Showing papers on "Molybdenum published in 2017"

Molybdenum Oxides – From Fundamentals to Functionality

Abstract: The properties and applications of molybdenum oxides are reviewed in depth. Molybdenum is found in various oxide stoichiometries, which have been employed for different high-value research and commercial applications. The great chemical and physical characteristics of molybdenum oxides make them versatile and highly tunable for incorporation in optical, electronic, catalytic, bio, and energy systems. Variations in the oxidation states allow manipulation of the crystal structure, morphology, oxygen vacancies, and dopants, to control and engineer electronic states. Despite this overwhelming functionality and potential, a definitive resource on molybdenum oxide is still unavailable. The aim here is to provide such a resource, while presenting an insightful outlook into future prospective applications for molybdenum oxides.

Enhancing Electrocatalytic Activity for Hydrogen Evolution by Strongly Coupled Molybdenum Nitride@Nitrogen-Doped Carbon Porous Nano-Octahedrons

Abstract: Developing highly efficient and affordable noble-metal-free catalysts toward the hydrogen evolution reaction (HER) is an important step toward the economical production of hydrogen. As a nonprecious-metal catalyst for the HER, molybdenum nitride (MoN) has excellent corrosion resistance and high electrical conductivity, but its catalytic activity is still inadequate. Here we report our findings in dramatically enhancing the HER activity of MoN by creating porous MoN@nitrogen-doped carbon (MoN-NC) nano-octahedrons derived from metal–organic frameworks (MOFs). The composite catalyst displays remarkably high catalytic activity, demonstrating a low overpotential of 62 mV at a current density of 10 mA cm–2 (η10), a small Tafel slope of 54 mV dec–1, and a large exchange current density of 0.778 mA cm–2 while maintaining good stability. The enhancement in catalytic properties is attributed to the unique nanostructure of the MoN, the high porosity of the electrode, and the synergistic effect between the MoN and th...

Recent progress in conversion reaction metal oxide anodes for Li-ion batteries

Abstract: Transition metal oxides (TMOs) based on conversion reactions are attractive candidate anode materials for lithium-ion batteries (LIBs) because of their high theoretical capacity and safety characteristics. In this review, we have summarized recent progress in the rational design and efficient synthesis of TMOs with controllable morphologies, compositions, and micro-/nanostructures, along with their Li storage behaviors. Single metal oxides of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), ruthenium (Ru), chromium (Cr), molybdenum (Mo), and tungsten (W) and their common binary metal oxides have been discussed in this review. Finally, the less well-known merits of conversion reactions are put forward, and the design of metal oxide electrodes making full use of these merits has been proposed.

Boron‐Dependency of Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction

Abstract: Molybdenum-based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum borides Mo2 B, α-MoB, β-MoB, and MoB2 by arc-melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X-ray photoelectron spectroscopy (XPS) for the first time; MoB2 and β-MoB show excellent activity in the same range as the recently reported α-MoB and β-Mo2 C phases, while the molybdenum richest phase Mo2 B show significantly lower HER activity, indicating a strong boron-dependency of these borides for the HER. In addition, MoB2 and β-MoB show long-term cycle stability in acidic solution.

The structure of vanadium nitrogenase reveals an unusual bridging ligand

Abstract: Nitrogenases catalyze the reduction of dinitrogen (N2) gas to ammonium at a complex heterometallic cofactor. This most commonly occurs at the FeMo cofactor (FeMoco), a [Mo-7Fe-9S-C] cluster whose exact reactivity and substrate-binding mode remain unknown. Alternative nitrogenases replace molybdenum with either vanadium or iron and differ in reactivity, most prominently in the ability of vanadium nitrogenase to reduce CO to hydrocarbons. Here we report the 1.35-A structure of vanadium nitrogenase from Azotobacter vinelandii. The 240-kDa protein contains an additional α-helical subunit that is not present in molybdenum nitrogenase. The FeV cofactor (FeVco) is a [V-7Fe-8S-C] cluster with a homocitrate ligand to vanadium. Unexpectedly, it lacks one sulfide ion compared to FeMoco, which is replaced by a bridging ligand, likely a μ-1,3-carbonate. The anion fits into a pocket within the protein that is obstructed in molybdenum nitrogenase, and its different chemical character helps to rationalize the altered chemical properties of this unique N2- and CO-fixing enzyme.

