscope and transmission electron microscope analyses revealed that the vertical alignment of carbon nanofibers has tens of microns long with a uniform diameter ranging from 115 to 131 nm. High purity of 93% and a high yield of 12 g of CNFs were obtained. These outcomes indicate that identifying the optimal values for process parameters is important for synthesizing high quality and high CNF yield.

Influence of Preliminary UV Irradiation on the Formation of Carbon Nanofibers on the Surface of Chlorinated Polyvinyl Chloride Under the Action of a High-Power Ion Beam

Influence of Preliminary UV Irradiation on the Formation of Carbon Nanofibers on the Surface of Chlorinated Polyvinyl Chloride Under the Action of a High-Power Ion Beam

Enhancement in Electromagnetic Wave Shielding Effectiveness through the Formation of Carbon Nanofiber Hybrids on Carbon-Based Nonwoven Fabrics.

The selective hybrid formation of numerous tiny carbon nanofibers (CNFs) in carbon-based nonwoven fabrics (c-NFs), namely CNFs formed only on the surfaces of individual carbon fibers (i-CFs) constituting c-NFs and not on the surfaces of carbon microcoils (CMCs), could be formed by the incorporation of H2 gas flow into the C2H2 + SF6 gas flow in a thermal chemical vapor deposition system. On the other hand, the nonselective hybrid formation of numerous tiny CNFs in c-NFs, that is, tiny CNFs formed on the surfaces of both i-CFs and CMCs, could be achieved by simply modulating the SF6 gas flow on and off in continuous cycles during the reaction. Detailed mechanisms are suggested for the selective or nonselective formation of tiny CNFs in c-NFs. Furthermore, the electromagnetic wave shielding effectiveness (SE) values of the samples were investigated across operating frequencies in the 8.0–12.0 GHz range. Compared with previously reported total SE values, the presently measured values rank in the top tier. Although hybrid formation reduced the electrical conductivity of the native c-NFs, the total SE values of the native c-NFs greatly increased following hybrid formation. This dramatic improvement in the total SE values is ascribed to the increased thickness of c-NFs after hybrid formation and the electromagnetic wave absorption enhancement caused by the intrinsic characteristics of CMCs and the numerous intersections of tiny CNFs.

Formation of Carbon Nanofibers on the Surface of a Photoresist under the Action of a Powerful Ion Beam of Nanosecond Duration

Formation of Carbon Nanofibers on the Surface of a Photoresist under the Action of a Powerful Ion Beam of Nanosecond Duration

Formation of carbon nanofibers with Ni catalyst supported on a micro-mesoporous glass

The Ni/SiO2 system is one of the most interesting to produce COx-free H2 and valuable carbon nanofibers (CNFs) by the catalytic decomposition of CH4. SiO2 is one of the most effective support while Ni catalyst displays long life and high activity. We studied the catalytic chemical vapor deposition (CCVD) process of CH4 within Ni/glass system at relatively low temperature (600 °C) during long times (3 h), varying the amount of the catalyst (2.3–17.8% Ni(%)) and the carbon source (100:200 to 100:0, CH4:N2). As the amount of Ni and CH4 increases, the formation of CNFs is enhanced giving as a result CNFs/glass materials with more amount, longer and thicker CNFs. The initial microstructure of the glass support and the way of Ni catalyst is deposited play a decisive role. Pristine porous glass displays a microstructe of interconnected mesopores which are progressively filled with Ni, producing ink-bottle pores with open ends. After the CCVD process as the amount of Ni or CH4 increases, the porosity of the Ni-doped glass is reduced due to the progressively filling of the mesopores (4 nm) with CNFs. Furthermore, due to the formation of large entanglements of CNFs new pores appear (20–70 nm) depending on the processing conditions. Fish-bone with hollow core and bamboo-like CNFs are found over the surface and also inside the porous glass support. It is observed a base-growth mechanism due to the strong interaction between the catalyst and the support, which prevents the Ni deactivation enhancing its activity for long times.

