Molybdenum Oxide Research Articles

Reverse water gas-shift reaction product driven dynamic activation of molybdenum nitride catalyst surface

In heterogeneous catalysis catalyst activation is often observed during the reaction process, which is mostly attributed to the induction by reactants. In this work we report that surface structure of molybdenum nitride (MoNx) catalyst exhibits a high dependency on the partial pressure or concentration of reaction products i.e., CO and H2O in reverse water gas-shift reaction (RWGS) (CO2:H2 = 1:3) but not reactants of CO2 and H2. Molybdenum oxide (MoOx) overlayers formed by oxidation with H2O are observed at reaction pressure below 10 mbar or with low partial pressure of CO/H2O products, while CO-induced surface carbonization happens at reaction pressure above 100 mbar and with high partial pressure of CO/H2O products. The reaction products induce restructuring of MoNx surface into more active molybdenum carbide (MoCx) to increase the reaction rate and make for higher partial pressure CO, which in turn promote further surface carbonization of MoNx. We refer to this as the positive feedback between catalytic activity and catalyst activation in RWGS, which should be widely present in heterogeneous catalysis.

Promoted Catalytic Activity of CoSx@MoSx/MoOx Supported on Carbon Papers for Electrocatalytic Hydrogen Evolution Reaction

Developing cost-effective and stable materials for the electrocatalysis of hydrogen evolution reaction (HER) remains challenging. In this study, efficient catalysts for HER were synthesized by integrating the cobalt and molybdenum oxides via electrodeposition, followed by subsequent sulfurization of the as-prepared oxides using chemical vapor deposition (CVD). This methodology allowed the incorporation of both cobalt and molybdenum components into the catalyst in a single step. The as-synthesized CoSx@MoSx/MoOx-based catalysts exhibited excellent hydrogen production performance in acidic media owing to the presence of Co-S and Mo-S bonds in the hybrid structure. Particularly, CoSx@MoSx/MoOx(90@360) and MoSx@CoOx(180@180) displayed the best HER performances with low overpotentials of 80 mV and 150 mV, respectively. The catalysts were highly stable, with their stability preserved for over 1000 cycles with marginal reduction in overall efficiency. Therefore, these findings suggest the potential of CoSx@MoSx/MoOx and MoSx@CoOx composites as ideal candidates for developing low-cost catalysts for electrochemical hydrogen production.

Empirical investigation of the effect of adding nanoparticles to HB-80 gas turbine oil: Evaluation of thermophysical behaviors

The current study aims to conduct an empirical investigation on the performance of copper (II) oxide (CuO), Graphene Oxide (GO), and Molybdenum (VI) Oxide (MoO3) nanoparticles as additives for HB-80 base lubricant and their effects on essential characteristics such as density, flashpoint and flammability, cloud point and pour point, viscosity and viscosity indicators, thermal conductivity coefficient, friction coefficient and wear. The test results show that nanoparticles have minor effects on density and viscosity but managed to improve viscosity indicators. Flashpoint, flammability, cloud point, and pour point all increased after the addition of nanoparticles. The increase in the concentration of nanoparticles also improved and increased the lubricant's thermal conductivity coefficient; the highest increase was 11.3 % compared to the base oil with the addition of 1 wt% CuO. Adding nanoparticles to lubricant decreases wear and friction coefficient by creating a lubricant film, especially at lower nanoparticle concentrations, which leads to a more stable lubricant film by nanoparticles. Copper (II) Oxide nanoparticles had the best performance in reducing friction coefficient and wear at 0.2 wt% with 22.86 % and 63.92 % reduction compared to the base oil, respectively.

