Showing papers on "Carbide published in 2015"
TL;DR: In this article, the synthesis of quasi-two-dimensional carbide (Ti 3 C 2 ), with the name of MXene, by immersing Ti 3 AlC 2 in 40% or 49% hydrofluoric acid (HF) at 0, 15, or 60°C was investigated.
Abstract: We investigated the synthesis of quasi-two-dimensional carbide (Ti 3 C 2 ), with the name of MXene, by immersing Ti 3 AlC 2 in 40% or 49% hydrofluoric acid (HF) at 0 °C, 15 °C or 60 °C. The influences of time, temperature, and source of Ti 3 AlC 2 on the synthesis were researched. It was found that Ti 3 C 2 synthesized from pressureless synthesized Ti 3 AlC 2 was highly oriented compared to that from hot-pressed Ti 3 AlC 2 . As-synthesized Ti 3 C 2 could be further exfoliated by intercalation with urea, dimethylsulfoxide or ammonia. From the results of thermogravimetry and differential scanning calorimetry, Ti 3 C 2 MXene with F/OH termination was found to be stable in argon atmosphere at temperature up to 800 °C. In oxygen atmosphere, at 200 °C, parts of MXene layers were oxidized to obtain an interesting structure: anatase nano-crystals were evenly distributed on 2D Ti 3 C 2 layers. At 1000 °C, MXene layers were completely oxidized and anatase phase fully transformed to rutile in oxygen atmosphere.
520 citations
TL;DR: Meso-/macroporous nitrogen-doped carbon architectures with iron carbide encapsulated in graphitic layers are fabricated by a facile approach and are the most promising alternative to a Pt catalyst for use in electrochemical energy devices.
Abstract: Meso-/macroporous nitrogen-doped carbon architectures with iron carbide encapsulated in graphitic layers are fabricated by a facile approach. This efficient and robust material exhibits superior catalytic performance toward the oxygen reduction reaction in both acidic and alkaline solutions and is the most promising alternative to a Pt catalyst for use in electrochemical energy devices.
507 citations
TL;DR: The field of supercapacitors (electrochemical capacitors) is constantly evolving and the global motivation is to create devices that possess a significant energy density without compromising the power density as mentioned in this paper.
Abstract: The field of supercapacitors (electrochemical capacitors) is constantly evolving. The global motivation is to create devices that possess a significant energy density without compromising the power density. To achieve this goal, new materials must be discovered and complex electrode architectures developed.
463 citations
TL;DR: The transition metal carbide nanocrystalline M3C-GNRs catalyst exhibits superior enhanced electrocatalystic activity for oxygen reduction reaction (ORR), including low Tafel slope, positive onset potential, high electron transfer number, and long-term stability.
Abstract: Transition metal carbide nanocrystalline M3C (M: Fe, Co, Ni) encapsulated in graphitic shells supported with vertically aligned graphene nanoribbons (VA-GNRs) are synthesized through a hot filament chemical vapor deposition (HF-CVD) method. The process is based on the direct reaction between iron group metals (Fe, Co, Ni) and carbon source, which are facilely get high purity carbide nanocrystals (NCs) and avoid any other impurity at relatively low temperature. The M3C-GNRs exhibit superior enhanced electrocatalystic activity for oxygen reduction reaction (ORR), including low Tafel slope (39, 41, and 45 mV dec–1 for Fe3C-GNRs, Co3C-GNRs, and Ni3C-GNRs, respectively), positive onset potential (∼0.8 V), high electron transfer number (∼4), and long-term stability (no obvious drop after 20 000 s test). The M3C-GNRs catalyst also exhibits remarkable hydrogen evolution reaction (HER) activity with a large cathodic current density of 166.6, 79.6, and 116.4 mA cm–2 at an overpotential of 200 mV, low onset overpote...
431 citations
TL;DR: In this paper, a novel bimetallic carbide nanostructure consisting of Mo2C and WC is synthesized for hydrogen evolution reaction (HER) and the residual carbon contributes positively to the activity, besides its role of protecting carbide from oxidation.
