Carbon-Encapsulated Nickel Nanoparticles Research Articles

Nitrogen-doped carbon as selectively permeable layer to enhance the anti-poisoning ability of hydrogen oxidation reaction catalysts for hydroxide exchange membrane fuel cells

The use of platinum group metals (PGMs) as the catalysts and the requirement of high purity H2 are the two aspects resulting in the high cost of the polymer electrolyte membrane fuel cells. Herein, we report that nitrogen-doped carbon encapsulated nickel nanoparticles (Ni@NC) as stable hydrogen oxidation reaction catalysts, which allows the use of PGM-free anode catalysts durably and feeding crude hydrogen. The hydroxide exchange membrane fuel cell using Ni@NC as the anode catalyst illustrates steady performance for more than 200 h, while the Ni/C cell fails within 7 h. The current density loss is less than 10% by feeding H2 with 100 ppm of CO for 24 h, which is much better than those using Pt/C or Ni/C. The anti-poisoning feature is attributed to the block effect of the NC shell, while the defects allow the permeation of H2, thus catalyzing the hydrogen oxidation reaction.

NMR study of magnetic nanoparticles Ni@C

The 61Ni, 13C NMR spectra of carbon encapsulated nickel nanoparticles have been obtained. It has been shown that the cores of the particles consist of metallic nickel with face-centered cubic structure, nickel carbide Ni3C and carbon-nickel solid solution. The carbon shell of nanoparticles is a highly defective structure and close to an amorphous glassy-like carbon.

Hybrid carbon nanotubes/graphene/nickel fluffy spheres for fast magnetic separation and efficient removal of organic solvents from water

Carbon nanotubes/graphene/nickel (CNT-G-Ni) fluffy spheres were synthesized using renewable carbon sources. Carbon-encapsulated nickel nanoparticles (CENNs) were prepared by hydrothermal carbonization (HTC) of potato starch and nickel nitrate, and then followed by catalytic graphitization at 900 °C. The prepared GENNs were cracked at 700 °C in biogas, during which graphene shells over GENNs were peeled off and formed graphene nanoplatelets, and simultaneously multiwall carbon nanotubes (MWCNTs) were formed over nickel particles and in-situ integrated into graphene nanoplatelets to obtain CNT-G-Ni fluffy spheres. The prepared 3D nanocomposite was investigated for the removal of organic solvent from water and its adsorption capacity above 110 g/g.

Ni(II)-Dimeric Complex-Derived Nitrogen-Doped Graphitized Carbon-Encapsulated Nickel Nanoparticles: Efficient Trifunctional Electrocatalyst for Oxygen Reduction Reaction, Oxygen Evolution Reaction, and Hydrogen Evolution Reaction

The successful commercialization of fuel cells and electrolyzer is limited to the cost and instability issues associated with electrocatalysts (platinum/platinum-based catalysts) used. Hence, there is critical challenge to develop stable, non-platinum-based catalysts with multifunctionality and better durability that can efficiently replace platinum. While a sufficient number of bifunctional catalysts are now known in the literature, development of trifunctional catalyst is rarely reported. Herein, we report the development of nitrogen-doped graphitized carbon-encapsulated Ni nanoparticles-based catalyst (Ni-NC700) from an easy derivable Ni(II)-dimeric complex. Microstructural studies reveal that the catalyst annealed at 700 °C has 4–5 layers of graphene sheets forming a shell surrounding the Ni nanoparticles. This catalyst exhibits outstanding trifunctional catalytic performance with onset potential of 0.86, 1.52, and −0.02 V (vs RHE) for oxygen reduction reaction, oxygen evolution reaction, and hydrogen...

