Molybdenum Nitride Research Articles

Ammonia Synthesis through Hydrolysis of a Trianionic Pincer Ligand‐Supported Molybdenum–Nitride Complex

Reported is the hydrolysis of a homogeneous Mo-nitride complex bearing a trianionic pincer-type ligand to produce ammonia. Treating the anionic [(ONO)]Mo≡N(OtBu)]Ph3 PCH3 with two equivalents of water produces ammonia and the dioxo complex [(ONO)]MoO2 ]Ph3 PCH3 . X-Ray crystal structures of the starting nitrido complex and product dioxo complex are presented. Evidence for ammonia release comes from GC-MS and deuterium-labelling studies. The reaction is presented in the context of a two-stage solar thermochemical dinitrogen fixation process as the solid-state nitride hydrolysis step.

Deposition of molybdenum nitride thin layers on substrates of stainless steel AISI304 using a Mather-type of plasma focus device

This study focuses on effects of number of shots and the distance from the top of anode on Mo–N deposition process on the surfaces of AISI304 samples using a low energy (2.8 kJ) plasma focus device (AECS PF-1) at room temperature. The structural, morphological, elemental composition, surface roughness and micro-hardness properties of treated surfaces were investigated versus the number of shots and the axial distance from the anode. The obtained XRD spectra show that some of the treated surfaces were in crystalline phase with [Formula: see text]-Mo2N (FCC) structure (at 3 cm with 10–40 shots and at 5 cm with 30 and 40 shots) and some others had amorphous structure at 5 cm with 10 and 20 shots and at 7 cm with 10–40 shots. SEM images indicate that the thermal effect occurred at 3 cm and the deposition process of Mo–N at 5 cm and 7 cm from the anode with an increase in number of shots. The atomic ratio for nitrogen was 10.62%, 12.88%, and for molybdenum it was 0.23%, 3.36% at 3 cm, respectively. The atomic ratio for nitrogen has achieved 14.95% and 22.17%, however, the atomic ratio for molybdenum was 2.11% and 7.17 % at 5 cm, respectively. The surface roughness and size of grains on the surface of deposited layers were investigated by AFM analysis. Furthermore, the variation in the micro-hardness of the Mo–N thin layers deposited by different number of shots at different distances from the tip of anode was explained, qualitatively, on the basis of morphological characteristics of the thin layers. The decreasing rates of hardness in the case of 10 shots were 146%, 117% and 112%, and at 40 shots were 237%, 149% and 141% with the increasing of distances 3, 5 and 7 cm, respectively.

Mesoporous Thin-Wall Molybdenum Nitride for Fast and Stable Na/Li Storage.

Sluggish reaction kinetics induced by the poor solid-state ion diffusion and low electrical conductivity of electrode materials are currently in conflict with increasing fast-charge needs for sodium-ion batteries (SIBs) based on conversion mechanism. Herein, mesoporous, conductive, thin-wall three-dimensional (3D) skeletons of molybdenum nitride (meso-Mo2N) were established and employed as anodes to facilitate the rate performance of SIBs. Mesoporous channels (∼9.3 nm) with very thin walls (<8 nm) and conductive networks in meso-Mo2N enable the rapid Na+ infiltrability/diffusion and fast electron migration, respectively. The facilitated ion diffusion/transfer ability is corroborated by cyclic voltammetry tests and galvanostatic intermittent titration technique with a higher Na+ diffusion coefficient and a larger Na+ diffusion-dominated capacity. Consequently, meso-Mo2N exhibits a superior rate capability and a steady specific capacity of 158 mAh g-1 at 1 A g-1 after 1000 cycles for SIBs, surpassing the nonporous Mo2N and even the previously reported Mo2N. Furthermore, the proof of concept can be also extended to enhanced Li storage. Such a mesostructured design with 3D mesoporous, conductive thin walls of electrodes is a promising strategy for achieving fast-charging and high-performance Na/Li storage.