Abstract: Development of nonnoble metal catalysts for hydrogen evolution reaction (HER) is critical to enable an efficient production of hydrogen at low cost and large scale. In this work, a novel bimetallic carbide nanostructure consisting of Mo2C and WC is synthesized. Based on a highly conductive WC backbone, nanosized Mo2C particles are integrated onto WC, forming a well-defined and highly robust nanowire structure. More importantly, it is found that electrochemical activation can partially remove surface carbon and activate the catalyst by changing its surface hydrophilicity. As a result, the residual carbon contributes positively to the activity, besides its role of protecting carbide from oxidation. Benefiting from the structure, the catalyst achieves high activity, stable electrolysis towards HER.
312 citations
TL;DR: In this article, the synthesis of a two-dimensional transition metal carbide, Mo2C (MXene), obtained by immersing Mo2Ga2C thin films in hydrofluoric acid was reported.
296 citations
TL;DR: The unique properties of 2D materials, such as graphene or transition metal dichalcogenides, have been attracting much attention in the past decade, and metallically conductive and even superconducting transition metal carbides are entering the game.
Abstract: The unique properties of 2D materials, such as graphene or transition metal dichalcogenides, have been attracting much attention in the past decade. Now, metallically conductive and even superconducting transition metal carbides are entering the game.
266 citations
TL;DR: In this paper, a wide range of magnetic iron-doped molybdenum carbide (Mo2-xFexC) nanomaterials were synthesized by a unique amine-metal oxide composite method.
Abstract: Molybdenum-based materials have been widely investigated recently as promising alternatives to platinum for catalyzing the hydrogen evolution reaction (HER). Molybdenum carbide is one of the most studied transition-metal carbides because of its cheap price, high abundance, good conductivity, and catalytic activity. In order to further improve the catalytic activity of molybdenum carbide, some modifications have been applied. In this paper, a wide range of magnetic iron-doped molybdenum carbide (Mo2–xFexC) nanomaterials were synthesized by a unique amine–metal oxide composite method. The amount of iron dopants was controlled by setting different iron/molybdenum ratios in the precursors. Iron-doped molybdenum carbide nanomaterials were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, Raman microscopy, and X-ray photoelectron spectroscopy. Electrocatalytic HER tests were used to demonstrate the catalytic activity upon addition ...
228 citations
TL;DR: In this paper, the formation of the stable cobalt carbide and the Co-Co2C interface are found to be essential for the observed reactivity, and they synthesized successfully cobalt metal-car carbide (Co-Co 2C) catalysts, which present remarkable activity and selectivity for high alpha-alcohols via the Fischer-Tropsch reaction.
Abstract: Utilization of nonprecious transition metals for high alcohols synthesis is of a great importance in heterogeneous catalysis. We synthesized successfully cobalt metal-carbide (Co–Co2C) catalysts, which present remarkable activity and selectivity for high alpha-alcohols via the Fischer–Tropsch reaction. The formation of the stable cobalt carbide and the Co–Co2C interface are found to be essential for the observed reactivity. Density functional theory calculations show that Co2C is highly efficient for CO nondissociative adsorption, behaving as noble-metal-like, whereas the Co metal is highly active for CO dissociative adsorption and the subsequent carbon-chain growth. The interface between the cobalt metal and its carbide phase, as well as the dual sites available at the interface for facile CO insertion to hydrocarbon, could be used to rationalize the design of the nonprecious transition metal catalysts for the oxygenates in syngas conversion.
206 citations
TL;DR: In this article, the effect of mass loading on the electrochemical properties of Ti3C2 electrodes was studied by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and impedance spectrum test.
183 citations
TL;DR: In this article, a modified model for predicting the carbon concentration after the partitioning step was proposed to explain the experimental results by assuming carbon equilibria between austenite, ferrite and cementite under a constrained condition.
TL;DR: In this article, a new CO2 sorbent was prepared from carbide slag, aluminum nitrate hydrate and glycerol water solution by combustion synthesis method by combustion method.