Size tunable carbon-encapsulated nickel nanoparticles synthesized by pyrolysis of nickel acetate tetrahydrate

In this study, size control of carbon-encapsulated nickel nanoparticles (CENiNPs) synthesized by direct thermal decomposition of Ni(CH3COO)2.4H2O (NiAc) was possible by varying systematically the initial amount of the precursor during its pyrolysis. The reaction was conducted inside a thermogravimetric analyzer coupled to a quadrupole mass spectrometer for evolved gas analysis. By heating non-isothermally different initial amounts of NiAc (100–400 mg) in an argon flow at 10 °C/min from room temperature to 500 °C, CENiNPs were readily obtained, in which a thin layer of carbon resulting from the breakdown of the anion protects their metallic core from spontaneous oxidation. High resolution transmission electron microscopy and methane catalytic decomposition tests revealed that this encapsulating layer can also exert a significant role in the control of the size distribution (40–140 nm) and catalytic activity of the resultant CENiNPs. Temperature programmed oxidation of the CENiNPs identified preliminary some surface carbon species responsible for the packing of the catalytically-active metallic core. This simple and cost-effective method emerges as a competitive way to manufacture and conserve highly active CENiNPs.

N-doped carbon encapsulated nickel nanoparticles: rational fabrication and ultra-high performance for ethanol oxidation

N-doped carbon encapsulated nickel nanoparticles (NiNC) are prepared from mixtures of nickel salt, glucose and urea by a simple heating protocol. A higher viscosity of the mixture inhibits the migration of Ni species such that highly dispersed and very small Ni nanoparticles form during heat treatment. The sizes of the Ni nanoparticles can be controlled by adjusting the composition of the raw mixtures. The optimized sample of NiNC-4 contains Ni nanoparticles of 2.02nm in size which afford a large metal surface area of 400.7m2g−1 and a high nitrogen content of 7.21 at%. An ultra-high current density of 327mAcm−2 is achieved in 0.1M NaOH electrolyte containing 1M ethanol using NiNC–4 as the electrocatalyst. NiNC-4 electrodes also exhibit a good long-term cycling stability. After 500 cycles, 89% of the initial current density is sustained in 0.1M NaOH electrolyte containing 0.5M ethanol. 96.8% of the initial current density is retained by moving the NiNC–4 electrode into fresh 0.1M NaOH solution with 0.5M ethanol after 500 cycles. The excellent electrocatalytic properties of NiNC–4 for ethanol oxidation stem from the synergistic effect of the porous carbon substrate, abundant N-containing groups and the small nickel nanoparticle size.

The microwave absorption properties of carbon-encapsulated nickel nanoparticles/silicone resin flexible absorbing material

Carbon-encapsulated nickel nanoparticles (Ni@C) with soft magnetic nickel nanoparticle core and dielectric carbon shell were synthesized by a modified arc-discharge method. The calculated reflection loss (RL) of Ni@C/paraffin composites and the measured RL of Ni@C/silicone coatings were studied at thicknesses of 1–3 mm and Ni@C contents of 40–60 wt%. Ni@C nanoparticles show good microwave absorption properties in 2–18 GHz. The minimum calculated RL is −39.82 dB with 60 wt% Ni@C at 3 mm, and the calculated RL <−10 dB can be obtained in the frequency of 5–13.41 GHz. Meanwhile, the minimum measured RL reaches −20.54 dB with 60 wt% Ni@C loading at 2.5 mm and the widest bandwidth of measured RL <−10 dB is 3.64 GHz with 60 wt% Ni@C loading at 1.5 mm.

Synthesis and Characterization of Carbon-Encapsulated Nickel Nanoparticles from De-Oiled Asphalt

Carbon-encapsulated Ni nanoparticles with the size of 5 to 30 nm were synthesized from de-oiled asphalt (DOA) by heat-treatment at 1800 °C with nickel powder. The nanoparticles exhibited well-constructed core-shell structures, with Ni cores and graphitic shells. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) examinations confirmed that the carbon-encapsulated Ni nanoparticles were uniformly dispersed in carbon matrix and the Ni nanoparticles were surrounded by several carbon layers with well ordered arrangement. The formation of the core-shell nanoparticles was selectively controlled by adjusting the ratio of de-oiled asphalt to nickel powders. The possible growth model for the carbon-encapsulated Ni nanoparticles was discussed briefly. This result presents a simple and controllable way to synthesize carbon-encapsulated nickel nanoparticles.

