Solid-gas Phase Preparation Method for Porous Molybdenum Trioxide

A novel solid-gas reaction preparation technology was used to adjust the composition and microstructure of the composite crystal materials by changing the preparation parameters. Compared with the commonly used sol-gel method, acid base neutralization sedimentation method, hydrothermal method, and gas phase deposition method, the technology was relatively simplified and the elemental composition was controllable, without the use of openings and additives. A kind of multi-element composite porous metal oxide was obtained by pre-intercalation and decarburization. In order to increase the porosity of MoO3 material and promote the adsorption and diffusion of reactant molecules, the microstructure of MoO3 was studied. The preparation process of porous molybdenum trioxide by solid gas combination process was discussed, which provides an innovative idea for the design and preparation of new materials with a large specific surface area and other desirable properties.

Realizing the Long Lifespan of Molybdenum Trioxide in Aqueous Aluminum Ion Batteries Through Potential Regulation

MoO_(3) is one of the most promising anode materials for aqueous aluminum batteries due to its high theoretical capacity and suitable aluminum insertion/de-insertion potential.However,the inferior cycling stability limits its further application,and the failure mechanism is still unclear.In this article,we provide a straightforward potential regulation technique to manage phase evolution during the charge/discharge process,which ultimately results in a markedly enhanced MoO_(3) electrode cycling stability.The failure mechanism study reveals that the excessive oxidation of the electrode during charge/discharge generates the H_(0.34)MoO_(3) phase,which has high solubility and is the primary cause of MoO_(3) deactivation.Although the dissolved Mo species will be deposited onto the electrode sheet again,the deposition is not electrochemically active and cannot contribute to the capacitance.Controlling the cutoff potential prevented the production of H_(0.34)MoO_(3),resulting in excellent cycling performance(80.1% capacity retention after 4000 cycles).The as-assembled α-MoO_(3)//MnO_(2) full battery exhibits high discharge plateaus(1.4 and 0.9 V),large specific capacity(200 mAhg^(-1) at 2 Ag^(-1)),and ultra-high coulombic efficiency(99%).The research presented here may contribute to the development of highly stable electrode materials for aqueous batteries.

Tuning the layer structure of molybdenum trioxide towards high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries(ZIBs) have attracted significant attentions because of low cost and high reliability. However, conventional ZIBs are severely limited by the development of high energy density cathode materials with reversible Zn^(2+)insertion/extraction. Herein, a conducting polymer intercalated MoO_(3)(PMO) with extensively extended interlayer spacing is developed as a high-performance ZIBs cathode material. The interlayer spacing of PMO is prominently increased which results in an improved Zn^(2+)mobility during charge and discharge process. More significantly, the electrochemical results reveals that the intercalation of PANI facilitates the charge storage and reinforces the layered structure of MoO_(3), leading to a high capacity and good cycling stability. DFT calculation further reveals the intercalation of PANI into MoO_(3)significantly lower Zn^(2+)diffusion barrier. Benefit from these advantages, the ZIBs based on PMO electrode delivers a considerable capacity of 157 m Ah/g at 0.5 A/g and ameliorative stability with 63.4%capacity retention after 1000 cycles.

Low-temperature Synthesis of Large-area Films of Molybdenum Trioxide Microbelts in Air and the Dependence of Their Field Emission Performance on Growth Conditions

A simple method is introduced for the preparation of large-area films of molybdenum trioxide （MoO3） microbelts. It is found that such films can be grown on indium tin oxide （ITO） glasses or silicon substrates at low temperatures by thermal evaporation deposition in air without using catalyst. Field emission measurements show that the turn-on field of the MoO3 microbelts is as low as 2.2 V/μm required to obtain a current density of 10 μA/cm^2, The combination of the simplicity of the growth method and the attractive field emission performance makes it a potential low-cost technique for the preparation of large-area field emission cold cathode material.

Reduction characteristics of molybdenum trioxide with aluminum and silicon

Thermodynamics for reduction of molybdenum oxides by aluminum and silicon were calculated, and the results show that reduction reaction is feasible at a certain temperature region. Compared to the presence of CaO or CaCO3, reduction products of molybdenum trioxide with aluminum and silicon at various temperatures were detected by X-ray diffraction （XRD）. Results show that molybdenum trioxide is reduced by aluminum or silicon step by step, and the intermediate product is MOO2. At 1000 ℃, molybdenum trioxide could be reduced to metal Mo by aluminum, and in the presence of CaO, metal Mo as the reduction product appears even at 800 ℃. In contrast, silicon could barely reduce molybdenum trioxide to metal Mo even at 1200℃. In the presence of CaO or CaCO3, reducibility of silicon increases significantly, and the reduction products are metal Mo and MoSi2. Altogether, CaO or CaCO3 performs two major roles in reduction process： restraining sublimation of MoO3 and decreasing the temperature of reducing MoO3 to metal Mo.

