Molybdenum Bronze Research Articles

Heterogeneous Structure of Ni-Mo Nanoalloys Decorated on MoOx for an Efficient Hydrogen Evolution Reaction Using Hydrogen Spillover.

Herein, a heterogeneous structure of Ni-Mo catalyst comprising Ni4Mo nanoalloys decorated on a MoOx matrix via electrodeposition is introduced. This catalyst exhibits remarkable hydrogen evolution reaction (HER) activity across a range of pH conditions. The heterogeneous Ni-Mo catalyst showed low overpotentials only of 24 and 86, 21 and 60, and 37 and 168mV to produce a current density of 10 and 100mAcm-2 (η10 and η100) in alkaline, acidic, and neutral media, respectively, which represents one of the most active catalysts for the HER. The enhanced activity is attributed to the hydrogen spillover effect, where hydrogen atoms migrate between the Ni4Mo alloys and the MoOx matrix, forming hydrogen molybdenum bronze as additional active sites. Additionally, the Ni4Mo facilitated the water dissociation process, which helps the Volmer step in the alkaline/neutral HER. Through electrochemical analysis, in situ Raman spectroscopy, and density functional theory calculations, the fast HER mechanism is elucidated.

Effect of molybdenum disulfide and bronze on tribological behaviors of polytetrafluoroethylene composites

The present paper explains study of the tribological behavior for composite materials having the filler combinations of Molybdenum Disulfide and Bronze with base material of Polytetrafluoroethylene. Polytetrafluoroethylene (PTFE) is polymer based compound also named as Teflon discovered by Roy J. Plunkett in the year 1938 with melting point of 327 °C. It is a crystalline solid with good stability from –2700C to + 2600C and is chemically inert to known reagents and solvents. The fillers used are 10 % Molybdenum Disulfide and Bronze is varied in the proportions as 15 %, 25 % and 40 %. The experimental testing is done using the ASTM G99 standards with three different sampling experiments. The experiments are analyzed using Taguchi and Grey Regression Analysis.The experimental samples are tested using Energy Dispersive Spectroscopy and Scanning Electron microscopy. The results of the analysis of variance for this type of materials combinations shows the optimum level of parametric setting as A3B1C3D3 corresponding to factors conditions load (3Kg), sliding distance (2Km), velocity (3.29 m/s) and material (PTFE + 40 %Bronze + 10 %MoS2). The maximum values of grey relational grades for the corresponding the factors are load (0.7610), sliding distance (0.6570), velocity (0.6688) and material (0.7176) from the ANOVA table for the experimental results. The rank order for the analysis are load > sliding distance > velocity > material. Also it can be noted that the load (50 %), material (20 %) have dominant effect on the coefficient of friction and wear. Among the interaction the effect of load-sliding distance (8 %) is considerable one.

Bulk Contact Between Silver Nanowires Top Electrode and Interface Layer Enables High Performance of Full‐Solution‐Processed Semitransparent Organic Solar Cell Module

The solution‐processed electrode is key to the full‐solution‐processed organic solar cells (OSCs). Silver nanowires (AgNWs) are considered as an attractive solution‐processed electrode due to their low sheet resistance and high transmittance. However, the traditional “line‐plane” contact between AgNWs and the interface buffer layer is insufficient, resulting in the low performance of full‐solution‐processed OSCs. Herein, a bulk contact structure is reported between AgNWs and interface, formed by inserting the interface layer material, such as HMoOx (hydrogen molybdenum bronze) into the AgNWs networks. The extra HMoOx can be connected with the bottom interface buffer layer, forming a longitudinal network, and wrapping the AgNWs in the longitudinal interfacial layer. This bulk contact electrode‐interface structure increases the area of AgNWs/interface layers, promoting charge transfer and collection. Besides, the top‐injected method can enable the formation of a water‐based ink film on the top of the organic layer, as well as avoid solvent erosion between AgNWs and the interface layer. Based on the bulk contact electrode‐interface structure, this work realized high performance of 12.27% and 9.54% for 0.09 cm2 small‐area device and 10.8 cm2 full‐solution‐processed semitransparent mini‐module. These results provide a new idea for full‐solution‐processed OSCs preparation.