Magnetic resonance study of carbon encapsulated Ni nanoparticles

Abstract Magnetic resonance study of six samples consisting of carbon encapsulated nickel nanoparticles or carbon nanotubes ended with such nickel nanoparticles was carried out at room temperature. Samples of Ni/C were prepared by carburization of nanocrystalline nickel by ethylene (C2H4) and methane (CH4). Hydrocarbons decomposition on nickel nanoparticles was done at temperatures 500, 600 and 700°C. Magnetic resonance spectra of samples designated as CH4/500, CH4/600, CH4/700, C2H4/500, C2H4/600 and C2H4/700 were obtained by Bruker E 500 spectrometer. The integrated intensities of the resonance spectra were correlated with the carburization conditions (temperature, type of hydrocarbon) during samples preparation. A core-shell model of the investigated samples allowed rough estimation of appropriate shell sizes.

Size Prediction of Carbon-Encapsulated Nickel Nanoparticles

A simple theoretical model to predict the size control of carbon-encapsulated metal nanoparticles is developed using heat transfer and carbon diffusion theories. Taking carbon-encapsulated nickel nanoparticles as an example, the minimum size of carbon-encapsulated structure that can be formed as a function of the ambient temperature is calculated and the effect of activation energies for carbon diffusion on the size of carbon-encapsulated nickel nanoparticles is examined. The theoretical results are in good agreement with the experiment, suggesting that our model can be used to guide the size-controlled synthesis of carbon-encapsulated metal nanoparticles.

Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-ray Absorption, Emission, and Photoelectron Spectroscopies

Electronic structure of nickel nanoparticles encapsulated in carbon was characterized by photoelectron, X-ray absorption, and X-ray emission spectroscopies. Experimental spectra are compared with the density of states calculated in the frame of the density functional theory. The carbon shell of Ni nanoparticles has been found to be multilayer graphene with significant (about 6%) amount of Stone--Wales defects. Results of the experiments evidence protection of the metallic nanoparticles from the environmental degradation by providing a barrier against oxidation at least for two years. Exposure in air for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles with coverage of functional groups.

Synthesis of Carbon Encapsulated Nickel Nanoparticles by Laser Ablation in Liquid

Carbon encapsulated nickel nanoparticles (CENNPs) with high purity were fabricated by laser ablation of nickel target in ethanol. The size of CENNPs varies from tens to hundreds of nanometers, and CENNPs show two kinds of typical morphologies i. e. a nickel core with a carbon shell or a nickel core with two carbon shells. Transmission electron microscopy indicated that the CENNPs formed as a result of laser evaporation of the nickel target and the decomposition of ethanol, whose carbon atoms mixed with the nickel vapor, and Ni/C liquid droplets appeared during the cooling stage. The carbon shells formed by precipitation of carbon atoms on the surface of the nickel cores led to the formation of CENNPs.

Characterization of Carbon-Encapsulated Nickel and Iron Nanoparticles by Means of X-ray Absorption and Photoelectron Spectroscopy

Nickel and iron nanoparticles encapsulated in carbon were synthesized by contactless levitation melting of metal drops and their evaporation in a flow of an inert gas containing a hydrocarbon. The products were characterized by means of transmission electron microscopy, photoelectron spectroscopy, and X-ray absorption spectroscopy. It was established that carbon coating protects the metallic nanoparticles from the environmental degradation by providing a barrier against oxidation and ensures stability of the ferromagnetic core metal inside that provides their extremely high catalytic activity, biocompatibility, and nontoxicity.

Substrate Effects on the Morphology of Carbon Encapsulated Nickel Nanoparticles Grown by Surface Diffusion Assisted Phase Separation

Encapsulated nanoparticles formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices or as large scale templates for nan...

