MoS2 Clusters Research Articles

Customizing dumbbell-shaped heterostructured artificial photosystems steering versatile photoredox catalysis.

Benefiting from their excellent light-capturing ability, suitable energy band structure and abundant active sites, transition metal chalcogenides (TMCs) have been attracting widespread attention in heterogeneous photocatalysis. Nonetheless, TMCs still suffer from sluggish charge transfer kinetics, a rapid charge recombination rate and poor stability, rendering the construction of high-performance artificial photosystems challenging. Here, a ternary dumbbell-shaped CdS/MoS2/CuS heterostructure with spatially separated catalytically active sites has been elaborately designed. In such a heterostructured nanoarchitecture, MoS2 clusters, selectively grown on both ends of the CdS nanowires (NWs), act as terminal electron collectors, while CuS nanolayers, coated on the sidewalls of CdS NWs through ion exchange, form a P-N heterojunction with the CdS NW framework, which accelerates the migration of holes from CdS to CuS, effectively suppressing the oxidation of sulfide ions and improving the stability of CdS NWs. The well-defined dumbbell-shaped CdS/MoS2/CuS ternary heterostructure provides a structural basis for spatially precise regulation of the charge migration pathway, where photogenerated electrons and holes directionally migrate to the MoS2 and CuS catalytic sites, respectively, ultimately achieving efficient carrier separation and significantly enhancing photoactivity for both photocatalytic hydrogen generation and selective organic transformation under visible light. Moreover, we have also ascertained that such ion exchange and interface configuration engineering strategies are universal. Our work features a simple yet efficient strategy for smartly designing multi-component heterostructures to precisely modulate spatially vectorial charge separation at the nanoscale for solar-to-hydrogen conversion.

Heterogeneous Ti3C2Tx MXene-MWCNT@MoS2 Film for Enhanced Long-Term Electromagnetic Interference Shielding in the Moisture Environment.

MXene, as a novel two-dimensional (2D) material, has unique inherent features such as lightweight, flexibility, high electrical conductivity, customizable surface chemistry, and facile solution processability. However, utilizing MXene (Ti3C2Tx) films for long-term electromagnetic interference (EMI) shielding poses challenges, as they are susceptible to chemical deterioration through oxidation into TiO2. In this work, an ultrathin heterogeneous film of Ti3C2Tx MXene integrated with multiwalled carbon nanotubes supporting MoS2 clusters (MXene/MWCNT@MoS2) was developed. The heterogeneous film with 15 wt % of MWCNT@MoS2 clusters exhibited improved EMI shielding performance such as the highest EMI shielding effectiveness of 50 dB and the specific shielding effectiveness of 20,355 dB cm2 g -1, mainly attributed to the excellent electrical conductivity, distinctive porous structure, and multiple interfacial interactions. The heterogeneous films underwent extended exposure to a moisture environment (35 days), and their structural stability and EMI shielding performance were enhanced by the integration of MWCNT@MoS2 clusters. As a result, the engineered heterostructure of multilayered hybrid films holds promise as a viable option for improving the EMI shielding effectiveness and stability of Ti3C2Tx MXene.

Atomic-level insights into single-layer Co-promoted MoS2 clusters supported on a rutile TiO2(110) model oxide support

Single-layer mixed metal transition metal dichalcodenides (TMDCs), such as Co-promoted MoS2 supported on metal oxide supports like TiO2, have a wide range of applications in heterogeneous, electro- and photocatalysis, energy harvesting, and energy storage. In this work, we present atomic-level insights into the interaction between single-layer Co-promoted MoS2 clusters and a model oxide rutile TiO2(110) support. We have used physical vapor deposition (PVD) to synthesize a precursor containing bimetallic Co-Mo nanoparticles supported on (1 × 1) TiO2(110). We sulfide this precursor using an H2S background of 1 × 10−3 mbar at 650 K to synthesize the Co-promoted MoS2 clusters. We use a combination of scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) to analyze the Co-promoted MoS2 clusters. We compare our results with that of pristine MoS2 clusters supported on TiO2(110), synthesized by an identical procedure, but without the Co atoms. We demonstrate that Co addition enhances the yield of (Co-promoted) MoS2 clusters, in comparison to sulfidation of Mo nanoparticles to form MoS2 clusters. Additionally, we also find that the Co-promoted MoS2 clusters have predominantly high-index edge terminations which likely are stabilized by Co-S-Ti and Mo-S-Ti linkages to an (3 × 1) S-TiO2 structure formed during the sulfidation. This causes an increase in the local density of states (LDOS) at the BRIM sites, thereby increasing their contrast in the STM images at the linkage sites. We have used our experimental results to propose a candidate atomic model for the Co-promoted MoS2 clusters supported on TiO2(110).