Co(OH)2 Intercalated in MoO3 by Molecular Electrodeposition Resulting in a Conductive Material: A Molybdenum Bronze for Efficient Electrocatalytic Hydrogen Evolution

Co(OH)₂ Intercalated in MoO₃ by Molecular Electrodeposition Resulting in a Conductive Material: A Molybdenum Bronze for Efficient Electrocatalytic Hydrogen Evolution

The Influence of Electrode Constituents on Hydrogen Evolution Reaction on Phosphate W- and Mo-Bronze-Based Electrodes

Phosphate tungsten bronze (WPB) and phosphate molybdenum bronze (MoPB) were synthesized and modified with rhenium. The existing phases were established by X-ray powder diffraction (XRPD), electron paramagnetic spectroscopy (EPR) and Field emission scanning electron microscopy (FESEM). The electroactivity of bronze samples, with and without rhenium for hydrogen evolution reaction (HER) was tested. The influence of carbon black presence in the catalytic ink on the electrochemical activity was investigated. Collected results provide insight into the effects of the constituents of an electrode on its electrochemical activity.

Guidelines for the synthesis of molybdenum nitride: Understanding the mechanism and the control of crystallographic phase and nitrogen content

Bulk (Mo2N) and supported molybdenum nitride (Mo2N/TiO2, Mo2N/CeO2) were synthesized by reduction-nitridation of bulk and supported MoO3 under a mixture of N2/H2. We investigated the mechanism of formation of molybdenum nitrides by coupling elemental analysis, in situ and ex situ XRD, Raman spectroscopy, in situ XPS/UPS spectroscopy and DFT calculation. We showed that it is possible to control the crystallographic phase and degree of nitridation (i.e. nitrogen vacancies) by adjusting the parameters of the synthesis, including the heating rate and final temperature, the nature, composition and flow of gas during reduction/nitridation and cooling. We demonstrated that β-Mo2N and γ-Mo2N go through the same intermediates: molybdenum bronze, MoO2 and Mo. The final crystallographic phase of the nitride depends mainly on the temperature rate and gas hourly space velocity employed during the synthesis, as they impact the crystallite size of the intermediates and the kinetics of reduction and nitridation. Molybdenum nitride clusters (<0.5 nm) are formed on TiO2.

NIR‐II Photo‐Amplified Sonodynamic Therapy Using Sodium Molybdenum Bronze Nanoplatform against Subcutaneous Staphylococcus Aureus Infection

AbstractUltrasound (US)‐mediated sonodynamic therapy (SDT) has the advantages of non‐invasiveness and deep tissue penetration. Nanosystems are prominently used in sonosensitization; however, most nano‐sonosensitizers have a low reactive oxygen species (ROS) yield, thus restraining the application of SDT. Sodium molybdenum bronze nanoparticles (SMB NPs) with rich oxygen vacancies are developed and interlayer gaps of molybdenum trioxide nanobelts are expanded. Owing to the increased oxygen vacancy density and wide interlayer gap‐induced narrower band gap of SMB NPs, the electrons (e–) and holes (h+) generated by US are separated more rapidly, and oxygen vacancies prevent electrons–holes recombination under US irradiation. SMB NPs exhibit a second near‐infrared (NIR‐II) photothermal effect to promote the generation of ROS by the sonosensitizer. The SMB NPs system is successfully realized to eliminate Staphylococcus aureus (S. aureus) and dissipate biofilm. Therefore, multimodal therapy using SMB NPs serves as an effective and promising regimen for deep‐seated bacterial infections. The newly developed Mo‐based sonosensitizer is presented for the first time to demonstrate excellent antimicrobial activity through hyperthermia‐promoting SDT therapeutics. This work proposes a novel strategy in the field of NIR‐II photo‐amplified SDT with Mo‐based materials for bacterial eradication and other important biomedical applications.

In Situ X-ray Diffraction Studies on the Production Process of Molybdenum.

During the production of molybdenum, the first reduction step of molybdenum trioxide to molybdenum dioxide is crucial in directing important product properties like particle size and oxygen content. In this study, the influence of heating rate, hydrogen flow, and potassium content on the reduction of MoO3 has been investigated via in situ X-ray powder diffraction. For low heating rates, a molybdenum bronze HxMoO3 could be confirmed as an intermediate, while γ-Mo4O11 can only be observed at high heating rates. Molybdenum formation at temperatures as low as 873 K can be controlled via hydrogen flow. The potassium content of reactants has a direct influence on the amount of Mo4O11 formed during the reaction as well as rates of Mo4O11 and MoO2 formation.

