Molybdenum Carbide Nanoparticles Research Articles

Electrochemically synthesized N-doped molybdenum carbide nanoparticles for efficient catalysis of hydrogen evolution reaction

An efficient catalyst for hydrogen evolution reaction (HER), nanostructured nitrogen-doped molybdenum carbide (β-Mo2C), is reported in this work. The catalyst is prepared via a novel one-step solid-state electrolytic reduction of a mixture of MoS2 and polypyrrole nanofiber in molten CaCl2 at 850 °C. As comparison, a series of Mo2C materials are prepared by the method using different carbon precursors. TEM tests show that the as-prepared N-doped Mo2C is composed of near-spherical nanoparticles with the particle sizes of about 40–60 nm. Nitrogen-doping of Mo2C is shown to facilitate the exposure of active centers on the surface of the sample, concurrently modify the electronic property of Mo2C to promote electron transfer for HER. As a result, the optimized N-doped Mo2C (Mo2C-PPyF-1/1) displays a low onset potential of 78.1 mV for HER and a Tafel slope of 59.6 mV dec−1 in 0.5 M H2SO4, meanwhile exhibits high activity and stability in a broad pH range (0–14). Furthermore, the synthesis method is extended to fabricate other N-doped transition metal carbides (NbC, TaC and TiC). All of the N-doped materials exhibit significantly enhanced activity compared to the undoped ones.

A Reusable N-Doped-Carbon-Coated Mo2 C Composite Counter Electrode for High-Efficiency Dye-Sensitized Solar Cells.

The design and development of efficient and stable nonprecious-metal-based catalysts for counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) has received a great deal of attention. In this work, molybdenum carbide nanoparticles homogeneously distributed in a nitrogen-rich carbon matrix (Mo2 C@NC) have been synthesized from inexpensive raw materials (polyoxometalate and dicyandiamide) by a facile one-step solid-phase synthesis method. The novel Mo2 C@NC hybrid was not only used as a CE in a DSSC, but also showed superior catalytic activity towards I3- /I- as a redox electrolyte. The power conversion efficiency of a DSSC with Mo2 C@NC as the CE was as high as 6.49 %, comparable to that with Pt (6.38 %). The CE was prepared by a drop-coating method, without the addition of another conductive polymer. Most importantly, the method circumvents the problem of the sample falling off from the fluorine-doped tin oxide (FTO), and the CE could be repeatedly reused with unchanged efficiency. Therefore, it opens the way for the development of platinum-free catalysts with low cost, simple processing, good stability, and high efficiency.

An extremely active and durable Mo2C/graphene-like carbon based electrocatalyst for hydrogen evolution reaction

The efficiency of hydrogen production from electrolysis of water is severely limited by the sluggish kinetics of hydrogen evolution reaction (HER). Here we report our findings in the development of a very active and durable HER electrocatalyst derived from a one-pot synthesis of highly porous molybdenum carbide (Mo2C) nanoparticles uniformly dispersed on nitrogen-doped graphene-like carbon. The nanocomposite catalyst displays excellent HER activity and durability in an acidic electrolyte among all non-noble-metal catalysts ever reported. The remarkable performance is attributed to the unique nanostructure of the Mo2C phase, the conductive nitrogen-doped graphene-like carbon network, the high porosity of the hybrid, and the synergistic effect between the Mo2C and the carbon substrate. Further, the facile and low-cost synthetic strategy for preparation of such nanostructures may open up opportunities for exploiting other high-performance electrocatalysts for various applications.

Low-temperature CO removal

Catalysis Carbon monoxide deactivates fuel cell catalysts, so it must be removed from H2 generated from hydrocarbons on site. Yao et al. developed a catalyst composed of layered gold clusters on molybdenum carbide (MoC) nanoparticles to convert CO through its reaction with water into H2 and CO2 at temperatures as low as 150°C. Water was activated on MoC to form surface hydroxyl groups, which then reacted with CO adsorbed on the gold clusters. Science , this issue p. [389][1] [1]: /lookup/doi/10.1126/science.aah4321

Interconnected Molybdenum Carbide-Based Nanoribbons for Highly Efficient and Ultrastable Hydrogen Evolution.

Electrocatalytic hydrogen evolution reaction (HER) is of great significance to produce clean, sustainable, and cost-effective hydrogen. However, the development of low-cost and high-efficiency non-noble-metal catalysts with a combination of superior catalytic activity and long-time stability still remains a challenge. Herein, we demonstrate a rationally designed three-dimensional architecture assembled from one-dimensional molybdenum carbide (MoC)-based nanoribbons where the MoC nanoparticles are embedded within the nitrogen-doped crystallized carbon nanolayers (MoC@NC nanoribbon). Such unique architecture of the MoC@NC nanoribbon not only provides abundant edge active sites and multielectron pathways for efficient mass/charge transportation but also greatly accelerates the hydrogen release from the reaction surface, thus boosting its electrocatalytic performances for HER either in an acid or in an alkaline aqueous solution. This advance provides a promising candidate toward the replacement of the noble-metal-based catalysts for a highly stable and efficient HER electrocatalysis.