Electrochemistry of Molybdenum Single Crystals and Thin Wires in Cyanide and Gold Cyanide Electrolytes

Thin wires of molybdenum coated with gold are used for space applications and the adhesion of the gold layer is decisive for their use. The surface morphology of the wires is determined by the manufacturing process and preferential orientation of single crystal surfaces is expected. In this work three different single crystal surfaces were studied together with a 20 μm molybdenum wire to elucidate the importance of surface morphology on the electrodeposition process for gold. Electrochemical impedance spectroscopy was used to study the molybdenum samples in the absence and presence of gold cyanide complexes. The results show large pseudocapacitance prior to gold deposition, indicating the presence of a thin molybdenum oxide film on the surface. Thus, the electrodeposition takes place on the surface oxide and is afflicted with a nucleation overpotential. The overpotential is only slightly dependent on the single crystal orientation, while it is more negative for the wire. The adhesion of gold on the flat single crystal surfaces is weak but marginally better on the wire. This clearly shows that strong chemical binding to the surface is absent and that other processes, such as physical interlocking of the gold layer is necessary for good adhesion.

Study on the Thermal Stability of Molybdenum Oxide‐Passivated Silicon Solar Cells

Dopant‐free heterojunction (HJ) solar cells are known for their simple process conditions and low parasitic absorption. However, stability issues remain one of the major obstacles for further development of cells with transition metal oxides (TMOs). Therefore, this research demonstrates the mechanism of thermal annealing degradation effects on TMOs/silicon (Si) HJ, namely, the infiltration of oxygen from air and the bidirectional diffusion of oxygen from TMOs, by investigating a typical molybdenum oxide (MoOx)/Si contact. A dense Au interlayer is introduced to block the interdiffusion of oxygen from the MoOx/Si interface and its surrounding environment. As a result, the dense layer slows down the interfacial oxidation of MoOx/Si and the degradation of the MoOx work function, thus improving the stability of the MoOx/Si HJ to 200 °C. The diffusion of oxygen from MoOx to the MoOx/Si interface will be critical to further promote the thermal stability of the devices thereafter, especially for the cells with i‐a‐Si:H layer as the passivation layer. To attain stable dopant‐free cells with MoOx, it is crucial to prevent oxygen diffusion into Si while maintaining a high MoOx work function and a thin SiOx layer at the interface.

Suppressed Gold Penetration with the Molybdenum Oxide Interlayer to Increase Power Conversion Efficiency of Perovskite Solar Cells

Perovskite solar cells (PSCs) have undergone an unprecedentedly rapid development in both power conversion efficiency (PCE) and operational durability. However, a number of unknown challenges remain before PSC products are ready to launch. Herein, it is demonstrated that the vacuum deposition of gold (Au) onto the organic hole‐transport layer (HTL) results in Au penetration into the perovskite layer. This Au penetration proves to be a limiting factor in PCE due to detrimental carrier recombination caused by the penetrated Au component inside the perovskite light absorber. To mitigate this issue, a thin molybdenum oxide (MoOx) interlayer between the organic HTL and the Au electrode is introduced, effectively reducing the Au penetration and suppressing the carrier recombination. Consequently, this MoOx introduction increases PCEs from ≈16.9% to ≈19.6% by ≈2.7%. Furthermore, using the MoOx interlayer improves the long‐term durability of PSCs. These findings are crucial in elucidating a basic mechanism that limits PCE and in advancing the fabrication of PSC products with even higher performance.

Load-carrying capacity and tribomechanism of DDA/MADE modified MoO3 nanoparticle as an additive for alkylated naphthalene base oil

Metal oxide nanoparticles as lubricant additives have attracted much attention, thanks to their excellent anti-wear ability and load-carrying capacity. Unfortunately, organic molybdenum, a small molecule auxiliary of zinc dialkyldithiophosphate (ZDDP) with high reactivity, exhibits poor load-bearing capacity. Therefore, molybdenum oxide nanoparticle (denoted as MONP) was surface-capped by dodecylamine (DDA) and maleic anhydride dodecyl ester (MADE) to obtain DDA/MADE-MONP, an organic-inorganic nanohybrid as a potential replacement of sulfur- and phosphorus-free commercial organic molybdenum additive (Organic-Mo). The as-prepared DDA/MADE-MONP nanohybrid was characterized by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy; and its effect on the load-bearing capacity of an alkylated naphthalene base oil (AN30), as used alone and combined with ZDDP, was investigated. Results show that, whether used alone or combined with ZDDP, the as-prepared DDA/MADE-MONP has better load-bearing capacity than the commercial organic molybdenum additive. The reason lies in that DDA/MADE-MONP can release MoO3 nanocores during the friction process to fill up the pits on the worn steel surface and form a dense protective tribofilm.