Membrane-less MoO_(3-x)@TiO_(2)-bromine battery with excellent rate capability and cyclic stability

Bromine has attracted significant attention as a cathode material for aqueous batteries due to its high reduction potential of 1.05 V(Br_(3)^(-)+2e~-■3Br~-),impressive theoretical specific capacity of 223 mA h g^(-1),and rapid reaction kinetics in the electrolyte.However,searching for compatible anode materials to match with bromine has posed a challenge due to its highly corrosive nature.In this study,we developed oxygen-deficient MoO_(3) with TiO_(2) coating(referred to as MoO_(3-x)@TiO_(2))as an anode material to pair with a bromine cathode in static full batteries.The oxygen deficiency contributes to enhanced electronic and protonic diffusion within the MoO_(3-x)lattice,while the TiO_(2) coating mitigates structural dissolution and proton trapping during cycling.The MoO_(3-x)@TiO_(2) demonstrates fast charge storage kinetics and excellent resistance to bromine corrosion.The impressive compatibility between MoO_(3-x)@TiO_(2) and bromine enables the construction of membrane-less full batteries with exceptional rate capability and cyclic stability.The MoO_(3-x)@TiO_(2)-bromine battery achieves an energy density of70.8 W h kg^(-1)at a power density of 328.1 W kg^(-1),showcasing an impressive long-term cyclic life of 20,000 cycles.Our study provides valuable insights for the development of high-performance aqueous secondary batteries.

Dispersion and Structure Studies of Molybdenum Oxide on Anatase TiO_2

X-ray photoelectron spectroscopy(XPS) and extended X-ray absorption fine structure(EXAFS) were used to characterize the structure of the mixture of molybdenum oxide and anatase calcined at 723 K. The results indicate that molybdenum oxide can disperse onto the surface of anatase(TiO 2) and the dispersion threshold is 11.2 mg in per gram of MoO 3 or 4.8 Mo atoms/nm 2 TiO 2. When the content of MoO 3 is below the dispersion threshold, MoO 3 species is in highly dispersed state interacting strongly with TiO 2 support and in discrete tetrahedral coordination, [MoO 4], on the surface of TiO 2. When the MoO 3 loading is above this value, MoO 3 exists in both dispersed phase and crystalline phase. MoO 3 in dispersed phase is still a discrete [MoO 4] tetrahedron; MoO 3 in crystal phase is in octahedral coordination.

Electromagnetic and Thermal Characteristics of Molybdenite Concentrate in Microwave Field

In modern metallurgical industry,microwave thermal technique has many advantages as one efficient energy treatment in an electromagnetic form,such as internal self-generated heat,easy access to control a volumetric heating process,and consensus on cleanliness,convenience and high efficiency of energy use.Both permittivity and permeability of molybdenite concentrate were measured for a further discussion about its electromagnetic heating coupling.A bidirectional coupling physics field in numerical modeling was undertaken to evaluate the microwave absorption potential and dielectric heating performance of molybdenite concentrate by the multi-physics finite element method.The electromagnetic morphology and the field distribution strength were described in the microwave reaction cavity.The electromagnetic field strength and the dissipation coefficient induced by temperature variation were represented throughout the whole heat chamber and at key parts of interest.Dependent temperature distribution was compared with that being obtained from a scenario by thermal conduction with a stable heat source.The molybdenite concentrate would be heated at surrounding temperature up to 593℃for 10 min by microwave energy that was transmitted by a rectangular waveguide.Scanning electron microscopy(SEM)patterns suggested that the polished and neat crystalline molybdenum trioxide(MoO_(3))products were achieved by the microwave heating process.The superiority via utilizing microwave thermal technique is expounded in the preparation strategy for molybdenum oxide or molybdenum metal.

Characterization of V_2O_5/MoO_3 composite photocatalysts prepared via electrospinning and their photodegradation activity for dimethyl phthalate

Vanadium pentoxide（V2O5）/molybdenum trioxide（MoO 3） composites with different molar ratios of vanadium（V） to molybdenum（Mo） were synthesized via a simple electrospinning technique. The photocatalytic activity of the composites were evaluated by their ability to photodegrade methylene blue and dimethyl phthalate（DMP） under visible-light irradiation. Compared with pure V2O5 and MoO 3,the V2O5/MoO 3 composites showed enhanced visible-light photocatalytic activity because of a V 3d impurity energy level and the formation of heterostructures at the interface between V2O5 and MoO 3. The optimal molar ratio of V to Mo in the V2O5/MoO 3 composites was found to be around 1/2. Furthermore,high-performance liquid chromatographic monitoring revealed that phthalic acid was the main intermediate in the photocatalytic degradation process of DMP.

SO_2-tolerant Pt-MoO_3/C catalyst for oxygen reduction reaction

A Pt-MoO3/C catalyst,aimed to eliminate the harmful effect of sulfur dioxide（SCb） on the performance of Pt nanoparticles（NPs） for catalysis of oxygen reduction reaction（ORR） in proton exchange membrane fuel cells（PEMFC）,is developed and characterized by TEM,XRD and XPS.The results reveal that Pt-MoO3/C catalyst exhibits not only a higher catalytic activity,but also a better SO2 poisoning resistance and a better recovery performance than the commercial Pt/C catalyst does.

