Covalent Cross-Linking of 2H-MoS2 Nanosheets

The combination of 2D materials opens a wide range of possibilities to create new-generation structures with multiple applications. Covalently cross-linked approaches are a ground-breaking strategy for the formation of homo or heterostructures made by design. However, the covalent assembly of transition metal dichalcogenides flakes is relatively underexplored. Here, a simple covalent cross-linking method to build 2H-MoS₂–MoS₂ homostructures is described, using commercially available bismaleimides. These assemblies are mainly connected vertically, basal plane to basal plane, creating specific molecular sized spaces between MoS₂ sheets. Therefore, this straightforward approach gives access to the controlled connection of sulfide-based 2D materials.     

In Situ Formation of a MoS2‐Based Inorganic–Organic Nanocomposite by Directed Thermal Decomposition

Nanocomposites based on molybdenum disulfide (MoS₂) and different carbon modifications are intensively investigated in several areas of applications due to their intriguing optical and electrical properties. Addition of a third element may enhance the functionality and application areas of such nanocomposites. Herein, we present a facile synthetic approach based on directed thermal decomposition of (Ph₄P)₂MoS₄ generating MoS₂ nanocomposites containing carbon and phosphorous. Decomposition at 250 °C yields a composite material with significantly enlarged MoS₂ interlayer distances caused by in situ formation of Ph₃PS bonded to the MoS₂ slabs through Mo?S bonds and (Ph₄P)₂S molecules in the van der Waals gap, as was evidenced by ³¹P solid‐state NMR spectroscopy. Visible‐light‐driven hydrogen generation demonstrates a high catalytic performance of the materials.     

Interlayer-expanded MoS<Subscript>2</Subscript>/graphene composites as anode materials for high-performance lithium-ion batteries

A facile strategy was developed to prepare interlayer-expanded MoS₂/graphene composites through a one-step hydrothermal reaction method. MoS₂ nanosheets with several-layer thickness were observed to uniformly grow on the surface of graphene sheets. And the interlayer spacing of MoS₂ in the composites was determined to expand to 0.95 nm by ammonium ions intercalation. The MoS₂/graphene composites show excellent lithium storage performance as anode materials for Li-ion batteries. Through gathering advantages including expanded interlayers, several-layer thickness, and composited graphene, the composites exhibit reversible capacity of 1030.6 mAh g^?1 at the current density of 100 mA g^?1 and still retain a high specific capacity of 725.7 mAh g^?1 at a higher current density of 1000 mA g^?1 after 50 cycles.     

Directly Imaging and Regulating the Nanoscale Inhomogeneity of S-Vacancies in Molybdenum Disulfide Monolayer during Electrocatalytic Hydrogen Evolution

The study of electron transfer event on two-dimensional (2D) layered transition metal dichalcogenides has attracted tremendous attentions attributing to their promising applications in electrochemical devices. Herein, we demonstrate an opto-electrochemical strategy to directly map and regulate electron transfer event on molybdenum disulfide (MoS₂) monolayer by combining bright field (BF) imaging technique with electrochemical modulation. The heterogeneity of electrochemical activity on MoS₂ monolayer down to nanoscale is resolved spatiotemporally. The thermodynamics of MoS₂ monolayer is measured during electrocatalytic hydrogen evolution, and the Arrhenius correlations are obtained. We validate that the defect generation engineered by oxygen plasma bombardment dramatically enhances the local electrochemical activity of MoS₂ monolayer, which can be attributed to point defects of S-vacancies as evidenced. Furthermore, by comparing the difference of electron transfer event on MoS₂ with various layers, the interlayer coupling effect is uncovered. This study represents a facile method to image the heterogeneity of electrochemical properties for nanomaterials with atomic thickness and regulate the local activity within the plane by extrinsic factors. It also has potential applications in the design and evaluation of high-performance layered electrochemical systems down to nanoscale.     

