Molybdenum Oxysulfide Research Articles

Attenuating the Polysulfide Shuttle Mechanism by Separator Coating.

Lithium-sulfur batteries have a high energy density but lack cycle stability to reach market maturity. This is mainly due to the polysulfide shuttle mechanism, i. e., the leaching of active material from the cathode into the electrolyte and subsequent side reactions. We demonstrate how to attenuate the polysulfide shuttle by magnetron sputtering molybdenum oxysulfide, manganese oxide, and chromium oxide onto microporous polypropylene separators. The morphology of the amorphous coatings was analyzed by SEM and XRD. Electrochemical cyclization quantified how these coatings improved Coulombic efficiency and cycle stability. These tests were conducted in half cells. We compare the different performances of the different coatings with the known chemical and adsorption properties of the respective coating materials.

Void space expanded hierarchical battery-type composite material for high-capacity hybrid supercapacitors

Synergetic modulation of battery-type materials with excellent electrochemical activity is an important feature to elevate the energy storage performance in the hybrid supercapacitors (HySCs). In this study, we synthesized a void space expanded nickel sulfide@nickel molybdenum oxysulfide on Ni foam (NixSy@NiMoOx-1Sy/Ni foam) using wet-chemical sulfurization technique. The growth solution, composed of sulfur ions, partially converts NiMo DHs into NiMoOx-1Sy and the Ni foam substrate into NixSy, resulting in the formation of a hybrid-composite. Increased mass-loading growth of NixSy@NiMoOx-1Sy/Ni foam and multi-oxidation states of nickel species in the composite were confirmed using the X-ray photoelectron spectroscopy analysis. The binder-free NixSy@NiMoOx-1Sy/Ni foam electrode was electrochemically cycled in aqueous KOH electrolyte, demonstrating battery-type redox behavior with enhanced capacity (310.6 mAh/g) compared to the NixSy/Ni foam (221.1 mAh/g) and NiMo DHs/Ni foam (142.5 mAh/g) electrodes, which could be ascribed to the improved electrical conductivity, adequate electrolyte diffusivity, and fast charge transfer properties. Furthermore, a two-electrode system based HySC was assembled using the battery-type NixSy@NiMoOx-1Sy/Ni foam and capacitive-type activated carbon, enabling a maximum energy density (58.8 Wh/kg) and power density (2666.7 W/kg) with good cycling stability and coulombic efficiency. The high-performance HySCs were used to power-up portable lighting devices, demonstrating their practical use in real-time applications.

Spectroscopic visualization of intermediate phases during CVD synthesis of MoS2

Chemical vapor deposition (CVD) is the broadly used technique in the synthesis of 2D materials for various electronic and optoelectronic devices. In this study, we aim to understand the precise phase transition of molybdenum trioxide (MoO3), the most commonly used transition metal precursor, under the influence of sulfur in a CVD process that ultimately leads to the growth of mono-to few-layer molybdenum disulfide (MoS2) with varying morphologies. For this, we employed a space-confined growth method and carried out a methodical spectroscopic analysis to understand the step-by-step reduction of MoO3 under reaction with sulfur vapors and its subsequent transformation to MoS2 on a SiO2 substrate. The sulfur-promoted reduction of MoO3 forming molybdenum dioxide (MoO2), followed by molybdenum oxysulfide (MoOS2) to MoOS2/MoS2 hybrid crystals, and finally monolayer (few layer) triangle (hexagonal) MoS2 crystals, is discussed. The results show that the nucleation presumably initiated by oxy-chalcogenide micro-particles that serve as heterogeneous monolayer nucleation sites. We validate our findings with optical and scanning electron microscope images, micro-Raman, photoluminescence (PL), and x-ray photoelectron spectroscopy (XPS) studies. Our findings can contribute to a better understanding of the growth processes of sequential sulfurization reactions.

