Amorphous Molybdenum Research Articles

Mo-modified Pt/C electrocatalyst prepared by the catalytic decomposition of molybdenum peroxo-complexes for the hydrogen oxidation reaction with enhanced CO tolerance

Commercial 20 % Pt/C catalyst was modified by molybdenum via catalytic decomposition of peroxocomplexes of molybdenum with the subsequent reduction of the Pt2Mo1/C precursor in H2 flow at 600 °C. The detailed HRTEM, EDX, XRD and XPS studies showed that amorphous molybdenum oxide was deposited on Pt particles surface and partially on carbon support. After reduction of the Pt2Mo1/C precursor, the substantial Mo fraction merges the structure of Pt particles thus forming PtMo alloy with reduced lattice parameter, while the rest of molybdenum covers the surface of PtMo particles as MoO3. The presented method of Mo-modification of Pt-based catalysts provides rather simple way to vary Pt:Mo molar ratio. Electrochemical study revealed that the amount of the surface MoO3 plays a key role in the CO tolerance of the PtMo/C catalyst. As prepared Pt2Mo1/C precursor is 15 times superior to the Pt/C catalyst in the CO-tolerance. After reduction, the Pt2Mo1/C electrocatalyst exhibits extremely high CO-tolerance, more than 100 times higher than that of the pristine commercial platinum catalyst.

Simultaneous Defect Passivation and Co‐Catalyst Engineering Leads to Superior Photocatalytic Hydrogen Evolution on Metal Halide Perovskites

AbstractMetal halide perovskites (MHPs) have emerged as attractive candidates for producing green hydrogen via photocatalytic pathway. However, the presence of abundant defects and absence of efficient hydrogen evolution reaction (HER) active sites on MHPs seriously limit the solar‐to‐chemical (STC) conversion efficiency. Herein, to address this issue, we present a bi‐functionalization strategy through decorating MHPs with a molecular molybdenum‐sulfur‐containing co‐catalyst precursor. By virtue of the strong chemical interaction between lead and sulfur and the good dispersion of the molecular co‐catalyst precursor in the deposition solution, a uniform and intimate decoration of the MHPs surface with lead sulfide (PbS) and amorphous molybdenum sulfide (MoSx) co‐catalysts is obtained simultaneously. We show that the PbS co‐catalyst can effectively passivate the Pb‐related defects on the MHPs surface, thus retarding the charge recombination and promoting the charge transfer efficiency significantly. The amorphous MoSx co‐catalyst further promotes the extraction of photogenerated electrons from MHPs and facilitates the HER catalysis. Consequently, drastically enhanced photocatalytic HER activities are obtained on representative MHPs through the synergistic functionalization of PbS and MoSx co‐catalysts. A solar‐to‐chemical (STC) conversion efficiency of ca. 4.63 % is achieved on the bi‐functionalized FAPbBr3‐xIx (FA=CH(NH2)2), which is among the highest values reported for MHPs.

Simultaneous Defect Passivation and Co-Catalyst Engineering Leads to Superior Photocatalytic Hydrogen Evolution on Metal Halide Perovskites.

Metal halide perovskites (MHPs) have emerged as attractive candidates for producing green hydrogen via photocatalytic pathway. However, the presence of abundant defects and absence of efficient hydrogen evolution reaction (HER) active sites on MHPs seriously limit the solar-to-chemical (STC) conversion efficiency. Herein, to address this issue, we present a bi-functionalization strategy through decorating MHPs with a molecular molybdenum-sulfur-containing co-catalyst precursor. By virtue of the strong chemical interaction between lead and sulfur and the good dispersion of the molecular co-catalyst precursor in the deposition solution, a uniform and intimate decoration of the MHPs surface with lead sulfide (PbS) and amorphous molybdenum sulfide (MoSx) co-catalysts is obtained simultaneously. We show that the PbS co-catalyst can effectively passivate the Pb-related defects on the MHPs surface, thus retarding the charge recombination and promoting the charge transfer efficiency significantly. The amorphous MoSx co-catalyst further promotes the extraction of photogenerated electrons from MHPs and facilitates the HER catalysis. Consequently, drastically enhanced photocatalytic HER activities are obtained on representative MHPs through the synergistic functionalization of PbS and MoSx co-catalysts. A solar-to-chemical (STC) conversion efficiency of ca. 4.63 % is achieved on the bi-functionalized FAPbBr3-xIx (FA=CH(NH2)2), which is among the highest values reported for MHPs.