Wood-structured, hydrophilic, low-tortuosity thick electrode enables high-performance supercapacitor

It is a natural ingenuity to ignite the aspiration of wood-structured biomaterials with largely-distributed porosity, mechanical integrity, and tunable functionalities in energy engineering. As a hierarchically architectured carbon scaffold with well-aligned channels and high active-mass loading, free-standing wood thick electrode expedites the electron/ion transfer kinetics to heighten storage capacitance. Herein, we have facilely designed a holey wood-structured bulk electrode (a thickness of ∼1 mm) with the depositing of MoS2 and NiS2 clusters by a tandem hydrothermal and pyrolysis strategy for the efficient supercapacitors. In the perpendicular direction, artificial small holes (∼ 0.5 mm diameter) are drilled across the 3D-wood thick electrode to perforate the growth channels, hence ameliorating ion migration as well as reducing diffused impedance. Benefitting from the vertical low-tortuosity channels, high charge conductivities, superhydrophilic interface, reversible redox behavior, and excellent mechanical stability, the superior areal capacitance (7806–8538 mF cm−2 at a current density of 10 mA cm−2) and long-term cycling lifespan (∼ 100 % retention over 10,000 cycles even at 100 mA cm−2) of wood thick electrodes (energy densities of 0.287 −0.423 mWh cm−2 in the asymmetric supercapacitors) are achieved without the structural deformation. The wood-structured, self-supporting thick electrode sketch a promising blueprint of high-performance biocompatible supercapacitors with maximum active-substance loading and monolithic low-tortuosity design that also can be popularized to rechargeable batteries.

Design and Realization of Ni Clusters in MoS2@Ni/RGO Catalysts for Alkaline Efficient Hydrogen Evolution Reaction.

Due to their almost zero relative hydrogen atom adsorption-free energy, MoS2-based materials have received substantial study. However, their poor electronic conductivity and limited number of catalytic active sites hinder their widespread use in hydrogen evolution reactions. On the other hand, metal clusters offer numerous active sites. In this study, by loading Ni metal clusters on MoS2 and combining them with the better electrical conductivity of graphene, the overpotential of the hydrogen evolution reaction was reduced from 165 mV to 92 mV at 10 mA·cm-2. This demonstrates that a successful method for effectively designing water decomposition is the use of synergistic interactions resulting from interfacial electron transfer between MoS2 and Ni metal clusters.

A Hybrid‐Density Functional Theory Study of Intrinsic Point Defects in MX2 (M = Mo, W; X = S, Se) Monolayers

Defects can strongly influence the electronic, optical, and mechanical properties of 2D materials, making defect stability under different thermodynamic conditions crucial for material–property engineering. Herein, an account of the structural and electronic characteristics of point defects in monolayer transition metal dichalcogenides MX2 with M = Mo/W and X = S/Se is investigated through density functional theory using the hybrid HSE06 exchange–correlation functional including many‐body dispersion corrections. For the simulation of charged defects, a charge compensation scheme based on the virtual crystal approximation (VCA) is employed. The study relates the stability and the electronic structure of charged vacancy defects in monolayer MoS2 to an explicit calculation of the S monovacancy in MoS2 supported on Au(111), and finds convincing indication that the defect is negatively charged. Moreover, it is shown that the finite‐temperature vibrational contributions to the free energy of defect formation can change the stability transition between adatoms and monovacancies by 300–400 K. Finally, defect vibrational properties are probed by calculating a tip‐enhanced Raman scattering image of a vibrational mode of a MoS2 cluster with and without an S monovacancy.