Topochemical synthesis of holey 2D molybdenum nitrides nanosheets via lime-assisted nitridation of layered MoS2

In this study, we introduced a facile and efficient method for the large-scale synthesis of porous 2D molybdenum nitrides nanosheets via the topochemical nitridation of MoS2 by NH3 with the assistance of CaO at 750 °C–820 °C. The presence of CaO can noticeably promote the reduction rate of MoS2 by generating CaS. After acidic leaching, porous 2D MoN, a mixture of 2D MoN and Mo2N, as well as Mo2N nanosheets with the thickness of about 7 nm and pore size of about 10.5 nm were successfully prepared at different temperatures. When the temperature increased from 750 °C to 820 °C, the product gradually changed from MoN to Mo2N. Due to the weak Van der Waals forces between the layers of MoS2, the topochemical substitution of S in MoS2 by N led to the exfoliating of layers. The large difference of crystal structures and volume between precursor and product, as well as the high reaction rate led to the formation of porous structure of molybdenum nitrides.

Quantum dots of molybdenum nitride embedded in continuously distributed polyaniline as novel electrode material for supercapacitor

Molybdenum nitride (Mo2N) and molybdenum nitride/polyaniline composites (Mo2N@PANI) have been prepared by simple static precipitation and in situ growth methods. The morphological and structural properties and chemical composition of the prepared materials have been analyzed by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The obtained results illustrate that in molybdenum nitride/polyaniline composites, polyaniline has been allocate continuously embedded with the quantum dots of molybdenum. Therefore, the formation of quantum dots of molybdenum and its uniform distribution in polyaniline bulk suggested that the synthesized materials could be used as an electrode material of supercapacitors. From the results of electrochemical analysis, the mass ratio capacitance of molybdenum nitride/polyaniline composites have been found to be 111.8 F/g at 0.5 A/g, while the mass ratio capacitance of pure molybdenum nitride is only 47.5 F/g at the same current density. Hence, obtained results clearly confirm that molybdenum nitride/polyaniline composites nanostructured quantum dot material is one of the best and novel electrode materials for high performed supercapacitors which exhibits excellent electrochemical properties.

Novel synthesis of molybdenum nitride/oxide on AISI-316 steel assisted with active screen plasma treatment

In this work, novel synthesis of molybdenum nitride/oxide coating on AISI-316 is attained by active screen plasma (ASP) treatment, using molybdenum active screen (AS). Molybdenum nitride is synthesized in N2-H2 environment, while oxidation is carried out in O2-H2 and O2-Ar environment. The synthesized coatings are characterized by microhardness tester, X-ray diffraction and scanning electron microscopy . The results show a successful synthesis of coating with improved hardness. This study illustrates that using molybdenum active screen, molybdenum nitride/oxide coating can be produced and industrial compatibility of this technique increases the effectiveness of these results on wide-scale engineering applications.

Hydrogen Evolution Reaction on Atomic Layer Deposited Molybdenum Nitride (MoNx) Thin Film on Highly Porous Carbon Cloth-Based Substrate

Using the atomic layer deposition (ALD) technique, a uniform, and conformal thin film of molybdenum nitride (MoNx) is successfully coated on to a highly porous carbon cloth-based substrate. The precursor used in ALD-MoNx is molybdenum hexacarbonyl (Mo(Co)6), and ammonia is used as the nitrogen source, while the temperature and number of ALD cycles are set at 225︒C and 700 cycles, respectively. The phase, surface characteristic, thickness, and conformal deposition of the film is established using XRD, XPS and SEM imaging, respectively. A conformal and uniform film with a thickness of 25–30 nm, and with overall composition c.a. Mo0.59N0.41 is observed. The as-deposited film exhibits predominantly amorphous characteristic, with a minor nanocrystalline nature. The film has noticeable oxygen contamination, mainly at the surface. Hydrogen evolution reaction (HER) performance of the as-prepared electrode is evaluated in 0.5 M H2SO4 electrolyte in a conventional three-electrode setup using the Ag/AgCl (3 M KCl) and graphite rod, as reference and counter electrode, respectively. The electrode exhibits good HER performance attributed to the high surface area of the substrate. Further, the porous structure of the electrode is systematically investigated using SEM imaging, and electrochemical impedance spectroscopy (EIS). A direct correlation of pore geometry is established by studying the HER at different overpotential, electrode composition, and nature of the electrolyte. Acknowledgement This work was financially supported by the MOTIE (Ministry of Trade, Industry & Energy (#10080651) and KSRC (Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device and the Advanced Technology Center Program (#10077265) funded by the MOTIE (Ministry of Trade, Industry & Energy) of the Republic of Korea

