Metal-carbon Nanocomposites Research Articles

Nickel-supported metal-carbon nanocomposites: New catalysts of hydrogenation of phenylacetylene

Nickel-containing metal-carbon nanocomposites (Ni@C) synthesized by levitation melting in a flow of an inert gas-hydrocarbon mixture were used as catalysts of the hydrogenation of phenylacetylene (PA). The nanocomposites were characterized by X-ray photoelectron spectroscopy, simultaneous thermal analysis, and temperature-programmed reduction. The nickel-carbon nanocomposites were stable on storage in air, with only 13% of the total amount of nickel oxidized after 3.5 years of storage. In addition to nanoparticles completely covered with carbon, the composites contained partially coated metal particles, which are readily oxidized in air. Both types of particles exhibited the catalytic activity in phenylacetylene hydrogenation. At higher contents of nickel partially coated with carbon, the activity increased and the selectivity of styrene formation decreased. The minimum half-conversion temperature (75°C) was determined for a specially prepared Ni@C sample with an increased content of oxidized nickel (28%). The maximum selectivity of styrene formation (∼75% at 150°C) was recorded in the presence of the sample with the smallest amount of oxidized nickel (less than 4%).

Novel metal carbon nanocomposites and carbon nanocrystalline material with promising properties for the development of electronics

New materials based on carbon nanocrystalline material and metal carbon nanocomposites, which have specific properties and are promising for the use in the fabrication of electron and electrochemical sensor devices and catalysts, have been suggested for the development of electronics.

Understanding the surface chemistry of carbon nanotubes: Toward a rational design of Ru nanocatalysts

A comprehensive experimental and theoretical study of the surface chemistry of ruthenium nanoparticles supported on/in multi-walled carbon nanotubes (CNTs) is reported that could pave the way to the rational design of metal–carbon nanocomposites. It is shown that the oxidation of CNTs by nitric acid that creates various oxygen surface functional groups (SFGs) on the CNT external surface is a crucial step for metal grafting. In particular, it is demonstrated that carboxylic acid, carboxylic anhydride, and lactone groups act as anchoring centers for the Ru precursor, presumably as surface acetato ligands. The HNO3 treatment that also allows CNT opening contributes to the endohedral Ru deposition. The stability of Ru nanoparticles, modeled by a Ru13 cluster, on different adsorption sites follows the order: Gr-DV-(COOH)2>Gr-DV>Gr (where DV is a double vacancy and Gr the graphene surface). It is evidenced that, after a high-temperature treatment performed in order to remove the SFGs, the Ru/CNT material can react with oxygen from air via a surface reconstruction reaction, which reforms a stable Ru-acetato interface. The mechanism of this reaction has been investigated by DFT. These Ru/CNT catalysts are extremely stable, keeping a mean particle size <2nm, even after heating at 973K under a hydrogen atmosphere.

Magnetic Nanocomposites Formed by FeNi3 Nanoparticles Embedded in Graphene. Application as Supercapacitors

A general family of magnetic nanocomposites formed by FeNi3 ferromagnetic nanoparticles (NPs) embedded in a graphitized carbon matrix is reported. The soft chemical approach used relies on the catalytic effect of the NPs resulting from the thermal decomposition of the layered double hydroxide precursor, which acts as a multilayered nanoreactor enabling the formation of a range of carbon nanoforms (CNFs). This is followed by acid treatment of the as‐prepared nanocomposites to isolate the different CNFs formed. These range from carbon nano‐onions to graphene depending on the temperature of the thermal decomposition. This synthetic process paves the way for the rational design of metal–carbon nanocomposites with controllable composition as precursors of nanocarbons or even graphene. The coexistence of metal NPs and nanostructured carbon is a major source of applications. As a proof of concept, the electrochemical performance of these metal–carbon hybrid supercapacitors is studied under high discharging current densities and they exhibit high values of specific capacitance and excellent rate capabilities.

Non-monotonous evolution of hybrid PVD–PECVD process characteristics on hydrocarbon supply

Hybrid PVD–PECVD process of titanium sputtering in argon and acetylene atmosphere combines aspects of both conventional techniques: sputtering of titanium target (PVD) and acetylene as a source of carbon (PECVD). This process can be used for preparation of metal carbon nanocomposites (MeC/C(:H)) or DLC layers doped with metal (DLC:Me). The aim of this paper is to describe and understand elementary processes influencing the hybrid PVD–PECVD process. A non-monotonous dependence of cathode voltage and current, total pressure and spectral line intensities on acetylene supply flow is reported. Explanation of non-monotonous evolutions through the analysis of the target state correlating the process characteristics with properties of coatings prepared by this process is proposed.