Decoupling hydrophilicity and superaerophobicity on amorphous molybdenum sulfide for high-rate water splitting

The development of water splitting electrocatalysts with earth-abundant materials capable of delivering high current density is crucial for sustainable H2 production. However, the mass transfer including reactants and bubbles usually suffered from the shielding effect of gas adhesion under such circumstance. Here, we report a surface engineering strategy over amorphous molybdenum sulfide (a-MoSx) to synergistically boost its generation and departure of gas bubbles. To begin with, a hydrophilic surface featuring hydroxy groups was constructed via palladium−doping induced sulfur vacancies on a-MoSx, which could enhance the local access of aqueous reactant. Furthermore, the departure of gas bubbles could be accelerated by regulating the roughness of the synthesized Pd-MoSx(OH)y nanoarrays. For demonstration purpose of practical applications, the bifunctional Pd-MoSx(OH)y nanoarrays could deliver a high current density of 1000 mA cm−2 at 1.99 V for overall water splitting over 100 h.

Interfacial linkage modulated amorphous molybdenum sulfide/bismuth halide perovskite heterojunction for enhanced visible-light-driven photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution is a promising approach for direct solar-to-fuel conversion. Although significant research efforts have been put on the development of lead-free metal halide perovskites to reach excellent optoelectronic properties, their rational design for efficient heterojunction photocatalytic systems still poses challenges. Here, we report a new strategy to tailor the interface of hybrid tri(dimethylammonium) hexaiodobismuthate (DMA3BiI6) and amorphous molybdenum sulfide (a-MoSx) heterojunctions. Specifically, a-MoSx was prepared with abundant apical S2– or bridging S22– ligands to allow coupling with DMA3BiI6 via an interfacial Mo–S–Bi linkage. The as-obtained heterostructures were found to show an improved visible-light-driven photocatalytic hydrogen evolution in hydroiodic acid splitting under mild conditions reaching a superior hydrogen evolution rate of around 750 µmol g−1 h−1 and an apparent quantum efficiency (AQE) of 13.0 % at 420 nm. The high activity was kept after a long-term performance test for 3 days.

Low-frequency electrodynamics in the mixed state of superconducting NbN and a-MoGe films using two-coil mutual inductance technique

We investigate the low-frequency electrodynamics in the vortex state of two type-II superconducting films, namely, a moderate-to-strongly pinned Niobium Nitride (NbN) and a very weakly pinned amorphous Molybdenum Germanium (a-MoGe) film. We employ a two-coil mutual inductance technique to extract the complex penetration depth, λ~ . The sample response is studied through the temperature variation of λ~ in the mixed state, where we employ a model developed by Coffey and Clem (the CC model) to extract different vortex lattice (VL) parameters, such as the restoring pinning force constant (Labusch parameter), VL drag coefficient and pinning potential barrier. We observe that a consistent description of the inductive and dissipative part of the response is only possible when we take the viscous drag on the vortices to be several orders of magnitude larger than the viscous drag estimated from the Bardeen–Stephen model.

Amorphous molybdenum sulfide nanosheets composed of [Mo3S13]2- active-site motifs for enhancing conversion of Fe3+/Fe2+ in Fenton reaction under neutral condition

Molybdenum disulfide (MoS2) edges have been considered as effective active sites to promote Fenton reaction, whereas the basal plane is inert. It is dauntingly challenging to maximally exposure edge active sites and active the basal plane. Inspired that [Mo3S13]2- clusters is basic structural unit of MoS2 edge, amorphous molybdenum sulfide (a-MoSx) nanosheets composed of [Mo3S13]2- active-site motifs may be an ideal co-catalyst for Fenton reaction. Herein, accordion-like a-MoSx nanosheets were successfully designed and prepared by one step oil-heating method. The as-synthesized a-MoSx exhibited superior activity in co-catalytic Fenton degradation of tetracycline (TC, 10 mg/L) than that of MoS2, which could reach 94.73 % within 5 min under neutral condition. This is attributed to the better Mo-S coordination mode or surrounding environment to accelerate the rate-limiting step of Fe3+/Fe2+ conversion, with DFT calculations indicating for Fe3+ on Mo4+ or S2-/S22- sites in a-MoSx a higher electron aggregation density and lower adsorption energy. Impressively, all the S atoms in a-MoSx have low adsorption energy with H atom, making that the co-catalytic Fenton reaction can be performed under neutral conditions. For a scale-up experiment, 5 L of TC wastewater (50 mg/L) was almost completely degraded after 120 min in the nickel foam/a-MoSx + H2O2 + Fe2+ system.

Amorphous MoS2 from a machine learning inter-atomic potential.