Self-Supported Biocarbon-Fiber Electrode Decorated with Molybdenum Carbide Nanoparticles for Highly Active Hydrogen-Evolution Reaction.

Devising and facilely synthesizing an efficient noble metal-free electrocatalyst for the acceleration of the sluggish kinetics in the hydrogen-evolution reaction (HER) is still a big challenge for electrolytic water splitting. Herein, we present a simple one-step approach for constructing self-supported biocarbon-fiber cloth decorated with molybdenum carbide nanoparticles (BCF/Mo2C) electrodes by a direct annealing treatment of the Mo oxyanions loaded cotton T-shirt. The Mo2C nanoparticles not only serve as the catalytic active sites toward the HER but also enhance the hydrophilicity and conductivity of resultant electrodes. As an integrated three-dimensional HER cathode catalyst, the BCF/Mo2C exhibits outstanding electrocatalytic performance with extremely low overpotentials of 88 and 115 mV to drive a current density of 20 mA cm-2 in alkaline and acidic media, respectively. In addition, it can continuously work for 50 h with little decrease in the cathodic current density in both alkaline and acidic solutions. Even better, self-supported tungsten carbide and vanadium carbide based electrodes also can be prepared by a similar synthesis process. This work will illuminate an entirely new avenue for the preparation of various self-supported three-dimensional electrodes made of transition-metal carbides for various applications.

Atomic-layered Au clusters on α-MoC as catalysts for the low-temperature water-gas shift reaction.

The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.

Growth of Molybdenum Carbide–Graphene Hybrids from Molybdenum Disulfide Atomic Layer Template

Molybdenum carbide–graphene hybrid constituting few-layer graphene and molybdenum carbide nanoparticles is synthesized by carburizing molybdenum disulfide atomic layer substrate. At the elevated temperature and reducing environment, molybdenum disulfide is reduced to molybdenum acting as the catalyst for graphene growth, while simultaneously molybdenum atoms are carburized to form molybdenum carbide. This hybrid has potential applications in heterogeneous catalysis.

Cobalt/molybdenum carbide@N-doped carbon as a bifunctional electrocatalyst for hydrogen and oxygen evolution reactions

A synergetic architecture composed of nitrogen-doped carbon encapsulating cobalt and molybdenum carbide nanoparticles (CoxMoy@NC) presents excellent performance towards both HER and OER catalysis in alkaline medium.

Nano-structured hybrid molybdenum carbides/nitrides generated in situ for HER applications

A highly efficient, low-cost (precious-metal-free), highly stable nanohybrid electrocatalyst containing carbon-supported molybdenum carbide and nitride nanoparticles of size ranging from 8 to 12 nm exhibit excellent HER catalytic activity.

Molybdenum carbide nanoparticles embedded in nitrogen-doped porous carbon nanofibers as a dual catalyst for hydrogen evolution and oxygen reduction reactions

An efficient dual catalyst of molybdenum carbide nanoparticles embedded nitrogen-doped porous carbon nanofibers (Mo2C/NPCNFs) has been developed for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The well-aligned and nanoporous identity of the desirable hybrid Mo2C/NPCNFs by an electrospun approach provides the good conductivity and rich active sites addressing excellent HER catalytic performance with an onset potential of −85 mV, a Tafel slope of 68 mV dec−1, and an exchange current density of 0.178 mA cm−2 in 0.5 M H2SO4. It is noting that the Mo2C/NPCNFs also shows remarkable ORR catalytic activity with an onset potential of ∼0.9 V, a half-potential of ∼0.77 V and a Tafel slope of 60.2 mV dec−1 at 1600 rpm in 0.1 M KOH. In addition, the experimental results demonstrate the core-shell 1D nanostructures boost the Mo2C/NPCNFs' stability of the durable catalytic activity over 10 h for both HER and ORR. This study designs a new structure for carbon-supported Mo2C composites, providing a distinctive course for the development of high-performance non-noble HER and ORR catalysts.

