Direct Current Arc Discharge Method Research Articles

Non-noble metal FeMn and single-walled carbon nanotubes nanocomposites as effective bifunctional electrocatalysts in alkaline media for oxygen/hydrogen revolution reactions

Single-walled carbon nanotubes (SWCNTs) are one of electrochemical materials with excellent electrical properties. Herein, we design the new FeMn x /SWCNTs nanocomposites which are synthesized in one step by the direct current (DC) arc discharge method. The overpotentials of oxygen/hydrogen revolution reactions of FeMn 1 /SWCNTs electrodes in alkaline solution are 190 and 317 mV respectively when the current density reaches 10 mA cm −2 . The synergistic effect between FeMn compounds and single-walled carbon nanotubes can not only increase the active sites of the composites, but also optimize the electronic structure of the composites, thereby significantly improving the OER and HER performance of the materials. This work provides an idea that the composites of SWCNTs and bimetallic hybrids have excellent electrocatalytic performance.

Bi@C Core-Shell Nanostructure as Anode for Sodium-Ion Batteries from One-Step Arc Discharge

Bismuth has a great potential as the anode for sodium-ion batteries (SIBs) because of the layered structure with large interlayer space, long mean free path, and high volumetric capacity. In this paper, carbon-coated bismuth (Bi@C) core-shell nanostructure has been in situ synthesized by one-step direct current (DC) arc discharge method for the first time. The Bi@C nanocomposite without further decoration or any other treatment exhibits superior electrochemical performance as anode for SIBs and delivers stable capacities of 356, 342, 334, 327, 325, 323, and 318[Formula: see text]mA[Formula: see text]h[Formula: see text]g[Formula: see text] at the current densities of 0.2, 0.5, 1, 3, 5, 7 and 10[Formula: see text]A[Formula: see text]g[Formula: see text], respectively. There is no obvious decay after 630 cycles with a capacity of 291[Formula: see text]mA[Formula: see text]h[Formula: see text]g[Formula: see text] at 10[Formula: see text]A[Formula: see text]g[Formula: see text], showing the excellent rate capability and long cycle stability in SIBs. Electrochemical tests proved that the ultra-fast charge–discharge performance is related to the fast redox kinetics of Na[Formula: see text] in layered structure of bismuth crystal. The Na[Formula: see text] storage mechanism of Bi@C nanocomposite anode was also investigated by cyclic voltammetry and in situ XRD. Based on experimental data, this paper proves that the arc discharge method is a simple and efficient method for preparing nanoscale electrode materials.

Aerosol synthesis of titanium nitride nanoparticles by direct current arc discharge method

Arc discharge synthesis has industrial relevance due to its low cost and scale-up potential. The production of titanium nitride nanoparticles was achieved by direct current arc discharge in an atmospheric-pressured ambient composed of N2 and Ar. We systematically investigated the effect of the synthesis parameters, including quench gas velocity, quench gas composition, and applied arc current, on the particle quality, yield, and size. It is found that increasing quench gas velocity enables to produce particles with a primary size of 10–15 nm, while titanium nitride particles of 20–50 nm are produced at low quench gas velocity based on scanning electron microscope (SEM) analysis. X-ray diffraction (XRD) results indicated that titanium nitride particles produced at various nitrogen compositions are almost stoichiometric, while the crystallite size increases almost 20 nm when increasing nitrogen contents in the quench gas. Quench gas composition also has a significant impact on the arc voltage as well as particle production rate. When increasing the nitrogen concentration from 20% to 100%, the production rate can be enhanced by a factor of three. Besides, raising the applied arc current from 12A to 50 A leads to a yield enhancement of factor 10. According to the Brunauer-Emmett-Teller (BET) measurement, the increase of applied arc current has a limited impact on primary particle size. The enhancement in particle production rate is mainly reflected by the larger agglomerate sizes and agglomerate number concentration. Additionally, based on experimental observations and previous studies, a mechanism is presented to explain the growth of deposits on the cathode tip.

Ferromagnetic anisotropy in scandium-doped AlN hierarchical nanostructures

We experimentally fabricated uniformly distributed single-, double- and six-sided Sc-doped AlN (AlN:Sc) nanodendrites by a plasma-assisted direct current arc discharge method. The crystal structure, composition, morphological and microstructures were characterized, and the physical mechanisms governing the formation of AlN:Sc nanodendrites were examined. It was found that the morphology and the crystal orientation of the AlN nanodendrites can be controlled by tuning the N2 pressure. The incorporation of Sc induces native point defects in AlN that contribute to the growth of hierarchical structures and affect the room-temperature photoluminescence. The AlN:Sc nanodendrites exhibit room-temperature anisotropic ferromagnetism, and this is strongly depend on the orientation of the nanodendrites. This work provides a facile strategy to fabricate complex hierarchical AlN:Sc nanostructures with manipulated magnetic properties which may find promising applications in spintronic nanodevices.