Evidence of ammonia synthesis by bulk diffusion in cobalt molybdenum particles in a CLAS process

For the first time ammonia-synthesis-on-nitridation has been reported in CoMo during a chemical looping ammonia synthesis experiment. The observation lends evidence to the existence of a dynamic surface, a shrinking core and counter diffusion. The Mars-van Krevlen mechanism involving surface and bulk exchange has been established for the CoMo system under H2:N2 atmospheres was extended into the CLAS domain and complicated by the existence of an unreacted oxide core containing molybdenum bronzes, HxMoO3. This OH−1 diffuses outward as the core is stabilized by N−3, resulting in the observation of gas phase H2O and NH3 in the absence of gaseous H2.

Single Crystals of α-MoO3-Intercalated {Ni(H2O)6}2+ and Electrocatalytic Water Reduction: Toward a Class of Molybdenum Bronzes.

We have successfully intercalated {NiII(H2O)6}2+ into the α-MoO3 layer, leading to the isolation of green single crystals of [MoVI2O6(CH3COO){NiII(H2O)6}0.5]·H2O (1). The homogeneous electrochemistry of 1 in its aqueous solution exhibits electrocatalytic hydrogen evolution reaction (HER) with concomitant electrochemical deposition of [HMo3VIMoVO12(CH3COO){NiII(H2O)5(OH)}] (2). Compound 2, a new molybdenum bronze, acts as an efficient and stable heterogeneous electrocatalyst for water reduction to molecular hydrogen. This work represents the first paradigm of a molybdenum bronze intercalating a transition metal-aqua ion.

Hydrodeoxygenation of Aromatic Ketones under Mild Conditions over Pd-loaded Hydrogen Molybdenum Bronze with Plasmonic Features

Abstract Reduction of α-MoO3via “hydrogen spillover” process mediated by noble metal nanoparticles leads to a formation of hydrogen molybdenum bronze with plasmon-induced optical features. We herein report that Pd-loaded hydrogen molybdenum bronze effectively promotes the hydrodeoxygenation of aromatic ketones to the corresponding alkyl aromatics at room temperature and under atmospheric pressure of H2. The catalyst shows a further enhanced catalytic activity under the irradiation of visible light due to the plasmonic effect.

Nearly fully opened charge density wave gap in the quasi-two-dimensional conductor γ−Mo4O11 : A comparative study with η−Mo4O11

The accommodation of Luttinger liquid behavior and unique quasiparticles in the charge density wave (CDW) state has led to renewed interest in the low-dimensional molybdenum bronzes. Here, the authors report a comprehensive experimental study on the quasi-two-dimensional CDW oxide bronzes Mo${}_{4}$O${}_{11}$, in which the CDW instability is dominated by hidden Fermi surface nesting, resulting in magnetic field induced quantum oscillations. Different from the monoclinic $\ensuremath{\eta}$ phase, the orthorhombic $\ensuremath{\gamma}$ phase shows a flexible CDW transition with a nearly fully opened gap, as seen in nonlinear transport behavior related to the CDW sliding motion, which is only observed in quasi-one-dimensional systems.

Pseudocapacitance improvement of polymolybdates-based metal–organic complexes via modification with hydrogen molybdenum bronze by electrochemical treatment

