Vanadium Carbide Nanoparticles Research Articles

Polyoxovanadate-derived Ir/VC/C nanocomposite for electrocatalytic hydrogen production

Polyoxovanadate was employed as precursor to design VC/C nanocomposite. The final product of Ir/VC/C nanocomposite was prepared after loading Ir nanoparticles from colloidal solution and such electrocatalyst delivered excellent performance for hydrogen evolution reaction in alkaline and acid conditions by promoting the H−OH bond cleavage. • Uniformly dispersed VC NPs were prepared from a decavanadate precursor. • The Ir/VC/C nanocomposite shows better HER electrocatalytic performance than the commercial Pt catalyst. • Water molecules are activated by the strong electron-withdrawing effect of VC and surface-adsorbed Ir NPs. Iridium nanoparticles (NPs) deliver excellent performance in electrocatalytic hydrogen evolution reaction (HER), but the high cost hinders their further application. Vanadium carbide (VC) is an inexpensive and stable material with a platinum-like d band center and suitable absorption/desorption capacity for active species in HER. However, there are few reports that combine the above two materials into a composited catalyst hitherto. In this work, we employed decavanadate as a precursor to prepare highly-dispersed VC NPs, which were further used as promoters for Ir NPs. The obtained Ir/VC/C nanocomposite exhibited low overpotentials and good stability under alkaline and acid conditions, even better than the commercial Pt/C. The water-splitting process is promoted by the synergistic effect between the strong electron-withdrawing nature of VC and the surface hydrogen adsorption of Ir NPs. This work demonstrates that VC can remarkably improve the electrocatalytic performance of Ir NPs, and the Ir/VC/C nanocomposite is a promising and alternative electrocatalyst for HER.

Scalable fabrication of vanadium carbide/graphene electrodes for high-energy and flexible microsupercapacitors

In-plane microsupercapacitors (MSCs) hold great promise for microscale power source, due to the extremely high power density and ultra-long cycling life. However, the scalable fabrication of flexible MSCs with high energy density remains a major challenge. Here, we demonstrate the fabrication of vanadium carbide/reduced graphene oxide (V8C7/rGO) MSCs via laser scribing on ammonium metavanadate/graphene oxide (NH4VO3/GO) films, prepared by efficient continuous centrifugal casting method. More than 20 MSCs can be produced on a flexible substrate in 30 min, showing the potential for scalable fabrication. The laser-induced V8C7/rGO shows highly porous microstructure, where vanadium carbide nanoparticles are in-situ synthesized and uniformly decorated on graphene nanosheets. The well-defined architecture endows V8C7/rGO MSCs with excellent electrochemical performance. The areal capacitance of these devices can be as high as 49.5 mF cm−2, 11 times higher than that of rGO MSCs. The volumetric energy density and power density can be up to 3.4 mWh cm−3 and 401 mW cm−3, respectively, competitive with the commercially available energy storage devices and most reported MSCs. In addition, V8C7/rGO MSCs show excellent flexibility and integrability, as well as long cycling life, promising for practical applications.

Processing, microstructure and mechanical properties of Ni1.5CoFeCu0.8Al0.2V0.5 high entropy alloy matrix composites reinforced by in-situ synthesized vanadium carbides

Three in-situ synthesized vanadium carbides (in the volume fraction of 5%, 10% and 15%, respectively) reinforced Ni1·5CoFeCu0·8Al0·2V0.5 high entropy alloy (HEA) matrix composites were prepared by adding V and C in equal molar ratio using mechanical alloying and spark plasma sintering techniques. The formation and evolution of vanadium carbide reinforcements as well as their influences on the microstructure and mechanical properties of HEA matrix composite were investigated intensively. The results show that after milling of 70 h part of V and C from raw materials reacted incompletely through the mechanism of solid-state diffusion at the interface, resulting in the generation of V2C and [VC] in the composite powders. Subsequently, owing to the enhanced atomic diffusion during sintering V2C in the intermediate state was further carbonized into [VC] and partial [VC] was transformed to ordered V8C7 in the consolidated composites. The addition of 5 vol% and 10 vol% vanadium carbides resulted in the significant refinement of grains in the HEA matrix due to the grain boundary pinning effect induced by in-situ generated fine reinforcements. However, grains of the composite containing 15 vol% vanadium carbides are coarser than those of the base HEA due to the serious agglomeration of in-situ synthesized reinforcements. With the increase of vanadium carbides content, mechanical properties of the HEA matrix composite do not change monotonously. The composite reinforced by 10 vol% vanadium carbides performs best among the three and its yield strengths at room temperature, 500 °C, 600 °C and 700 °C are about 1.2, 1.4, 2 and 2.5 times, respectively, than those of the base HEA. The improvement in mechanical properties of composite are attributed to grain boundary strengthening and dispersion strengthening caused by in-situ synthesized vanadium carbide nanoparticles.

Self-Supported Vanadium Carbide by an Electropolymerization-Assisted Method for Efficient Hydrogen Production.

