Molybdenum Source Research Articles

Electrochemical Formation of Amorphous Molybdenum Phosphosulfide for Enabling the Hydrogen Evolution Reaction in Alkaline and Acidic Media

The formation of a nonprecious metal catalyst that is active for the hydrogen evolution reaction (HER) over a wide pH range is of particular interest. In this work, a mixed anion electrocatalyst, namely, amorphous molybdenum phosphosulfide films containing oxygen were produced via a simple electrochemical process allowing the composition and morphology of the film to be controlled. The catalyst shows a homogeneous distribution of Mo, S, P, and O with a high number of active sites due to its amorphous state. (NH4)2MoS4 was used as a molybdenum and sulfur source, while NaPO2H2 was used as the phosphorus source. Thiourea was also investigated as an additional sulfur source during the electrodeposition process. The electrocatalyst was active for the HER in acidic media as expected, but showed excellent performance in alkaline media where Tafel slope values of 36 and 122 mV dec–1 were recorded, respectively. In addition, the electrocatalyst demonstrated long-term stability in both media for several hours. The materials were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and their physicochemical properties correlated to their electrocatalytic activity for the HER.

Carbon-coated molybdenum carbide nanosheets derived from molybdenum disulfide for hydrogen evolution reaction

The design and synthesis of efficient non-noble metal catalyst is important for the practical application of hydrogen evolution reaction (HER) from water electrolysis. In this study, molybdenum carbides were prepared by a novel synthetic method, which involved the first exfoliation of 2D MoS2 based on the principle of cold expansion of water below 4 °C and then carburization of exfoliated MoS2. In this method, MoS2 played roles of morphology template and molybdenum source simultaneously. Carbon-coated molybdenum carbide nanosheets were obtained and confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The stripping degree of MoS2 was found to have an important influence on physical properties and catalytic performance of molybdenum carbides. Interestingly, Mo2C nanosheets encapsulated in carbon nanotubes were observed when the MoS2 with a high peeling degree was used in the preparation. It showed high activity and good durability towards HER in acid solution.

Facile and controllable synthesis of molybdenum disulfide quantum dots for highly sensitive and selective sensing of copper ions**Project supported by the National Key R&D Program of China (Grant No. 2016YFA0202302), the National Natural Science Foundation of China (Grant Nos. 61335006, 61527817, and 61378073), the Overseas Expertise Introduction Center for Discipline Innovation, 111 Center, China, and the National Basic Research Program

Molybdenum disulfide quantum dots (MoS2QDs) were synthesized via a hydrothermal method using sodium molybdate and cysteine as molybdenum and sulfur sources, respectively. The optimal hydrothermal time was studied. Furthermore, the as synthesized water-soluble MoS2 QDs were used as a fluorescence probe for the sensitive and selective detection of copper ions. The fluorescence of the MoS2QDs was quenched after the addition of copper ions; the reason may be that the transfer of the excited electron from QDs to copper ions leads to the reduction of the radiative recombination. The fluorescence quenching of MoS2 QDs is linearly dependent on the copper ions concentration ranging from to , the limit of detection is , which is much lower than that of existing methods. Moreover, the MoS2 QDs show highly selectivity towards the detection of copper ions.

Molybdenum carbide embedded in carbon nanofiber as a 3D flexible anode with superior stability and high-rate performance for Li-ion batteries

The fabrication process and material design of flexible lithium-ion batteries (LIBs) are essential in flexible portable devices. In particular, the carbon nanofiber (CNF)-based active anodes with flexibility synthesized using an electrospinning technique showed fairly stable cycling performance in the LIBs. In this study, we synthesized the molybdenum carbide (MoC) embedded in CNFs as an anode for LIBs (MoC/CNF) using an electrospinning technique with amorphous Mo precursor and polyacrylonitrile as the molybdenum and carbon sources, respectively, and using a heating process under an N2 atmosphere. The as-prepared flexible MoC/CNF showed a 3D porous structure consisting of crystalline MoC and amorphous CNF. MoC/CNF, directly utilized as an active electrode without binder, conductor, or current collector, exhibited superior LIB performance, i.e. high capacity, cyclability, and high-rate properties. In particular, at a considerably high charge/discharge rate of 10 A g−1, the specific capacity of MoC/CNF (109 mAh g−1) was significantly higher than that of pure CNF electrode (3 mAh g−1).