MoS2 Nanosheets Supported on 3D Graphene Aerogel as a Highly Efficient Catalyst for Hydrogen Evolution

The development of efficient catalysts for electrochemical hydrogen evolution is essential for energy conversion technologies. Molybdenum disulfide (MoS₂) has emerged as a promising electrocatalyst for hydrogen evolution reaction, and its performance greatly depends on its exposed edge sites and conductivity. Layered MoS₂ nanosheets supported on a 3D graphene aerogel network (GA‐MoS₂) exhibit significant catalytic activity in hydrogen evolution. The GA‐MoS₂ composite displays a unique 3D architecture with large active surface areas, leading to high catalytic performance with low overpotential, high current density, and good stability.     

Self-Assembly Approach Towards MoS2-Embedded Hierarchical Porous Carbons for Enhanced Electrocatalytic Hydrogen Evolution

Transition metal-based nanoparticle-embedded carbon materials have received increasing attention for constructing next-generation electrochemical catalysts for energy storage and conversion. However, designing hybrid carbon materials with controllable hierarchical micro/mesoporous structures, excellent dispersion of metal nanoparticles, and multiple heteroatom-doping remains challenging. Here, a novel pyridinium-containing ionic hypercrosslinked micellar frameworks (IHMFs) prepared from the core–shell unimicelle of s-poly(tert-butyl acrylate)-b-poly(4-bromomethyl) styrene (s-PtBA-b-PBMS) and linear poly(4-vinylpyridine) were used as self-sacrificial templates for confined growth of molybdenum disulfide (MoS₂) inside cationic IHMFs through electrostatic interaction. After pyrolysis, MoS₂-anchored nitrogen-doped porous carbons possessing tunable hierarchical micro/mesoporous structures and favorable distributions of MoS₂ nanoparticles exhibited excellent electrocatalytic activity for hydrogen evolution reaction as well as small Tafel slope of 66.7 mV dec⁻¹, low onset potential, and excellent cycling stability under acidic condition. Crucially, hierarchical micro/mesoporous structure and high surface area could boost their catalytic hydrogen evolution performance. This approach provides a novel route for preparation of micro/mesoporous hybrid carbon materials with confined transition metal nanoparticles for electrochemical energy conversion.     

Single‐Step Synthesis of Mesoporous Carbon Nitride/Molybdenum Sulfide Nanohybrids for High‐Performance Sodium‐Ion Batteries

Molybdenum disulfide (MoS₂) is a promising candidate as a high‐performing anode material for sodium‐ion batteries (SIBs) due to its large interlayer spacing. However, it suffers from continued capacity fading. This problem could be overcome by hybridizing MoS₂ with nanostructured carbon‐based materials, but it is quite challenging. Herein, we demonstrate a single‐step strategy for the preparation of MoS₂ coupled with ordered mesoporous carbon nitride using a nanotemplating approach which involves the pyrolysis of phosphomolybdic acid hydrate (PMA), dithiooxamide (DTO) and 5‐amino‐1H‐tetrazole (5‐ATTZ) together in the porous channels of 3D mesoporous silica template. The sulfidation to MoS₂, polymerization to carbon nitride (CN) and their hybridization occur simultaneously within a mesoporous silica template during a calcination process. The CN/MoS₂ hybrid prepared by this unique approach is highly pure and exhibits good crystallinity as well as delivers excellent performance for SIBs with specific capacities of 605 and 431 mAhg^?1 at current densities of 100 and 1000 mAg^?1, respectively, for SIBs.     

MoS2 as a Co-Catalyst for Photocatalytic Hydrogen Production: A Mini Review

Molybdenum disulfide (MoS₂), with a two-dimensional (2D) structure, has attracted huge research interest due to its unique electrical, optical, and physicochemical properties. MoS₂ has been used as a co-catalyst for the synthesis of novel heterojunction composites with enhanced photocatalytic hydrogen production under solar light irradiation. In this review, we briefly highlight the atomic-scale structure of MoS₂ nanosheets. The top-down and bottom-up synthetic methods of MoS₂ nanosheets are described. Additionally, we discuss the formation of MoS₂ heterostructures with titanium dioxide (TiO₂), graphitic carbon nitride (g-C₃N₄), and other semiconductors and co-catalysts for enhanced photocatalytic hydrogen generation. This review addresses the challenges and future perspectives for enhancing solar hydrogen production performance in heterojunction materials using MoS₂ as a co-catalyst.     