Metal–carbon nanocomposites as the oxygen electrode for rechargeable lithium–air batteries

A key constituent in developing lithium–air batteries is the oxygen electrode, which facilitates the oxygen reduction reaction during the discharge process and the oxidation reaction of Li2O2 during the charge process. In this article, we report on the electrocatalytic activity of platinum, iridium, and platinum–iridium alloy in an oxygen electrode. The average crystallite size of the previous metal nanoparticles was less than 2nm, which were uniformly dispersed on the surface of chained Ketjenblack powder. Both chronoamperometry analysis and cell testing showed that Pt–Ir/C electrode exhibited superior activity and is the best electrode in this research. The discharge potentials for all three catalysts are similar, ∼2.81V vs. Li/Li+, and the discharge overpotential (∼0.15V) is very low. The charge overpotential for Pt–Ir/C composites was around 0.6V.

IR Laser-Irradiation of Metals in Vacuum and Hydrocarbons: Gas Phase Deposition of Metal-Carbon Nanocomposites

IR Laser-Irradiation of Metals in Vacuum and Hydrocarbons: Gas Phase Deposition of Metal-Carbon Nanocomposites

Formation of bimetal nanoparticles in the structure of C-Cu-Zn metal-carbon nanocomposite

Metal-carbon nanocomposites comprising carbon matrices of a graphite-like structure with dispersed CuZn2 and CuZn5 bimetal nanoparticles have been obtained for the first time under conditions of the IR pyrolysis of the precursor based on polyacrylonitrile and copper and zinc acetates (Zn : Cu ratio = 1 : 5). It has been demonstrated that the CuZn5 phase formation starts at 300°C, whereas the CuZn2 phase formation starts at T > 500°C. The CuZn2 and CuZn5 bimetal nanoparticles coexist in the structure of nanocom-posites obtained at T ≥ 700°C. Here the CuZn2 bimetal nanoparticle fraction increases with an increase in the intensity of the IR pyrolysis.

Nanostructured trimetallic Pt/FeRuC, Pt/NiRuC, and Pt/CoRuC catalysts for methanol electrooxidation

We report the preparation and characterization of metal–carbon nanocomposites (NiRuC, FeRuC, and CoRuC) with bimetallic Ni–Ru, Fe–Ru, and Co–Ru nanoparticles incorporated into the pore walls of ordered mesoporous carbon, which were synthesized via a template strategy. Pt nanoparticles were deposited on the nanocomposites separately, which is different from the traditional alloying method. Nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimetric analysis techniques were used to characterize the materials. It was found that bimetallic nanoparticles (Ni–Ru, Fe–Ru, and Ru–Co) are homogenously dispersed in the carbon matrix and Pt nanoparticles with a size of less than 5 nm are widely distributed within the nanocomposites. The Pt/CoRuC catalyst shows better catalytic activity for the methanol oxidation reaction (MOR) than Pt on FeRuC or NiRuC, and its performance is also closer to that of the commercial PtRu catalyst with a slightly higher metal loading. A kinetic-based impedance model was used to simulate the electrochemical properties of the catalysts and matches well with the MOR performances of the catalysts. The promotional effect of the bimetallic/carbon nanocomposites on the catalytic activity of Pt was evidenced, and more importantly, the ligand effect was demonstrated by our results to be the major factor in the enhancement. Our investigation not only provides further insight into the roles of Fe, Ni and Co in MOR, but also assists in the design and synthesis of the new types of nanostructured electrocatalyst supports.

Phase formation in nanocomposites of the C-Pd-Fe system

Metal-carbon nanocomposites consisting of a carbon matrix with dispersed nanosize bimetallic Pd-Fe particles were obtained. It was established that at 500–700°C, the bimetallic particles form a solid solution of iron in palladium. It was concluded that raising the intensity of infrared pyrolysis to 800–1100°C leads to the formation of intermetallic compounds whose composition depends on the temperature of nano-composite fabrication.