The preparation of highly pseudocapacitive electrode materials is important for development of supercapacitors. In this work, a kind of new electrode material, namely, hydrogen molybdenum bronze (HMB) modified polymolybdate-based metal–organic complex {Cu(3-H2bptzh)(H2O)2[γ-Mo8O26]}·(3-H2bptzh)·H2O (1) (1-HMB) was prepared by electrochemical treatment (3-bptzh = 1,4-bis(5-(3-pyridyl)tetrazolyl) -hexane), aiming for promoting the pseudocapability of polymolybdates-based complexes. The carbon cloth-based electrode with 1-HMB (1-HMB/CC-0.15), which was obtained through electrochemical treatment between potential range of − 0.15 and 0.5 V (vs. SCE) achieved a high specific capacitance of 807.2F g−1 at the current density of 1 A g−1. The active sites and the mixed valence brought by the amorphous HMB layer give rise to the improved pseudocapacitance. 1-HMB/CC-0.15 can maintain 89.7% of its initial capacitance after 5000 galvanostatic charge/discharge cycles. In order to probe the effect brought by the structure of complex precursor, two new polymolybdates-based complexes {Cu(3-H2bptzpe)2[γ-Mo8O26]} (2) and {Cu2(3-bptzp)2(H2O)4[γ-Mo8O26]} (3) (3-bptzpe = 1,4-bis(5-(3-pyridyl)tetrazolyl)-pentane, 3-bptzp = 1,4-bis(5-(3-pyridyl)tetrazolyl)-butane) were synthesized and used as electrode material precursors as well. However, no HMB was produced on the surface of complexes 2 and 3 by similar electrochemical treatment. 1-HMB/CC-0.15 is taken as cathode to assemble an asymmetric supercapacitor (ASC) device, which demonstrates an ultrahigh energy density of 23.71 Wh kg−1 at the power density of 0.7 KW kg−1. After 5000 galvanostatic charge/discharge cycles, the aqueous ASC device can retain 86.8% of its capacitance, showing good cyclic stability. The effects brought by the electrochemical treatment and the structure of complexes on the pseudocapacitive behavior are discussed, respectively.

Pressure-induced structural transitions triggering dimensional crossover in the lithium purple bronze Li0.9Mo6O17

At ambient pressure, lithium molybdenum purple bronze (Li0.9Mo6O17) is a quasi-one dimensional solid in which the anisotropic crystal structure and the linear dispersion of the underlying bands produced by electronic correlations possibly bring about a rare experimental realization of Tomomaga-Luttinger liquid physics. It is also the sole member of the broader purple molybdenum bronzes family where a Peierls instability has not been identified at low temperatures. The present study reports a pressure-induced series of phase transitions between 0 and 12 GPa. These transitions are strongly reflected in infrared spectroscopy, Raman spectroscopy, and x-ray diffraction. The most dramatic effect seen in optical conductivity is the metallization of the c-axis, concomitant to the decrease of conductivity along the b-axis. This indicates that high pressure drives the material away from its quasi-one dimensional behavior at ambient pressure. While the first pressure-induced structure of the series is resolved, the identification of the underlying mechanisms driving the dimensional change in the physics remains a challenge.

Direct Exfoliation of Conductive MoS2 Using Peroxide for Solid State Sensor and Catalytic Applications