Aligned MoOx/MoS2 Core–Shell Nanotubular Structures with a High Density of Reactive Sites Based on Self‐Ordered Anodic Molybdenum Oxide Nanotubes

The present work demonstrates the self‐organized formation of anodic molybdenum oxide nanotube arrays. The amorphous tubes can be crystallized to MoO₂ or MoO₃ and be converted fully or partially into molybdenum sulfide. Vertically aligned MoO_x/MoS₂ nanotubes can be formed when, under optimized conditions, defined MoS₂ sheets form in a layer by layer arrangement that provide a high density of reactive stacking misalignments (defects). These core–shell nanotube arrays consist of a conductive suboxide core and a functional high defect density MoS₂ coating. Such structures are highly promising for applications in electrocatalysis (hydrogen evolution) or ion insertion devices.     

Supramolecularly Bonded Layered Heterostructures Exhibiting HER Activity

van der Waals heterostructures formed by 2D materials have attracted much attention in the last few years. Recently, 2D nanosheets linked by covalent bonds have been found to exhibit novel properties. In the present study we have investigated supramolecular layered heterostructures formed by nanosheets of MoS₂ with BC₇N, g‐C₃N₄ and graphene. These materials have been synthesized via a non‐covalent host–guest synthetic design using cucurbit[8]uril (CB[8]) hosts. In addition to offering reversible disassembly, these heterostructures show good visible‐light‐driven hydrogen evolution reaction (HER) activity as well as reasonable gas adsorption and other properties.     

Ligand Modulation of Active Sites to Promote Cobalt-Doped 1T-MoS2 Electrocatalytic Hydrogen Evolution in Alkaline Media

Highly efficient hydrogen evolution reaction (HER) electrocatalyst will determine the mass distributions of hydrogen-powered clean technologies, while still faces grand challenges. In this work, a synergistic ligand modulation plus Co doping strategy is applied to 1T−MoS₂ catalyst via CoMo-metal-organic frameworks precursors, boosting the HER catalytic activity and durability of 1T−MoS₂. Confirmed by Cs corrected transmission electron microscope and X-ray absorption spectroscopy, the polydentate 1,2-bis(4-pyridyl)ethane ligand can stably link with two-dimensional 1T−MoS₂ layers through cobalt sites to expand interlayer spacing of MoS₂ (Co−1T−MoS₂-bpe), which promotes active site exposure, accelerates water dissociation, and optimizes the adsorption and desorption of H in alkaline HER processes. Theoretical calculations indicate the promotions in the electronic structure of 1T−MoS₂ originate in the formation of three-dimensional metal-organic constructs by linking π-conjugated ligand, which weakens the hybridization between Mo-3d and S-2p orbitals, and in turn makes S-2p orbital more suitable for hybridization with H-1s orbital. Therefore, Co−1T−MoS₂-bpe exhibits excellent stability and exceedingly low overpotential for alkaline HER (118 mV at 10 mA cm⁻²). In addition, integrated into an anion-exchange membrane water electrolyzer, Co−1T−MoS₂-bpe is much superior to the Pt/C catalyst at the large current densities. This study provides a feasible ligand modulation strategy for designs of two-dimensional catalysts.     

Electronic Structures and Thermoelectric Properties of Two-Dimensional MoS2/MoSe2 Heterostructures

Thermoelectric properties of bulk and bilayer two-dimensional (2D) MoS₂/MoSe₂ heterostructures are investigated using density functional theory in conjunction with semiclassical Boltzmann transport theory. It is predicted that the bulk 2D heterostructures could considerably enhance the thermoelectric properties as compared with the bulk MoSe₂. The enhancement originates from the reduction in the band gap and the presence of interlayer van der Waals interactions. We therefore propose the 2D MoS₂/MoSe₂ heterostructures as a possible candidate material for thermoelectric applications.     