MoS2 nanograins doped TiO2 nanofibers as intensified anodes for lithium ion batteries

To take advantage of the high-rate capabilities of a TiO2 anode, MoS2 nanoparticles were wrapped in TiO2 nanofibrous backbone through adding molybdenum source to organic titanium-based electrospinning system, followed by hydrothermal reaction in solution containing sulfur source and subsequent carbonization. Benefiting from the synergistic effect between TiO2 and MoS2, more active sites for lithium ions could be generated, which further maximized the advantage of each material to exhibit stable specific capacities of 479.78 mAh/g for Li-ion batteries after 100 cycles.

Hydrothermal synthesis of flower-like molybdenum disulfide microspheres and their application in electrochemical supercapacitors.

Three-dimensional flower-like molybdenum disulfide microspheres composed of nanosheets were prepared by a hydrothermal method using ammonium molybdate as the molybdenum source and thiourea as the sulfur source. Structural and morphological characterizations were performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of MoS2 electrode were studied by performing cyclic voltammetry (CV), galvanostatic charge–discharge analysis and electrochemical impedance spectroscopy (EIS). When used as an electrode material for supercapacitor, the hybrid MoS2 showed a high specific capacity of 518.7 F g−1 at a current density of 1 A g−1 and 275 F g−1 at a high discharge current density of 10 A g−1. In addition, a symmetric supercapacitor composed of MoS2 as positive and negative electrodes was prepared, which exhibited a high energy density of 12.46 W h kg−1 at a power density of 70 W kg−1 and still maintains an impressive energy density of 6.42 W h kg−1 at a large power density of 7000 W kg−1. The outstanding performance of the MoS2 electrode material indicates its great potential for applications in high-performance energy storage systems.

The impact of anthropogenic factors on the occurrence of molybdenum in stream and river sediments of central Upper Silesia (Southern Poland)

AbstractIn our study, a detailed survey was conducted with the aim to determine the distribution and possible anthropogenic sources of molybdenum in river and stream sediments in the central Upper Silesian Industrial Region (Southern Poland), where for many years, iron and zinc smelters as well as coking and thermal power plants were operating. At the same time, this has also been a residential area with the highest population density in the country. Sediments (1397 samples in total) were collected from rivers and streams, and analysed for the content of molybdenum and 22 other elements. ICP-AES and CV-AAS methods were applied for the determination of the content of elements. The studies revealed molybdenum content in the range of < 0.5–204.8 mg·kg−1with the average content 1.9 mg·kg−1. About half of the samples contained < 0.5 mg·kg−1of molybdenum, and only 4.6% of the samples showed values > 5 mg·kg−1. The spatial distribution of molybdenum demonstrated by the geochemical map has indicated that the principal factor determining its content in sediments is the discharge of wastewater from steelworks and their slag heaps. Another source of this element in sediments has been the waste of the historical mining of zinc ore and metallurgy of this metal. Additionally, molybdenum migration from landfills of power plants, coal combustion and Mo emission to the atmosphere and dust fall-out have been significant inputs of Mo pollution to the sediments.