Two-dimensional (2D) materials have attracted much attention over the last decade due to their high performance in nanoelectronic devices. The discovery of graphene opened up many opportunities to investigate and explore other 2D materials. There has been a drive to expand the toolbox of 2D materials to also include insulators and semiconductors with a variety of bandgaps. As a result, a wide range of materials have been discovered or predicted, with molybdenum disulfide (MoS2) being particularly popular. Using the semiconducting phase of MoS2 (2H-MoS2) requires a relatively high voltage to get sufficient conductivity due to the presence of a band gap. However, for applications in batteries, supercapacitors, electrocatalysts and solar cells, a substantially increased conductivity is required in order to achieve reasonable currents.1 The most common source of conductive MoS2 is metallic MoS2 (1T-MoS2) that has been prepared via the lithium intercalation process, which requires inert atmosphere processing and safety procedures.2 Hence, there is a desire to develop a safer and more efficient process to yield conductive MoS2. Defects play a very important role in modulating the electrical properties of MoS2. Sonication of MoS2 in an appropriate solvent results in many disordered structural defects. The most common defects on MoS2 are sulfur defects. These defects increase the energy level of the gap state and eventually deteriorate the device performance. Thiol based molecules are commonly used to reduce the number of sulfur defects on MoS2. Other molecules such as oxygen or organic super acids like bis(trifluoromethane) sulfonamide (TFSI) have also been reported to passivate the surface defect.3 Past research has mainly focused on the theoretical study of defective MoS2 and how to utilize those defects for improving photoluminescent efficiency. However, those defects can also be utilized to improve the conductivity of MoS2 as a safer alternative for applications in batteries, supercapacitors, solar cells, electrocatalyst and sensors.Conductive MoS2 (c-MoS2) can be used as active material for low-cost solid-state chemiresistive pH sensors.4 In chemiresistive sensors, conductivity changes are observed based on direct interactions between the active material and the analyte.5 Even though chemiresistive pH sensors based on exfoliated graphene, carbon nanotubes, or graphitic materials are available, their sensing response is limited to less than 20%.6 On the other hand, MoS2 has attracted great attention as a promising electrocatalyst for the hydrogen evaluation reaction (HER) because of abundant active sites at edge sites and on the basal plane for facilitating hydrogen production. Water splitting is the simplest and most convenient method to generate hydrogen. In industrial applications, an electrocatalyst is commonly used to accelerate the HER and reduce the overpotential. Even though 2H-MoS2 has good catalytic activity at the edge sites, its low electrical conductivity limits the achievable current density, resulting in a high Tafel value and making it unsuitable for practical application in HER.In this work, we show a simple and effective way to prepare few layer c-MoS2 under ambient conditions using 0.06 vol% aqueous hydrogen peroxide. We have demonstrated that the bulk conductivity of the conductive MoS2 that we prepared is up to seven orders of magnitude higher than that of the semiconducting phase of MoS2. The samples were also characterized with Hall measurements, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy which showed that hydrogen molybdenum bronze (HxMoO3) and substoichiometric MoO3−y help tune the conductivity of the nanometer-scale thin films without impacting the sulfur-to-molybdenum ratio. C-MoS2 was further functionalized with thiols to determine the number of residual reactive sites. An important goal of our work is to control the conductivity of the MoS2 thin films in safe and facile ways that enable their application in low-cost chemiresistive sensors in liquid environments. We fabricated chemiresistive pH sensors with centimeter channel lengths while maintaining low measurement voltages. We further measured the catalytic activity of c-MoS2 films in 0.5 M H2SO4 electrolyte solution with three electrode systems using linear sweep voltammetry (LSV) which showed a lower Tafel value at 10 mA/cm2 current density. The lower Tafel value demonstrated that c-MoS2 has potential to use as catalyst for HER. Our study furthers the understanding of conductive forms of MoS2, and also opens up a new pathway for next generation electronic and energy conversion devices.

Visible light photodegradation of dyes and paracetamol by direct sensitization mechanism onto metallic MoO2 nanocrystals

MoO2 nanocrystals were prepared by solvothermal treatment of a Mo chloromethoxide at 250 °C in oleic acid. The monoclinic MoO2 phase, with a mean crystallite size of 29 nm, formed through reduction of molybdenum bronzes. The as-prepared MoO2 nanocrystals were free from organics, allowing their use in photodegradation tests of organic pollutants (methylene blue, rhodamine B, paracetamol), without any preliminary purification treatment of the nanocrystals. It was found that MoO2 was an efficient adsorbent of methylene blue (43 mg g−1 for 1.5 × 10−4 M concentration) in the dark and an efficient photodegradation catalyst under visible light (all methylene blue removed from the solution after 240 min). From the analysis of the combined photodegradation tests of rhodamine B and paracetamol, it was clarified that direct sensitization was responsible for photodegradation. This finding was related to the work function value of metallic MoO2, placed at more negative values if compared with other metallic materials.

Quantum oscillations and magnetic field induced Fermi surface reconstruction in the charge density wave state of A0.9Mo6O17 (A=Na,K)

We present a detailed study of the magnetotransport properties of the charge density wave state in quasi-two-dimensional purple bronze ${\mathrm{Na}}_{0.9}{\mathrm{Mo}}_{6}{\mathrm{O}}_{17}$ under pulsed fields up to 62 T. Pronounced Shubnikov--de Haas (SdH) oscillations of three frequencies have been observed in the field induced charge density/spin density wave state of the present compound. The two slow oscillations are attributed to the reconstructed electron and hole pockets near the ${M}^{\ensuremath{'}}$ point of the Brillouin zone (BZ). The highest-frequency oscillations correspond to an orbit occupying 18.1% of the BZ, which is consistent with the hexagonal electron Fermi surface in the normal state. The appearance of the highest-frequency oscillations can be explained by the magnetic breakdown between the electron pockets at the ${M}^{\ensuremath{'}}$ point. This magnetic breakdown behavior has also been observed in ${\mathrm{K}}_{0.9}{\mathrm{Mo}}_{6}{\mathrm{O}}_{17}$ under very high field range up to 80 T. Based on analyses of the high field SdH oscillations, we propose a possible Fermi surface structure of ${\mathrm{Na}}_{0.9}{\mathrm{Mo}}_{6}{\mathrm{O}}_{17}$.