Cubic SiC nanowire synthesis by DC arc discharge under ambient air conditions

Silicon carbide (SiC) is a widely used material characterized by unique physical and chemical properties. In the paper, cubic silicon carbide nanowires are synthesized via the non-vacuum DC (direct current) arc discharge method. DC arc is generated between the graphite rod and the graphite crucible under ambient air conditions without any vacuum or applying special defenses to the used atmosphere equipment. According to experimental data, the percentage of silicon carbide of the total product in interval from 70 A to 100 A increases from 3.9% up to 26.7% (mass), and in interval from 130 A to 200 A of arc discharge current decreases from 26.1% down to 19.9% (mass). The silicon carbide wires are characterized by the typical core-shell SiC–SiOx structure. It is possible to control the phase composition and increase the yield of SiC by changing the arc discharge current amplitude. The optimal synthesis parameters using the DC source with the maximum current of 200 A are a current of 200 A, synthesis time of 12 s and a silicon fraction in the initial mixture not more than 25% (mass) to completely process the initial silicon into its carbide.

Percolative Composites with Carbon Nanohorns: Low-Frequency and Ultra-High Frequency Response.

We systematically studied the electromagnetic properties of carbon nanohorns (CNHs) and polystyrene composites filled with CNHs in static regime, low frequency and microwave regions. CNHs were synthesized using the direct current arc-discharge method using solid graphite rods and graphite rods filled by melamine mixed with graphite powder. Transmission electron microscopy and thermo-gravimetric analysis showed that CNH agglomerates are the main product, while the addition of melamine promotes the formation of graphite balls. Graphitic contamination causes the internal leakage of inter-agglomerate capacity, lowering the permittivity and enhancing the conductivity of composites. The permittivity of CNH/polystyrene composites increases with the filler fraction, and near the dielectric threshold electromagnetic characteristics of the composites exhibit critical behaviour. Our results suggest that CNHs with relatively high values of permittivity and contact resistance could be used as high-k materials.

DC Arc discharge synthesized zirconia nanoparticles: shed light on arc current effects on size, crystal structure, optical properties and formation mechanism

In this study zirconia nanoparticles (NPs) were successfully synthesized via the direct current (DC) arc discharge method in water. Formation mechanism of NPs and the effect of arc current on morphological, structural and optical properties of NPs have been studied. The NPs were synthesized at four different currents in the 40–160 A range. SEM observations showed NPs are spherical in shape and their average size decrease from 40 to 22 nm by increasing the current from 40 to 160 A. XRD analysis revealed phase composition of NPs is a mixture of tetragonal and monoclinic for all the samples, and the phase fraction of NPs are arc current dependent in such a way that an increase in the current leads to an increase in the weight percent of the tetragonal phase. UV–vis spectroscopy indicated that the NPs exhibit optical characteristics of the wide energy band gap semiconductors with a significant amount of oxygen deficiency. Also the effect of the arc current on the energy band gap of NPs were investigated. An increase in the arc current decreases energy band gap of the NPs from 3.8 to 3.0 eV. Optical emission spectroscopy (OES) studies demonstrate formation of zirconia NPs at temperatures as high as 4953 K, thereby zirconium exited species react with some of oxygen containing species. Finally, Thermal radiation measurement is proposed as a nondestructive method to evaluate the active mechanisms in an arc discharge zone beside other methods such as OES.

Controllable synthesis of carbon nanomaterials by direct current arc discharge from the inner wall of the chamber

A direct current (DC) has been applied to prepare many carbon nanomaterials, including fullerene, graphene, and carbon nanohorns (CNHs) from inner wall of chamber. However, the growth mechanism of these carbon nanomaterials is not clear. Amorphous spherical carbon nanoparticles (SCNs), the typical ‘dahlia-like’ CNHs, and graphene with the layer numbers of 2–5 were synthesized controllably from the inner wall of the chamber by DC arc discharge method using argon, nitrogen, and hydrogen as buffer gas. Simultaneously, the effect of buffer gas pressure on the morphology of carbon nanomaterials was investigated systematically. Furthermore, the formation mechanism of these carbon nanomaterials by DC arc discharge was also investigated. Given that argon atom was difficult to bond with the carbon cluster, the random bond between carbon clusters contributed to combine into amorphous SCNs; the CN bond was the key factor in the formation of CNHs, and hydrogen contributes to form graphene sheets by terminating carbon dangling bonds. With increasing the pressure of buffer gas, intense quenching resulted in formation of carbon nanomaterials with high purity. The study on the growth mechanism of carbon nanomaterials in the inner wall of chamber promotes the preparation of carbon nanomaterials controllable by arc discharge method.