Electrochromic Devices Based on 2D MoO3-x/PEDOT:PSS Composite Film with Boosted Ion Transport.

Electrochromic materials allow for optical modulation and have attracted much attention due to their bright future in applications such as smart windows and energy-saving displays. Two-dimensional (2D) molybdenum oxide nanoflakes with combined advantages of high active specific surface area and natural layered structure should be highly potential candidates for electrochromic devices. However, the efficient top-down preparation of 2D MoO3 nanoflakes is still a huge challenge and the sluggish ionic kinetics hinder its electrochromic performance. Herein, we demonstrated a feasible thiourea-assisted exfoliation procedure, which can not only increase the yield but also reduce the thickness of 2D MoO3-x nanoflakes down to a few nanometers. Furthermore, electrophoretic-deposited MoO3-x nanoflakes were combined with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-conjugated polymer to simultaneously enhance the ionic kinetics and electronic conductivity, with a diffusion coefficient of 3.09 × 10-10 cm2 s-1 and a charge transport resistance of 33.7 Ω. The prepared 2D MoO3-x/PEDOT:PSS composite films exhibit improved electrochromic performance, including fast switching speed (7 s for bleaching, 5 s for coloring), enhanced coloration efficiency (87.1 cm2 C-1), and large transmittance modulation (ΔT = 65%). This study shows outstanding potential for 2D MoO3-x nanoflakes in electrochromic applications and opens new avenues for optimizing the ion transport in inorganic-organic composites, which will be possibly inspired for other electrochemical devices.

Selective hydroprocessing of diphenyl ether into benzene over in situ generated MoOx and WOx

The catalytic activity of molybdenum and tungsten oxides formed in situ from their carbonyls was studied in the hydroprocessing of diphenyl ether (DPE) for the first time. The MoOx and WOx catalysts obtained were characterized by XRD, XPS, HRTEM, EDX, Raman spectroscopy, and NH3TPD. The effect of various parameters on the substrate conversion and the yields of products was investigated. Oxygen vacancies (OVs) on the catalyst surface were found to be active sites in the DPE hydroprocessing. MoOx was more active than WOx due to more OVs on the surface of the catalyst. Benzene was obtained as a major product over both of catalysts with a highest yield of 87% (99% DPE conversion) over MoOx and of 69% (96% DPE conversion) over WOx.

A restricted dynamic surface self-reconstruction toward high-performance of direct seawater oxidation

The development of highly efficient electrocatalysts for direct seawater splitting with bifunctionality for inhibiting anodic oxidation reconstruction and selective oxygen evolution reactions is a major challenge. Herein, we report a direct seawater oxidation electrocatalyst that achieves long-term stability for more than 1000 h at 600 mA/cm2@η600 and high selectivity (Faraday efficiency of 100%). This catalyst revolves an amorphous molybdenum oxide layer constructed on the beaded-like cobalt oxide interface by atomic layer deposition technology. As demonstrated, a new restricted dynamic surface self-reconstruction mechanism is induced by the formation a stable reconstructed Co-Mo double hydroxide phase interface layer. The device assembled into a two-electrode flow cell for direct overall seawater electrolysis maintained at 1 A/cm2@1.93 V for 500 h with Faraday efficiency higher than 95%. Hydrogen generation rate reaches 419.4 mL/cm2/h, and the power consumption (4.62 KWh/m3 H2) is lower than that of pure water (5.0 KWh/m3 H2) at industrial current density.