Efficient Electrochemical/Electroless Deposition Synthesis Routines for CO Tolerant Catalysts

Composite catalysts containing Pt and Mo-oxides are promising materials for anodic catalyst preparation in PEMFCs due to their high tolerance for CO-poisoning. The search for optimal preparation methods for these materials is an important task in modern electrochemical energetics.Two synthetic routines, namely electrodeposition and deposition under open-circuit conditions, were used for Pt-MoO x catalyst preparation. The prepared catalysts were characterized by a variety of modern physical methods (XRD, XPS, SEM, EDX); it was established that the material prepared by electroless deposition contains platinum shell upon platinum core. The materials obtained were tested in the reactions of CO adsorbate electrodeposition and dissolved CO-oxidation.It was found that molybdenum oxides in the composites prepared by electrodeposition broaden the major peak of CO-oxidation, but the peak maximum does not shift toward less positive values. Therefore, the CO monolayer is destabilized as a result of the contact with molybdenum oxides; however, only a small part of CO can be oxidized at these low potentials. Nevertheless, these catalysts are suitable for dissolved carbon monoxide oxidation. aPt·b(H x -2MoO3) composites were synthesized by the redox reaction of K2PtCl4 with reduced forms of hydrogen containing molybdenum bronzes. The CO desorption peak is broadened and shifted toward less positive potentials. aPt·b(H x -2MoO3) catalysts demonstrate high catalytic activity in the reaction of both adsorbed and dissolved CO oxidation. Therefore, one can conclude that both electrodeposition and electroless deposition are suitable methods for preparing PEMFC anode catalysts. Figure 1

Two-Phase Electrochemical Proton Transport and Storage in α-MoO3 for Proton Batteries

Summary Diffusion-controlled charge storage and phase transitions of electrodes are typical indicators of sluggish kinetics in battery chemistries. However, fast rate capabilities are found in an α-MoO3 proton intercalation electrode that presents both features. Here, the unique topochemistry is shown to involve multiple ion-electrode interactions and proceeds via two key steps: hydronium adsorption on surfaces and proton insertion into bulk lattices. This triggers structure transitions from MoO3 to hydrogen molybdenum bronzes (HMBs). Following the first process, subsequent rearrangements proceed only among HMBs phases with high reversibility and kinetics, thus providing structural explanations to the fast rate capability. At electrode-electrolyte interfaces, hydronium is the active charge carrier that initiates charge transfer and surface hydration, which are accompanied by water adsorption/desorption with reduced polarization and enhanced kinetics. Further water activity is shown to induce material dissolution during function. These findings offer fundamental insights in proton chemistries, which may form the basis of future high rate and capacity energy storage.

Reproducible Electrodeposition of Hydrogen Molybdenum Bronze Films and Electrochemical Reduction of Carbon Dioxide

Electrochemical synthesis of hydrogen bronze films including molybdenum, tungsten and vanadium are useful electrocatalytic films. This paper describes reproducible hydrogen molybdenum bronze film formation on indium tin oxide and carbon paper substrates by electrodeposition. Film formation is a kinetic process dependent on concentration, time and potential. Bulk electrolysis over time determined the dependence of film thickness on time of deposition. Once the films were prepared, the films were characterized by thickness, conductivity, XPS and X-Ray Diffraction. Cyclic voltammetry in dilute sulfuric acid confirmed that these films are not electrochromic. Hydrogen bronze films on conductive carbon paper were also prepared. Carbon dioxide bubbled into 0.5 M NaHCO3 using a hydrogen bronze film as the working electrode resulted in formate quantified by ion chromatography. Cyclic voltammetry and Tafel plots using the as deposited films in 0.5 M NaHCO3 saturated with CO2 showed catalytic activity toward reduction of carbon dioxide. A Farradaic efficiency of 8% was obtained with an applied potential of -0.4 V.