Molybdenum oxysulfide MoOS2 as a hydrogen evolution catalyst: On the possible role of coordinated oxygen

Amorphous molybdenum oxysulfide MoOS2 obtained by acidification of aqueous MoO2S22− solutions was structurally characterized and tested as a catalyst for hydrogen evolution reaction (HER). Raman, XPS and XAS characterizations show that the solid contains oligomers based on the Mo(V) core Mo2O2S4 units, exposing dangling MoO bonds and connected via Mo-S-Mo bridges. MoOS2 demonstrated higher HER activity than reference catalysts including nanocrystalline MoS2, amorphous MoS3 and MoS2/MoO2 composite obtained by thermal decomposition of MoOS2. DFT calculations suggest that introduction of oxygen adjacent to the disulfide bridges in the molybdenum coordination does not change significantly the free energy of hydrogen desorption, as compared with fully sulfided MoxSy clusters. Higher HER catalytic activity of the MoOS2 material was explained by abundance of disulfide S22− moieties able to dissociate hydrogen and by fine dispersion of the material.

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Coating of gallium-based liquid metal particles with molybdenum oxide and oxysulfide for electronic band structure modulation.

Liquid metal (LM) droplets are now used in many applications including catalysis, sensing, and flexible electronics. Consequently, the introduction of methods for on-demand alternating electronic properties of LMs is necessary. The active surface of LMs provides a unique environment for spontaneous chemical reactions that enable the formation of thin layers of functional materials for such modulations. Here, we showed the deposition of n-type MoOx and MoOxSy semiconductors on the surface of EGaIn LM droplets under mechanical agitation to successfully modulate their electronic structures. The "liquid solution"-"liquid metal" interaction resulted in the formation of oxide and oxysulfide layers on the surface of LM droplets. The comprehensive study of electronic and optical properties revealed a decrease in the band gap of the droplets after surface decoration with MoOx and MoOxSy, leading to deeper n-type doping of the materials. This method provides a facile procedure for engineering the electronic band structure of LM-based composites when they are necessary for various applications.

Biomass-derived N/P-doped molybdenum oxy-sulfides grown on Ni foam as low-cost electrocatalysts for hydrogen evolution reaction

Biomass-derived N/P-doped molybdenum oxy-sulfides grown on Ni foam as low-cost electrocatalysts for hydrogen evolution reaction

Chemical Properties and Electronic Structure of Molybdenum Oxysulfide Films for Advanced Photoelectrocatalysts for Hydrogen Production

Chemical Properties and Electronic Structure of Molybdenum Oxysulfide Films for Advanced Photoelectrocatalysts for Hydrogen Production

Catalytic synergism in Mn-heterostructured molybdenum oxysulfide hybridized with transition metal phosphides: A robust amorphous water oxidation catalyst

This work aimed to improve the catalytic behavior of semi-conductive amorphous molybdenum oxysulfide (aMoOxSy) as a weak oxygen evolution reaction (OER) catalyst. A simple galvanostatic procedure is employed to hybridize Nickel foam (NF)/Mn-doped aMoOxSy with some amorphous transition metal phosphides (TMPs). Mn-heterostructuring causes an impressive improvement in both morphological properties and OER activity by more than 300% compared with NF/MoOxSy. The hybridization with TMPs (Fe, Co, Ni and Cu) gives a trimetallic composite with strong interfacial interaction, long-term stability, and pronounced OER activity. Further consideration unveils how Mn-doping endows a dramatic synergism upon hybridization of MoOxSy with CoP and NiP (with current boosting≥600%). While no synergism was observed after multiple examinations of CuP and FeP. Density functional theory (DFT) calculations are performed to theoretically address the role of Mn on the electronic features of the hybridized MoOS and the included transition metals. The defined theoretical synergism coefficient (TSC,τ) adhered to the observed trends in the electrochemical measurements. Two independent suggested schemes demonstrate the interfacial coordination pathway of MoOS-based composite. Finally, the NF/Mn-MoOxSy/petals-like 2D NiP nanosheets are recommended as a robust and cost-effective electrocatalyst for OER. It requires overpotentials as low as 191, 299 and 366 mV at the current densities of 10, 100 and 500 mA cm−2, respectively, which are much superior to the benchmark NF/IrO2 catalyst.