Valorization of (Bio)Ethanol over MoO3/(WO3-ZrO2) Sol-Gel-like Catalysts

Bioethanol, which is currently produced commercially from a growing variety of renewable biomass and waste sources, is an appealing feedstock for the production of fuels and chemicals. The literature clearly shows that bioethanol is a versatile building block to be used in biorefineries. The ethanol conversion using several catalysts with acidic, basic, and redox characteristics results in a diverse assortment of high-value bioproducts. High-acidity tungsten zirconia-based catalysts are stated to compete with traditional zeolitic catalysts and can be employed in the dehydration of ethanol to ethylene, but for a low reaction temperature acetic acid is formed, which causes corrosion issues. WO3-ZrO2 (W/Zr = 1, atomic) catalysts modified with MoO3 were prepared by a sol-gel-like procedure and tested in a gas phase ethanol conversion in the presence of air. The citrate derived xerogels were annealed at 853 K for 12 h, allowing low surface area (<10 m2/g) materials with a Mo-W mixed-oxide-rich surface over tetragonal nanostructured zirconia. Catalysts with MoO3-loading produced mainly acetaldehyde, instead of ethylene, as a result of the high reducibility of Mo6+ when compared to W6+. During the reaction, the Mo6+ becomes partially reduced, but Mo6+/Mo5+ species are still active for methanol conversion with increased ethylene selectivity due to the high acidity of tetrahedral MOX species formed during the reaction. Adding water to ethanol, to simulate bioethanol, only leads to a slight inhibition in ethanol conversion over the MoO3/(WO3-ZrO2) catalysts. The results show that molybdenum oxide deposited on tungstated zirconia catalyst is active, with low sensitivity to water, for the valorization of bioethanol into high-value chemicals, such as ethylene and acetaldehyde, and whose selectivity can be tuned by changing the amount of MoO3 that is loaded. The MoO3/(WO3-ZrO2) catalysts prepared show catalytic behavior similar to that of noble metal-based catalysts reported in the literature for the dehydrogenation of bioethanol in high-value chemicals.

Scalable Synthesis of High-Quality Ultrathin Ferroelectric Magnesium Molybdenum Oxide.

The development of ultrathin, stable ferroelectric materials is crucial for advancing high-density, low-power electronic devices. Nonetheless, ultrathin ferroelectric materials are rare due to the critical size effect. Here, a novel ferroelectric material, magnesium molybdenum oxide (Mg2Mo3O8) is presented. High-quality ultrathin Mg2Mo3O8 crystals are synthesized using chemical vapor deposition (CVD). Ultrathin Mg2Mo3O8 has a wide bandgap (≈4.4eV) and nonlinear optical response. Mg2Mo3O8 crystals of varying thicknesses exhibit out-of-plane ferroelectric properties at room temperature, with ferroelectricity retained even at a 2nm thickness. The Mg2Mo3O8 exhibits a relatively large remanent polarization ranging from 33 to 52µCcm- 2, which is tunable by changing its thickness. Notably, Mg2Mo3O8 possesses a high Curie temperature (>980°C) across various thicknesses. Moreover, the as-grown Mg2Mo3O8 crystals display remarkable stability under harsh environments. This work introduces nolanites-type crystal into ultrathin ferroelectrics. The scalable synthesis of stable ultrathin ferroelectric Mg2Mo3O8 expands the scope of ferroelectric materials and may prosper applications of ferroelectrics.

Rapid synthesis of oxygen-defected molybdenum oxides quantum dots as efficient nanozymes for healing diabetic ulcers

Rapid synthesis of oxygen-defected molybdenum oxides quantum dots as efficient nanozymes for healing diabetic ulcers

Room Temperature Ultrafast Oxidative Desulfurization with Sodium Hypochlorite in the Presence of Silica-Supported Catalysts.