TL;DR: In this article, a model system for solid acid membrane electrolyser cells was presented, where metal carbide coated wires prepared by a two-step oxidation-carburization reaction of the metal wire surfaces were used as electrodes and allowed the measurement of the intrinsic catalytic properties of different transition metal carbides in direct comparison to Pt at 260-°C.
TL;DR: In this article, the method of preparation and study results of metal matrix composite coatings (MMC coating) in the system of Stellite-6 and tungsten carbides were investigated.
Abstract: The paper presents the method of preparation and study results of metal matrix composite coatings (MMC coating) in the system of Stellite-6 and tungsten carbides. Changes in microstructure, corrosion resistance, microhardness, phase and chemical composition as well as surface conditions were investigated. Stellite-6/WC MMC coatings were prepared by laser cladding technology using a 1 kW continuous wave Yb:YAG disk laser with a powder feeding system. Two different powder mixtures containing 30% and 60% of WC and three different values of laser beam power were used. It was found that increasing WC values caused an increase in microhardness on the cross-section of the produced coating in comparison to the substrate. Depending on the laser beam power, the coatings produced with 30% WC achieved microhardness in the range from about 350 HV0.05 (700 W) to about 680 HV0.05 (550 W). Twice as large amount of WC particles in the powder mixture resulted in increase of microhardness from about 700 HV0.05 (700 W) to about 1500 HV0.05 (550 W). In the coating M7C3, M6C and M23C6 carbides were identified by an X-ray diffraction method. Special attention was given to bondings between carbide particles and metal matrix, which had a characteristic microstructure. A reduction of corrosion resistance with increasing WC content in coating was also discovered.
TL;DR: In this article, high surface area nano-dimensional carbides of nine transition metals in group IV-VI have been synthesized using a salt flux method and uniformity was maintained throughout the investigation, from synthesis method to electrochemical tests, so that a comparison can be made for the various carbides for their catalytic activities towards hydrogen evolution reaction and oxygen reduction reaction (ORR).
Abstract: High surface area nano dimensional carbides of nine transition metals in group IV–VI have been synthesized using a salt flux method. Uniformity was maintained throughout the investigation, from synthesis method to electrochemical tests, so that a comparison can be made for the various carbides for their catalytic activities towards hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Catalytic activities are dependent on synthesis method which determines the properties of the catalyst, and electrochemical conditions. Maintaining uniformity throughout the investigation allows for a more balanced comparison of a family of materials. Activity of all nine carbides show increased HER activity compared to bare glassy carbon working electrode. Mo2C, WC, and V8C7 show particularly enhanced HER activity. Similarly, Mo2C, Cr3C2, and V8C7 have significant ORR activities. Using a wet impregnation method, dispersed platinum nanoparticles ranging between 3 and 5 nm were successfully deposited on the carbides. The Pt deposited carbides have as much as three times higher HER activity and four times higher ORR activity compared to commercially available Pt/C catalyst, and show enhanced stability under fuel cell conditions.
TL;DR: In this article, an extensive presence of intermetallic phases was observed in the cast products, as a result of both the inoculation by K 2 TiF 6 and the intensive reactivity of the carbides with the molten matrix.
TL;DR: In this article, a new layered ternary carbide, Mo2TiAlC2, was synthesized by heating an elemental mixture at 1600 degrees C for 4 h under an Ar flow.
TL;DR: The synthesis of carbon-coated cobalt-tungsten carbide nanoparticles that have proven to be efficient noble metal-free electrocatalysts for alkaline Her are reported, offering the exciting possibility of using carbon-armoured metal carbides for an efficient alkaline HER.
Abstract: The hydrogen evolution reaction (HER) is one of the two important half reactions in current water-alkali and chlor-alkali electrolyzers. To make this reaction energy-efficient, development of highly active and durable catalytic materials in an alkaline environment is required. Herein we report the synthesis of carbon-coated cobalt–tungsten carbide nanoparticles that have proven to be efficient noble metal-free electrocatalysts for alkaline HER. The catalyst affords a current density of 10 mA cm−2 at a low overpotential of 73 mV, which is close to that (33 mV) required by Pt/C to obtain the same current density. In addition, this catalyst operates stably at large current densities (>30 mA cm−1) for as long as 18 h, and gives nearly 100% Faradaic yield during alkaline HER. The excellent catalytic performance (activity and stability) of this nanocomposite material is attributed to the cooperative effect between nanosized bimetallic carbide and the carbon protection layer outside the metal carbide. The results presented herein offer the exciting possibility of using carbon-armoured metal carbides for an efficient alkaline HER, although pristine metal carbides are not, generally, chemically stable enough under such strong alkaline conditions.