Activated carbon-supported AgMoOS bimetallic oxysulfide as a catalyst for the photocatalytic hydrogen evolution and pollutants reduction

Activated carbon (AC) with high porosity and surface area as a catalyst carrier can enhance the catalytic activity and stability of metal nanoparticles with well dispersion to avoid aggregation. Herein, silver molybdenum oxysulfide (AgMoOS) nanoparticles supported by activated carbon with different porous sizes were synthesized through a facile method for photocatalytic H2 evolution reaction and pollutants reduction. The highest H2 evolution of 338.9 µmol/h was obtained by microporous AC-supported AgMoOS ([email protected]) under visible-light irradiation using Na2S/Na2SO3 as a hole scavenger reagent. Likewise, 76.9% of the 4-NP reduction is achieved by in-situ generated proton within 160 min. AC could lower the recombination rate of photo carriers due to its pore channels. Under the dark condition, 10 mg [email protected] completely reduced MB, MO, RhB, 4-NP, and Cr6+ within 4, 4, 9, 9, and 12 min, respectively. This excellent catalytic activity is due to a good dispersion of AgMoOS nanoparticles on AC-1, electron hopping transport of Mo4+→ Mo6+ ions, and surface oxygen vacancy. [email protected] catalyst also exhibits good stability and efficiency that provides a practical catalytic application to reduce chemical pollutants and environmental remediation.

Detection of Trace Water Based on Electro-oxidation of Molybdenum Disulfide Nanomaterials to Form Molybdenum Oxysulfide.

Molybdenum disulfide nanomaterials nowadays are very popular in electrocatalysis field due to their outstanding catalytic performance toward many electrochemical reactions. However, the electrochemical oxidation reaction of molybdenum disulfide nanomaterials in the range of positive potential has not been studied thoroughly. Herein, we have investigated electro-oxidation of molybdenum disulfide nanomaterials and put forward a new reaction mechanism: molybdenum disulfide nanomaterials are electro-oxidized with water to form molybdenum oxysulfide (MoOS2) and hydrogen ions, leading to the release of hydrogen on the counter electrode. Various characterization methods such as contact angle measurement, scanning electron microscope (SEM), transmission electron microscope (TEM) with energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), and gas chromatography (GC) were applied to attest the doping of oxygen and the generation of hydrogen. Based on this reaction, we constructed a novel ultrasensitive electrochemical sensor for detecting trace water with the minimum detectable content of 0.0010% (v/v) in various organic solvents and ionic liquids, which is comparable to the Karl Fischer titration, but with much simpler reagent.

Highly Sensitive NO2 Gas Sensors Based on MoS2@MoO3 Magnetic Heterostructure.

Recently, two-dimensional (2D) materials and their heterostructures have attracted considerable attention in gas sensing applications. In this work, we synthesized 2D MoS2@MoO3 heterostructures through post-sulfurization of α-MoO3 nanoribbons grown via vapor phase transport (VPT) and demonstrated highly sensitive NO2 gas sensors based on the hybrid heterostructures. The morphological, structural, and compositional properties of the MoS2@MoO3 hybrids were studied by a combination of advanced characterization techniques revealing a core-shell structure with the coexistence of 2H-MoS2 multilayers and intermediate molybdenum oxysulfides on the surface of α-MoO3. The MoS2@MoO3 hybrids also exhibit room-temperature ferromagnetism, revealed by vibrating sample magnetometry (VSM), as a result of the sulfurization process. The MoS2@MoO3 gas sensors display a p-type-like response towards NO2 with a detection limit of 0.15 ppm at a working temperature of 125 °C, as well as superb selectivity and reversibility. This p-type-like sensing behavior is attributed to the heterointerface of MoS2-MoO3 where interfacial charge transfer leads to a p-type inversion layer in MoS2, and is enhanced by magnetic dipole interactions between the paramagnetic NO2 and the ferromagnetic sensing layer. Our study demonstrates the promising application of 2D molybdenum hybrid compounds in gas sensing applications with a unique combination of electronic and magnetic properties.

Rearrangement and decomposition pathways of bare and hydrogenated molybdenum oxysulfides in the gas phase.