Solvothermal temperature-control of active 1T phase in carbon cloth-supported MoS2 and Pt-Ni cluster electrodeposition for hydrogen evolution reaction

Establishing synthetic guidance that enables phase optimization with minimized by-products is an important task in modifying atomic arrangements and electronic structures of MoS2 through a solvothermal approach. Herein, a synthetic strategy to manipulate the 1 T and 2 H phases within MoS2 nanosheets on a support carbon cloth (MoS2/CC) is successfully demonstrated via a facile and efficient temperature-controlled solvothermal method. The 1 T and 2 H in MoS2/CC are well-characterized and quantified using Raman and XPS, revealing that MoS2/CC synthesized at 220 ºC (denoted as MoS2/CC(220)) has the highest 1 T phase content (∼ 60 %). The distinctive atomic arrangement of 1 T and 2 H are distinguished by HR-TEM. We also successfully electrodeposited Pt-Ni nanoclusters on the 1 T-rich MoS2 (Pt-Ni@MoS2/CC), which accounts for a substantially enhanced HER performance. This study highlights the capability of phase manipulation in two-dimensional MoS2 nanosheets via a one-pot solvothermal approach, which is essential for application-specified phase engineering.

The effect of microwave electric field on sulfur vacancies formation over the edge sites of Co/Ni-promoted and unpromoted MoS2 catalysts through DFT investigations

The elementary reactions for the formations of sulfur vacancies over various edges of Mo-based active phases were systematically investigated and compared under the action with/without microwave electric field via DFT calculations. The results reveal that the H2 dissociation is extremely difficult over the M−edge of pure MoS2 clusters. The partial doping of Co/Ni can significantly reduce the difficulty, while the difficulty over the S-edge is obviously lower than that of the M−edge. Compared with CoMoS-I, H2 dissociation becomes more favorable over the S-edge of NiMoS. The atomic H migration is unlikely to occur over the edge of MoS2, however, it becomes spontaneous after being dopped by Co/Ni along specific paths. The effect of electric field direction differs on each step of the vacancy formation over various edges. Either EX+ (the field applied along the direction of the x-axis) or EX- field would highly benefit H2 dissociation, H migration and H2S desorption on both M−edge and sulfur edge, thus it presents great significance that microwave, the existence of variable electromagnetic field is conducive to the formation of sulfur vacancies. The findings would shed more light on understanding the promotion mechanism of Co/Ni doping and microwaves on the HDS process.

Spatially isolated neutral excitons via clusters on trilayer MoS2.

In spite of having a large exciton binding energy, two-dimensional (2D) transition metal dichalcogenides (TMDs) are limited as light-emitting materials because the spectral weight of neutral excitons decreases exponentially with increasing the excitation density. That is, neutral excitons easily transfer to trions, and exciton-exciton annihilation (EEA) occurs due to the strengthening of exciton kinetic energy in the layered structure. In here, we come up with an isolated neutral exciton system, maintaining its high spectral weight when the carrier density increased, which is achieved via MoS2 clusters on a MoS2 trilayer directly synthesized by metal-organic chemical vapor deposition (MOCVD). While increasing the excitation density, trions are decomposed by spatial confinement at the saturation level of its full width at half maximum (FWHM), and simultaneously the spectral weight of neutral excitons restarts to increase. Furthermore, we reveal the causality relationship between trions and B excitons, providing a keen insight into organic interactions among radiative recombination processes in 2D TMDs.

In Situ Scanning Transmission Electron Microscopy Study of MoS2 Formation on Graphene with a Deep-Learning Framework.