Sulfur and Nitrogen Dual-Doped Molybdenum Phosphide Nanocrystallites as an Active and Stable Hydrogen Evolution Reaction Electrocatalyst in Acidic and Alkaline Media

Abstract: Sulfur and nitrogen dual-doped molybdenum phosphides (MoP/SN) are synthesized via a (thio)urea-phosphate-assisted strategy in which the reductant (thio)urea acts as S and N source and phosphoric acid provides the P atom. The MoP/SN nanoparticles are generated by in situ phosphidation of indigenously synthesized ammonium phosphate-coated P-doped MoSx nanoparticles in a hydrogen atmosphere. Then, MoP/SN is anchored on graphene to obtain a hybrid electrocatalyst (MoP/SNG) that exhibits high activity and stability for electrochemical hydrogen evolution from water in both acidic and basic electrolytes, outperforming most MoP-based electrocatalysts reported in the literature. The dual doping and hybridization with graphene enhance electron conductivity of MoP and stabilize small MoP nanoparticles to increase activity and stability, especially in acid electrolytes.

Electronic properties of reduced molybdenum oxides

Abstract: The electronic properties of MoO3 and reduced molybdenum oxide phases are studied by density functional theory (DFT) alongside characterization of mixed phase MoOx films. Molybdenum oxide is utilized in compositions ranging from MoO3 to MoO2 with several intermediary phases. With increasing degree of reduction, the lattice collapses and the layered MoO3 structure is lost. This affects the electronic and optical properties, which range from the wide band gap semiconductor MoO3 to metallic MoO2. DFT is used to determine the stability of the most relevant molybdenum oxide phases, in comparison to oxygen vacancies in the layered MoO3 lattice. The non-layered phases are more stable than the layered MoO3 structure for all oxygen stoichiometries of MoOx studied where 2 ≤ x < 3. Reduction and lattice collapse leads to strong changes in the electronic density of states, especially the filling of the Mo 4d states. The DFT predictions are compared to experimental studies of molybdenum oxide films within the same range of oxygen stoichiometries. We find that whilst MoO2 is easily distinguished from MoO3, intermediate phases and phase mixtures have similar electronic structures. The effect of the different band structures is seen in the electrical conductivity and optical transmittance of the films. Insight into the oxide phase stability ranges and mixtures is not only important for understanding molybdenum oxide films for optoelectronic applications, but is also relevant to other transition metal oxides, such as WO3, which exist in analogous forms.

Highly active two dimensional α-MoO3−x for the electrocatalytic hydrogen evolution reaction

Abstract: The development of earth-abundant electrocatalysts for hydrogen evolution, with high activity and stability, is of great interest in the field of clean energy. The highly tunable chemical and physical properties of earth-abundant molybdenum oxides make them versatile for their incorporation into electrochemical and catalytic systems. Due to the layered crystal arrangement of orthorhombic α-MoO3, this material can be exfoliated into two dimensional (2D) nanosheets, featuring a large surface area. Variations in the oxidation states of molybdenum facilitate the crystal structure, morphology and oxygen vacancy tuning, making these oxide compounds suitable for electrochemical activities. Here, oxygen deficient 2D α-MoO3−x nanosheets (x = 0.045) are successfully synthesised, using a liquid phase exfoliation method, which display superior activity for the electrocatalytic hydrogen evolution reaction (HER) with a low overpotential and fast electron transfer. In alkaline media, the 2D compound exhibits an overpotential value of 142 mV at the standard current density of 10 mA cm−2 with excellent stability. Here, the 2D morphology, structural defects and oxygen vacancies in the planar construction of molybdenum oxide nanosheets significantly increase the active sites of the catalyst, which act as key factors to promote the HER performance. This work presents 2D α-MoO3−x nanosheets as strong candidates for the HER.