Bifunctional Electrocatalyst with 0D/2D Heterostructure for Highly Efficient Hydrogen and Oxygen Generation

A novel MoS₂ quantum dots/CoSe₂ nanosheet (MoS₂ QDs/CoSe₂) hybrid with 0D/2D heterostructure has been developed. The CoSe₂ nanosheets (NSs) enable an excellent oxygen evolution reaction (OER) activity with increasing vacancy configuration on one hand, while the MoS₂ QDs serve as an eminent hydrogen evolution reaction (HER) catalyst on the other. By integrating MoS₂ QDs and CoSe₂ NSs, the hybrid exhibits excellent electrocatalytic performances in HER and OER. The unique 0D/2D hetero‐interface increases the exposed active sites and facilitates electron transfer, thereby boosting the electrocatalytic activity. Relatively low overpotentials of 82 mV and 280 mV are required to drive the current density of 10 mA/cm² for HER and OER, with corresponding Tafel slopes of 69 and 75 mV/dec, respectively. As such, this work provides an efficient yet simple approach to construct bifunctional electrocatalysts with enhanced activity and stability.     

Ionic‐Liquid‐Mediated Active‐Site Control of MoS2 for the Electrocatalytic Hydrogen Evolution Reaction

The layered crystal MoS₂ has been proposed as an alternative to noble metals as the electrocatalyst for the hydrogen evolution reaction (HER). However, the activity of this catalyst is limited by the number of available edge sites. It was previously shown that, by using an imidazolium ionic liquid as synthesis medium, nanometre‐size crystal layers of MoS₂ can be prepared which exhibit a very high number of active edge sites as well as a de‐layered morphology, both of which contribute to HER electrocatalytic activity. Herein, it is examined how to control these features synthetically by using a range of ionic liquids as synthesis media. Non‐coordinating ILs with a planar heterocyclic cation produced MoS₂ with the de‐layered morphology, which was subsequently shown to be highly advantageous for HER electrocatalytic activity. The results furthermore suggest that the crystallinity, and in turn the catalytic activity, of the MoS₂ layers can be improved by employing an IL with specific solvation properties. These results provide the basis for a synthetic strategy for increasing the HER electrocatalytic activity of MoS₂ by tuning its crystal properties, and thus improving its potential for use in hydrogen production technologies.     

WS2/MoS2 Heterostructures through Thermal Treatment of MoS2 Layers Electrostatically Functionalized with W3S4 Molecular Clusters

The preparation of 2D stacked layers combining flakes of different nature gives rise to countless numbers of heterostructures where new band alignments, defined at the interfaces, control the electronic properties of the system. Among the large family of 2D/2D heterostructures, the one formed by the combination of the most common semiconducting transition metal dichalcogenides, WS₂/MoS₂, has awakened great interest owing to its photovoltaic and photoelectrochemical properties. Solution as well as dry physical methods have been developed to optimize the synthesis of these heterostructures. Here, a suspension of negatively charged MoS₂ flakes is mixed with a methanolic solution of a cationic W₃S₄-core cluster, giving rise to a homogeneous distribution of the clusters over the layers. In a second step, a calcination of this molecular/2D heterostructure under N₂ leads to the formation of clean WS₂/MoS₂ heterostructures, where the photoluminescence of both counterparts is quenched, proving an efficient interlayer coupling. Thus, this chemical method combines the advantages of a solution approach (simple, scalable, and low-cost) with the good quality interfaces reached by using more complicated traditional physical methods.     

Defect Engineering of MoS2 and Its Impacts on Electrocatalytic and Photocatalytic Behavior in Hydrogen Evolution Reactions

Molybdenum disulfide (MoS₂) has been regarded as a favorable photocatalytic co‐catalyst and efficient hydrogen evolution reaction (HER) electrocatalyst alternative to expensive noble‐metals catalysts, owing to earth‐abundance, proper band gap, high surface area, and fast electron transfer ability. In order to achieve a higher catalytic efficiency, defects strategies such as phase engineering and vacancy introduction are considered as promising methods for natural 2H‐MoS₂ to increase its active sites and promote electron transfer rate. In this study, we report a new two‐step defect engineering process to generate vacancies‐rich hybrid‐phase MoS₂ and to introduce Ru particles at the same time, which includes hydrothermal reaction and a subsequent hydrogen reduction. Compositional and structural properties of the synthesized defects‐rich MoS₂ are investigated by XRD, XPS, XAFS and Raman measurements, and the electrochemical hydrogen evolution reaction performance, as well as photocatalytic hydrogen evolution performance in the ammonia borane dehydrogenation are evaluated. Both catalytic activities are boosted with the increase of defects concentrations in MoS₂, which ascertains that the defects engineering is a promising route to promote catalytic performance of MoS₂.     