Dissecting the Re-Os molybdenite geochronometer

Rhenium and osmium isotopes have been used for decades to date the formation of molybdenite (MoS2), a common mineral in ore deposits and the world’s main source of molybdenum and rhenium. Understanding the distribution of parent 187Re and radiogenic daughter 187Os isotopes in molybdenite is critical in interpreting isotopic measurements because it can compromise the accurate determination and interpretation of mineralization ages. In order to resolve the controls on the distribution of these elements, chemical and isotope mapping of MoS2 grains from representative porphyry copper-molybdenum deposits were performed using electron microprobe and nano-scale secondary ion mass spectrometry. Our results show a heterogeneous distribution of 185,187Re and 192Os isotopes in MoS2, and that both 187Re and 187Os isotopes are not decoupled as previously thought. We conclude that Re and Os are structurally bound or present as nanoparticles in or next to molybdenite grains, recording a complex formation history and hindering the use of microbeam techniques for Re-Os molybdenite dating. Our study opens new avenues to explore the effects of isotope nuggeting in geochronometers.

Sheet-like orthorhombic MoO3 nanostructures prepared via hydrothermal approach for visible-light-driven photocatalytic application

In the present work, sheet-like α-MoO3 nanostructures (NS) were prepared by a simple hydrothermal method using ammonium heptamolybdate tetrahydrate as a molybdenum source and nitric acid. The synthesized α-MoO3 NS have been characterized structurally and morphologically using various analytical techniques. The PXRD, FT-IR, Raman and XPS spectroscopic analysis results revealed the formation of phase pure α-MoO3. The SEM–EDX analysis further confirms the purity of the synthesized α-MoO3 NS. FE-SEM and HR-TEM results indicated that the synthesized α-MoO3 has sheet-like morphology. Further, the obtained α-MoO3 NS could be used as the effective photocatalyst for the degradation of methylene blue and rhodamine B dyes. It was found that > 95% dye degradation efficiency was achieved for both the organic dyes within 90 min irradiation times. This enhanced photocatalytic activity of α-MoO3 can be attributed to the presence of a greater number of active sites in the sheet-like morphology that are more vulnerable for adsorption of organic dyes and subsequent elimination by decomposition under visible-light condition.

Template-assisted sol–gel synthesis of porous MoS2/C nanocomposites as anode materials for lithium-ion batteries

Porous MoS2/C nanocomposites have been successfully via a sol–gel route with ammonium molybdatetetrahydrate ((NH4)6Mo7O24·4H2O) as molybdenum source, glucose as carbon source and tetramethyloxysilane (TMOS) as gelation accelerator, subsequently followed by high-temperature sulfuration and further NaOH etching to remove silica template derived from TMOS. The as-prepared MoS2/C nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption–desorption, and the effect of molybdenum precursor mass on the synthesis of product was also investigated. The Mo and TMOS mass ratio obviously affects the gelation time, phase composition and morphology of the resultant product, and an appropriate Mo and TMOS mass ratio allows the formation of lamellar structure as well as perfect MoS2 phase. The as-prepared MoS2/C nanocomposite with Mo and TMOS mass ratio of 7:3 exhibits a BET surface area of 31 m2g−1 and a mesopore size of 20 nm, and demonstrates good electrochemical performances with 400 mA h g−1 specific reversible capacity after 60 cycles owing to the pore structure and synergistic effect between MoS2 and amorphous carbon.

Naturally Occurring versus Anthropogenic Sources of Elevated Molybdenum in Groundwater: Evidence for Geogenic Contamination from Southeast Wisconsin, United States