Platinum group metal-free NiMo hydrogen oxidation catalysts: high performance and durability in alkaline exchange membrane fuel cells

Abstract: We introduce a new platinum group metal-free (PGM-free) hydrogen oxidation electrocatalyst with superior performance in anodes of alkaline exchange membrane fuel cells (AEMFCs). A carbon-supported bimetallic nickel–molybdenum catalyst was synthesized by thermal reduction of transition metal precursors on the surface of a carbon support (KetjenBlack 600J). The mass-weighted activity of 4.5 A gMe−1 determined in a liquid electrolyte 0.1 M NaOH using a rotating disk electrode (RDE) technique is comparable to the value reported for Pd/C with a comparable particle size under similar conditions. This NiMo/KB catalyst was integrated in a membrane electrode assembly (MEA) using an alkaline exchange membrane and ionomer. Single AEMFC tests performed in a H2/O2 configuration resulted in a record power density output of 120 mW cm−2 at 0.5 V, the MEA was found to be durable under the conditions of potential hold of 0.7 V for 115 h. For the first time, operando X-ray computed tomography (CT) experiments were performed demonstrating liquid water formation at the PGM-free anode during cell operation, and in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and X-ray absorption spectroscopy (APXAS) were used to study the role of molybdenum in hydrogen adsorption.

Molybdenum chloride catalysts for Z -selective olefin metathesis reactions

Abstract: The development of catalyst-controlled stereoselective olefin metathesis processes has been a pivotal recent advance in chemistry. The incorporation of appropriate ligands within complexes based on molybdenum, tungsten and ruthenium has led to reactivity and selectivity levels that were previously inaccessible. Here we show that molybdenum monoaryloxide chloride complexes furnish higher-energy (Z) isomers of trifluoromethyl-substituted alkenes through cross-metathesis reactions with the commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene. Furthermore, otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloroethene and 1,2-dibromoethene can be effected with substantially improved efficiency and Z selectivity. The use of such molybdenum monoaryloxide chloride complexes enables the synthesis of representative biologically active molecules and trifluoromethyl analogues of medicinally relevant compounds. The origins of the activity and selectivity levels observed, which contradict previously proposed principles, are elucidated with the aid of density functional theory calculations.

An Oxygen-Insensitive Hydrogen Evolution Catalyst Coated by a Molybdenum-Based Layer for Overall Water Splitting

Abstract: For overall water-splitting systems, it is essential to establish O2-insensitive cathodes that allow cogeneration of H2 and O2. An acid-tolerant electrocatalyst is described, which employs a Mo-coating on a metal surface to achieve selective H2 evolution in the presence of O2. In operando X-ray absorption spectroscopy identified reduced Pt covered with an amorphous molybdenum oxyhydroxide hydrate with a local structural order composed of polyanionic trimeric units of molybdenum(IV). The Mo layer likely hinders O2 gas permeation, impeding contact with active Pt. Photocatalytic overall water splitting proceeded using MoOx/Pt/SrTiO3 with inhibited water formation from H2 and O2, which is the prevailing back reaction on the bare Pt/SrTiO3 photocatalyst. The Mo coating was stable in acidic media for multiple hours of overall water splitting by membraneless electrolysis and photocatalysis.

Well-dispersed molybdenum nitrides on a nitrogen-doped carbon matrix for highly efficient hydrogen evolution in alkaline media

Abstract: Well-dispersed and highly efficient molybdenum nitrides on a nitrogen-doped carbon matrix (Mo2N@NC) are reported as a new and active electrocatalyst for hydrogen evolution in alkaline electrolyte. The key point in fabricating this catalyst is using HNO3-treated melamine, other than pristine melamine, as carbon and nitrogen pools to realize the complete nitridation of MoO3 to Mo2N nanoparticles of 4 nm size and at the same time to generate a nitrogen-doped carbon matrix to support these nanoparticles by thermolysis under an Ar atmosphere. The as-prepared Mo2N@NC exhibits excellent HER activity in 1 M KOH with a pretty low overpotential of 85 mV to achieve a current density of 10 mA cm−2 and a small Tafel slope of 54 mV dec−1, which is among the best for Mo-based compounds and better than those of most non-noble metal electrocatalysts to date in alkaline media. It is also much better than those of the incomplete nitride compounds (MoO2/Mo2N@NC) and the mixture of nitrides and carbides (Mo2N/Mo2C@NC) fabricated under similar conditions, from aspects of overpotential, Tafel slope, exchange current density, conductivity, active surface area and turnover frequencies. Therefore, Mo2N represents a new kind of very active HER catalyst in alkaline electrolyte. Also, this work provides an effective method to fabricate metal nitrides/carbon composites for other applications.