Plasma-assisted synthesis of ZnSe hollow microspheres with strong red emission

We demonstrate the growth of ZnSe microspheres in large quantities by using a mixture of Zn and Se as precursors via direct current arc discharge method without the addition of any catalyst or template. The as-obtained samples were characterized by X-ray diffraction, Raman, energy-dispersive X-ray spectrometry, scanning and transmission electron microscopy, and ultraviolet-visible reflectance spectroscopy. The majority of the ZnSe microspheres which were composed of ZnSe nanoparticles exhibited perfectly spherical morphology and a distinct hollow structure with a relatively rough surface. The growth mechanism of ZnSe hollow microspheres has been discussed. Room-temperature excitation and emission spectra as well as the fluorescence lifetime of ZnSe hollow microspheres were measured and the results showed ZnSe hollow microspheres exhibit an intensive wide broad emission bands from 550 to 750 nm upon 470 nm excitation with fast decay time 1.09 ms and CIE chromaticity coordinates (0.65, 0.34), which was ascribed to characteristic structure defects (vacancies and interstitials) in ZnSe. Additionally, the temperature dependent emission behavior was measured and discussed.

The electromagnetic properties and microwave absorbing performance of titanium carbide attached single-walled carbon nanotubes

The titanium carbide nanoparticles attached single-walled carbon nanotubes (TiC-SWCNTs) were mass-produced by an argon–hydrogen direct current arc discharge method using TiO2 and Fe added carbon rod as anode. The composites of TiC-SWCNTs in the paraffin matrix were investigated in the frequency range of 2–18 GHz by a vector network analyzer. The electromagnetic (EM) parameter and reflection loss (RL) properties were simulated by transmission line theory and the microwave absorption mechanisms for the dielectric loss and magnetic loss were discussed in detail. The results indicate that the TiC-SWCNTs prepared by 4 at.% TiO2 added anode exhibited the best microwave absorption property due to better impedance matching, whose RL value reached − 45.6 dB at 14.2 GHz and the absorption bandwidth below − 10 dB was up to 5.7 GHz. Furthermore, the matching thickness of the absorber is 1.8 mm and the filler loading of TiC-SWCNTs in the matrix is 20 wt%. It is expected that the TiC attached SWCNTs nanocomposite will be an excellent candidate for microwave absorption and provide a new idea to prepare weak magnetic EM wave absorber.

Preparation of Nickel Nanoparticles by Direct Current Arc Discharge Method and Their Catalytic Application in Hybrid Na-Air Battery

Nickel nanoparticles were prepared by the arc discharge method. Argon and argon/hydrogen mixtures were used as plasma gas; the evaporation of anode material chiefly resulted in the formation of different arc-anode attachments at different hydrogen concentrations. The concentration of hydrogen was fixed at 0, 30, and 50 vol% in argon arc, corresponding to diffuse, multiple, and constricted arc-anode attachments, respectively, which were observed by using a high-speed camera. The images of the cathode and anode jets were observed with a suitable band-pass filter. The relationship between the area change of the cathode/anode jet and the synchronous voltage/current waveform was studied. By investigating diverse arc-anode attachments, the effect of hydrogen concentration on the features of nickel nanoparticles were investigated, finding that 50 vol% H2 concentration has high productivity, fine crystallinity, and appropriate size distribution. The synthesized nickel nanoparticles were then used as catalysts in a hybrid sodium–air battery. Compared with commercial a silver nanoparticle catalyst and carbon black, nickel nanoparticles have better electrocatalytic performance. The promising electrocatalytic activity of nickel nanoparticles can be ascribed to their good crystallinity, effective activation sites, and Ni/NiO composite structures. Nickel nanoparticles prepared by the direct current (DC) arc discharge method have the potential to be applied as catalysts on a large scale.