Amorphous molybdenum disulfide has shown potential as a hydrogen evolution catalyst, but the origin of its high activity is unclear, as is its atomic structure. Here, we have developed a classical inter-atomic potential using the charge equilibration neural network method, and we have employed it to generate atomic models of amorphous MoS2 by melting and quenching processes. The amorphous phase contains an abundance of molybdenum and sulfur atoms in low coordination. Besides the 6-coordinated molybdenum typical of the crystalline phases, a substantial fraction displays coordinations 4 and 5. The amorphous phase is also characterized by the appearance of direct S-S bonds. Density functional theory shows that the amorphous phase is metallic, with a considerable contribution of the 4-coordinated molybdenum to the density of states at the Fermi level. S-S bonds are related to the reduction of sulfur, with the excess electrons spread over several molybdenum atoms. Moreover, S-S bond formation is associated with a distinctive broadening of the 3s states, which could be exploited for experimental characterization of the amorphous phases. The large variety of local environments and the high density of electronic states at the Fermi level may play a positive role in increasing the electrocatalytic activity of this compound.

Features of the Application of Promising Catalysts from Amorphous Molybdenum Sulfide in the Creation of p-Si and pn-Si Photocathodes for the Production of Hydrogen in an Acidic Solution

Features of the Application of Promising Catalysts from Amorphous Molybdenum Sulfide in the Creation of p-Si and pn-Si Photocathodes for the Production of Hydrogen in an Acidic Solution

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.

Structural regulation of amorphous molybdenum sulfide by atomic palladium doping for hydrogen evolution

Molybdenum sulfide materials have long been considered as attractive non-precious-metal electrocatalysts for the hydrogen evolution reaction (HER). However, comparing with the crystalline counterpart, amorphous MoSx has been less investigated previously. We here propose to increase the catalytical activity of a-MoSx by raising the reactant concentration at the catalytic interface via a chemical doping approach. The reconstruction of coordination structure of a-MoSx via Pd doping induces the formation of abundant unsaturated S atoms. Moreover, the reactant friendly catalytic interface is constructed through introducing hydrophilic groups to a-MoSx. The doped a-MoSx catalyst exhibits significantly enhanced HER activity in both acid and alkaline media.

Post-annealing in ultra-high vacuum or nitrogen plasma for MoS2 thin films deposited by magnetron sputtering

The thin films of amorphous molybdenum disulfide were deposited at room temperature by magnetron sputtering technique. Post-annealing process in ultra-high vacuum (∼10−8 Pa) or nitrogen plasma environments at the temperatures of 300, 400, 500, and 700 °C have been first proposed to enhance the microstructure and optical properties of MoS2 thin films. The phase transformation of MoS2 thin films from amorphous to polycrystalline was characterized by in situ reflection high-energy electron diffraction during the post-annealing process. The microstructure of MoS2 thin films was also analyzed by Raman spectrum and X-ray diffractometer after the post-annealing process. In addition, the thermal analysis of the differential scanning calorimeter and optical measurement of photoreflectance confirmed the phase transformation of MoS2 thin films. The analysis of photoreflectance also estimated the exciton transition at the bandgap energy of 2.038 eV at 0 K, attributed by the crystalline MoS2 film annealed at 700 °C in ultra-high vacuum. The surface chemical composition of MoS2 thin films has been identified by X-ray photoelectron spectroscopy, but the desulfurization of MoS2 was observed after post-annealing in ultra-high vacuum. Moreover, the preferred orientation of (004) plane in the MoS2 films was performed as the increase in post-annealing temperature.

Sulfur-rich MoS3 cathode for high-performance room-temperature liquid and solid-state lithium metal batteries

Sulfur-based compounds have been considered one of the most attractive cathode materials for next-generation batteries owing to their high energy density and environmental benignity. Among them, metal sulfides like MoS2 show high conductivity as well as intrinsic catalytic activity, however, the sulfur content and specific capacity are relatively low. In this article, we proposed a sulfur-rich amorphous molybdenum trisulfide‑carbon nanotubes (MoS3-CNT) cathode via in situ deposition. Benefiting from the enhanced electrical conductivity and enriched abundant reactive sites, the cathode exhibits impressive performance when assembled as liquid and solid-state lithium metal batteries at room temperature. In liquid lithium metal batteries, optimized MoS3-CNT20% cathode exhibits an impressive high specific capacity of 900.7 mAh/g in the first cycle, while the cycling stability is poor (35.4% after 50 cycles) owing to severe shuttle effect. When fabricated with polymer solid-state electrolyte, the cycling stability could be significantly improved to 85.7% after 50 cycles with an initial capacity of 314.2 mAh/g. This study provides a rational strategy for developing high-performance metal sulfide cathodes thus helping sustainable development.

