Transition Metal Carbide Nanoparticles Research Articles

Decoration of transition metal carbide nanoparticles on reduced graphene oxide for the efficient bulk heterojunction organic photovoltaics

Herein, we fabricated the bulk heterojunction organic photovoltaics (OPV) using the different hybrid composites doped novel combination of PBDB-T:PCBM/hybrid-nanostructures with the architecture of ITO/HTL/active-layer/LiF/Al. Structural and morphological characteristics were evidently established the formation of W2C@rGO and Mo2C@rGO composites by the simple chemical reduction process. The different concentrations of prepared nanocomposites were doped with polymer PBDB-T:PCBM matrix to modify the active layer properties in the OPV devices. The Mo2C@rGO and W2C@rGO (10 vol%) composites using tuned active realized the improved power conversion efficiency (PCE) of 6.98 and 6.84%, respectively which is quite high compared to the pure PBDB-T: PCBM active layer (PCE = 5.61%) and bare rGO (6.66%), Mo2C (6.43%) and W2C (6.20%) outcomes. The procured results explored that the W2C@rGO and Mo2C@rGO hybrid incorporated active layers facilitate the swift charge transport and extraction possibility to achieve the high efficiency photovoltaic devices.

Room Temperature Ion Beam Synthesis of Ultra-Fine Molybdenum Carbide Nanoparticles: Toward a Scalable Fabrication Route for Earth-Abundant Electrodes.

Molybdenum carbides are promising low-cost electrocatalysts for electrolyzers, fuel cells, and batteries. However, synthesis of ultrafine, phase-pure carbide nanoparticles (diameter<5nm) with large surface areas remains challenging due to uncontrollable agglomeration that occurs during traditional high temperature syntheses. This work presents a scalable, physical approach to synthesize molybdenum carbide nanoparticles at room temperature by ion implantation. By tuning the implantation conditions, various molybdenum carbide phases, stoichiometries, and nanoparticle sizes can be accessed. For instance, molybdenum ion implantation into glassy carbon at 30keV energy and to a fluence of 9×1016 atcm-2 yields a surface η-Mo3 C2 with a particle diameter of (10±1)nm. Molybdenum implantation into glassy carbon at 60keV to a fluence of 6×1016 atcm-2 yields a buried layer of ultrafine γ'-MoC/η-MoC nanoparticles. Carbon ion implantation at 20keV into a molybdenum thin film produces a 40nm thick layer primarily composed of β-Mo2 C. The formation of nanoparticles in each molybdenum carbide phase is explained based on the Mo-C phase diagram and Monte-Carlo simulations of ion-solid interactions invoking the thermal spike model. The approaches presented are widely applicable for synthesis of other transition metal carbide nanoparticles as well.

Transition Metal Carbide Core/Shell Nanoparticles by Ultra-Short Laser Ablation in Liquid.

Transition metal carbide nanoparticles are a class of technological interesting materials with a wide range of applications. Among metal carbides, tantalum carbides have good compatibility with the biological environment while molybdenum carbides are used as catalyst in electrochemical reactions. Laser ablation of bulk transition metal targets in some liquids is here reported and laser ablation in organic solvents is used as simple synthetic strategy for the production of carbide nanostructures. Herein, the nanoparticles produced by ultra-short laser ablation of tantalum and molybdenum in water, acetone, ethanol and toluene have been characterized by TEM, XRD and XPS analysis. The combined effect of metal and solvent chemical and physical properties on the composition of the nanomaterials obtained has been pointed out. In particular, the different reactivity of Ta and Mo with respect to oxidizing species determines the composition of particles obtained in water, on the other hand the organic solvents decomposition allows to obtain transition metal carbide (TMC) nanoparticles. The observed carbonaceous shell formed on TMC allows to protect the particle’s carbidic core and to improve and tailor the applications of these nanomaterials.

Facile Synthesis of Uniform Metal Carbide Nanoparticles from Metal-Organic Frameworks by Laser Metallurgy.

