Showing papers on "Molybdenum published in 2022"

Dynamic Dissolution and Re-adsorption of Molybdate Ion in Iron Incorporated Nickel-molybdenum Oxyhydroxide for Promoting Oxygen Evolution Reaction

Abstract: Transition metal-based pre-catalysts undergo drastic reconstruction to form the active catalysts during the alkaline oxygen evolution reaction (OER). However, the effect of escaped inactive ion from pre-catalysts themselves is usually ignored during reconstruction processes. Here, we investigate the effect of inactive MoO 4 2- escaped from a pre-catalyst of Fe incorporated nickel-molybdenum oxyhydroxide (NiMo-Fe) on OER performance. The results of in-situ Raman and X-ray photoelectron spectroscopy reveal that MoO 4 2- can be easily dissolved into KOH electrolyte and re-adsorbed on surface of catalyst during OER processes, which delivers a promoting effect on OER performance. The dissolution of MoO 4 2- is beneficial for increasing the reconstruction degree of NiMo-Fe to form the active phase of NiFeOOH. Theoretical calculations demonstrate that the re-adsorbed MoO 4 2- is favorable for the adsorption of the OOH* intermediate, thus boosts the OER activity. As expected, the NiMo-Fe shows a superior electrocatalytic performance for OER, outperforming the pre-catalyst without Mo species. This finding enriches the knowledge of inactive-ion effect on alkaline OER performance and offers a path for developing efficient electrocatalysts. The promotion effect of the inactive MoO 4 2- on OER performance was discovered and systematic understood. The MoO 4 2- in pre-catalyst is easily dissolved into the KOH electrolyte, which can enhance the reconstruction degree of pre-catalyst to active species. The re-adsorbed MoO 4 2- can improve the OER activity by facilitating adsorption of the OOH* intermediate. • An efficient electrocatalyst of Fe incorporated NiMo oxyhydroxide is prepared through an electrochemical strategy for OER. • The dynamic dissolution and re-adsorption behavior of MoO 4 2- is discovered and contributes to an enhanced OER performance. • The re-adsorbed MoO 4 2- is beneficial for the adsorption of OOH* intermediate, thus promotes OER activity.

Multiphase Molybdenum Carbide Doped Carbon Hollow Sphere Engineering: The Superiority of Unique Double-Shell Structure in Microwave Absorption.

Abstract: In order to achieve excellent electromagnetic wave (EMW) absorption properties, the microstructure design and component control of the absorber are critical. In this study, three different structures made of Mo2 C/C hollow spheres are prepared and their microwave absorption behavior is investigated. The Mo2 C/C double-shell hollow spheres consisting of an outer thin shell and an inner rough thick shell with multiple EMW loss mechanisms exhibit good microwave absorption properties. In order to further improve the microwave absorption properties, MoC1-x /C double-shell hollow spheres with different crystalline phases of molybdenum carbide are prepared to further optimize the EMW loss capability of the materials. Finally, MoC1-x /C double-shell hollow spheres with α-phase molybdenum carbide have the best microwave absorption properties. When the filling is 20 wt.%, the minimum reflection loss at 1.8 mm is -50.55 dB and the effective absorption bandwidth at 2 mm is 5.36 GHz, which is expected to be a microwave absorber with the characteristics of "thin, light, wide, and strong".

Single‐Atom Molybdenum Engineered Platinum Nanocatalyst for Boosted Alkaline Hydrogen Oxidation

Abstract: Engineering the surface electrochemistry at the atomic level can precisely and effectively manipulate the reactivity and durability of catalysts. Herein, a novel single‐atom fine‐tailoring strategy based on a highly hydrophilic Mo‐bifunctional promoter is proposed to greatly boost the hydrogen oxidation reaction (HOR) on Pt catalysts. The single‐atom Mo‐modified nanometer Pt anchored on porous N‐doped carbon (Mo‐Pt/NC) is developed via a pyrolysis–adsorption–reduction process. The designed Mo‐Pt/NC exhibits a remarkable mass‐specific kinetic current reaching 1584 mA mg−1Pt in 0.1 m KOH, which is nearly 11‐fold and fourfold higher than the activities of commercial Pt/C and Pt/NC counterparts respectively, and such extraordinary HOR behavior even exceeds those of documented Pt‐related catalysts. Electrochemical and spectroscopic studies indicate that hydrophilic Mo single‐atom sites can not only regulate the electronic microenvironment of Pt sites for attenuated H* adsorption, but they also serve as energetic H2O*‐adsorption promoters to jointly facilitate the HOR kinetics. Moreover, the anti‐CO poisoning capability of Mo‐Pt/NC is markedly enhanced by this Mo‐modified electronic effect. This work gives a significant guideline for the design of high‐performance HOR catalysts and other advanced catalysts.