微米尺寸二硫化钼层间化合物的电化学制备及其储镁性能

采用一种简便的电化学方法制备了有机阳离子(1-丁基-3-甲基咪唑阳离子,BMIM~+)插层的微米尺寸MoS_2层间化合物,并将其用作镁离子电池正极材料。所制备的MoS_2层间化合物(MoS_2-BMIM~+)具有扩大的层间距(0.98 nm),能有效降低Mg~(2+)的嵌入/脱出势垒,为存储Mg~(2+)提供了更多的活性位点,从而表现出显著提高的充电比容量和良好的倍率性能。MoS_2-BMIM~+在20 mA·g~(-1)电流密度下的充电比容量可达101.93 mAh·g~(-1)(约4倍于初始体相MoS_2)。我们进一步证明了这一方法同样适用于插层1-丁基-1-甲基吡咯烷双阳离子(Pyr~+_(14)),所得化合物的层间距为1.04 nm。     

二硫化钼纳米片/碳纳米纤维杂化材料的制备及其析氢性能

以碳纳米纤维(CNFs)作为负载基体和反应器采用静电纺丝技术和碳化工艺生长和调控二硫化钼(MoS_2)纳米片。通过改变前驱体溶液浓度来调控纳米片的形貌和结构,利用MoS_2纳米片的高催化活性和CNFs高比表面积、良好的稳定性以及高电导率的协同作用,研究不同形貌和结构的杂化纳米材料在电催化析氢方面的应用,探索杂化材料形貌与性能之间的潜在规律。运用多种分析测试技术对制备得到的纳米杂化材料进行表征,并对所制备的MoS_2/CNFs杂化材料的电催化析氢性能(HER)进行研究,研究表明近似皮芯结构的MoS_2/CNFs-10杂化材料的电催化析氢性能最好,初始析氢过电位在220 mV,Tafel斜率为110m V·dec~(-1)。     

二硫化钼纳米片/碳纳米纤维杂化材料的制备及其析氢性能

以碳纳米纤维（CNFs）作为负载基体和反应器采用静电纺丝技术和碳化工艺生长和调控二硫化钼（MoS₂）纳米片。通过改变前驱体溶液浓度来调控纳米片的形貌和结构,利用MoS₂纳米片的高催化活性和CNFs高比表面积、良好的稳定性以及高电导率的协同作用,研究不同形貌和结构的杂化纳米材料在电催化析氢方面的应用,探索杂化材料形貌与性能之间的潜在规律。运用多种分析测试技术对制备得到的纳米杂化材料进行表征,并对所制备的MoS₂/CNFs杂化材料的电催化析氢性能（HER）进行研究,研究表明近似皮芯结构的MoS₂/CNFs-10杂化材料的电催化析氢性能最好,初始析氢过电位在220 mV,Tafel斜率为110 mV·dec^-1。     

An assessment of the role of morphology in thermal/thermo-oxidative degradation mechanism of PP/EVA/clay nanocomposites

In this study, morphological properties of polypropylene (PP)/ethylene vinyl acetate copolymer (EVA) (75/25 wt/wt) blend-based nanocomposites containing various amounts of organically modified montmorillonite (OMMT) were primarily investigated. The incorporation of compatibilizer into nanocomposites decreased EVA droplet size in PP matrix while increasing compatibilizer/OMMT ratio showed a dual behavior with respect to the variations of OMMT interlayer spacing. By a rough estimation it was found that at EVA droplet size of D_n = 0.43 μm, the highest OMMT interlayer spacing would be acheived. Increasing D_n had a negative effect on the OMMT interlayer spacing. Activation energy of thermal/thermo-oxidative degradation based on Flynn model was obtained. Isothermal degradation test was also performed and desired temperature range for predicting degradation behavior was obtained by means of a free prediction model. An attempt was made to establish a correlation between morphological and thermal/thermo-oxidative parameters and also charred residue morphology. A mechanism for degradation process was proposed according to the changes of chemical bonds during the degradation process probed by FTIR analysis.