We report the fast and efficient conversion of metal-organic frameworks (MOFs) to phase pure transition-metal carbide (TMC) nanoparticles with uniform size using laser as the energy source, consuming only 6 W power. Nanoparticles of HfC, ZrC, TiC, V8C7, α-MoC, Cr3C2, and FeCx with homogeneous sizes (varied between 6 and 20 nm) were successfully produced, among which HfC and ZrC nanoparticles were obtained, for the first time, with sizes less than 10 nm and in the pure phase. This method was operated directly in air, in stark contrast to traditional furnace heating and laser spray methods, where a protective atmosphere is required. The use of MOFs allowed us to precisely tune the composition of TMC nanoparticles by dialing in the right type and desirable amounts of organic linkers. FeCx nanoparticles doped with various percentages of nitrogen atoms were synthesized for the Fischer-Tropsch reaction without any pretreatment or activation. Extremely high iron time of yield (FTY) values were observed, 415 and 550 μmol gFe-1 s-1 (with addition of K), in a 40 h test without any decay in performance. A high olefin to paraffin ratio was achieved for C2 to C11 products, where the ratio for C3 was higher than 10.

Anion-Induced Size Selection of β-Mo2C Supported on Nitrogen-Doped Carbon Nanotubes for Electrocatalytic Hydrogen Evolution

Molybdenum carbide materials are considered to be promising hydrogen evolution reaction (HER) electrocatalysts due to their similar electronic structures and catalytic activities to Pt-based catalysts. Here, we report a facile synthesis of β-Mo2C nanoparticles supported on nitrogen-doped carbon nanotubes (Mo2C/N–C) through a one-step carbonization of Mo-containing anion-doped polyaniline nanotubes. It has been revealed that the size of the obtained Mo2C nanoparticles can be effectively tuned by applying different Mo-containing anions. With MoO42– from Na2MoO4, the as-prepared Mo2C/N–C(S) with ultrasmall (2–3 nm) Mo2C nanoparticles shows excellent electrocatalytic HER activity in acidic media, with an overpotential of 189 mV vs reversible hydrogen electrode (RHE) at a geometric current density of −10 mA cm–2 and a Tafel slope of 58 mV dec–1. This study opens up a new avenue for the size-controllable synthesis of transition metal carbide nanoparticles loaded on carbon supports for energy conversion applicat...

Ultrasmall Transition Metal Carbide Nanoparticles Encapsulated in N, S‐Doped Graphene for All‐pH Hydrogen Evolution

AbstractNoble metal free catalysts with high catalytic activity and excellent durability have long been pursued as alternatives of noble metal catalysts for renewable energy technologies. Herein, a facile one‐step method is reported to prepare ultrasmall transition metal carbide nanoparticles encapsulated in N, S‐doped graphene as noble‐metal‐free electrocatalysts for all‐pH hydrogen evolution, in which, high‐density MoCx (≈2.8 nm) or WCx (≈2.0 nm) nanoparticles are encapsulated in porous N, S‐doped graphene matrix. Both catalysts exhibit excellent hydrogen evolution reaction catalytic activity and durability in a wide range of pH from 0 to 14.

Durable and self-hydrating tungsten carbide-based composite polymer electrolyte membrane fuel cells

Proton conductivity of the polymer electrolyte membranes in fuel cells dictates their performance and requires sufficient water management. Here, we report a simple, scalable method to produce well-dispersed transition metal carbide nanoparticles. We demonstrate that these, when added as an additive to the proton exchange Nafion membrane, provide significant enhancement in power density and durability over 100 hours, surpassing both the baseline Nafion and platinum-containing recast Nafion membranes. Focused ion beam/scanning electron microscope tomography reveals the key membrane degradation mechanism. Density functional theory exposes that OH• and H• radicals adsorb more strongly from solution and reactions producing OH• are significantly more endergonic on tungsten carbide than on platinum. Consequently, tungsten carbide may be a promising catalyst in self-hydrating crossover gases while retarding desorption of and capturing free radicals formed at the cathode, resulting in enhanced membrane durability.