Mass production of Nickel@Carbon nanoparticles attached on single-walled carbon nanotube networks as highly efficient water splitting electrocatalyst

Herein, we develop a direct current arc discharge method which enables large-scale synthesis of nickel@carbon attached single-walled carbon nanotube networks as an electrocatalyst for highly efficient water splitting. Mass amount of Ni@C/SCN (～80 g) could be easily obtained. After optimization, the catalyst exhibits a superior performance of electrochemical water splitting, which allows a current density of 10 mA cm−2, with an overpotential of only 260 mV for OER and 198 mV for HER. The electrolyzer can achieve a current density of 10 mA cm−2 at 1.8 V.

Oxygen Evolution Activity of Co-Ni Nanochain Alloys: Promotion by Electron Injection.

Metal alloy nanoparticles have shown promising applications in electrocatalysis. However, the nanoparticles usually suffer from limited charge-transfer efficiency, which can be solved by preparing one-dimensional materials. Herein, Co-Ni alloy nanochains are prepared by a direct-current arc-discharge method. The nanochains, comprised of mutually coupled uniform nanospheres, can range up to several micrometers in size. When the alloy is exposed to air or under the electro-oxidation process, a metal-metal-oxide heterostructure is obtained. The alloy can inject electrons into the oxide, which makes it more suitable for electrocatalysis. The composition of the samples can be changed by varying the ratio of Ni/Co (i.e., Co, Co7 Ni3 , Co5 Ni5 , Co3 Ni7 , Ni) in the synthesis process. The nanochains show good oxygen evolution performance that correlates with the Ni/Co ratio. Co7 Ni3 demonstrates optimal activity with an onset point of 1.50 V vs. reversible hydrogen electrode (RHE) and overpotential of 350 mV at 10 mA cm-2 . The alloy nanochains also show excellent durability with 95.0 % current retention after a long-term test for 12 h.

Efficient Co@CoPx core–shell nanochains catalyst for the oxygen evolution reaction

Co@CoPx core–shell nanochains were prepared via a direct-current arc-discharge method and subsequent phosphorization at 350 °C.

Dopant concentration dependent magnetism of Sc-doped AlN nanowires

A series of room temperature ferromagnetic (RTFM) Al1-xScxN nanowires with Sc-dopant concentration x ranging from 0 to 4.7% were prepared by the direct reaction of different weight ratios of Al:Sc alloy with N2 gas using plasma assisted direct current (DC) arc discharge method. Powder X-ray diffraction (XRD) and Raman scattering spectra revealed that Sc incorporates into the AlN crystal lattice. With the increase of the Sc content, the wurtzite-structure AlN maintained with increasing volume of unit cell even when the Sc content reached 4.7 at.%, meanwhile, the Sc dopant concentration reached saturation, indicating the successful incorporation of Sc ions into AlN lattice. Scanning and transmission electron microscopy measurements show that the nanowires have uniform diameters of about 50–100 nm and are several tens of microns in length. Magnetic measurements revealed that the room temperature ferromagnetism increased with the increase of Sc dopant concentration and the ferromagnetism remained unchanged when the Sc content reached saturation.

The microwave absorbing properties of CoFe2 attached single walled carbon nanotube/BaFe12O19 nanocomposites

The CoFe2 attached single-walled carbon nanotubes (CoFe2@SWCNTs) and BaFe12O19 ferrite nanocomposites with different CoFe2@SWCNTs weight ratios (1, 3, 5, 7 wt%) were synthesized by a simple combination process. Then, the electromagnetic and microwave absorption properties were systematically investigated by a vector network analyzer in the frequency range of 2–18 GHz. High-quality CoFe2@SWCNTs were prepared by a direct current arc discharge method in one-step. BaFe12O19 nanocrystals were synthesized by a nitrate citric acid sol–gel auto-ignition method. The CoFe2@SWCNT/BaFe12O19 nanocomposites exhibited an efficient reflection loss (RL) and a wide absorption bandwidth. The minimum RL of −54.13 dB was observed at 11.84 GHz for the nanocomposite (5 wt% CoFe2@SWCNTs) with a thickness of 2.8 mm, 3.4 times greater than those without CoFe2@SWCNTs, and a broad absorption bandwidth of 4.64 GHz (<−10 dB) was achieved. In addition, the nanocomposite (1 wt% CoFe2@SWCNTs) shows a broader effective microwave absorption bandwidth of 7.12 GHz with a thickness of 1.9 mm. The experimental results reveal that the absorbing properties of the nanocomposites are greatly improved by controlling the CoFe2@SWCNTs weight ratio and the matching thickness of the absorber. This CoFe2@SWCNT/BaFe12O19 nanocomposite is anticipated to be applied in advanced microwave absorbers.