Synergistic effect of molybdenum nitride nanoparticles and nitrogen-doped carbon on enhanced photocatalytic hydrogen evolution performance of CdS nanorods

We successfully fabricate a new type of composite photocatalyst through modifying CdS nanorods using a noble-metal-free co-catalyst NC@Mo2N (molybdenum nitride deposited nitrogen-doped carbon matrix). The obtained CdS/NC@Mo2N composites show greatly enhanced photocatalytic hydrogen generation abilities. Among all studied samples, CdS/5% NC@Mo2N exhibited the optimal photocatalytic activity, owning a H2-production rate of 7294 μmol h−1 g−1 and showing an apparent quantum yield of 13.7%, which are almost five times higher than for the pure CdS. Moreover, through introducing the co-catalyst NC@Mo2N, the composites become more stable under a long term photocatalytic reaction as compared to pure CdS. The improved photocatalytic capability of the CdS/NC@Mo2N is mainly ascribed to the following two reasons: (1) Mo2N supplies abundant active sites for the water-spitting reaction and lowers the overpotential. (2) The nitrogen-doped carbon matrix promotes charge transfer and greatly enhances the conductivity of the composites.

Uniformly Decorated Molybdenum Carbide/Nitride Nanostructures on Biomass Templates for Hydrogen Evolution Reaction Applications.

Natural fibrils derived from biomass were used as a template to synthesize uniformly decorated nanoparticles (10–12 nm) of molybdenum carbide (Mo2C) and molybdenum nitride (Mo2N) supported on carbon. The nanoparticles have been synthesized through the carburization and nitridation of molybdenum on cotton fibrils, using a high-temperature solid-state reaction. The catalyst exhibits an onset potential of 110 mV and an overpotential of 167 mV to derive a cathodic current density of 10 mA cm–2. The electrocatalyst also demonstrates excellent long-term durability of more than 2500 cycles in acidic media with a Tafel slope value of 62 mV dec–1.

Molybdenum Nitrides, Carbides and Phosphides as Highly Efficient Catalysts for the (hydro)Deoxygenation Reaction

AbstractTransition metal nitrides, carbides and phosphides have the potential to replace the expensive and hazardous catalysts typically used for the conversion of fatty acids. However, there has been little research on the influence of treatment conditions and precursor nature on the properties of such catalytic systems. To better understand these dependencies, we synthesized a number of Mo catalysts by temperature‐programmed reduction (700‐900 °C; CH4/N2, N2/H2) using ammonium heptamolybdate, diammonium phosphate and hexamethylenetetramine (HMT) as Mo, C, N and P sources. The presence of HMT in the precursor mixtures ensured the synthesis of pure phase Mo2C, Mo2N and MoP. Catalytic activity in the (hydro)deoxygenation of stearic acid (240 min; 360 °C; 50 bar of H2) decreased in the following order: Mo2C&gt;Mo2N&gt;MoP. However, all of the studied Mo‐based catalysts showed good deoxygenation efficiency and, thus, represent excellent alternatives to traditional noble and sulfur‐containing catalysts.

Transmission Electron Microscopy (TEM) Studies on Nickel and Molybdenum Nitrides as Oxygen Reduction Reaction Catalysts

Transmission Electron Microscopy (TEM) Studies on Nickel and Molybdenum Nitrides as Oxygen Reduction Reaction Catalysts

Argon Bombardment of 4H Silicon Carbide Substrates for Tailored Schottky Diode Barrier Heights

In this paper, the impact of substrate preconditioning by ion bombardment in-situ in a conventional sputter equipment on n-doped 4H-silicon carbide (SiC) Schottky diodes with molybdenum nitride metallization is studied. By variation of the plasma power during argon ion bombardment, the effective barrier height is adjustable in the range from 0.66 to 0.96 eV, as deduced by current / voltage measurements over a wide temperature range. Therefore, this approach offers a straightforward method to tailor the Schottky barrier height over a significant range by introducing an insitu substrate pretreatment step available in most sputter equipment.