Atomic-scale information is essential for understanding and designing unique structures and properties of two-dimensional (2D) materials. Recent developments in in situ transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) enable research to provide abundant insights into the growth of nanomaterials. In this study, 2D MoS2 is synthesized on a suspended graphene substrate inside a TEM column through thermolysis of the ammonium tetrathiomolybdate (NH4)2MoS4 precursor at 500 °C. To avoid misinterpretation of the in situ STEM images, a deep-learning framework, DeepSTEM, is developed. The DeepSTEM framework successfully reconstructs an object function in atomic-resolution STEM imaging for accurate determination of the atomic structure and dynamic analysis. In situ STEM imaging with DeepSTEM enables observation of the edge configuration, formation, and reknitting progress of MoS2 clusters with the formation of a mirror twin boundary. The synthesized MoS2/graphene heterostructure shows various twist angles, as revealed by atomic-resolution TEM. This deep-learning framework-assisted in situ STEM imaging provides atomic information for in-depth studies on the growth and structure of 2D materials and shows the potential use of deep-learning techniques in 2D material research.

The Effect of MoS2 Active Site Dispersion on Suppression of Polycondensation Reactions during Heavy Oil Hydroconversion

In this work, the composition, structural and morphological features, and particle size of the active phase of the catalyst (MoS2), synthesized in-situ during the heavy oil hydroconversion performed in continuous flow reactor on lab-scale pilot flow unit at T = 450 °C, P = 6.0–9.0 MPa, V = 1.0 h−1, H2/feed = 1000 nL/L, catalyst concentration C (Mo) = 0.01–0.08%wt have been studied. It has been shown that MoS2 formed during hydroconversion is represented by nanosized particles stabilized by polycondensation products as a result of strong adsorption and aggregation with the components of the hydroconversion reaction medium. The influence of morphological characteristics of catalyst nanoparticles on the feed conversion, the yield of gaseous and liquid products, and the quality of distillate fractions, as well as the yield of polycondensation products, have been studied. It has been established that an increase in MoS2 active site dispersion, both due to a decreased plate length and lower stacking numbers in MoS2 cluster, enhances hydroconversion effectivity, particularly, in suppressing polycondensation reactions.

Theoretical Study on Tuning Band Gap and Electronic Properties of Atomically Thin Nanostructured MoS2/Metal Cluster Heterostructures.

Nano-heterostructures have attracted immense attention recently due to their remarkable interfacial properties determined by the heterointerface of different nanostructures. Here, using first-principles density functional theory (DFT) calculations, we examine what range the variable electronic properties such as the electronic band gap can be tuned by combining two dissimilar nanostructures consisting of atomically thin nanostructured MoS2 clusters with small silver and gold nanoparticles (Ag/Au NPs). Most interestingly, our calculations show that the electronic band gap of the nanostructured MoS2 cluster can be tuned from 2.48 to 1.58 and 1.61 eV, by the formation of heterostructures with silver and gold metal nanoclusters, respectively. This band gap is ideal for various applications ranging from flexible nanoelectronics to nanophotonics applications. Furthermore, the adsorption of H2 molecules on both nano-heterostructures is investigated, and the computed binding energies are found to be within the desirable range. The reported theoretical results provide inspiration for engineering various optoelectronic applications for nanostructured MoS2-based heterostructures.

Electronic Properties of Triangle Molybdenum Disulfide (MoS2) Clusters with Different Sizes and Edges.

The electronic structures and transition properties of three types of triangle MoS2 clusters, A (Mo edge passivated with two S atoms), B (Mo edge passivated with one S atom), and C (S edge) have been explored using quantum chemistry methods. The highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of B and C is larger than that of A, due to the absence of the dangling of edge S atoms. The frontier orbitals (FMOs) of A can be divided into two categories, edge states from S3p at the edge and hybrid states of Mo4d and S3p covering the whole cluster. Due to edge/corner states appearing in the FMOs of triangle MoS2 clusters, their absorption spectra show unique characteristics along with the edge structure and size.

The influence of microwave electric field on the sulfur vacancy formation over MoS2 clusters and the corresponding properties: A DFT study

Deep hydrodesulfurization (HDS) is the key method for clean oil production to meet the strict environmental regulations. Density functional theory (DFT) was performed to provide theoretical insight into the influence of microwave electric field on the adsorption of H2 molecular and sulfur vacancy formation on different edges of MoS2 nanocrystallite. The influence of the electric field on the structure and electrical properties of MoS2 nanocrystallites with sulfur vacancies was also theoretically analyzed. It was found that electric field in a specific direction enhances the adsorption of H2 on the edge of MoS2 cluster. Its application also benefits the spontaneous formation of specific S vacancy on the S edge and increases the active site number of the cluster. The presented results would provide new insights into understanding the promotion mechanism of microwave on the HDS process.