Preparation, Characterization, and Surface Modification of Carbon-Encapsulated Nickel Nanoparticles

Carbon-encapsulated nanonickel particles were prepared by heating nickel acetate highly dispersed in cured phenolic resin at 673 K in N2. The metallic nickel cores were about 50—80 nm in diameter, completely encapsulated with carbon shells about 10 nm thick. No byproduct, such as carbides, carbon rods, and carbon fibers, were formed in the samples prepared this way. The carbon shells prevented the metallic nickel cores from oxidation by air at high temperatures. The metallic cores remained even after the encapsulated particles were treated with 6 M hydrochloric acid solution for 24 h. The surface of the encapsulated particles was originally hydrophobic due to the hydrophobic property of the carbon shells formed under the high carbonization temperature. The treatment of the encapsulated particles with O3 at room temperature generated substantial amounts of carboxylic groups on the outer surface of carbon shells, leading to the hydrophilic surface of the encapsulated nanonickel particles.

Artificial Construction of the Magnetically Separable Nanocatalyst by Anchoring Pt Nanoparticles on Functionalized Carbon-Encapsulated Nickel Nanoparticles

A magnetically separable nanocatalyst consisting of 2−5-nm Pt particles dispersed on carbon-encapsulated nickel nanoparticles has been artificially constructed. The magnetically separable function of the nanocatalyst is well demonstrated by recycled hydrogenation of nitrobenzene to aniline. The construction process has been clearly illuminated, which is composed of the nondestructive functionalization of magnetic Ni(C) nanocapsules with carboxylic acid end groups and then the immobilization of Pt nanoparticles. This strategy should be applicable to the construction of some other magnetically separable nanocatalysts.

Carbon encapsulated nickel nanoparticles synthesized by a modified alcohol catalytic chemical vapor deposition method

Abstract In this work, a simple and cost-efficient method was demonstrated for the production of carbon encapsulated nickel nanoparticles (CENPs). The CENPs were synthesized from nickel oxide by a modified alcohol catalytic chemical vapor deposition method at atmospheric pressure. Structural characterizations using scanning electron microscopy, transmission electron microscopy and X-ray diffraction indicated that the Ni-core mean diameter and the graphite-layer mean thickness were 98 ± 31 nm and 65 ± 35 nm, respectively. Room temperature magnetization results showed a ferromagnetic behavior of the CENPs, in which the saturation magnetization decreased with decreasing the Ni-to-C ratio whereas the coercivity increased with decreasing the Ni-core diameter.

Chemical Functionalization of Magnetic Carbon-Encapsulated Nanoparticles Based on Acid Oxidation

Carbon-encapsulated nickel nanoparticles were used as the representative magnetic carbon-encapsulated nanoparticles for chemical functionalization. After oxidation with the mixed acid of H2SO4/HNO3 under a moderate ultrasonic bath, carboxylic acid groups (-COOH) were effectively generated on the fullerene-like carbon shells, which in turn were utilized to covalently link octadecylamine through an amide reaction. The whole chemical process is well characterized by many methods such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry-differential scanning calorimetry, transmission electron microscopy, and so on, and the self-consistent experimental results were obtained. The results suggested that the magnetic nanoparticles could be well protected, while their magnetic properties could be utilized to guide the transfer of the grafted functional species on the particle surface. This provides many possibilities for potential applications in chemical and biochemical fields.

Synthesis of nickel nanoparticles and carbon encapsulated nickel nanoparticles supported on carbon nanotubes

Nickel nanoparticles were prepared and uniformly supported on multi-walled carbon nanotubes (MWCNTs) by reduction route with CNTs as a reducing agent at 600 °C. As-prepared nickel nanoparticles were single crystalline with a face-center-cubic phase and a size distribution ranging from 10 to 50 nm, and they were characterized by transmission electron microscopy (TEM), high-resolution TEM and X-ray diffraction (XRD). These nickel nanoparticles would be coated with graphene layers, when they were exposed to acetylene at 600 °C. The coercivity values of nickel nanoparticles were superior to that of bulk nickel at room temperature.