Nitridation of the metallic Mo2C(001) surface from NH3 dissociative adsorption—A DFT study

Adsorption and sequential decomposition of ammonia on the metallic Mo2C(001) surface have been systematically computed using periodic density functional theory under the consideration of van der Waals dispersion correction (PBE-D3). It is found that NH3 adsorption prefers the top sites from low to saturation coverage. For the adsorption of surface NH2, bridge and hollow sites are possible at low coverage and only bridge sites are preferred at high coverage up to saturation. The adsorption of surface NH and N prefers the hollow sites. Sequential decomposition of NH3 into surface NH2, NH and N has low barrier and is highly exothermic. On the basis of surface Mo atoms, the saturation coverage of surface NH3, NH2, NH and N by using NH3 as nitridation agent is 0.75, 1.0, 1.0 and 0.5 monolayer, respectively. These results provide the basis for the study of surface properties and catalytic reaction of nitrided Mo2C surfaces. The dissociative adsorption of ammonia among others metals and molybdenum nitrides has been categorized and compared.

Effect of heat treatment on structure and properties of molybdenum nitride and molybdenum carbonitride films prepared by magnetron sputtering

The molybdenum nitride (MoN) film with multiphase structure (Mo2N, MoN and Mo) was successfully prepared using magnetron sputtering. The mechanical and tribological performances of the MoN film were both further improved by C-doping and heat treatment. The results show that compared to the MoN film, the MoCN film has smoother and denser microstructure, lower friction coefficient and wear rate, and an increased hardness of 28 GPa. The improved performance exhibited by the MoCN film is mainly attributed to the lubricating effect of forming amorphous carbon after doping with C element and high hardness of the sp3 CC hybrid bond. However, different results exhibited on the MoN and MoCN films after heat treatment at 400 °C. Both the mechanical and tribological properties were improved in the MoN film but reduced in the MoCN film. This may be related to different crystallization of Mo and the change of amorphous carbon in the different film. This suggests that heat treatment is of great importance to the properties of MoN and MoCN films.

Influence of 3d transition-metal substitution on the oxygen reduction reaction electrocatalysis of ternary nitrides in acid

The development of non-precious, acid-stable, oxygen reduction reaction (ORR) electrocatalysts can significantly aid the commercialization of proton exchange membrane fuel cells (PEMFCs). We report a survey of the ORR electrocatalysis on 3d metal substituted (M = Mn, Fe, Co) molybdenum and tungsten nitrides in acidic environments. We find that molybdate catalysts are more active than tungstates, with the specific activity depending on the chemistry of the substituted 3d metal. In both families, more electronegative 3d metals led to higher ORR activity (i.e., Co > Fe > Mn). We attribute this result to the ability of the more electronegative 3d metal to withdraw electrons from the Mo- or W-based active sites, effectively oxidizing the metal centers of the catalysts. Based on our observation, future nitride ORR electrocatalysts can be further optimized by oxidizing the Mo sites further by, for example, adding even more electronegative dopant metals or incorporating anion vacancies.

Evaluation of hydrogen evolution reaction activity of molybdenum nitride thin films on their nitrogen content

We report preparation and electrochemical properties of molybdenum nitride MoxN (x from 1 to 2) and Mo thin films prepared by the magnetron sputtering. We adjusted amount of nitrogen during reactive sputtering, to achieve different ratios of Mo:N in the films. We could prepare well-defined and extremely smooth films. We determined hydrogen evolution reaction (HER) activity and other kinetics parameters such as Tafel slopes and exchange current densities. Corrosion stability at anodic potentials was also evaluated from onset potentials of dissolution of prepared films. We found that MoxN thin film HER activity dependence on nitrogen content in the film exhibits volcano-like diagram. From XRD measurements we identified several phases present in the films from pure Mo to β-Mo2N and δ-MoN. We find that β-Mo2N phase has the highest HER activity. Stability of studied nitrides at anodic potentials increases with increasing content of nitrogen. Mo films sputtered at high substrate temperatures exhibit higher HER activity than MoxN systems. In addition, with increasing substrate temperature during sputtering, HER activity of pure Mo thin films increases.