A series of silica-supported catalysts containing molybdenum, tungsten, and vanadium oxides as the active phase was investigated in the process of oxidative desulfurization with sodium hypochlorite. It was shown for the first time that catalysts containing vanadium oxide as the active phase are more stable under oxidation conditions with sodium hypochlorite and retain their effectiveness at increased dosages of the oxidant and at high initial sulfur contents. The catalysts were characterized in detail by a complex of methods: Fourier transform infrared, X-ray spectral fluorescence, transmission electron microscopy, scanning electron microscopy, and low-temperature nitrogen adsorption/desorption. Key factors affecting the oxidation of dibenzothiophene (DBT) were investigated: oxidant and catalyst amount, oxidation time, initial sulfur content, and acetonitrile amount. Under optimized conditions, the DBT conversion rate was 100% in 5 min at room temperature (25 °C), NaClO/S molar ratio 6:1, catalyst amount 2 wt %. In the real sample of the straight-run diesel fraction, the sulfur content was reduced from 10,100 to 3030 ppm. The V(10%)/SiO2 catalyst retains its activity for 5 oxidation-regeneration cycles.

Catalytic enhancement of graphene oxide by trace molybdenum oxide nanoparticles doping: Optimized electrocatalyst for green hydrogen production

Hydrogen is a clean and renewable energy source that is often regarded as a powerful alternative to traditional fossil fuels. The hydrogen evolution reaction (HER), and oxygen evolution reaction (OER) are the critical stage in this technique, and an effective catalyst must be used to limit its significant overpotential. This report delves into the evaluation of MoO3/rGO-1000 as a cutting-edge electrocatalyst for green hydrogen production. The MoO3/rGO-1000 demonstrated exceptional HER stability and activity for 14 h, exhibiting an overpotential of 35 mV at a current density of 10 mAcm−2. Furthermore, the MoO3/rGO-1000, showed excellent OER activity having a lower overpotential of 213 mV at 10 mAcm−2. The enhanced results may be due to the synergistic effects, and by its inherent metallic conductivity and capacity to adsorb oxygen-containing molecules with high efficiency, MoO3 offers an abundance of active sites for water oxidation throughout the OER process. In the interim, rGO functions as a highly effective electron conductor, improving overall electrocatalytic activity by facilitating charge transfer. Thus, this study concludes that the introduction of MoO3 into graphene oxide significantly enhances the catalytic activities for hydrogen production.

Engineering of local electron properties optimization in single-atom catalysts enabling sustainable photocatalytic conversion of N2 into NH3

Photocatalytic synthesis of ammonia (NH3) from nitrogen (N2) offers a promising strategy for carbon neutrality, as it avoids the energy-intensive and carbon-emitting industrial processes. The exploration of high-efficiency N2 photofixation systems for photocatalytic N2 reduction reaction (pNRR) is critical but it remains a challenge since the lack of rational structural design and atomic-level insights into molecular N2 activation mechanism. Herein, an atomically dispersed single-atom palladium (Pd) active sites decorated oxygen-deficient molybdenum oxide (Pd/MoO3-x) was creatively designed for assessing pNRR performance. Interestingly, the integration of single-atom Pd active sites in MoO3-x can significantly weaken the N≡N bond of adsorbed N2 and effectively lower the activation energy barrier during the pNRR process. This is attributed to the fact that the modified Pd single-atom sites of Pd/MoO3-x play a dominant role in the N2 spontaneous adsorption process as well as possess a remarkable photogenerated electron trapping ability, which could be assisted to inject electrons into N2 antibonding orbital, thus significantly accelerates the reaction kinetics. Consequently, the Pd/MoO3-x photocatalyst reaches an impressive NH3 yield rate of 103.2 μggcat.−1h−1, which is superior to that of pristine MoO3-x (21.2 μggcat.−1h−1) and commercial MoO3 (6.5 μggcat.−1h−1), respectively. The present study not only creates a reliable approach to expand efficient N2 photofixation system under mild conditions through the fabrication of atomically dispersed monometallic active sites, but also offers atomic-level insights into the underlying mechanism of pNRR catalytic process.