Molybdenum sulfides and molybdenum oxysulfides are considered a promising and cheap alternative to platinum as a catalyst for the hydrogen evolution reaction (HER). To better understand possible rearrangements during catalyst activation, we perform collision induced dissociation experiments in the gas phase with eight different molybdenum oxysulfides, namely [Mo2O2S6]2-, [Mo2O2S6]-, [Mo2O2S5]2-, [Mo2O2S5]-, [Mo2O2S4]-, [HMo2O2S6]-, [HMo2O2S5]- and [HMo2O2S4]-, on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. We identify fragmentation channels of the molybdenum oxysulfides and their interconnections. Together with quantum chemical calculations, the results show that [Mo2O2S4]- is a particularly stable species against further dissociation, which is reached from all starting species with relatively low collision energies. Most interestingly, H atom loss is the only fragmentation channel observed for [HMo2O2S4]- at low collision energies, which relates to potential HER activity, since two such H atom binding sites on a surface may act together to release H2. The calculations reveal that multiple isomers are often very close in energy, especially for the hydrogenated species, i.e., atomic hydrogen can bind at various sites of the clusters. S2 groups play a decisive role in hydrogen adsorption. These are further features with potential relevance for HER catalysis.

Uv-to-Ir Photocatalytic Continuous Gas-Phase Co2 Reduction Over Ni-Doped Molybdenum Oxysulfide Nanolayers: In Situ EPR and Drifts Study

Uv-to-Ir Photocatalytic Continuous Gas-Phase Co2 Reduction Over Ni-Doped Molybdenum Oxysulfide Nanolayers: In Situ EPR and Drifts Study

Catalytic Synergism in Mn-Heterostructured Molybdenum Oxysulfide Hybridized with Transition Metal Phosphates: A Robust Amorphous Water Oxidation Catalyst

Catalytic Synergism in Mn-Heterostructured Molybdenum Oxysulfide Hybridized with Transition Metal Phosphates: A Robust Amorphous Water Oxidation Catalyst

Uv-to-Ir Photocatalytic Continuous Gas-Phase Co2 Reduction Over Ni-Doped Molybdenum Oxysulfide Nanolayers: In Situ EPR and Drifts Study

Uv-to-Ir Photocatalytic Continuous Gas-Phase Co2 Reduction Over Ni-Doped Molybdenum Oxysulfide Nanolayers: In Situ EPR and Drifts Study

A sustainable molybdenum oxysulphide-cobalt phosphate photocatalyst for effectual solar-driven water splitting

IntroductionHydrogen is considered as a clean alternative green energy future fuel. Since the Honda-Fujishima effect for photoelectrochemical water splitting is known, there has been a substantial boost in this field. Numerous photocatalysts based on metals, semiconductors, and organic-inorganic hybrid-systems have been proposed. Several factors limit their efficiency, e.g., a stable PEC-WS setup, absorbing visible light, well-aligned band energy for charge transfer, electrons and holes, and their separation to avoid recombination and limited water redox reactions. Metallic doping and impregnation of stable and efficient co-catalysts such as Pt, Ag, and Au showed enhanced PEC-WS. We used Cobalt-based co-catalyst with molybdenum oxysulfide photocatalyst for effectual solar-driven water splitting. ObjectivesTo develop photocatalysts for efficient PEC processes capable of absorbing sufficient visible light, good band energy for effective charge transfer, inexpensive, significant solar-to-chemical energy conversion efficiencies. Above all, it is developing such PEC-WS systems that will be commercially viable for renewable energy resources. MethodsWe prepared Molybdenum oxysulphide-cobalt phosphate photocatalyst for PEC-WS through a facile hydrothermal route using ammonium heptamolybdate, thiourea, and metallic Cobalt precursors. ResultsAn effectual photocatalyst is produced for solar-driven water splitting. The conformal morphology of MoOxSy-CoPi nanoflowers is a significant feature, as observed under FE-SEM and HR-TEM. XRD confirmed the degree of purity and orthorhombic crystal structure of MoOxSy-CoPi. EDX and XPS identify the elemental compositions and corresponding oxidation states of each atom. A 2.44 eV band-gap energy is calculated for MoOxSy-CoPi from the diffused reflectance spectrum. Photo- Electrochemical Studies (PEC) under 1-SUN solar irradiation revealed 7-8 folds enhanced photocurrent (∼ 3.5 mA/cm2) generated from MoOxSy-CoPi/FTO in comparison to Co-PI/FTO (∼ 0.5 mA/cm2) and MoOxSy-/FTO respectively, within 0.5 M Na2SO4 electrolyte (@pH=7) and standard three electrodes electrochemical cell. ConclusionOur results showed MoOxSy-CoPi as promising photocatalyst material for improved solar-driven photoelectrochemical water splitting system.