Molybdenum (Mo) is an essential trace nutrient but has negative health effects at high concentrations. Groundwater typically has low Mo (<2 μg/L), and elevated levels are associated with anthropogenic contamination, although geogenic sources have also been reported. Coal combustion residues (CCRs) are enriched in Mo, and thus present a potential anthropogenic contamination source. Here, we use diagnostic geochemical tracers combined with groundwater residence time indicators to investigate the sources of Mo in drinking-water wells from shallow aquifers in a region of widespread CCR disposal in southeastern Wisconsin. Samples from drinking-water wells were collected in areas near and away from known CCR disposal sites, and analyzed for Mo and inorganic geochemistry indicators, including boron and strontium isotope ratios, along with groundwater tritium-helium and radiogenic 4He in-growth age-dating techniques. Mo concentrations ranged from <1 to 149 μg/L. Concentrations exceeding the U.S. Environmental Protection Agency health advisory of 40 μg/L were found in deeper, older groundwater (mean residence time >300 y). The B (δ11B = 22.9 ± 3.5‰) and Sr (87Sr/86Sr = 0.70923 ± 0.00024) isotope ratios were not consistent with the expected isotope fingerprints of CCRs, but rather mimic the compositions of local lithologies. The isotope signatures combined with mean groundwater residence times of more than 300 years for groundwater with high Mo concentrations support a geogenic source of Mo to the groundwater, rather than CCR-induced contamination. This study demonstrates the utility of a multi-isotope approach to distinguish between fossil fuel-related and natural sources of groundwater contamination.

Synthesis of molybdenum nitride (Mo2N) nanoflakes via in-situ reduction-nitridation

Nanoflakes of molybdenum nitride (β-Mo2N) has been synthesized via a simple reduction-nitridation route using ammonium heptamolybdate tetrahydrate (AHM) as a source of both molybdenum and nitrogen and magnesium (Mg) as reducing agent in an autoclave. Sodium azide has been used as an additional nitrogen source to enhance nitridation for the formation of single phase β-Mo2N at 700 °C. The structural, morphological and magnetic behavior of as synthesized samples were investigated. The mean particle size was calculated by Scherrer formula. Williamson-Hall method was adopted to calculate the amount of strain in the nano particles. The effect of holding time, synthesis temperature and variation of Mo and N content has been studied. The as synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and vibrating sample magnetometer (VSM). XRD peaks confirmed the formation of pure phase β-Mo2N, while, microstructural analysis exhibited flake/plate-like morphology. VSM data depicted that synthesized samples were predominantly diamagnetic in nature. On the basis of XRD, structural and morphological results, a synthesis mechanism has been framed for the formation of Mo2N in an autoclave.

Dietary determinants of urinary molybdenum levels in Mexican women: a pilot study.

This study determined the main dietary sources of urinary molybdenum (Mo) concentrations in a sample of 124 pregnant women in Mexico. Dietary data was collected during pregnancy, through a semi-qualitative food frequency questionnaire, with information of 84 foods. Urine Mo levels were determined by atomic absorption spectrometry, for at least two trimesters of pregnancy. The associations with Mo levels were estimated by generalized mixed effect regression models. Between 5.8 to 12.7% of the samples were above the 95th percentile of urinary Mo distribution reported by National Health and Nutrition Examination Survey (NHANES) 2009-2010 for women (151 μg/L and 148 μg/g creatinine). After bootstrap resampling was conducted, women with high-consumption of hot peppers (β=1.34μg/g; 95% CI: 1.00-1.80; p= 0.05) had marginally higher urinary Mo concentration levels, creatinine adjusted, compared to women with low-consumption. Hot chili pepper consumption may contribute to body burden Mo levels in this population.

MoS2@rGO Nanoflakes as High Performance Anode Materials in Sodium Ion Batteries

A simple one-pot hydrothermal method is developed for fabrication of MoS2@rGO nanoflakes using the economical MoO3 as the molybdenum source. Benefiting from the unique nanoarchitecture, high MoS2 loading (90.3 wt%) and the expanded interlayer spacing, the as-prepared MoS2@rGO nanoflakes exhibit greatly enhanced sodium storage performances including a high reversible specific capacity of 441 mAh g−1 at a current density of 0.2 A g−1, high rate capability, and excellent capacity retention of 93.2% after 300 cycles.