Hierarchical Structure of NiMo Hydrodesulfurization Catalysts Determined by Ptychographic X-Ray Computed Tomography.

Hydrodesulphurization, the removal of sulphur from crude oils, is an essential catalytic process in the petroleum industry safeguarding the production of clean hydrocarbons. Sulphur removal is critical for the functionality of downstream processes and vital to the elimination of environmental pollutants. The effectiveness of such an endeavour is among other factors determined by the structural arrangement of the heterogeneous catalyst. Namely, the accessibility of the catalytically active molybdenum disulphide (MoS2 ) slabs located on the surfaces of a porous alumina carrier. Here, we examined a series of pristine sulfided Mo and NiMo hydrodesulphurization catalysts of increasing metal loading prepared on commercial alumina carriers using ptychographic X-ray computed nanotomography. Structural analysis revealed a build consisting of two interwoven support matrix elements differing in nanoporosity. With increasing metal loading, approaching that of industrial catalysts, these matrix elements exhibit a progressively dissimilar MoS2 surface coverage as well as MoS2 cluster formation at the matrix element boundaries. This is suggestive of metal deposition limitations and/ or catalyst activation and following prohibitive of optimal catalytic utilization. These results will allow for diffusivity calculations, a better rationale of current generation catalyst performance as well as a better distribution of the active phase in next-generation hydrodesulphurization catalysts.

Hierarchical Structure of NiMo Hydrodesulfurization Catalysts Determined by Ptychographic X‐Ray Computed Tomography

AbstractHydrodesulphurization, the removal of sulphur from crude oils, is an essential catalytic process in the petroleum industry safeguarding the production of clean hydrocarbons. Sulphur removal is critical for the functionality of downstream processes and vital to the elimination of environmental pollutants. The effectiveness of such an endeavour is among other factors determined by the structural arrangement of the heterogeneous catalyst. Namely, the accessibility of the catalytically active molybdenum disulphide (MoS2) slabs located on the surfaces of a porous alumina carrier. Here, we examined a series of pristine sulfided Mo and NiMo hydrodesulphurization catalysts of increasing metal loading prepared on commercial alumina carriers using ptychographic X‐ray computed nanotomography. Structural analysis revealed a build consisting of two interwoven support matrix elements differing in nanoporosity. With increasing metal loading, approaching that of industrial catalysts, these matrix elements exhibit a progressively dissimilar MoS2 surface coverage as well as MoS2 cluster formation at the matrix element boundaries. This is suggestive of metal deposition limitations and/ or catalyst activation and following prohibitive of optimal catalytic utilization. These results will allow for diffusivity calculations, a better rationale of current generation catalyst performance as well as a better distribution of the active phase in next‐generation hydrodesulphurization catalysts.

Adsorption behavior of thiophene on MoS2 under a microwave electric field via DFT and MD studies

The adsorption behavior of sulfide over catalyst is the key to determine the desulfurization efficiency and its proceeding route. Molecular dynamics and density functional theory calculations were performed to provide theoretical insight into the effect of microwave electric field on the adsorption of thiophene over different MoS2 nanocrystallites, and investigate the electronic distribution. The adsorption position and configuration were significantly affected by microwave field, and the polarities of thiophene molecule and MoS2 were strengthened, which is beneficial to the cleavage of the thiophene C–S bond. Mo atoms lose charge in a large area and have a strong electrophilic effect after the generation of S vacancy, inducing S component adsorption on active sites. The hydrodesulfurization (HDS) selectivity is modified by affecting the priority of potential adsorption. Thiophene favors to η5 adsorption over multilayer dispersed MoS2 clusters under microwave field, inducing the HDS reactions to proceed along the hydrogenation route.

Graphene Supported MoS2 Structures with High Defect Density for an Efficient HER Electrocatalysts.