Controllable synthesis of molybdenum-based electrocatalysts for a hydrogen evolution reaction

Abstract: In order to explore low-cost, high efficiency, precious metal-free materials for electrochemical water splitting, three types of molybdenum-based compounds (MoO2, MoC and Mo2C) were synthesized by tuning the ratio of glucose and ammonium molybdate via a two-step procedure. TEM images reveal a uniform dispersion of the three molybdenum-based nanoparticles on the carbon support, and in particular, MoC and Mo2C exhibit ultra-small particle sizes which are lower than 3 nm. When used as catalysts for the HER in both acid and basic media, Mo2C exhibits the best catalytic activity with a small overpotential of 135 mV in acid media and 96 mV in alkaline media at a current density of 10 mA cm−2, which is about 105 mV and 30 mV higher than that with Pt/C, respectively. The enhanced catalytic activity of Mo2C could originate from the excellent crystal structure, the high electronic conductivity of the carbon support with a high degree of graphitization and the ultra-small particle size, which provides a large surface area and active sites.

Atomic Layer Deposition of Crystalline MoS2 Thin Films: New Molybdenum Precursor for Low‐Temperature Film Growth

Abstract: DOI: 10.1002/admi.201700123 Compared to the most well-known 2D material, graphene, which is a semi-metal, the semiconducting 2H phase of MoS2 is advantageous in having a band gap suitable for electronic applications. In bulk form, MoS2 has an indirect band gap of 1.3 eV, which increases as a function of decreasing film thickness. In monolayer MoS2 (thickness ≈0.6 nm), the band gap becomes direct with a width of 1.8 eV.[1] Importantly, to meet the requirements of different applications, properties of MoS2 and other TMDCs can be tuned by controlling the thickness,[1] doping and alloying,[5–8] surface modification and functionalization,[9–11] strain,[12,13] and by creating heterostructures with other 2D materials.[6,14–16] The appealing properties of TMDCs have led to a wide range of proposed applications. MoS2 has been extensively studied as a channel material in conventional field-effect transistors,[17–21] as well as phototransistors and other optoelectronic devices.[16,21,22] The 2D structure of TMDCs plays a crucial role in possible applications relying on more exotic quantum phenomena, such as valleytronics.[23,24] MoS2 has also shown promise in, for example, catalysis,[25] batteries,[26] photovoltaics,[27] sensors,[28] and medicine.[29] The production of high-quality, large-area MoS2 films with a thickness controllable down to a monolayer, as required in many of the aforementioned applications, still remains a major challenge. Additionally, in many cases, the processing temperature should be kept as low as possible in order to avoid damaging sensitive substrates, such as polymers or nanostructures. Initially, flakes of monolayer MoS2 were produced from natural MoS2 crystals using micromechanical exfoliation, a topdown method capable of producing high-quality monolayers, albeit with poor throughput as well as limited control over flake thickness and dimensions.[4,30,31] Liquid-phase exfoliation of bulk crystals, on the other hand, offers good scalability, but often suffers from limited flake size, poor crystallinity, or contamination.[4,31,32] Bottom-up methods offer a more controllable way to produce MoS2 films. High-quality MoS2 thin films are most commonly deposited by chemical vapor deposition (CVD) or sulfurization of metal or metal oxide thin films. The most common Molybdenum disulfide (MoS2) is a semiconducting 2D material, which has evoked wide interest due to its unique properties. However, the lack of controlled and scalable methods for the production of MoS2 films at low temperatures remains a major hindrance on its way to applications. In this work, atomic layer deposition (ALD) is used to deposit crystalline MoS2 thin films at a relatively low temperature of 300 °C. A new molybdenum precursor, Mo(thd)3 (thd = 2,2,6,6-tetramethylheptane-3,5-dionato), is synthesized, characterized, and used for film deposition with H2S as the sulfur precursor. Self-limiting growth with a low growth rate of ≈0.025 Å cycle−1, straightforward thickness control, and large-area uniformity are demonstrated. Film crystallinity is found to be relatively good considering the low deposition temperature, but the films have significant surface roughness. Additionally, chemical composition as well as optical and wetting properties are evaluated. MoS2 films are deposited on a variety of substrates, which reveal notable differences in growth rate, surface morphology, and crystallinity. The growth of crystalline MoS2 films at comparably low temperatures by ALD contributes toward the use of MoS2 for applications with a limited thermal budget.