N,P,S-codoped C@nano-Mo2C as an efficient catalyst for high selective synthesis of methanol from CO2 hydrogenation

With the protic ionic liquid consisting of N-butylimidazolium molybdophosphate and N-butylimidazolium p-toluenesulfonate as carbon source, molybdenum source and N,P,S-doping source, the catalysts of N,P,S-codoped C@nano-Mo2C (N,P,S-dC@Mo2C) were prepared by temperature-programmed carbonization method in a N2/H2 atmosphere. The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) demonstrated that N,P,S-dC@Mo2C was successfully synthesized and the morphology of N,P,S-dC@Mo2C was characterized by transmission electron microscopy (TEM). In the hydrogenation of CO2 to form methanol, N,P,S-dC@Mo2C showed highly catalytic activity and selectivity. When the N,P,S-dC@Mo2C-1073K was employed as a catalyst, the methanol selectivity of 91% was achieved with CO2 conversion of 19%. Moreover, the N,P,S-dC@Mo2C-1073K catalyst showed the excellent stability and its catalytic activity and selectivity was not decreased when the catalytic reaction was run continuously for 100h in the fixed bed reactor.

MoO2@MoS2Nanoarchitectures for High-Loading Advanced Lithium-Ion Battery Anodes

The capacity loading per unit area is of importance as specific capacity while evaluating the lithium-ion battery anode. However, the low conductivity of several advanced anode materials (such as molybdenum sulfide, MoS2) prohibits the wide application of materials. Nanostructural engineering becomes a key to overcome the obstacles. A one-step in situ conversion reaction is employed to synthesize molybdenum oxide (MoO2)–MoS2 core–shell nanoarchitectures (MoO2@MoS2) by partially sulfiding MoO2 into MoS2 using sulfur. The MoO2@MoS2 displays a 3D architecture constructed by hundreds of MoS2 ultrathin sheets with several layers arranged and fixed to an MoO2 particle vertically with the size in the range of 200–500 nm. MoO2 acts as the molybdenum source for the synthesis of MoS2, as well as the conductive substrate. The designed 3D architectures with empty space between MoS2 layers can prevent the damage originated from volume change of MoS2 undergoing charge/discharge process. The lithium storage capacities of the MoO2@MoS2 3D architectures are higher and the stability has been significantly improved compared to pure MoS2. 4 mAh cm−2 capacity loading of MoO2@MoS2 has been achieved with a specific capacity of more than 1000 mAh g−1.

Hydrothermal preparation of MoS2 nanoflake arrays on Cu foil with enhanced supercapacitive property

Hexagonal MoS2 nanoflake arrays (h-MNFs) have been synthesized directly via hydrothermal route with Cu foil as substrate, (NH4)6Mo7O24·4H2O as the molybdenum source, CN2H4S as the sulfur source and reductant, and (CH3)2CHOH as the dispersant. The micro morphology and crystallinity of MNFs are analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman microscopy (RM). The morphological change and growth process of MNFs are investigated, basing on the samples at different hydrothermal reaction times. Moreover, the supercapacitive properties of MNFs have been examined. It is found that MNFs has a good cycling invertibility (93%) and stability (90%) after 5000 cycles, a relatively high specific capacitance (420Fg−1), a low charge transport resistance (1.8Ω) and available energy densities ranging from 21 to 17Whkg−1 with corresponding practical power densities ranging from 150 to 3000Wkg−1.

Diagnostics for molybdenum and tungsten erosion and transport in NSTX-U.

A comprehensive set of spectroscopic diagnostics is planned in the National Spherical Torus Experiment Upgrade to connect measurements of molybdenum and tungsten divertor sources to scrape-off layer (SOL) and core impurity transport, supporting the installation of high-Z plasma facing components which is scheduled to begin with a row of molybdenum tiles. Imaging with narrow-bandpass interference filters and high-resolution spectroscopy will be coupled to estimate divertor impurity influxes. Vacuum ultraviolet and extreme ultraviolet spectrometers will allow connecting high-Z sources to SOL transport and core impurity content. The high-Z diagnostics suite complements the existing measurements for low-Z impurities (carbon and lithium), critical for the characterization of sputtering of high-Z materials.