TL;DR: In this article, the authors demonstrate that the size of the carbide particle is a critical factor for the activity and stability of carbon supported tungsten-and molybdenum carbide catalysts in (hydro-)deoxygenation reactions.
TL;DR: In this article, the mechanical properties of hot pressed zirconium diboride-silicon carbide-boron carbide (ZrB2-SiC-B4C) ceramics were characterized from room temperature up to 2200°C in an argon atmosphere.
Abstract: The mechanical properties of hot pressed zirconium diboride–silicon carbide–boron carbide (ZrB2–SiC–B4C) ceramics were characterized from room temperature up to 2200 °C in an argon atmosphere. The average ZrB2 grain size was 3.0 μm. The SiC particles segregated into clusters, and the largest clusters were >30 μm in diameter. The room temperature flexural strength was 700 MPa, decreasing to 540 MPa at 1800 °C and to 260 MPa at 2200 °C. The strength was controlled by the SiC cluster size up to 1800 °C. At higher temperatures, strength was controlled by formation of liquid phases, and precipitation of large BN and B–O–C–N inclusions. The mechanical behavior of these materials changes at ∼1800 °C, meaning that extrapolation of properties from lower temperatures is not accurate. Mechanical behavior in the ultra-high temperature regime was dominated by impurities and changes in microstructure. Therefore, the use of higher purity materials could lead to significant improvements in ultra-high temperature strength.
TL;DR: In this article, it was shown that carbon is the light element in the core of Earth's core and that a high-pressure phase of iron carbide modifies iron's elastic properties under inner core conditions.
Abstract: Earth’s core exhibits similar elastic properties to rubber. Experiments show that a high-pressure phase of iron carbide modifies iron’s elastic properties under inner-core conditions, suggesting that carbon is the light element in the core.
TL;DR: In this paper, the authors investigated the hydrotreatment of liquefied lignocellulosic biomass at 300°C under the total pressure of 8MPa in a slurry reactor over unsupported molybdenum (disulphide, dioxide, carbide and carbide) and tungsten catalysts.
Abstract: Hydrotreatment of liquefied lignocellulosic biomass was investigated at 300 °C under the total pressure of 8 MPa in a slurry reactor over unsupported molybdenum (disulphide, dioxide and carbide) and tungsten (disulphide) catalysts. Novel nanostructured urchin-like MoS2 and inorganic-fullerene MoS2 interconnected with carbon materials were synthetized and tested, while the influence of metal variation and the sulphide replacement with carbide or oxide was also investigated by using commercially available MoS2, Mo2C, MoO2 and WS2. Catalysts were structurally characterised by field-emission scanning (SEM) and high-resolution transmission (HRTEM) electron microscopies, energy-dispersive X-ray (EDX) and Raman spectroscopies, as well as X-ray diffraction (XRD). The hydrodeoxygenation (HDO), decarbonylation, decarboxylation and hydrocracking kinetics of depolymerised cellulose, hemicellulose and lignin were determined according to the transformation of their functional groups in liquid phase, and the corresponding gaseous products by an innovative lumped kinetic model based on Fourier transform infrared spectroscopy. Unsupported MoS2 catalysts showed high hydrogenolysis selectivity, the morphology clearly affecting its rate. A high HDO activity reflected in the mass balance and phase distribution of the upgraded liquid product by reducing tar residue and increasing the yield of oil phase with the gross calorific value of 38 MJ kg−1 and oxygen content below 8.5 wt%.