Thinner 2D α-MoO_(3) makes setting up memristors easier

Two-dimensional(2D)metal oxide α-MoO_(3) shows great potentials because of its very high dielectric constant,air stability and anisotropic phonon polaritons.However,a method to produce ultrathin single crystallineα-MoO_(3) with high transferability for functional device architecture is lacking.Herein,we report on the controllable synthesis of ultrathinα-MoO_(3) single crystals via chemical vapor deposition(CVD)assisted by plasma pretreatment.We also carried out systematic computational work to explicate the mechanism for the slantly-oriented growth of thin nanosheets on plasma-pretreated substrate.The method possesses certain universality to synthesize other ultrathin oxide materials,such as Bi_(2)O_(3) and Sb_(2)O_(3) nanosheets.As-grownα-MoO_(3) presents a high dielectric constant(≈40),ultrathin thickness(≈3 nm)and high transferability.Memristors withα-MoO_(3) as the functional layers show excellent performance featuring high on/off ratio of approximately 104,much lower set voltage around 0.5 V,and highly repetitive voltage sweep endurance.The power consumption of MoO_(3) memristors is significantly reduced,resulted from reduced thickness of the MoO_(3) nanosheets.Single crystal ultrathinα-MoO_(3) shows great potentials in post-Moore memristor and the synthesis of CVD assisted by plasma pretreatment approach points to a new route for materials growth.

Oxygen vacancy-rich MoO_(3)nanorods as photocatalysts for photo-assisted Li-O_(2) batteries

Photo-assisted lithium-oxygen(Li-O_(2))batteries have been developed as a new system to reduce a large overpotential in the Li-O_(2)batteries.However,constructing an optimized photocatalyst is still a challenge to achieve broad light absorption and a low recombined rate of photoexcited electrons and holes.Herein,oxygen vacancy-rich molybdenum trioxide(MoO_(3-x))nanorods are employed as photocatalysts to accelerate kinetics of cathode reactions in the photo-assisted Li-O_(2)batteries.Oxygen vacancies on the MoO_(3-x)nanorods can not only increase light-harvesting capability but also improve electrochemical activity for the cathode reactions.Under illumination,the photoexcited electrons and holes are effectively separated on the MoO_(3-x)nanorods.During discharging,activated O2 is reduced to Li_(2)O_(2)by the photoexcited electrons from the MoO_(3-x)nanorods.The photoexcited holes can promote the decomposition of Li_(2)O_(2)during subsequent charging.Accordingly,the photo-assisted Li-O_(2)batteries with the MoO_(3-x)nanorods deliver an ultralow overpotential of 0.22 V,considerable rate capability,and good reversibility.We think that this work could give a reference for the exploitation and application of the photocatalysts in the photo-assisted Li-O_(2)batteries.

Piezoresistive effect in MoO3 nanobelts and its application in strain-enhanced oxygen sensors

MoO3 nanobelts （NBs） having different properties have been synthesized via a physical vapor deposition （PVD） method. The crystallographic structures and morphologies of the NBs were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Electrical measurements were performed and the profound piezoresistive effect in MoO3 experimentally studied and verified. Factors that influence the gauge factor, such as NB size, doping concentration and atmosphere composition, are discussed and analyzed. Gas sensing performance was also tested in devices and it was demonstrated that by applying strain to the gas sensor, its sensing performance could be effectively tuned and enhanced. This study provides the first demonstration of significant piezoresistivity in MoO3 NBs and the first illustration of a generic mechanism by means of which this effect can be coupled with other electronic modulation measures to afford better device performance and broader material functionality.

Carbothermic Reduction of MoO_3 for Direct Alloying Process

The thermodynamics of Mo-O- C and Ca-Mc-O-C systems was studied in order to understand the carbothermic reduction of molybdenum trioxide, and kinetic studies were also carried out by means of thermogravimetrie analysis under argon atmosphere with a heating rate of 10 ℃/min. Subsequently, reaction products at various temperatures were identified by X-ray diffraction （XRD） and the results confirmed the previous thermodynamics analysis. Mean- while, it was found that intermediate products MoO2 and CaMoO4 appeared in the process of carbothermic reduction of MoO3 with or without CaO, which were subsequently reduced to Mo or molybdenum carbide. An experimentally determined reaction mechanism was proposed and discussed. The reduction reaction of MoO3 with carbon could be divided into two stages. The first stage includes the direct reaction between MoO3 and carbon and the carbon gasifica- tion reaction. The second stage is the gas-solid reaction between CO and MoO2, and the diffusion of gases through the surface of MoO2 determines the overall reaction rate. The activation energies of the mixtures with or without CaO were estimated to be 56.6 and 52.9 kJ/mol, respectively.