Molybdenum diboride nanoparticles as a highly efficient electrocatalyst for the hydrogen evolution reaction

Abstract: Non-noble metal nanomaterials (molybdenum sulfides, phosphides, carbides, and nitrides) have recently emerged as highly active electrocatalysts for the hydrogen evolution reaction (HER). Molybdenum borides in contrast have not been studied for their HER activity at the nanoscale, however, they were recently shown to be already efficient HER catalysts in the bulk (microscale). In this study, we report on the first nanocrystalline molybdenum boride (MoB2) synthesized by a simple, one-step, relatively low temperature (650 °C) and environmentally benign redox-assisted solid state metathesis (SSM) reaction. The obtained MoB2 nanospheres exhibit a low onset overpotential of 154 mV at 10 mA cm−2, a Tafel slope of 49 mV dec−1 and high stability. Furthermore, density functional theory (DFT) calculations show that several surfaces are active and that the optimum evolution of H2 occurs at a hydrogen coverage between 75% and 100% on the B-terminated {001} surface. These experimental and theoretical results open new avenues to design new architectures of inexpensive and highly efficient boron-based HER catalysts, such as boride nanospheres (with maximum active sites) or materials with B-terminated surfaces (e.g. {001} nanosheets of AlB2-type borides or even the recently discovered borophene and related 2D compounds).

Ultrathin molybdenum boride films for highly efficient catalysis of the hydrogen evolution reaction

Abstract: All molybdenum borides with various phases such as Mo2B, α-MoB, β-MoB, and MoB2 have been found to possess excellent electrocatalytic hydrogen evolution reaction (HER) activity. Ultrathin two-dimensional (2D) borides are expected to have both maximized surface active sites and fast electron transport, ensuring higher HER activity. Here we report the large-area preparation of ultrathin hexagonal Mo3B films of 6.48 nm thickness on Mo foils by chemical vapour deposition using a mixture of boron and boron oxide powders as the boron source, and hydrogen gas as both the carrier and reducing gas. The ultrathin film exhibits fantastic stability in acidic solution and has a small Tafel slope of 52 mV dec−1 which is the lowest value so far reported for molybdenum boride catalysts. Furthermore, our first-principles calculations show that the ultrathin Mo3B film is metallic, which facilitates fast electron transport along the active edges of the thin film for enhancing the HER activity.

BCN network-encapsulated multiple phases of molybdenum carbide for efficient hydrogen evolution reactions in acidic and alkaline media

Abstract: Five phases of molybdenum carbide encapsulated by a boron–carbon–nitrogen (BCN) network are synthesized by decomposition of a Mo–imidazole-borate organometallic complex with slight variations in the imidazole-borate ligand structure The method relies on the restrained in situ carburization reaction between Mo atoms and imidazole-borate ligands on an atomic scale, thus generating molybdenum carbide nanoparticles encapsulated conformally by the BCN shell All phases of molybdenum carbide demonstrate excellent electrocatalytic hydrogen evolution reaction (HER) activity and stability in both acidic and basic electrolytes outperforming most of molybdenum carbides reported in the literature Hexagonal β-Mo2C@BCN consistently exhibits the most outstanding performance under all conditions The less active cubic α and hexagonal η phases also display enhanced HER activity and stability due to the promotional effect of the BCN shell The dual natured (electrophilic and nucleophilic) BCN layers can protect molybdenum carbide nanoparticles from corrosion and agglomeration, and improve their electrocatalytic activity by serving as an electron transfer medium and providing ample adsorption sites for water due to enhanced wetting properties

Telluriding monolayer MoS2 and WS2 via alkali metal scooter.