Molybdenum Nitride Nanocrystals Anchored on Phosphorus-Incorporated Carbon Fabric as a Negative Electrode for High-Performance Asymmetric Pseudocapacitor

SummaryPseudocapacitors hold great promise to provide high energy-storing capacity; however, their capacitances are still far below their theoretical values and they deliver much lower power than the traditional electric double-layer capacitors due to poor ionic accessibility. Here, we have engineered MoN nanoparticles as pseudocapacitive material on phosphorus-incorporated carbon fabric with enhanced ionic affinity and thermodynamic stability. This nanocomposite boosts surface redox kinetics, leading to pseudocapacitance of 400 mF/cm2 (2-fold higher than that of molybdenum nitride-based electrodes) with rapid charge-discharge rates. Density functional theory simulations are used to explain the origin of the good performance of MoN@P-CF in proton-based aqueous electrolytes. Finally, an all-pseudocapacitive solid-state asymmetric cell was assembled using MoN@P-CF and RuO2 (RuO2@CF) as negative and positive electrodes, respectively, which delivered good energy density with low relaxation time constant (τ0) of 13 ms (significantly lower than that of carbon-based supercapacitors).

Self-Combustion Synthesis of Novel Metastable Ternary Molybdenum Nitrides

Ternary metal nitrides are a promising class of functional materials, but their variety has been limited by the challenging nature of nitride synthesis. Here, we demonstrate a facile self-combustio...

Nanostructured molybdenum nitride-based coatings: Effect of nitrogen concentration on microstructure and mechanical properties

Molybdenum nitride (MoNx) coatings were deposited onto AISI M2 tool steel substrates (hardened to HRC 60) by magnetron sputtering. The nitrogen content was controlled by means of a closed-loop optical emission monitor. The coating microstructure was examined by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. This showed that the increased nitrogen content led to a transformation from body-centered cubic α-Mo phase to γ-Mo2N phase (NaCl-B1 type) and then to a face-centered cubic MoN phase. The mechanical and tribological properties of these coatings were evaluated by nano-indentation, wear and scratch testing. The γ-Mo2N coating showed the highest hardness and the highest values of H (hardness)/E* (effective elastic modulus) and H3/E* ratio. During scratch and wear tests, the γ-Mo2N coating exhibited the best resistance to deformation and the lowest wear rate.

Design of Materials for Electroreduction of Nitrogen to Ammonia: A Computational Perspective

Theoretical studies and computational modeling play a key role in predicting various properties of catalytic materials, including their activity and selectivity towards a desired electro-catalytic pathway. In the last decade, density functional theory calculations have been used to study the activity and selectivity of various materials for the nitrogen electroreduction, an extremely important aspect in the development of novel technologies for the ammonia synthesis. However, the design of an ideal electro-catalyst that exhibits high activity for nitrogen reduction to ammonia while at the same time suppresses the competing hydrogen evolution reaction is still an ongoing pursuit. Here we will use the example of molybdenum nitride and molybdenum carbide to illustrate different aspects in the design of materials for nitrogen electroreduction to ammonia and discuss different challenges associated with this effort [1, 2]. We will first present calculations of free energy diagrams and kinetic volcano plots aimed at understanding the activity of different surfaces of the molybdenum nitride (Mo2N) and molybdenum carbides (MoC and Mo2C) towards hydrogen evolution reaction and nitrogen electroreduction to ammonia. Secondly, we will discuss the thermodynamics calculations directed towards understanding the stability of these materials at different cell potentials and pH. Namely, our results show that at the nitrogen reduction potentials the catalytic surface can be covered with the H-adatoms rather than the N-adatoms. In addition, the carbides and nitrides can be converted to oxynitrides or oxides, which can lead to the decrease in the activity and durability of the catalytic material. Molybdenum carbides and nitrides will be used to illustrate how computational modeling can direct the design of the active sites with highest efficiency for nitrogen reduction to ammonia, but also support the optimization of reaction conditions to ensure the catalyst durability. [1] I. Matanovic, F. H. Garzon, and N. J. Henson, Electro-reduction of Nitrogen on Molybdenum Nitride: Structure, Energetics, and Vibrational Spectra from DFT, Phys. Chem. Chem. Phys. 2014, 16: 3014-3026. [2] I. Matanovic and F. H. Garzon, Nitrogen Electroreduction and Hydrogen Evolution on Cubic Molybdenum Carbide: A Density Functional Study, Phys. Chem. Chem. Phys. 2018, 20: 14679-14687.