Preparation and structure of metal-carbon nanocomposites Cu-C

Cu-C nanocomposites were obtained during the infrared pyrolysis of a precursor based on polyacrylonitrile and copper acetate. In such nanocomposites, Cu particles were dispersed in the graphitelike carbon matrix. Cu nanoparticle sizes were from 15 to 20 nm and did not depend on the preparation temperature in the range 300–600°C. At T = 700–800°C, the average size of Cu nanoparticles increased to 40 nm. In this case structuring of the carbon phase was observed.

Formation and growth mechanisms of ion-induced iron–carbon nanocomposites at room temperature

The irradiation of graphite surfaces with a simultaneous Fe supply have resulted into the development of various types of carbon nanocomposites. Their morphologies – diameter, density, length and apex angle strongly depend on the ratios of Fe deposition rate ( D Fe) to ion sputtering rate ( S ion). By optimizing the ratio of D Fe/ S ion (2.40%), the denser and well-aligned Fe–carbon nanocomposite fibers (Fe–CNFs) could be obtained, whose average length and diameter were 0.95 μm and 17 nm, respectively. As confirmed by energy-dispersive X-ray analysis, the Fe–CNFs with amorphous-like or fine-polycrystalline phase were surely composed of carbon and Fe. Two types of growth models have been employed to explain the formation of metal–carbon nanocomposites.

Self-organized formation of layered carbon–copper nanocomposite films by ion deposition

The quasi-simultaneous deposition of low energy-mass-selected C+ and metal+ ions leads to the formation of metal–carbon nanocomposites. In the case of C+ and Cu+ deposition, a homogeneous distribution of small copper clusters in an amorphous carbon matrix is expected. However, at a certain C+/Cu+ fluence ratio and energy range, alternately metal-rich and metal-deficient layers in an amorphous carbon matrix with periods in the nm range develop have been observed. The metal-rich layers consist of densely distributed crystalline Cu particles while the metal-deficient layers are amorphous and contain only few and small Cu clusters. The formation of multilayers can be described by an interplay of sputtering, surface segregation, ion induced diffusion, and the stability of small clusters against ion bombardment. This formation has been investigated for the a-C:Cu system with respect to the ion energy and the C+/Cu+ fluence ratio. The sputter coefficient SM=rfSCCu+SCuCu is the parameter to switch between layer growth (SM<1) and homogeneous cluster distribution (SM>1).

Nanostructured carbide surfaces prepared by surfactant sputtering

Nanostructured surface layers of titanium carbide and tungsten carbide were prepared on tetrahedral amorphous carbon (ta-C) films using the surfactant sputtering technique. Surfactant sputtering is a novel ion beam erosion technique, which utilizes the steady state coverage of a substrate surface with foreign atoms simultaneously during sputter erosion by combined ion irradiation and atom deposition. These foreign atoms act as surfactants, which strongly modify the substrate sputtering yield on atomic to macroscopic length scales. The novel technique allows smoothing of surfaces, the generation of novel surface patterns and nanostructures, controlled shaping of surfaces on the nanometer scale and the formation of ultra-thin compound surface layers. We have sputter eroded ta-C films using 5keV Xe ions under continuous deposition of either tungsten or titanium surfactants. This leads to the steady state formation of a WxC or a TiC/a-C nanocomposite surface layer of few nm thickness. Depending on the ion angle of incidence the layer is either smooth or nanostructured with a ripple- or dot-like surface topography. We have analyzed the surface topography, the composition and microstructure of the metal-carbon nanocomposites, and compare coverage dependent sputtering yields with SRIM and TRIDYN simulations.

The hydrodechlorination of chlorobenzene in the vapor phase in the presence of metal-carbon nanocomposites based on nickel, palladium, and iron

Metal-carbon nanocomposites based on nickel, palladium, and iron and bimetallic palladium-nickel-carbon nanocomposites were for the first time used as catalysts of hydrodechlorination of chlorobenzene in the vapor phase in the atmosphere of hydrogen. Nickel and Pd-Ni nanoparticles completely coated by a carbon layer not only were stable to oxidation and agglomeration but also exhibited considerable activity in hydrodechlorination of chlorobenzene at temperatures much lower than those at which dechlorination on carbon carriers occurred. The dependence of catalytic properties (activity, selectivity, and stability) on temperature and nanocomposite composition was studied. Depending on the nature of the metal, the composition of bimetallic particles and temperature the selectivity could be changed, and the reaction could be directed toward the formation of benzene or cyclohexane. Carbon coating was stable under reaction conditions at least up to 350°C and did not hinder hydrodechlorination. Substrate adsorption likely occurred on the outside carbon surface of composite particles. The activity and structure of Ni@C composite remained almost unchanged after triple cycling over the temperature range from 50 to 350°C in a flow system.