Amorphous MoOx loaded on N-doped carbon-modified SiO2 for strongly enhanced oxidative desulfurization activity

Transition-metal oxides (TMOs) are good catalyst candidates for oxidation desulfurization (ODS) reaction, and its excellent dispersion in carriers could exert great influence on its catalytic performance. However, improving its catalytic activity still remains challenging. Herein, the amorphous molybdenum oxide (MoOx) was synthesized as the active sites for ODS reaction. Via a facile adsorption-pyrolysis approach, the amorphous MoOx was dispersedly immobilized onto N-doped carbon layer (NC)-encapsulated SiO2 using zinc pyridine porphyrin (ZnTPyP) and phosphomolybdic acid (PMo12)-modified SiO2 nanocomposites as precursor, obtaining the MoOx@NC@SiO2 catalyst. Owing to the wonderful pre-dispersion of Mo sources on the precursor leaded by the electrostatic interaction and spacial effect, the confinement effect of the derived carbon matrix, and the strong Mo-N bonds, the growth of MoOx crystal could be inhibited in pyrolysis procedure, ensuring the amorphous structure and good dispersion of MoOx species on SiO2. The as-prepared MoOx@NC@SiO2 exhibits excellent oxidation desulfurization (ODS) performances, and could promote the complete oxidation of DBT in model fuel into DBTO2 at the theoretical O/S molar ratio of 2, due to the perfect activation of all oxygen atoms of H2O2 by the amorphous MoOx. In addition, a plausible ODS mechanism over MoOx@NC@SiO2 is depicted to be the •OH radicals. Moreover, MoOx@NC@SiO2 still displays an outstanding reusability over at least 10 cycles owing to the encapsulation of NC layers and the strong Mo-N bonds. Therefore, this work provides a promising catalyst for industrial ODS application, and opens up a new avenue for developing the amorphous TMOs catalysts.

Comparative study on gas-sensing properties of amorphous MoS2 nanoparticles and crystalline MoS2 nanoflowers

High-performance gas sensors for the field of gas sensing have drawn a lot of attention to molybdenum sulfide materials, but there is little research on the influence of crystallization state of MoS2 on gas sensitivity performance. In this study, amorphous MoS2 and crystalline MoS2 were prepared by the hydrothermal method. Then, the gas-sensing characteristics of the as-synthesized amorphous MoS2 and crystalline MoS2 toward NO2 gas were thoroughly investigated and compared. According to the results, with an excellent response value of 1.99 toward 5 ppm NO2 at room temperature, the crystalline MoS2 gas sensor outperformed the amorphous one, while that of the amorphous MoS2 under the same condition was 1.25. However, Four times faster recovery periods were observed in the amorphous MoS2 sample compared to the crystalline MoS2 sample. At the same time, the recovery level of amorphous MoS2 is high and can be fully restored. We discovered that the primary cause of the strong recovery performance of amorphous MoS2 is the presence of localized states that facilitate the easy transition of electrons from the conduction band to the valence band, allowing for effective recombination with the holes. Additionally, the surface of the material absorbs a significant amount of oxygen, which will occupy more of the NO2 adsorption site and hasten the desorption of NO2. This work may aid in the development of gas sensors based on amorphous molybdenum sulfide.

MOF-derived amorphous molybdenum trioxide anchored on nitrogen-doped porous carbon by facile in situ annealing for efficient oxidative desulfurization

Electron transfer between supports and metal oxides is of great significance in optimizing the catalytic activity, while this is still an open issue for understanding its real role in the oxidative desulfurization (ODS) process. Herein, the defective molybdenum trioxide derived from molybdenum-based metal–organic frameworks was highly dispersed on nitrogen-doped porous carbon (VO-MoO3@NPC) by a single-step carbonization treatment. The uniform integration of organic moieties and the unique porous structure of carbonaceous materials are conductive to the active site exposure and mass transfer process during the ODS reaction. Meanwhile, richer oxygen vacancies are generated due to the weakened Mo-O bonds, which is pertinent to the promoted electron transfer between nitrogen-doped porous carbon and molybdenum trioxide by shrinking the band gap. The results manifest that the obtained VO-MoO3@NPC realizes an extraordinary desulfurization efficiency of 99.1% within 20 min, as well as a stable recyclability of up to 9 times. Furthermore, the catalyst delivers an extremely remarkable turnover frequency of 96.2 h−1, which is far superior to that of previously reported molybdenum-based catalysts. This manuscript provides new inspiration for designing excellent ODS catalysts by introducing electron-rich nitrogen to construct strong metal-support interactions.