Exploring efficient electrodes toward the hydrogen evolution reaction (HER) remains a great challenge for large-scale hydrogen production. Owing to its high earth abundance, low electrical resistivity, and small density, vanadium carbide (VC) is a promising HER electrode candidate but has been rarely explored. In this work, VC nanoparticles encased in nitrogen-doped carbon matrix on carbon cloth (VC@NC/CC) were prepared as a binder-free HER cathode through electropolymerization followed by carbothermal reduction under argon. In the first step of pyrrole electropolymerization, the VO4 3- anions, serving as both vanadium source and supporting electrolyte, were homogeneously incorporated in the positively charged polypyrrole (PPy) framework through coulombic interaction. The electropolymerization was effective for preparation of binder-free metal carbide materials with various polymer monomers as carbon source, which was favorable for the high performance of metal carbide electrodes. During the pyrolysis process, the polymeric hybrids were converted to VC nanoparticles and entrapped in the PPy-derived N-doped carbon matrix. The optimized VC@NC/CC electrode exhibited high catalytic activity and durability in both acidic and alkaline media. The use of VC for efficient HER is remarkable, and such a convenient and versatile electropolymerization-assisted method is appealing for the fabrication of industrially scalable large-area VC electrodes for efficient hydrogen production.

Vanadium carbide nanoparticles incorporation in carbon nanofibers for room-temperature sodium sulfur batteries: Confining, trapping, and catalyzing

Room-temperature sodium-sulfur (RT Na-S) batteries have aroused extensive interest from researchers owing to the high theoretical volumetric energy density, nontoxicity and low-cost. However, poor conductivity of sulfur and high solubility of polysulfides in electrolyte are two major challenges for the practical application of the RT Na-S batteries. Herein, we report a three dimensional self-supported structure with Vanadium carbide (VC) nanoparticles embeddedin carbon nanofibers for RT Na-S batteries. Finally, the VC-CNFs@S electrode displays a reversible capacity of 379 mAh g−1 after 2000 cycles at 0.5C with a high capacity retention of 96.2%. Such outstanding electrochemical property is ascribed to the “confining – trapping – catalyzing” effect of VC-CNFs structure.

Hydrogen diffusion and trapping in V-microalloyed mooring chain steels

In this paper, three different microalloyed steels were designed to investigate the effect of V on hydrogen trapping and diffusion in mooring chain steel by electrochemical hydrogen permeation technique and Atom Probe Tomography (APT). According to the results, the addition of V in mooring chain steel can decrease the hydrogen diffusion coefficient, and the calculated activation energy for hydrogen revealed that vanadium carbide nanoparticles in steel can trap hydrogen effectively.

Vanadium Carbide Based Composite for High Performance Oxygen Reduction Reaction and Lithium Ion Batteries

The fabrication of novel multifunctional nanohybrids of vanadium carbide nanoparticles decorated reduced graphene oxide (RGO) is presented. The resulting composite exhibits large specific surface area and enhanced electrical conductivity, which can effectively increase the number of active sites and facilitate the charge transport. As a result, the V8C7/RGO electrode demonstrates comparable oxygen reduction reaction (ORR) catalytic activity with commercial Pt/C in terms of high electron transfer number, high current density and good durability. In particular, the onset potential of the as-prepared sample is only about 50 mV lower than that of the Pt/C catalyst. When the V8C7/RGO was evaluated as anode material for lithium ion batteries (LIBs), the V8C7/RGO nanocomposite shows a high reversible specific capacity (1st-cycle charge capacity of 995.8 mAh g−1 at 0.1 A g−1), a long cycling life (specific capacity of 349.6 mAh g−1 after 400 cycles at 10 A g−1), and an excellent rate performance (e. g. specific capacity of 277.2 mAh g−1 at 10 A g−1).

Vanadium carbide nanoparticles encapsulated in graphitic carbon network nanosheets: A high-efficiency electrocatalyst for hydrogen evolution reaction

A hierarchical nanosheet structure comprising isolated vanadium carbide nanoparticles encapsulated in a highly conductive mesoporous graphitic carbon network (VC-NS) is synthesized by a hydrothermal reaction and subsequent low-temperature magnesium thermic reaction. It has a large specific surface area and boasts highly efficient HER (hydrogen evolution reaction) activity such as very small overpotential, fast proton discharge kinetics, and excellent durability. The small Tafel slope of 56 mV dec−1 with a low overpotential of only 98 mV at 10mAcm−2 is quite close to that of the commercial 20% Pt/C catalyst. The excellent durability is indicated by the overpotential shift of only 10 mV after 10000 cyclic voltammetric cycles at a current density of 80mAcm−2. The high-performance precious-metal-free electrocatalyst is promising in HER and related energy generation applications.

Microstructural evolution, coarsening behavior of vanadium carbide and mechanical properties in the simulated heat-affected zone of modified medium manganese steel

The microstructural evolution, coarsening behavior of vanadium carbide (VC) and the mechanical properties of the simulated heat-affected zone (HAZ) of modified medium manganese steel (MMMS) were investigated as a function of peak temperature (Tp). Cementite precipitated at the grain boundary at 650°C–850°C, and the formation of a carbide network was not observed even at a higher Tp. The nucleation of VC precipitates occurred at a Tp of 650°C, and with increasing Tp, they grew at a rate that is greater than the theoretical value calculated according to the volume diffusion-controlled mechanism. However, coarse VC particles disappeared when the Tp reached 1250°C, and VC particles less than 2.0nm precipitated during cooling. The lattice parameter of austenite in the simulated HAZ first decreased with VC precipitation, then increased with VC dissolution and finally decreased again at 1250°C due to VC regeneration. Meanwhile, the formation of the VC nanoparticles increased the microhardness and tensile strength of the simulated HAZ.