The development of novel efficient and robust electrocatalysts with sufficient active sites is one of the key parameters for hydrogen evolution reactions (HER) catalysis, which plays a key role in hydrogen production for clean energy harvesting. Recently, two-dimensional (2D) materials, especially those based upon transition metal dichalcogenides such as molybdenum disulfide (MoS2), have gained attention for the catalysis of hydrogen production because of their exceptional properties. Innovative strategies have been developed to engineer these material systems for improvements in their catalytic activity. Toward this aim, the facile growth of MoS2 clusters by sulfurization of molybdenum dioxide (MoO2) particles supported on reduced graphene oxide (rGO) foams using the chemical vapor deposition (CVD) method is reported. This approach created various morphologies of MoS2 with large edges and defect densities on the basal plane of rGO supported MoS2 structures, which are considered as active sites for HER catalysis. In addition, MoS2 nanostructures on the surface of the porous rGO network show robust physical interactions, such as van der Waals and π-π interactions between MoS2 and rGO. These features result in an improved process to yield a suitable HER catalyst. In order to gain a better understanding of the improvement of this MoS2-based HER catalyst, fully atomistic molecular dynamics (MD) simulations of different defect geometries were also performed.

Controlled Design of Well‐Dispersed Ultrathin MoS2 Nanosheets inside Hollow Carbon Skeleton: Toward Fast Potassium Storage by Constructing Spacious “Houses” for K Ions

AbstractThe large volume expansion induced by K+ intercalation is always a big challenge for designing high‐performance electrode materials in potassium‐ion storage system. Based on the idea that large‐sized ions should accommodate big “houses,” a facile‐induced growth strategy is proposed to achieve the self‐loading of MoS2 clusters inside a hollow tubular carbon skeleton (HTCS). Meantime, a step‐by‐step intercalation technology is employed to tune the interlayer distance and the layer number of MoS2. Based on the above, the ED‐MoS2@CT hybrids are achieved by self‐loading and anchoring the well‐dispersed ultrathin MoS2 nanosheets on the inner surface of HTCSs. This unique compositing model not only alleviates the mechanical strain efficiently, but also provides spacious “roads” (hollow tubular carbon skeleton) and “houses” (interlayer expanded ultrathin MoS2 sheets) for fast K+ transition and storage. As an anode of potassium‐ion batteries, the resultant ED‐MoS2@CT electrode delivers a high specific capacity of 148.5 mAh g−1 at 2 A g−1 after 10 000 cycles with only 0.002% fading per cycle. The assembled ED‐MoS2@CT//PC potassium‐ion hybrid supercapacitor device shows a high energy density of 148 Wh kg−1 at a power density of 965 W kg−1, which is comparable to that of lithium‐ion hybrid supercapacitors.

Active site manipulation in MoS2 cluster electrocatalysts by transition metal doping.

The development of non-platinum group metal catalysts for the hydrogen evolution reaction (HER) in water electrolyser devices is essential for their widespread and sustainable deployment. In recent years, molybdenum disulfide (MoS2) catalysts have received significant attention as they not only exhibit good electrocatalytic HER activity but also, crucially, acid-stability. However, further performance enhancement is required for these materials to be competitive with Pt and to that end transition metal doping of MoS2 has been explored as a route to further increasing its catalytic activity. In this work, cluster beam deposition was employed to produce controlled cobalt-doped MoS2 clusters (MoS2-Co). We demonstrate that, in contrast to previous observations of performance enhancement in MoS2 resulting from nickel doping (MoS2-Ni), the introduction of Co has a detrimental effect on HER activity. The contrasting behaviours of Ni and Co doping are rationalized by density functional theory (DFT) calculations, which suggest that HER-active surface vacancies are deactivated by combination with Co dopant atoms, whilst their activity is retained, or even partially enhanced, by combination with Ni dopant atoms. Furthermore, the adatom dopant-vacancy combination kinetics appear to be more than three orders of magnitude faster in MoS2-Co than for MoS2-Ni. These findings highlight a fundamental difference in the influence of transition metal dopants on the HER performance of MoS2 electrocatalysts and stress the importance of considering surface atomic defects when predicting their behaviour.