Synthesis of defect-engineered molybdenum sulfides on reduced graphene oxide for enhanced hydrogen evolution reaction kinetics

Amorphous molybdenum sulfide (a-MoS3) is a promising non-precious electrocatalyst for hydrogen evolution reaction owing to the abundant defective active sites. Here in, we show a rapid microwave-assisted synthesis method to produce a-MoS3 catalysts on reduced graphene oxide (rGO) substrates. The a-MoS3 reported in this study comprise of two possible 1D chain-like structures, i.e., with molybdenum (IV) in Weber's model and molybdenum (V) in Hibble's model, unlike the polymeric cluster type a-MoS3 structures reported in literature. Thermal annealing of the microwave-prepared a-MoS3 produced a family of defect-engineered MoSx/rGO hybrids, from a-MoS3 to crystalline MoS2, which showed tunable HER activities. XPS analysis provided in-depth understanding of the compositional changes in MoSx/rGO with thermal annealing. The a-MoS3/rGO 250 (annealed at 250 °C) exhibited the highest HER catalytic activity among all the MoSx/rGO hybrids, with an overpotential of 208 mV at 10 mA/cm2, a low Tafel slope of 52 mV/decade, a high double layer capacitance of 3.7 mF/cm2 and a high TOF value of 0.43 H2/s per site at the HER overpotential of 208 mV. The excellent HER activity is attributed to both MoV and sulfur active sites. This study provides a controllable, scalable and rapid synthesis method to produce 1D chain-like a-MoS3 structures for HER electrocatalysis.

Ultrafast synthesis of amorphous molybdenum sulfide by magnetic induction heating for hydrogen evolution reaction

Molybdenum sulfides have emerged as viable alternatives to noble-metal catalysts for green hydrogen production via the hydrogen evolution reaction (HER). Herein, magnetic induction heating (MIH) is exploited for the rapid preparation of carbon-supported MoSx nanocomposites. The sample prepared at 200 A for 10 s shows an amorphous Mo3S7Cly-like structure and a low overpotential (η10) of −184 mV at 10 mA cm−2 in acidic media, whereas samples prepared at higher induction currents display a largely crystalline MoS2 structure and drastically lower HER performance. This is due to the formation of dimeric Mo6S14 moieties in amorphous MoSx that is facilitated by the loss of Cl residues during electrochemical reaction and enhanced H adsorption at both the S and Mo sites, in comparison to crystalline MoS2, as shown in First-principles calculations. These results show that MIH may be used as a powerful tool in the preparation of nonequilibrium structures as high-performance electrocatalysts.

From Well-Defined Clusters to Functional Materials: Molecular Engineering of Amorphous Molybdenum Sulfides for Hydrogen Evolution Electrocatalysis

From Well-Defined Clusters to Functional Materials: Molecular Engineering of Amorphous Molybdenum Sulfides for Hydrogen Evolution Electrocatalysis

Tolerance to deformation and flux pinning in superconducting amorphous molybdenum nitride thin films grown on flexible polyimide

We investigate the superconducting properties of 80 nm thick amorphous MoNx films fabricated via reactive sputtering on silicon and flexible commercial polyimide substrates. The samples are grown at room temperature using reactive sputtering with a gas mixture of N2 and Ar. The mechanical deformation tolerance for films on polyimide is evaluated by comparing the superconducting critical temperature (Tc) and critical current density (Jc) when the films are attached to cooper surfaces with varying curvatures. The amorphous films exhibit a Tc of 8.2 K on silicon and 7.9 K on polyimide. Our results demonstrate a significant enhancement in flux pinning for the thin films grown on polyimide, with the Jc at self-field and 3 K increasing from approximately 0.5 MA/cm2 to around 1 MA/cm2. Analyses of Jc as a function of the magnetic field, angle, and temperature reveal that the films on polyimide exhibit remarkable resilience to deformation. Interestingly, comparable Jc values are observed when the samples are affixed to both flat and cylindrical surfaces with diameters of 2.5 cm. This observation suggests that vortex dissipation predominantly occurs through flux motion in the region experiencing the maximum Lorentz force. Furthermore, the films maintain Tc without any discernible changes in resistivity when fixed to cylindrical surfaces with 1.2 cm diameters. However, there is a significant drop in vortex pinning, indicating reduced pinning capability in the stressed regions. The high deformation tolerance of amorphous MoNx renders it highly suitable for cryogenic electronics applications, providing a viable alternative to the commonly utilized metallic Nb.