A novel AgMoOS bimetallic oxysulfide catalyst for highly efficiency catalytic reduction of organic dyes and Chromium (VI)

To detoxify chemical pollutants discharge from industries, the researchers pursue always to get new, cost-effective, environmentally friendly and efficient technologies. Herein, novel silver molybdenum oxysulfide (AgMoOS) catalyst which is monoclinic structure with spherical shape nanoparticle and uniform distribution of its elemental composition was successfully synthesized by a facile method. The catalytic performance of AgMoOS was employed for the reduction of methylene blue (MB), methyl orange (MO), 4-Nitrophenol (4-NP), Rhodamine B (RhB) and Chromium (VI) in presence of NaBH4 under dark condition and a fastest reduction activity was obtained with 2-AgMoOS. A 10 mg of 2-AgMoOS completely reduced 100 mL of 20 ppm of MB, MO, 4-NP, RhB and Cr6+ within 6, 6, 15, 24 and 24 min, respectively and the reduction kinetic data indicated that the catalytic activity of all AgMoOS catalysts toward these chemical pollutants followed the order: MB > MO > 4-NP > RhB > Cr6+ ions. The re-usability data toward the reduction of MB, cyclic voltammogram, XPS and XRD spectrum of 2-AgMoOS after the reaction were confirmed a good stability and durability of AgMoOS catalyst. Hence, AgMoOS is an efficient catalyst and provides a practical application for toxic organic dyes degradation and toxic inorganic pollutants containing waste water treatment and other environmental issues.

Hydrophilic Character of Single-Layer MoS2 Grown on Ag(111).

The study of MoS2/metal interfaces is crucial for engineering efficient semiconductor–metal contacts in 2D MoS2-based devices. Here we investigate a MoS2/Ag heterostructure fabricated by growing a single MoS2 layer on Ag(111) by pulsed laser deposition under ultrahigh vacuum (UHV) conditions. The surface structure is observed in situ by scanning tunneling microscopy, revealing the hexagonal moiré pattern characteristic of the clean MoS2/Ag(111) interface. Ex situ Raman spectroscopy reveals an anomalous behavior of vibrational modes, induced by the strong MoS2–Ag interaction. After few-hours exposure to ambient conditions the Raman response significantly changes and the formation of molybdenum oxysulfides is revealed by X-ray photoelectron spectroscopy. These effects are due to the interplay with water vapor and can be reversed by a moderate UHV annealing. A polymeric (PMMA) capping is demonstrated to hinder water-induced modifications, preserving the original interface quality for months.

Selective N2/H2O adsorption onto 2D amphiphilic amorphous photocatalysts for ambient gas-phase nitrogen fixation

The gas-phase Haber–Bosch process has been the main industrial source of ammonia over the last century. However, its reliance on high temperature and high pressure for enormous energy input emits greenhouse gas to air and is associated with the depletion of fossil fuels. The need of the hour is to replace this method with environmentally sustainable processes, among which, photocatalytic nitrogen reduction has attracted much attention. In this work, we report a low cost, scalable manufacturing of gas-phase photoreactors for nitrogen reduction under ambient conditions based on 2D amorphous molybdenum oxysulfides, i.e. MoS2+x-MoO3-y composites. They show excellent nitrogen reduction efficiencies of ∼141 μmol/g/h with remarkably stable performance. The amphiphilic MoS2+x and MoO3-y composites selectively chemisorb and activate N2 and H2O molecules, respectively, and enable multiple photodriven redox reactions towards NH3 evolution. Such photoreactors for ambient ammonia synthesis provides a potentially feasible route towards next-generation gas-phase industrial ammonia production.