Abstract: The conversion of chalcogen atoms to other types in transition metal dichalcogenides has significant advantages for tuning bandgaps and constructing in-plane heterojunctions; however, difficulty arises from the conversion of sulfur or selenium to tellurium atoms owing to the low decomposition temperature of tellurides. Here, we propose the use of sodium for converting monolayer molybdenum disulfide (MoS2) to molybdenum ditelluride (MoTe2) under Te-rich vapors. Sodium easily anchors tellurium and reduces the exchange barrier energy by scooting the tellurium to replace sulfur. The conversion was initiated at the edges and grain boundaries of MoS2, followed by complete conversion in the entire region. By controlling sodium concentration and reaction temperature of monolayer MoS2, we tailored various phases such as semiconducting 2H-MoTe2, metallic 1T'-MoTe2, and 2H-MoS2-x Te x alloys. This concept was further extended to WS2. A high valley polarization of ~37% in circularly polarized photoluminescence was obtained in the monolayer WS2-x Te x alloy at room temperature.

Efficient and Stable Perovskite Solar Cells Using Molybdenum Tris(dithiolene)s as p-Dopants for Spiro-OMeTAD

Abstract: Metal halide perovskite solar cells have now reached efficiencies of over 22%. To date, the most efficient perovskite solar cells have the n-i-p device architecture and use 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene or poly(triarylamine) as the hole transport material (HTM), which are typically doped with lithium bis((trifluomethyl)sulfonyl)amide (Li-TFSI). Li-TFSI is hygroscopic and detrimental to the long-term performance of the solar cells, limiting its practical use. In this work, we successfully replace Li-TFSI by molybdenum tris(1-(methoxycarbonyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), Mo(tfd-CO2Me)3, or molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), Mo(tfd-COCF3)3. With these two dopants, we achieve stabilized power conversion efficiencies up to 16.7% and 15.7% with average efficiencies of 14.8% ± 1.1% and 14.4% ± 1.2%, respectively. Moreover, we observe a significant enhancement of the long-term stability of perovskite solar cells und...

Effect of the support on the hydrodeoxygenation of m-cresol over molybdenum oxide based catalysts

Abstract: The hydrodeoxygenation (HDO) of m-cresol was investigated over supported molybdenum oxide catalysts at 340 °C under 4 MPa as total pressure. All catalysts were fully characterized using several techniques such as atomic absorption, N2 physisorption, XRD, H2-TPR, NH3-TPD, Raman spectroscopy, TEM analysis and oxygen chemisorption. It was noted that the reducibility of molybdenum species depends on the support used and follows the same order than the one determined from the HDO activity, i.e. MoOx/Al2O3 > MoOx/SBA–15 > MoOx/SiO2. In addition, the use of an ordered mesoporous silica support (SBA-5) or an acidic support (Al2O3) favored significantly the dispersion of MoOx particles compared to SiO2. Under these experimental conditions, m-cresol transformation underwent through two parallel deoxygenation routes which involved either the direct C O bond scission leading to toluene (DDO route), or the total hydrogenation of the aromatic ring yielding mainly to a mixture of methylcyclohexene isomers (HYD route). Regardless of the support used, the DDO route was always predominant. A reaction mechanism was proposed to explain the formation of toluene, the main product observed from HDO of m-cresol. To explain the formation of this aromatic, a selective adsorption through the oxygen atom of the phenolic reactant on oxygen vacancies, acting as HDO active sites, was proposed.