Various Carbon Metal Nanocomposites for Lithium Ion Batteries and Direct Methanol Fuel Cells

In this review, the recent activities in our laboratory for the synthesis of metal carbon nanocomposites are presented. Different types of carbon (carbon nanotube-CNT, mesoporous carbon-MC, carbon aerogel-CA) metal nanocomposites (Sn, Ni/CNT, Sn/MC, Pt/ CNT, Pt/ MC, Pt/ CA) were synthesized by various methods as novel electrodes and electrocatalysts for lithium ion batteries and direct methanol fuel cells. The physical and electrochemical properties of these nanocomposites were characterized by XRD, SEM, TEM, CV, charge/discharge measurements, etc. These novel carbon supported metal nanocomposites exhibit great potential to substitute the current used anodes materials for lithium ion batteries or electrocatalysts for direct methanol fuel cells.

Structure and magnetic properties of metal-carbon nanocomposites based on IR-pyrolized poly(acrylonitrile) and iron

Metal-carbon nanocomposites, namely, IR-pyrolized poly(acrylonitrile)/Fe (IR-PAN/Fe) were produced and studied. The structure and magnetic properties of the composites were studied for various synthesis conditions. Nanosized carbon objects (nanospheres) and iron carbide nanoparticles were revealed in the composite structure. The magnetic properties of the nanocomposites prepared at various IR-annealing temperatures were studied.

Metal-containing diamond-like nanocomposite temperature sensors

Metal-carbon nanocomposites are characterized by a number of unique properties, perspective for the various-type sensor applications. Presented experimental data of the conductivity of amorphous tungsten- and niobium-containing carbon-silicon nanocomposite films show the possibility to design the advanced wide-range temperature sensors, which are expected to possess the chemical stability, biocompatibility, mechanical, and other properties typical for this class of materials. The investigated films were deposited onto polycrystalline substrates using combination of Plasma Enhanced Chemical Vapor Deposition (PECVD) of siloxane vapors and DC magnetron co-sputtering of metal target. The conductivity σ of the films, measured using standard 4-probe technique in the temperature range 80-400K, is characterized by the gradual decrease with temperature. The experimental σ(T) dependences are well fitted by the power-law expression, σ(T) = σ0+aTn, where σ0, a, and n are the fitting parameters dependent on the type of metal and the value of metal concentration. The electron transport mechanism in the investigated amorphous metal-containing carbon-silicon nanocomposite films is discussed in the framework of the model of inelastic tunneling of electrons in amorphous insulators in the presence of the structural transformation in the carbon-silicon host matrix. The evolution of the structure of the carbon phase by metal concentration increase was studied by Raman spectroscopy.

METAL ATOMS IN CARBON NANOTUBES AND RELATED NANOPARTICLES

The paper reviews the present state of research in the field of metal-carbon nanocomposites and the interaction of metal atoms with graphitic structures. Metal crystals can be encapsulated within graphitic shells of cylindrical, spherical, or other geometry. Various chemical and physical production methods to generate metal containing carbon nanotubes and possible microscopic formation mechanisms are presented. In this context, the role of metals as catalysts in the formation of single-walled carbon nanotubes is discussed. The interaction of metal atoms with the graphitic lattice is of particular interest. In situ electron microscopy is used to study the behaviour of individual metal atoms in a graphitic lattice. Furthermore, novel nanostructures can be generated under electron irradiation. Finally, an overview of theoretical studies using molecular dynamics and tight binding calculations of the carbon-metal interaction is given.

The scanning tunneling microscopy and scanning tunneling spectroscopy of amorphous carbon

The most important methods for studying the surface of amorphous diamond-like carbon are scanning tunneling microscopy and scanning tunneling spectroscopy. In this review, publications concerned with studying the topography and electronic properties of the surface of amorphous diamond-like carbon films using a tunneling microscope are considered; related publications devoted to the microprobe study of field emission from amorphous carbon and to the tunneling microscopy of metal-carbon nanocomposites are also reviewed.