Molybdenum Carbide Anchored on Graphene Nanoribbons as Highly Efficient All-pH Hydrogen Evolution Reaction Electrocatalyst

The demand for exploiting hydrogen as a new energy source has driven the development of feasible, efficient, and low-cost electrocatalysts for hydrogen evolution reaction (HER) in different reaction media. Herein, we report the synthesis of molybdenum carbide (Mo2C) nanoparticles anchored on graphene nanoribbons (GNRs) as HER electrocatalyst that can function well under acidic, basic, and neutral conditions. GNRs obtained by unzipping carbon nanotubes (CNTs) display strip-like structure, offering abundant active sites for growing Mo2C nanoparticles. Furthermore, GNRs could provide a fast electron transport pathway as well as large exposed surface area to allow full impregnation of electrolytes. Coupling with the anticorrosion feature of Mo2C nanoparticles, the Mo2C–GNR hybrid exhibits outstanding electrocatalytic performance in all of the acidic, basic, and neutral media, making it promising as a highly efficient electrocatalyst under conditions at all pH values.

Controllable synthesis of molybdenum carbide nanoparticles embedded in porous graphitized carbon matrixes as efficient electrocatalyst for hydrogen evolution reaction

Molybdenum carbide nanoparticles embedded in porous sheet-like graphitized carbon matrixes (Mo2C/C) were controllably synthesized by a simple one-step solid reaction strategy. Remarkably, the porous graphitized carbon matrixes, which can efficiently restrain Mo2C nanoparticles from aggregation and improve the conductivity of the synthesized composites, are derived from the economic and environment-friendly agricultural by-product of cornstalks. Thanks to the novel structure, small size, large surface active area and high conductivity, the Mo2C/C composites exhibits superior performance when they are used as electrocatalyst in 0.5M H2SO4 for hydrogen evolution reaction (HER). The overpotential (η10) to achieve a current density of 10mAcm−2 is low to 114mV, and the Tafel slope is only 52mVdec−1. Besides, the Mo2C/C composites show large exchange current density (j0) of 0.286mAcm−2. Furthermore, the synthesized sample behaves excellent stability over 20h in acidic media for HER. More interestingly, the Mo2C/C composites behave comparable activities and stability in basic condition with those in acidic condition, which is meritorious.

Highly active nonprecious metal hydrogen evolution electrocatalyst: ultrafine molybdenum carbide nanoparticles embedded into a 3D nitrogen-implanted carbon matrix

The generation of clean and sustainable hydrogen fuel through water splitting demands efficient and robust earth-abundant catalysts for the hydrogen evolution reaction (HER). A new hybrid, which was fabricated by incorporating molybdenum carbide (MoxC) nanoparticles into a nitrogen-implanted three-dimensional carbon matrix (MoCN-3D), was developed as a highly active and durable nonprecious metal electrocatalyst for HER. The porous architecture of MoCN-3D can provide continuous mass transportation with a minimal diffusion resistance and thus produce effective electrocatalytic kinetics in both acidic and alkaline media. Experimental observations in combination with density functional theory calculations reveal that the effective coupling between molybdenum carbide nanoparticles and the carbon matrix, as well as N hybrid coordination, can modify the electronic Fermi level of the final hybrid, which synergistically reduces the proton adsorption and the reduction barrier during electrocatalytic HER. A three-dimensional, porous catalytic framework makes it easier to flow water past active sites that turn this molecule into hydrogen. The hunt for cheaper alternatives to platinum catalysts for water splitting led Jinhua Ye from Tianjin University in China and co-workers to investigate molybdenum carbide (Mo2C). These catalysts show significant hydrogen evolution when confined to nanoscale shapes. The researchers enhanced this behaviour by replacing imidazole-zinc units in a zeolite-type metal organic framework with molybdenum. Heating at high temperature turned the sieve-like template into a new composite containing ultrafine Mo2C nanoparticles and a three-dimensional matrix of graphitic carbon implanted with nitrogen atoms. The physical structure of this material improves mass transport of reagents to and from catalytic surface sites, while favorable interactions between Mo2C and the carbon matrix lower energy barriers needed to slice water apart. A new hybrid, fabricated by incorporating molybdenum carbide (Mo2C) nanoparticles into nitrogen-implanted three-dimensional carbon matrix (MoCN-3D), has been developed as a highly active and durable nonprecious metal electrocatalyst for HER. The porous architecture of the developed catalyst MoCN-3D can provide continuous mass transportation with a minimal diffusion resistance and thus produce effective electrocatalytic kinetics in both acidic and alkaline media.

Molybdenum Carbide Nanoparticles on Carbon Nanotubes and Carbon Xerogel: Low-Cost Cathodes for Hydrogen Production by Alkaline Water Electrolysis.