Fabrication of TiO2/Carbon Photocatalyst using Submerged DC Arc Discharged in Ethanol/Acetic Acid Medium

This study aimed to fabricate a modified photocatalyst of TiO2/C to enhance its performance. The fabrication was achieved using the submerged direct current (DC) arc-discharge method employing two graphite electrodes, one of which was filled with a mixture of carbon powder, TiO2, and binder, in ethanol with acetic acid added in various concentrations. The arc-discharge method was conducted by flowing a current of 10–20 A (~20 V). X-ray diffraction (XRD) patterns showed significant placements of the main peak characteristics of TiO2, C graphite, and titanium carbide. The surface analysis using Fourier transform infrared spectroscopy (FTIR) revealed that fabricated TiO2/C nanoparticles had stretching vibrations of Ti─O, C─H, C═O, C-O, O-H and C═C in the regions of 450–550 cm-1, 2900–2880 cm-1, 1690–1760 cm-1, 1050–1300 cm-1, 3400–3700 cm-1 and ~1600 cm-1, respectively. In addition, the study investigated the photocatalysts of unmodified and modified TiO2/C for photodegradation of methylene blue (MB) dye solution under mercury lamp irradiation. The effectiveness of the degradation was defined by the decrease in 60-minute absorbance under a UV-Vis spectrophotometer. Modified TiO2/C proved to be significantly more efficient in reducing dye concentrations, reaching ~70%. It indicated that the oxygen-containing functional groups have been successfully attached to the surface of the nanoparticles and played a role in enhancing photocatalytic activity.

Interface evolution in the platelet-like SiC@C and SiC@SiO2 monocrystal nanocapsules

Carbon-coated SiC@C nanocapsules (NCs) with a hexagonal platelet-like morphology were fabricated by a simple direct current (DC) arc-discharge plasma method. The SiC@C NCs were monocrystalline, 120–150 nm in size, and approximately 50 nm thick. The formation of the as-prepared SiC@C NCs included nucleation of truncated octahedral SiC seeds and subsequent anisotropic growth of the seeds into hexagonal nanoplatelets in a carbon-rich atmosphere. The disordered carbon layers on the SiC@C NCs were converted into SiO2 shells of SiC@SiO2 NCs by heat treatment at 650 °C in air, during which the shape and inherent characteristics of the crystalline SiC core were obtained. The interface evolution from carbon to SiO2 shells endowed the SiC@SiO2 NCs with enhanced photocatalytic activity due to the hydrophilic and transparent nature of the SiO2 shell, as well as to the photosensitive SiC nanocrystals. The band gap of the nanostructured SiC core was determined to be 2.70 eV. The SiC@SiO2 NCs degraded approximately 95% of methylene blue in 160 min under visible light irradiation.

Synthesis, photoluminescence and ferromagnetic properties of pencil-like Y doped AlN microrods

The pencil-like Y doped AlN (AlN:Y) microrods were synthesized by the direct reactions of Al:Y alloy with N2 gas using plasma assisted direct current (DC) arc discharge method. Structural and morphological analyses of as-synthesized microrods have been carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The AlN:Y microrods usually have pencil-like geometries, with lengths up to several tens micrometers and diameters 5–10µm. Photoluminescence (PL) and Magnetization hysteresis loop studies were carried out to understand the optical and ferromagnetic properties of pencil-like AlN:Y microrods. The quite broad emission band centered at 537nm and room-temperature ferromagnetism which originate from high concentration of Al vacancies and surface defects has been observed for the pencil-like AlN:Y microrods.

Highly concentrated amino group-functionalized graphite encapsulated magnetic nanoparticles fabricated by a one-step arc discharge method

In this work, we apply a one-step direct current arc discharge method to synthesize graphite-encapsulated magnetic nanoparticles functionalized with a high concentration of amino groups uniformly without further modification or any other pre/post-treatment procedures. The synthesis was accomplished by adding different molar ratios of NH3 into He/CH4 gas mixture under various gas pressures. The optimized number of functionalized amino groups is evaluated to be ∼3.22 × 105 per nanoparticle prepared at 50 Torr with 0.1% of NH3. As the molar ratios of NH3 decrease from 1.0% to 0.1%, the optical emission peaks of CN and NH are intensified gradually, and the surface structural integrities also increase. These results indicate that NH3 not only provides -NH or -NH2 fragment species to introduce amino groups incorporating with the dangling bonds activated by H radicals, but also constructs networks to flatten the outmost graphitic surfaces of encapsulated nanoparticles. As the working gas pressure changes from 25 to 100 Torr, the outmost shells formed by the dissociated CH4/NH3 molecules tend to be relatively less disordered.