Phase controlled synthesis of transition metal carbide nanocrystals by ultrafast flash Joule heating

Abstract: Abstract Nanoscale carbides enhance ultra-strong ceramics and show activity as high-performance catalysts. Traditional lengthy carburization methods for carbide syntheses usually result in coked surface, large particle size, and uncontrolled phase. Here, a flash Joule heating process is developed for ultrafast synthesis of carbide nanocrystals within 1 s. Various interstitial transition metal carbides (TiC, ZrC, HfC, VC, NbC, TaC, Cr 2 C 3 , MoC, and W 2 C) and covalent carbides (B 4 C and SiC) are produced using low-cost precursors. By controlling pulse voltages, phase-pure molybdenum carbides including β-Mo 2 C and metastable α-MoC 1-x and η-MoC 1-x are selectively synthesized, demonstrating the excellent phase engineering ability of the flash Joule heating by broadly tunable energy input that can exceed 3000 K coupled with kinetically controlled ultrafast cooling (>10 4 K s −1 ). Theoretical calculation reveals carbon vacancies as the driving factor for topotactic transition of carbide phases. The phase-dependent hydrogen evolution capability of molybdenum carbides is investigated with β-Mo 2 C showing the best performance.

Phase controlled synthesis of transition metal carbide nanocrystals by ultrafast flash Joule heating

Abstract: Abstract Nanoscale carbides enhance ultra-strong ceramics and show activity as high-performance catalysts. Traditional lengthy carburization methods for carbide syntheses usually result in coked surface, large particle size, and uncontrolled phase. Here, a flash Joule heating process is developed for ultrafast synthesis of carbide nanocrystals within 1 s. Various interstitial transition metal carbides (TiC, ZrC, HfC, VC, NbC, TaC, Cr 2 C 3 , MoC, and W 2 C) and covalent carbides (B 4 C and SiC) are produced using low-cost precursors. By controlling pulse voltages, phase-pure molybdenum carbides including β-Mo 2 C and metastable α-MoC 1-x and η-MoC 1-x are selectively synthesized, demonstrating the excellent phase engineering ability of the flash Joule heating by broadly tunable energy input that can exceed 3000 K coupled with kinetically controlled ultrafast cooling (>10 4 K s −1 ). Theoretical calculation reveals carbon vacancies as the driving factor for topotactic transition of carbide phases. The phase-dependent hydrogen evolution capability of molybdenum carbides is investigated with β-Mo 2 C showing the best performance.

A high-quality-factor ultra-narrowband perfect metamaterial absorber based on monolayer molybdenum disulfide

Abstract: In order to significantly improve the absorption efficiency of monolayer molybdenum disulfide (M-MoS 2 ), an ultra-narrowband M-MoS 2 metamaterial absorber was obtained through theoretical analysis and numerical calculation using the finite difference time domain method. The physical mechanism can be better analyzed through critical coupling and guided mode resonance. Its absorption rate at λ = 806.41 nm is as high as 99.8%, which is more than 12 times that of bare M-MoS 2 . From the simulation results, adjusting the geometric parameters of the structure can control the resonant wavelength range of the M-MoS 2 . In addition, we also found that the maximum quality factor is 1256.8. The numerical result shows that the design provides new possibilities for ultra-narrowband M-MoS 2 perfect absorbers in the near-infrared spectrum. The results of this work indicate that the designed structure has excellent prospects for application in wavelength-selective photoluminescence and photodetection.

Bifunctional P-Intercalated and Doped Metallic (1T)-Copper Molybdenum Sulfide Ultrathin 2D-Nanosheets with Enlarged Interlayers for Efficient Overall Water Splitting.

Abstract: Metallic (1T) molybdenum disulfide (MoS2) is a much better electrocatalyst than the semiconducting (2H) MoS2 because of its superior conductivity, presence of active basal planes, and bulky interlayers. However, the lack of thermodynamic stability has hindered its practical uses. The insertion of transition metals and nonmetals in the interlayers and the crystal is known to improve both the thermodynamic stability and the catalytic efficacy of 1T-MoS2. In this study, for the first time we have developed an electrocatalyst for water splitting based on metallic copper molybdenum sulfide (1T-CMS). The present catalyst, P-doped and intercalated 1T-CMS ultrathin 2D nanosheets on carbon cloth (P-1T-CMS@CC), demonstrates excellent catalytic efficacy for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). It required an overpotential of 95 mV for HER and of 284 mV for OER at a current density of 10 mA cm-2. The P-1T-CMS@CC(+ -) device also shows excellent performance, requiring a cell voltage of only 1.51 V at a current density of 10 mA cm-2.

Detection of glucose concentration using a surface plasmon resonance biosensor based on barium titanate layers and molybdenum disulphide sheets

Abstract: Diabetes is rapidly becoming a serious and life-threatening disease. It affects 415 million persons worldwide and is a leading cause of death among those aged 20 to 59. It is essential to develop a rapid-detection, accurate and sensitive glucose detector. In this work, a biosensor based on surface plasmon resonance (SPR) is proposed theoretically for the detection of glucose concentration. To realize higher sensitivity, the proposed SPR sensor contains a barium titanate layer placed between the metal (Ag) thin film and the molybdenum disulphide layer. Barium titanate material shows notable dielectric properties, such as low loss and a high index of refraction. It is expected to give a large shift in the resonance angle caused by a tiny change in the analyte refractive index. By optimizing the thicknesses of barium titanate and Ag and the number of molybdenum disulphide layers, the proposed biosensor can exhibit an ultra-high sensitivity of 307.36 deg RIU−1. The extremely high sensitivity makes the proposed SPR-based biosensor encouraging to be used in many fields of biosensing.