Low-cost molybdenum carbide (Mo2 C) nanoparticles supported on carbon nanotubes (CNTs) and on carbon xerogel (CXG) were prepared and their activity for the hydrogen evolution reaction (HER) was evaluated in 8 m KOH aqueous electrolyte at 25-85 °C. Measurements of the HER by linear scan voltammetry allowed us to determine Tafel slopes of 71 and 74 mV dec(-1) at 25 °C for Mo2 C/CNT and Mo2 C/CXG, respectively. Stability tests were also performed, which showed the steady performance of the two electrocatalysts. Moreover, the HER kinetics at Mo2 C/CNT was enhanced significantly after the long-term stability tests. The specific activity of both materials was high, and a higher stability was obtained for the activated Mo2 C/CNT (40 A g(-1) at -0.40 V vs. the reversible hydrogen electrode).

Application of topological analysis of the electron localization function to the complexes of molybdenum carbide nanoparticles with unsaturated hydrocarbons

The catalytic transformation of the heavy aromatics in bitumen into lighter components is the key to the upgrading and refining of the oil sands. To understand the chemical bonding in molybdenum carbide nanoparticle (MCNP) catalysts and the chemisorption bonds between the MCNPs and unsaturated hydrocarbons, the topological analysis of the electron localization function was applied to various MCNPs and their complexes with unsaturated hydrocarbons. For some of the smaller complexes, comparisons are made with the atoms in molecules approach, including the calculation of delocalization indices. The results are interpreted in the Lewis bonding scheme. It was found that the Mo–C bonding can be highly ionic in cases like Mo8C12 and MoC but shows significant covalent character in Mo2C, Mo3C, and Mo28C14. The chemisorption bonds between hydrocarbons and the MCNPs involve electron sharing of various types with strong covalent character. The strong three– or four–center interactions determine the adsorption configurations of the hydrocarbons on the MCNPs. Derivatives of benzene show some different bonding features, which depend strongly on the substituent or the heteroatom.

Graphene Porous Foam Loaded with Molybdenum Carbide Nanoparticulate Electrocatalyst for Effective Hydrogen Generation.

A facile method is developed for the synthesis of graphene porous foam (Gr PF) loaded with dispersed molybdenum carbide (Mo2 C) nanoparticles; the material exhibits effective catalytic activity in the hydrogen evolution reaction (HER). Mo2 C/Gr PF is synthesized by the carbonization of glucose and the carbothermal reduction of hexaammonium molybdate in a confined space defined by the intervals between sodium chloride nanoparticles. The synthesis in the confined space results in thin Gr PF (≈8 nm) loaded with aggregation-free small Mo2 C nanoparticles [(13±2) nm]. The overpotential required for a current density of 20 mA cm(-2) in the electrochemical hydrogen generation is as small as 199 mV in acidic solution and 380 mV in basic solution. The performance is superior to that of a Mo2 C/C composite and compares favorably to those reported for Mo2 C nanostructures. The Mo2 C/Gr PF affords stable water electrolysis in both acidic and basic solution and exhibits nearly 100 % faradaic efficiency. The prominent performance, long-term stability, and high faradic efficiency make Mo2 C/Gr PF a promising HER catalyst for practical hydrogen generation from water electrolysis.

Facile synthesis of hollow carbon microspheres embedded with molybdenum carbide nanoparticles as an efficient electrocatalyst for hydrogen generation

Hollow carbon microspheres embedded with molybdenum carbide nanoparticles are prepared via ultrasonic spray pyrolysis. The product exhibits an enhanced HER activity and good stability in the long-term operation both in acidic and basic solution.

N-Doped graphene-coated molybdenum carbide nanoparticles as highly efficient electrocatalysts for the hydrogen evolution reaction

New N-doped graphene-coated molybdenum carbide nanoparticles are prepared, which exhibit superior electrocatalytic activity and long-term durability for the hydrogen evolution reaction.

Molybdenum carbide nanoparticles as a catalyst for the hydrogen evolution reaction and the effect of pH

Molybdenum carbide nanoparticles supported on carbon catalysts have been prepared by a modified carbothermal reduction method. The soft carburization conditions of this method allow the preparation of nanoparticulate Mo2C even with a high Mo loading (50wt.%). The catalytic activity for the hydrogen evolution reaction was analyzed both in an electrochemical cell at various pH and in a laboratory-scale electrolyzer. These nanoparticles were found to be very active in catalyzing hydrogen evolution reaction in acidic media and appeared to promote kinetics leaning toward the Volmer–Heyrovský mechanism at low pH. Moreover, the Mo2C/C catalyst was shown to be suitable for hydrogen production in a laboratory-scale electrolysis cell, retaining its performance during a four-week durability experiment. Thus this study implies that the investigated Mo2C/C electrocatalyst is a promising alternative to platinum as a cathode material for electrolytic hydrogen production because of its favorable kinetics and stability.