Wet-chemistry synthesis of cobalt carbide nanoparticles as highly active and stable electrocatalyst for hydrogen evolution reaction

Transition metal carbide (TMC) nanomaterials are promising alternatives to Pt, and are widely used as heterogeneous electrocatalysts for the electrochemical hydrogen evolution reaction (HER). In this work, a bromide-induced wet-chemistry strategy to synthesize Co2C nanoparticles (NPs) was developed. Such NPs exhibited high electrocatalytic activity (η = 181 mV for j = −10 mA·cm−2) and long-term stability (no obvious performance decrease after 4,000 cycles) for the HER. This study will pave the way for the design and fabrication of TMC NPs via a wet-chemistry method, and will have significant impacts on broader areas such as nanocatalysis and energy conversion.

Self-assembly of noble metal monolayers on transition metal carbide nanoparticle catalysts.

We demonstrated the self-assembly of transition metal carbide nanoparticles coated with atomically thin noble metal monolayers by carburizing mixtures of noble metal salts and transition metal oxides encapsulated in removable silica templates. This approach allows for control of the final core-shell architecture, including particle size, monolayer coverage, and heterometallic composition. Carbon-supported Ti(0.1)W(0.9)C nanoparticles coated with Pt or bimetallic PtRu monolayers exhibited enhanced resistance to sintering and CO poisoning, achieving an order of magnitude increase in specific activity over commercial catalysts for methanol electrooxidation after 10,000 cycles. These core-shell materials provide a new direction to reduce the loading, enhance the activity, and increase the stability of noble metal catalysts.

Tough core-shell catalysts

Catalysis One approach for increasing the activity of precious metals in catalysis is to coat them onto less expensive earth-abundant transition metal cores such as nickel, but often these structures alloy and deactivate during reactions. Hunt et al. synthesized several types of transition metal carbide nanoparticles coated with atomically thin precious-metal shells. Titanium-doped tungsten carbide nanoparticles with platinum-ruthenium shells were highly active for methanol electrooxidation, stable over 10,000 cycles, and resistant to CO deactivation. Science , this issue p. [974][1] [1]: /lookup/doi/10.1126/science.aad8471

An expeditious synthesis of early transition metal carbide nanoparticles on graphitic carbons.

An expeditious synthesis of metal carbide nanoparticles onto various carbon supports is demonstrated. The procedure is versatile and readily yields TiC, VC, Mo2C and W2C nanoparticles on different types of carbons. The reaction is initiated at room temperature and proceeds within seconds. This novel synthetic route paves the way for a large variety of metal carbide-carbon nanocomposites that may be implemented in emerging nanotechnology fields.

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 °C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 °C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 °C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

Route to transition metal carbide nanoparticles through cyanamide and metal oxides

We have designed an efficient route to the synthesis of transition metal carbide nanoparticles starting from an organic reagent cyanamide and transition metal oxides. Four technologically important metal carbide nanoparticles such as tungsten carbide, niobium carbide, tantalum carbide and vanadium carbide were synthesized successfully at moderate temperatures. It is found that cyanamide is an efficient carburization reagent and that the metal oxides are completely transmitted into the corresponding carbide nanoparticles. A possible mechanism is proposed to explain the results of the reaction between cyanamide and the metal oxides.

Synthesis of transition metal carbide nanoparticles through melamine and metal oxides

By a facile reaction route, we synthesized five technologically important transition metal carbide nanoparticles including cubic NbC, TaC, VC, hexagonal WC and MoC at relatively low temperatures. Here, in this rapid reaction process, we choose an organic reagent melamine and transition metal oxides as reaction precursors. The experimental results indicate that melamine is a highly efficient carburization reagent, and the metal oxides are completely converted into the corresponding carbides at relatively low temperatures. It is found that NbC, TaC, VC and WC are composed of fine nanoparticles having average size of 7, 13, 5 and 18 nm with a fairly narrow size distribution, respectively. The potential reaction mechanism between melamine and transition metal oxides and some new characteristics involved in this route are presented and discussed.