TL;DR: The discovery of a new hexagonal Mo2Ga2C phase, wherein two Ga layers – instead of one – are stacked in a simple hexagonal arrangement in between Mo2C layers is reported.
Patent•
06 Feb 2015
TL;DR: In this paper, a layer of silicon carbide can be provided under process conditions that employ one or more silicon-containing precursors that have one ormore silicon-hydrogen bonds and/or silicon-silicon bonds.
Abstract: Disclosed are methods and systems for providing silicon carbide films. A layer of silicon carbide can be provided under process conditions that employ one or more silicon-containing precursors that have one or more silicon-hydrogen bonds and/or silicon-silicon bonds. The silicon-containing precursors may also have one or more silicon-oxygen bonds and/or silicon-carbon bonds. One or more radical species in a substantially low energy state can react with the silicon-containing precursors to form the silicon carbide film. The one or more radical species can be formed in a remote plasma source.
TL;DR: In this article, two graphene-like carbide derived carbons (CDC-Gs) were produced by chlorination of SiC nanosheets obtained by magnesio-thermal reduction at moderate temperature of silica/graphene oxide nanocomposites.
TL;DR: Online mass spectrometry coupled with X-ray photoelectron spectroscopy unequivocally demonstrates that lithium peroxide is simultaneously oxidized together with the Li(x)MoO3-passivated conductive interface formed on the carbide, owing to their close redox potentials.
Abstract: The development of nonaqueous Li-oxygen batteries, which relies on the reversible reaction of Li + O2 to give lithium peroxide (Li2O2), is challenged by several factors, not the least being the high charging voltage that results when carbon is typically employed as the cathode host. We report here on the remarkably low 3.2 V potential for Li2O2 oxidation on a passivated nanostructured metallic carbide (Mo2C), carbon-free cathode host. Online mass spectrometry coupled with X-ray photoelectron spectroscopy unequivocally demonstrates that lithium peroxide is simultaneously oxidized together with the Li(x)MoO3-passivated conductive interface formed on the carbide, owing to their close redox potentials. The process rejuvenates the surface on each cycle upon electrochemical charge by releasing Li(x)MoO3 into the electrolyte, explaining the low charging potential.
TL;DR: In this article, the authors derived elastic constants, electronic density of states, and activation energies for carbon vacancy migration as a function of carbon content to elucidate their effect on the hardening responses.
Abstract: For group VB transition metal carbides, as compared to group IVB carbides, an anomalous rise in hardness occurs for substoichiometric carbon concentrations as compared to the stoichiometric monocarbides. Here we report the computationally derived elastic constants, electronic density of states, and activation energies for carbon vacancy migration as a function of carbon content to elucidate their effect on the hardening responses. The changes in elastic properties with respect to carbon vacancy concentration show similar behaviors of elastic softening and decreasing hardness for all of the cubic carbides. The consistent trends of vacancy diffusion energy barriers between all of the group IVB and VB transition metal carbides also suggests that carbon diffusion may not be a significant contributor to the reported hardness differences. Consequently, we propose that the anomalous hardening for substoichiometric behavior is a competition between elastic constant softening and a microstructural-based effect, i.e. domain hardening, that is present in group VB carbides but not in group IVB carbides.
TL;DR: In this article, Mossbauer effect spectroscopy (MES) was used to characterize steel microstructures with martensite and austenite that exhibit promising property combinations for third generation advanced high strength steels.
TL;DR: In this article, the effect of tempering temperature on the microstructure and electrochemical behavior of 13.5-wt. Cr-type martensitic stainless steel (MMS) in 3.5% NaCl aqueous solution was studied.
Patent•
26 Jun 2015TL;DR: In this paper, the methods of forming thin-film structures including metal carbide material, and structures and devices including the metal-carbide material are disclosed, which enables tuning of various metal-carbide material properties, including resistivity, current leakage, and work function.
Abstract: Methods of forming thin-film structures including metal carbide material, and structures and devices including the metal carbide material are disclosed. Exemplary structures include metal carbide material formed using two or more different processes (e.g., two or more different precursors), which enables tuning of various metal carbide material properties, including resistivity, current leakage, and work function.