Method for preventing line bending during metal fill process

Abstract: Provided herein are methods and apparatuses for reducing line bending when depositing a metal such as tungsten, molybdenum, ruthenium, or cobalt into features on substrates by periodically exposing the feature to nitrogen, oxygen, or ammonia during atomic layer deposition, chemical vapor deposition, or sequential chemical vapor deposition to reduce interactions between metal deposited onto sidewalls of a feature. Methods are suitable for deposition into V-shaped features.

CVD Mo DEPOSITION BY USING MoOCl4

Abstract: A method of forming a molybdenum-containing material on a substrate is described, in which the substrate is contacted with molybdenum oxytetrachloride (MoOCl4) vapor under vapor deposition conditions, to deposit the molybdenum-containing material on the substrate. In various implementations, a diborane contact of the substrate may be employed to establish favorable nucleation conditions for the subsequent bulk deposition of molybdenum, e.g., by chemical vapor deposition (CVD) techniques such as pulsed CVD.

Highly Stable Molybdenum Disulfide Protected Silicon Photocathodes for Photoelectrochemical Water Splitting

Abstract: Developing materials, interfaces, and devices with improved stability remains one of the key challenges in the field of photoelectrochemical water splitting. As a barrier to corrosion, molybdenum disulfide is a particularly attractive protection layer for photocathodes due to its inherent stability in acid, the low permeability of its basal planes, and the excellent hydrogen evolution reaction (HER) activity the MoS2 edge. Here, we demonstrate a stable silicon photocathode containing a protecting layer consisting of molybdenum disulfide, molybdenum silicide, and silicon oxide which operates continuously for two months. We make comparisons between this system and another molybdenum sulfide–silicon photocathode embodiment, taking both systems to catastrophic failure during photoelectrochemical stability measurements and exploring mechanisms of degradation. X-ray photoelectron spectroscopy and transmission electron microscopy provide key insights into the origins of stability.

Potassium-Promoted Molybdenum Carbide as a Highly Active and Selective Catalyst for CO2 Conversion to CO

Abstract: The high concentration of CO2 bound in seawater represents a significant opportunity to extract and use this CO2 as a C1 feedstock for synthetic fuels. Using an existing process, CO2 and H2 can be concurrently extracted from seawater and then catalytically reacted to produce synthetic fuel. Hydrogenating CO2 directly into liquid hydrocarbons is exceptionally difficult, but by first identifying a catalyst for selective CO production through the reverse water-gas shift (RWGS) reaction, CO can then be hydrogenated to fuel through Fischer-Tropsch (FT) synthesis. Results of this study demonstrate that potassium-promoted molybdenum carbide supported on γ-Al2 O3 (K-Mo2 C/γ-Al2 O3 ) is a low-cost, stable, and highly selective catalyst for RWGS over a wide range of conversions. These findings are supported by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations.

Drastically enhanced hydrogen evolution activity by 2D to 3D structural transition in anion-engineered molybdenum disulfide thin films for efficient Si-based water splitting photocathodes

Abstract: We synthesized transferrable and transparent anion-engineered molybdenum disulfide thin-film catalysts through a simple thermolysis method by using [(NH4)2MoS4] solution and powder precursors with different sulphur/phosphorus weight ratios. The synthesized sulphur-doped molybdenum phosphide (S:MoP) thin film changed from a two-dimensional van der Waals structure to a three-dimensional hexagonal structure by introduction of phosphorus atoms in the MoS2 thin film. The S:MoP thin film catalyst, which is composed of cheap and earth abundant elements, could provide the lowest onset potential and the highest photocurrent density for planar p-type Si photocathodes. The density functional theory calculations indicate that the surface of S:MoP thin films absorb hydrogen better than that of MoS2 thin films. The structurally engineered thin film catalyst facilitates the easy transfer of photogenerated electrons from the p-Si light absorber to the electrolyte. Anion-engineering of the MoS2 thin film catalyst would be an efficient way to enhance the catalytic activity for photoelectrochemical water splitting.

Deposition of molybdenum thin films using a molybdenum carbonyl precursor

Abstract: Transition metal precursors are disclosed herein along with methods of using these precursors to deposit metal thin films. Advantageous properties of these precursors and methods are also disclosed, as well as superior films that can be achieved with the precursors and methods.