NiMo As Non-Precious Metal Catalyst for Hydrogen Oxdiation Reaction in Alkaline Media

Fuel cell is environment-friendly power source which has high efficiency in generating electricity. Polymer electrolyte fuel cell uses hydrogen as a fuel that only produces water as byproduct which does not cause any pollution. Currently, commercialized Nafion-based polymer electrolyte membrane fuel cell (PEMFC) applied Pt/C as both cathode and anode catalyst which cause cost inefficiency in manufacturing fuel cell stack. Anion exchange membrane fuel cell (AEMFC) is being developed to combine advantages of both PEMFC and traditional alkaline fuel cell (AFC). By adopting solid membrane as electrolyte, leakage problem and insoluble salt precipitation could be solved. Furthermore, alkaline condition enhances oxygen reduction reaction (ORR) kinetics which obstructs cell power in PEMFC. However, stability of membrane is still in issue, and hydrogen oxidation reaction (HOR) kinetics are significantly diminished [1], which leads to higher Pt loading. This research is focusing at slow HOR kinetics and reducing catalyst cost by replacing Pt into non-precious metals such as transition metals. One of the well-known HOR catalyst for alkaline fuel cell is nickel. Several studies show nickel has catalytic activity of hydrogen oxidation in alkaline media [2,3], but it’s not enough to overcome precious metals such as platinum. Therefore, diverse researches tried to enhance activity of nickel by expanding surface area or doping other elements [4]. However, these catalytic activities were only tested in 6 M KOH, 60~80 ℃ condition, which is identical to real cell operating condition. NiMo catalyst was synthesized by electrodeposition method which is cost-effective way to produce. Nickel chloride is used for nickel source, and sodium molybdate worked as molybdenum source. Galvanostatic electrodeposition was applied to synthesize NiMo catalyst. Rotating disk electrode (RDE) was used to remove evolved hydrogen efficiently. HOR activity was measured in hydrogen saturated 0.1 M KOH solution. RDE was used to control diffusion with 1600 rpm speed. Experiment was held at room temperature. To remove capacitive current, steady state polarization method was applied for measuring HOR activity. Figure 1 shows HOR current of commercial Pt/C, electrodepositied NiMo, Ni. Adding small amount of Mo in Ni increases HOR current significantly. At overpotential of 20 mVRHE, Pt/C shows current density of 1.12 mA/cm2, where NiMo has 0.86 mA/cm2which is about 77% of Pt/C HOR activity. Reference [1] W. Sheng, et al., J. Electrochem. Soc. 157 (11), B1529 (2010) [2] T. Tomida, et al., J. Electrochem. Soc. 136 (11), 3296 (1989) [3] H. K. Lee, et al., Mat. Chem. Phys., 55, 89 (1998) [4] J. A. Linnekoski, J. Fuel Cell Sci. Tech., 4, 45 (2007) Figure 1

Hydrothermal synthesis of layer-controlled MoS2/graphene composite aerogels for lithium-ion battery anode materials

Layer-controlled MoS2/graphene aerogels (MoS2/GA) composites are synthesized by a facile hydrothermal route, in which few-layer (5–15 layers) MoS2 nanosheets with high crystalline are decorated on the surface of graphene nanosheets homogeneously and tightly. The number of the MoS2 layers can be easily controlled through adjusting the amount of molybdenum source in the reaction system. Moreover, the growth mechanism of the lay-controlled MoS2/GA composites is proposed. The three-dimensional MoS2/GA with macroporous micro-structure not only shortens the transportation length of electrons and ions, but also restrains the re-stacking of MoS2 effectively, stabilizing the electrode structure during repeated charging/discharging processes. Electrochemical tests demonstrate that this few-layer MoS2/GA composite exhibits a high reversible capacity of 1085.0mAhg−1 at current density of 100mAg−1, as well as extraordinarily high cycling stability and rate capability.