Fe3C nanoparticles and carbon nanofiber decorated N-doped carbon framework for bifunctional water splitting

Transition metal carbides have been widely developed as bifunctional electrocatalysts for water splitting due to their attractive superiority, however, the further environment of their performance still remains a significant challenge. Herein, a novel hierarchical hybrid of Fe3C nanoparticles and carbon nanofibers supported N-doped carbon framework (Fe3C@CNF/NC-950 °C) was developed by in situ high-temperature pyrolysis. The introduction of tripolycyanamide induced the formation of carbon nanofibers (CNF), fabricating the hierarchical architecture of 1D CNF and 2D carbon framework. Benefiting from the integration of multicomponent active phases, including Fe3C nanoparticles, carbon nanofibers and N-doped carbon framework, Fe3C@CNF/NC-950 °C hybrid electrode presents remarkable electrocatalytic performances toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), as well as robust durability, highlighting Fe3C@CNF/NC-950 °C as promising alternative of noble-metal-based materials.

Synthesis, Characterisation, and Performance Evaluation of Promoted Ni‐Based Catalysts for Thermocatalytic Decomposition of Methane

AbstractThermocatalyatic decomposition (TCD) of methane to COX free hydrogen and carbon nanofibre (CNF) was investigated over a series of self‐designed monometallic Ni catalyst and bimetallic Ni−Cu and Ni−Pd catalysts. The catalysts were synthesised from the wet impregnation method and characterised using a series of complementary techniques include TGA, XRD, BET, TPR, FESEM, TEM, and Raman Spectroscopy. Despite a substantial reduction of surface area in the promoted catalysts, the catalytic activity of the promoted catalyst was enhanced due to the nature of the process which is a metal‐catalysed reaction. As a whole, bimetallic Pd−Ni catalyst with a surface area of 2.76 m2 g−1 possesed the highest conversion of 77 % after 6 h reaction. The overall TCD reaction was found to be first‐order with the calculated activation energy, Ea of 38 kJ mol−1. The methane consumption rates at 1023 K and 1073 K were 0.5 mol s−1gcat−1 and 0.58×104 mol s−1gcat−1 respectively. Meanwhile, the methane consumption rates improved considerably from 0.58 mol s−1gcat−1 to 0.67×104 mol s−1gcat−1 under the methane partial pressure of 41 kPa. The XRD profile of the fresh catalysts revealed that mixed oxides were formed over the surface of the support upon the addition of Cu and Pd to 50 %Ni/Al2O3. Moreover, the formation of carbon nanofibers followed both tip and base growth mechanisms as evident from the TEM images. Larger and wider carbon fibres were found in the Pd promoted catalyst.

Edge-Plane Exposed N-Doped Carbon Nanofibers Toward Fast K-Ion Adsorption/Diffusion Kinetics for K-Ion Capacitors

Sluggish kinetics severely limit the development of potassium-ion hybrid capacitors (PIHCs). Exposing active sites is recognized as an ideal strategy to resolve this issue, but the corresponding ma...

Effect of the Preliminary Heat Treatment of Chlorinated Polyvinyl Chloride on the Formation of Carbon Nanofibers on its Surface under High-Power Ion-Beam Irradiation

The effect of a high-power ion beam of nanosecond duration on layers of chlorinated polyvinyl chloride with a catalytic additive (ferrocene), which preliminarily underwent treatment in air or an inert medium in the temperature range 100–400°C, is studied. Heat treatment at 150°C for 1 h is shown to reduce the length of the formed carbon nanofibers by ~20 times. Disk-shaped depressions are observed on the surface of the polymer irradiated after treatment at 200°C due to the removal of a part of the surface layer. These depressions are likely associated with polymer embrittlement during heat treatment. A net-like structure is observed between these depressions. An increase in the treatment temperature to 400°C (in an inert medium) results in the formation of nanofibers with a length not exceeding 0.5 μm. The effect of preliminary heat treatment on the growth of carbon nanofibers and possible mechanisms of their growth under the influence of a high-power ion beam on a chloropolymer containing a catalytic additive is discussed.