Nature‐Inspired Design of Molybdenum–Selenium Dual‐Single‐Atom Electrocatalysts for CO2 Reduction

Abstract: Electrochemical CO2 reduction (ECR) is becoming an increasingly important technology for achieving carbon neutrality. Inspired by the structure of naturally occurring Mo‐dependent enzymes capable of activating CO2, a heteronuclear Mo–Se dual‐single‐atom electrocatalyst (MoSA–SeSA) for ECR into CO with a Faradaic efficiency of above 90% over a broad potential window from −0.4 to −1.0 V versus reversible hydrogen electrode is demonstrated here. Both operando characterization and theoretical simulation results verify that MoSA acts as central atoms that directly interact with the ECR feedstock and intermediates, whereas the SeSA adjacent to MoSA modulates the electronic structure of MoSA through long‐range electron delocalization for inhibiting MoSA poisoning caused by strong CO adsorption. In addition, the SeSAs far from MoSA help suppress the competing hydrogen evolution side reaction and accelerate the CO2 transport by repelling H2O. This work provides new insight into the precise regulation and in‐depth understanding of multisite synergistic catalysis at the atomic scale.

Dual Active Centers Bridged by Oxygen Vacancies of Ruthenium Single‐Atom Hybrids Supported on Molybdenum Oxide for Photocatalytic Ammonia Synthesis

Abstract: Photocatalytic synthesis of ammonia (NH3 ) holds significant potential compared with the Haber-Bosch process. However, the reported photocatalysts suffer from low efficiency owing to localized electron deficiency. Herein, Ru-SA (single atoms)/Hx MoO3-y hybrids with abundant of Mon+ (4

A molybdenum sulfo-oxide/cobalt oxysulfide Z-scheme heterojunction catalyst for efficient photocatalytic hydrogen production and pollutant reduction

Abstract: Sulfur-doped oxide (oxysulfide)/oxygen-doped sulfide (sulfo-oxide) with a Z-scheme heterogeneous interface improves the efficiency of photocatalytic hydrogen production.

Mo3+ hydride as the common origin of H2 evolution and selective NADH regeneration in molybdenum sulfide electrocatalysts

Abstract: Hydride transfers are key to a number of economically and environmentally important reactions, including H2 evolution and NADH regeneration. The electrochemical generation of hydrides can therefore drive the electrification of chemical reactions to improve their sustainability for a green economy. Catalysts containing molybdenum have recently been recognized as among the most promising non-precious catalysts for H2 evolution, but the mechanism by which molybdenum confers this activity remains debated. Here we show the presence of trapped Mo3+ hydride in amorphous molybdenum sulfide (a-MoSx) during the hydrogen evolution reaction and extend its catalytic role to the selective hydrogenation of the biologically important energy carrier NAD to its active 1,4-NADH form. Furthermore, this reactivity applies to other HER-active molybdenum sulfides. Our results demonstrate a direct role for molybdenum in heterogeneous H2 evolution. This mechanistic finding also reveals that molybdenum sulfides have potential as economic electrocatalysts for NADH regeneration in biocatalysis. The electrochemical generation of reactive hydrides has the potential to drive the electrification of chemical reactions. Now, a modified electron paramagnetic resonance set-up is put forward to demonstrate the role of Mo3+ hydride in amorphous MoSx to catalyse both the hydrogen evolution reaction and electrochemical NADH regeneration.

Facile Synthesis of Single Iron Atoms over MoS2 Nanosheets via Spontaneous Reduction for Highly Efficient Selective Oxidation of Alcohols.

Abstract: The facile creation of high-performance single-atom catalysts (SACs) is intriguing in heterogeneous catalysis, especially on 2D transition-metal dichalcogenides. An efficient spontaneous reduction approach to access atomically dispersed iron atoms supported over defect-containing MoS2 nanosheets is herein reported. Advanced characterization methods demonstrate that the isolated iron atoms situate atop of molybdenum atoms and coordinate with three neighboring sulfur atoms. This Fe SAC delivers exceptional catalytic efficiency (1 atm O2 @ 120 °C) in the selective oxidation of benzyl alcohol to benzaldehyde, with 99% selectivity under almost 100% conversion. The turnover frequency is calculated to be as high as 2105 h-1 . Moreover, it shows admirable recyclability, storage stability, and substrate tolerance. Density functional theory calculations reveal that the high catalytic activity stems from the optimized electronic structure of single iron atoms over the MoS2 support.