Development of Molybdenum oxide Promoted CeO2−SiO2 Mixed‐oxide Catalyst for Efficient Catalytic Oxidation of Benzylamine to N‐Benzylidenebenzylamine

AbstractThis study explores a rational synthesis of a molybdenum‐promoted Ce−Si mixed oxide catalyst (MoO3/CeO2−SiO2) to regulate synergies between MoO3 and SiO2 dopant on CeO2, achieving high selectivity in solvent‐free catalytic oxidative coupling of amines to imines using molecular O2 as the oxidant. Comparative efficiency tests were conducted with bare CeO2, CeO2−SiO2, and MoO3/CeO2 catalysts. Characterization techniques, including XRD, Raman spectroscopy, N2‐adsorption‐desorption analysis, FTIR, NH3−TPD, TEM, and XPS, were employed to assess textural properties, acidic features, promoter and dopant dispersion in CeO2 lattice, and oxygen defects. Mo/Ce−Si catalyst exhibited superior acidic sites and a higher concentration of Ce3+ ions (Iu/ITotal), indicating increased oxygen vacancies. This catalyst demonstrated exceptional performance in the oxidative coupling of benzylamine, providing higher conversion and selectivity to the corresponding imine. Remarkably, the Mo/Ce−Si catalyst maintained consistent performance over five recycling runs. The catalyst also proved effective for the selective oxidative coupling of various amine substrates with diverse steric and electronic properties. Experimental results confirmed a plausible reaction mechanism within the concise catalyst design.

Chemisorption-Induced Robust and Homogeneous Tungsten Disulfide Interlayer Enables Stable PEDOT-Free Organic Solar Cells with Over 19% Efficiency.

Construction of a high-quality charge transport layer (CTL) with intimate contact with the substrate via tailored interface engineering is crucial to increase the overall charge transfer kinetics and stability for a bulk-heterojunction (BHJ) organic solar cell (OSC). Here, we demonstrate a surface chemistry strategy to achieve a homogeneous composite hole transport layer (C-HTL) with robust substrate contact by self-assembling two-dimensional tungsten disulfide (WS2) nanosheets on a thin molybdenum oxide (MoO3) film-evaporated indium tin oxide (ITO) substrate. It is found that over such a well-defined C-HTL, WS2 is homogeneously tethered on the ITO/MoO3 substrate stemming from the strong electronic coupling interaction between the building blocks, which enables a favorable interfacial configuration in terms of uniformity. As a result, the D18:L8-BO-based OSC with C-HTL exhibits a power conversion efficiency (PCE) of 19.23%, an 11% improvement over the WS2-based control device, and the highest efficiency among single-junction PEDOT-free binary BHJ OSCs.

Interface study of molybdenum oxide thin films on n- and p-type crystalline silicon surface

Interface study of molybdenum oxide thin films on n- and p-type crystalline silicon surface

Novel green chemical mechanical polishing by controlling pH values and redox reaction for achieving atomic surface of a nickel alloy

Traditional chemical mechanical polishing (CMP) normally employs noxious slurries, leading to pollution to the environment. It is a challenge to achieve atomic surfaces of nickel (Ni) alloy using green CMP. To overcome this challenge, a novel green CMP was developed, including composite abrasives of ceria and silica, mandelic acid, hydrogen peroxide and deionized water. Using the developed green CMP, atomic surface with surface roughness Sa of 0.179 nm was achieved, under a scanning area of 50 × 50 μm2. Electrochemical tests indicate that the developed slurry has effective corrosion ability on Ni alloy. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy reveal that the Ni alloy was oxidized by hydrogen peroxide, forming oxides of Ni, chromium (Cr) and molybdenum (Mo). Cr and Mo oxides demonstrated better stability in mandelic acid, while Ni oxides reacted with hydrogen ions and produced Ni2+ and Ni3+ ions. The ions chelated with mandelic acid. Finally, the generated oxides and reaction products were removed by abrasives and a polishing pad under chemical and mechanical balanced functions. The developed green CMP paves a new avenue to obtain atomic surface of a Ni alloy for the possible applications of high-performance components in aerospace industry.