Synthesis and photoluminescence properties of in-situ synthesized core–shell (m-VC@C) nanocomposites

Core–shell structure of mesoporous vanadium carbide nanoparticles encapsulated with carbon layers (m-VC@C) have been successfully synthesized by single-step, non-toxic and economical route. The texture, morphology and optical properties of the obtained product were studied by various characterization techniques. X-ray diffraction analysis shows that the optimization of reaction time facilitates the reduction process of the precursor and hence carburization. High resolution transmission electron microscopy analysis reveals that the synthesized vanadium carbide nanoparticles with average size of 30–40 nm were encapsulated in 20–22 layers of carbon. High thermal stability of the obtained product was found at high temperatures. N2 adsorption/desorption isotherm shows that the sample has a specific surface area of 62.4560 m2/g and pore volume 0.30 cm3/g with pore size in the mesoporous range (3–14 nm). The formation mechanism of carbide and carbon layer has been explained on the basis of experimental results. The as-obtained m-VC@C shows good absorption and luminescence properties. Its application in photocatalytic degradation of the organic pollutant has been studied.

Kinetics and crystal geometry of precipitation of vanadium carbides at the interphase boundary upon pearlitic transformation of steel

In high-carbon vanadium steel, the temperature range (600°C and higher) and time (∼0.1 s) of the formation of vanadium carbide particles 5–10 nm in size at the interphase boundary upon pearlitic transformation have been established. Their distribution in ferrite has been subjected to crystallographic analysis with allowance for the habit of cementite plates. Based on the results of this analysis, a model has been suggested for the volume distribution of vanadium carbide nanoparticles in ferrite interlayers between cementite plates of the pearlitic colony in the form of successive (periodic) corrugated spherical surfaces with a period of ∼20 nm. This particle distribution is determined by the shape of the moving pearlite-austenite interphase boundary and by the direction of growth of the pearlitic colony.

Synthesis and Analysis of High Surface Area Vanadium Carbide Nanoparticles

Vanadium carbide is known for its applications due to extreme hardness and high melting point. In this present work, vanadium carbide nanoparticles have been synthesized in a specially designed stainless steel autoclave by solvothermal route using vanadium pentoxide (V2O5) as precursor along with a hydrocarbon acetone (C3H6O) in the presence of reducing agent magnesium (Mg). The optimization of reaction time was studied at constant temperature of 800oC. The product powder was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM) and Brunauer – Emmett – Teller (BET) techniques. The results indicate that the product was vanadium carbide having particle size of about 30 nm with high surface area.

Ion‐Exchange‐Assisted Synthesis of Pt‐VC Nanoparticles Loaded on Graphitized Carbon: A High‐Performance Nanocomposite Electrocatalyst for Oxygen‐Reduction Reactions

Carbide-based electrocatalysts are superior to traditional carbon-based electrocatalysts, such as the commercial Pt/C electrocatalysts, in terms of their mass activity and stability. Herein, we report a general approach for the preparation of a nanocomposite electrocatalyst of platinum and vanadium carbide nanoparticles that are loaded onto graphitized carbon. The nanocomposite, which was prepared in a localized and controlled fashion by using an ion-exchange process, was an effective electrocatalyst for the oxygen-reduction reaction (ORR). Both the stability and the durability of the Pt-VC/GC nanocomposite catalyst could be enhanced compared with the state-of-the-art Pt/C. This approach can be extended to the synthesis of other metal-carbide-based nanocatalysts. Moreover, this straightforward synthesis of high-performance composite nanocatalysts can be scaled up to meet the requirements for mass production.

Synthesis and characterization of vanadium carbide nanoparticles by thermal refluxing-derived precursors

Vanadium carbide (VC) nanoparticles were synthesized by a novel refluxing-derived precursor. The organic/inorganic hybrid precursor was prepared by a two-step refluxing method using hydrous V2O5 as vanadium source and n-dodecane as carbon source. The reaction process, phase composition, microstructure, and element composition of VC were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). The results showed that VC nanoparticles could be obtained at 900 °C for 1 h in flowing Argon (Ar), which was much lower than those of conventional synthesis methods. XRD pattern indicated that the product was face-centered cubic VC with a lattice constant a = 4.1626 A and average crystallite size of 22.3 nm. Raman spectra indicated that long time refluxing resulted in alkane dehydrogenation and the formation of coke on V2O5 nanoparticles. XPS investigations confirmed oxygen presence in VC lattice. Electron microscopy photographs showed the particle size ranged from 20 to 50 nm. All these results confirmed that the two-step refluxing method was a novel and feasible method to synthesize VC nanoparticles.